Patent Publication Number: US-10325890-B2

Title: Packaging a substrate with an LED into an interconnect structure only through top side landing pads on the substrate

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of, and claims priority under 35 U.S.C. § 120 from, nonprovisional U.S. patent application Ser. No. 15/660,958 entitled “Packaging a Substrate with an LED into an Interconnect Structure Only Through Top Side Landing Pads on the Substrate,” filed on Jul. 27, 2017, now U.S. Pat. No. 9,985,004. application Ser. No. 15/660,958, in turn, is a continuation of, and claims priority under 35 U.S.C. § 120 from, nonprovisional U.S. patent application Ser. No. 15/493,133 entitled “Packaging a Substrate with an LED into an Interconnect Structure Only Through Top Side Landing Pads on the Substrate,” filed on Apr. 21, 2017, now U.S. Pat. No. 9,893,039. application Ser. No. 15/493,133, in turn, is a continuation of, and claims priority under 35 U.S.C. § 120 from, nonprovisional U.S. patent application Ser. No. 15/067,145 entitled “Packaging a Substrate with an LED into an Interconnect Structure Only Through Top Side Landing Pads on the Substrate,” filed on Mar. 10, 2016, now U.S. Pat. No. 9,653,437. application Ser. No. 15/067,145, in turn, is a continuation of, and claims priority under 35 U.S.C. § 120 from, nonprovisional U.S. patent application Ser. No. 14/813,277 entitled “Packaging Photon Building Blocks Having Only Top Side Connections In A Molded Interconnect Structure,” filed on Jul. 30, 2015, now U.S. Pat. No. 9,312,465. application Ser. No. 14/813,277, in turn, is a continuation of, and claims priority under 35 U.S.C. § 120 from, nonprovisional U.S. patent application Ser. No. 14/156,617 entitled “Packaging Photon Building Blocks Having Only Top Side Connections In A Molded Interconnect Structure,” filed on Jan. 16, 2014, now U.S. Pat. No. 9,130,139. application Ser. No. 14/156,617, in turn, is a continuation of, and claims priority under 35 U.S.C. § 120 from, nonprovisional U.S. patent application Ser. No. 13/441,903 entitled “Packaging Photon Building Blocks Having Only Top Side Connections In A Molded Interconnect Structure,” filed on Apr. 8, 2012, now U.S. Pat. No. 8,652,860, which in turn is a continuation-in-part of, and claims priority under 35 U.S.C. § 120 from, the following three nonprovisional U.S. patent applications: patent application Ser. No. 12/987,148 entitled “Packaging Photon Building Blocks Having Only Top Side Connections in an Interconnect Structure,” filed on Jan. 9, 2011, now U.S. Pat. No. 8,354,684; patent application Ser. No. 13/284,835 entitled “Jetting a Highly Reflective Layer onto an LED Assembly,” filed on Oct. 28, 2011, now U.S. Pat. No. 9,461,023; and patent application Ser. No. 13/304,769 entitled “Micro-Bead Blasting Process for Removing a Silicone Flash Layer,” filed on Nov. 28, 2011, now U.S. Pat. No. 8,536,605. In addition, application Ser. No. 13/441,903 claims priority under 35 U.S.C. § 119 from U.S. provisional patent application Ser. No. 61/594,371 entitled “Packaging Photon Building Blocks Having Only Top Side Connections in a Molded Interconnect Structure,” filed on Feb. 2, 2012. The subject matter of each of the aforementioned patent documents is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to packaging light-emitting diodes and, more specifically, to a photon building block that can be packaged alone as an emitter or together with other photon building blocks as an array of emitters. 
     BACKGROUND INFORMATION 
     A light emitting diode (LED) is a solid state device that converts electrical energy to light. Light is emitted from active layers of semiconductor material sandwiched between oppositely doped layers when a voltage is applied across the doped layers. In order to use an LED chip, the chip is typically enclosed in a package that focuses the light and that protects the chip from being damaged. The LED package typically includes contact pads on the bottom for electrically connecting the LED package to an external circuit. Conventionally, an LED chip is designed to be packaged either as a discrete light emitter or with a group of LED chips in an array. The LED chip of the discrete light emitter is typically mounted on a carrier substrate, which in turn is mounted on a printed circuit board. The LED chips of the array, however, are typically mounted directed on the printed circuit board without using the carrier substrate. 
     Array products are not conventionally made using the discrete light emitters as building blocks. The carrier substrate of the discrete light emitter is typically considered needlessly to occupy space on the printed circuit board under an array. Moreover, conducting through-hole vias through the carrier substrate of the discrete light emitter would have to be reconfigured in order to connect properly to contact pads on the printed circuit board for each new array design. Thus, no carrier with a particular set of through-holes vias could be used as a standard building block. The problem of the through-hole vias in the discrete emitters can be solved by electrically connecting the LED chips to traces and contact pads on the top side of the carrier substrate. But eliminating the through-hole vias by connecting the LED chips to pads on the top side of the carrier substrate creates the new problem of how to connect the pads to a power source because the carrier substrate is no longer electrically coupled to the printed circuit board below. 
       FIG. 1  (prior art) shows an existing array product  10  with an array of twenty-four LED chips electrically connected to pads  11  on the top side of a carrier substrate  12 . Array product  10  is the XLamp® MP-L EasyWhite product manufactured by Cree, Inc. of Durham, N.C. In  FIG. 1 , carrier substrate  12  is mounted on a metal disk  13  as opposed to on a printed circuit board. Carrier substrate  12  is attached to metal disk  13  using thermal glue  14 . Array product  10  is inelegantly connected to power by hand soldering individual wires of the positive  15  and negative  16  power cord leads to the pads  11 . Array product  10  has no features that facilitate connecting the pads  11  on the top side of carrier substrate  12  to a power source in the board or plate below. And array product  10  is not configured to be incorporated into a group of array products. 
     When LEDs are packaged in arrays as opposed to as discrete light emitters, the LED chips of the arrays are mounted directly on a printed circuit board without the carrier substrate conventionally used with discrete light emitters. The LED chips packaged as arrays are electrically connected to contact pads and to traces in a top trace layer of the printed circuit board. The LED chips are wire bonded to the traces on the top side of the printed circuit board. The printed circuit board is then segmented to form discrete array light sources. Larger exposed areas of the traces on the top side form contact pads to which supply power is connected to each discrete array light source. 
     The LEDs are typically covered with a layer of phosphor before the array light sources on the printed circuit board are segmented or singulated. The phosphor converts a portion of the blue light generated by the LEDs to light in the yellow region of the optical spectrum. The combination of the blue and yellow light is perceived as “white” light by a human observer. Before the array light sources are segmented, the LEDs are typically covered by a layer of silicone that is formed into a lens above each light source. The layer of silicone also protects the LED chips and top-side wire bonds. 
     A slurry containing the phosphor has been conventionally dispensed manually into a ring or dam around the LED chips of each array light source. Then injection molding or casting molding has been used to form a lens above each array light source. The manufacturing process for LED light sources has been improved by combining the steps of dispensing the phosphor and forming the lens. By adding the phosphor to the silicone, the separate step of dispensing phosphor can be eliminated, and lenses are formed with phosphor dispersed throughout each lens. The lenses are formed using injection molding in which lens cavities that contain the LED dies are filled with the lens material, and the excess lens material is squeezed out of a leakage path. 
     When casting molding is used, a phosphor silicone slurry is first dispensed into the bottom half of each cavity, and then the top half of the cavity closes to define the lens structure and squeezes out the excessive lens material. The injection molding and casting molding processes have multiple disadvantages. First, the phosphor and the silicone are expensive, and the lens material that is squeezed out of the cavities is wasted. Second, the quality of the lenses formed with injection molding and casting molding is low because bubbles and nonuniformities remain in the finished product. 
     Fabricating an LED lens using these techniques is expensive because there are significant material losses and because non-standard semiconductor packaging technologies and equipment are used to package the lens. Therefore, systems and methods that reduce manufacturing costs by reducing waste and by making it easier to package LED dies/arrays using standard semiconductor packaging technologies and equipment are sought. In addition, systems and methods that enable LED package sizes to be shrunk to smaller sizes and to be handled using semiconductor packaging technologies and equipment are also sought. 
     SUMMARY 
     Systems and methods for manufacturing and processing LED devices using standard semiconductor packaging technologies and equipment are disclosed. The systems and methods enable LED package sizes to be shrunk to sizes that are smaller than can be made using conventional LED packaging technologies. In addition, a more efficient and less costly interface interconnect between an LED die/array and the packaging is disclosed. 
     A method of fabricating an LED system involves forming a lens over LED dies on a substrate with top-side contacts and then exposing the top-side contacts. The top-side contacts are disposed only on the top surface of the substrate. The substrate is provided with an array of LED dies disposed on the top surface of the substrate such that electrical connections to the array of LED dies are made only through the top-side contacts. The lens is formed over at least one of the LED dies using compression molding to shape a material that is disposed over substantially all of the top surface of the substrate. The top-side contacts that are covered by the material are then exposed by selectively removing the material from areas above the top-side contacts. 
     Another method of fabricating an LED system involves forming a lens over LED dies on a substrate, removing material from top-side contacts, and then cutting the substrate from a closed board. Electrical connections to the LED dies are made only through the top-side contacts. A molded lens is formed over LED dies that are disposed on the top surface of the substrate. The molded lens is formed using molding to shape a material that is disposed over substantially all of the top surface of the substrate. The material is then removed from areas above the top-side contacts, which are disposed only on the top surface of the substrate. The substrate is then cut from the closed board. The cutting leaves a pattern around all four sides of the singulated substrate. Thus, the entire perimeter of the substrate has a cut pattern, such as a v-cut pattern, a saw-blade cut pattern, a laser cut pattern, a punch-cut pattern, or a water-jet-cut pattern. 
     In embodiments where compression molding is used to form lenses of silicone over LED arrays on a metal core printed circuit board (MCPCB), a flash layer of silicone is left behind covering the contact pads that are later required to connect the arrays to power. A method for removing the silicone flash layer involves blasting abrasive particles in a stream of air at the silicone flash layer. The particles can be made of sodium bicarbonate, sodium sulfate, ammonium bicarbonate, silicon dioxide, aluminum oxide, or plastic or glass beads. The abrasive particles have a median diameter that is between forty and sixty microns. A nozzle is positioned within thirty millimeters of the top surface of the flash layer. The flow of air is generated by compressing the air to a pressure of more than one hundred pounds per square inch and allowing the compressed air to escape from a nozzle that has a diameter of less than two millimeters. The stream of air that exits from the nozzle is directed towards the top surface at an angle between five and thirty degrees away from normal to the top surface. The abrasive particles are added to the stream of air such that the particles are carried by the stream of air. The particles then collide into the top surface of the flash layer of silicone until the flash layer laterally above the contact pads is removed. 
     In some embodiments, an LED array light source includes LED dies mounted on a MCPCB and a lens above the LED dies formed from a layer of silicone. The MCPCB has a trace layer and a solder mask layer. The LED dies are electrically coupled to the trace layer. The solder mask layer is disposed over the trace layer. A contact pad is formed on the trace layer by an opening in the solder mask. The layer of silicone that is disposed over the LED dies forms an edge around the contact pad. The layer of silicone is not present laterally above the contact pad. The layer of silicone contains a trace amount of a blasting medium at the edge of the layer of silicone. The blasting medium is sodium bicarbonate, sodium sulfate, or ammonium bicarbonate. The layer of silicone can also contain phosphor. The trace amount of the blasting medium is embedded into the edge of the silicone around the contact pad when a flash layer of silicone is removed from above the contact pad by blasting abrasive particles of the blasting medium in a stream of air at the silicone flash layer. 
     In another embodiment, an LED array light source includes a printed circuit board (PCB), an LED die, a contact pad, and a layer of silicone. The PCB has a top side, a bottom side, and four top edges. The LED die and the contact pad are disposed on the top side of the PCB. The layer of silicone is disposed over the LED die and extends to each top edge of the PCB. However, the layer of silicone is not disposed laterally above a portion of the contact pad because the silicone has been removed by blasting abrasive particles in a stream of air at the layer of silicone. 
     In yet another embodiment, a high-pressure stream of water is used to remove the flash layer of silicone over the contact pads. The water is pressurized to a pressure of over fifty pounds per square inch and then forced through a nozzle with a diameter of less than one millimeter. The pressurized stream of water is aimed directly at the silicone flash layer over the contact pads until the flash layer is removed. Alternatively to using pure water, abrasive particles made of silica, aluminum oxide, or garnet can be added to the stream of water to allow the deflashing process to be performed at a lower water pressure compared to using pure water. 
     In some embodiments, standardized photon building blocks are used to make both discrete light emitters with one building block as well as array products with multiple building blocks. Each photon building block has one or more LED chips mounted on a carrier substrate. No electrical conductors pass between the top and bottom surfaces of the substrate. The photon building blocks are held in place by an interconnect structure that is attached to a heat sink. Examples of the interconnect structure include a molded interconnect device (MID), a lead frame device or a printed circuit board. 
     Landing pads on the top surface of the substrate of each photon building block are attached to contact pads disposed on the underside of a lip of the interconnect structure using solder or an adhesive. The lip extends over the substrate within the lateral boundary of the substrate. In a solder or SAC reflow process, the photon building blocks self-align within the interconnect structure. Molten SAC or solder alloy of the landing pads wets the metal plated contact pads, and the surface tension of the molten alloy pulls the landing pads under the contact pads. Conductors on the interconnect structure are electrically coupled to the LED dice in the photon building blocks through the contact pads and landing pads. The bottom surface of the interconnect structure is coplanar with the bottom surfaces of the substrates of the photon building blocks. 
     In some embodiments for array products, the substrates of multiple photon building blocks are supported by the interconnect structure. The substrates of all of the photon building blocks have substantially identical dimensions. A thermal interface material is placed on the upper surface of a heat sink, and the bottom surface of the interconnect structure contacts the thermal interface material. The interconnect structure is fastened to the heat sink by bolts that pass through holes in the interconnect structure. 
     A method of making both a discrete light emitter and an array product, which uses the same standardized photon building blocks supported by an interconnect structure, includes the step of mounting an LED die on a carrier substrate that has no electrical conductors passing from its top surface to its bottom surface. A landing pad on the top surface of the substrate is placed under and adjacent to a contact pad disposed on the underside of a lip of the interconnect structure. In order to place the landing pad under the contact pad, the lip of the interconnect structure is placed over the top surface of the substrate and within the lateral boundary of the substrate. 
     A conductor disposed on or in an interconnect structure is electrically connecting to an LED die on a photon building block by bonding a landing pad to a contact pad. A landing pad can be bonded to a contact pad by heating the metal alloy of the landing pad such that the landing pad aligns with the metal contact pad. Alternatively, the landing pad can be bonded to the contact pad using anisotropic conductive adhesive film (ACF) technology. After the landing pad is aligned with and bonded to the contact pad, the bottom surface of the substrate is substantially coplanar with the bottom surface of the interconnect structure. 
     When this method is used to make an array product with multiple photon building blocks, a second lip of the interconnect structure is placed over the top surface of the substrate of a second photon building block, and a second landing pad on the second substrate is placed under and adjacent to a second contact pad under a lip of the interconnect structure. The second substrate of the second photon building block has dimensions that are substantially identical to those of the substrate of the first photon building block. A second conductor of the interconnect structure is electrically connected to a second LED die on the second photon building block by bonding the second landing pad to the second contact pad. After the second landing pad is bonded to the second contact pad, the bottom surface of the substrate of the second photon building block is substantially coplanar to the bottom surface of the interconnect structure. 
     A thermal interface material is then placed over the upper surface of a heat sink. The bottom surfaces of the interconnect structure and of the substrates of the photon building blocks are placed over the thermal interface material. 
     In some embodiments, a novel light emitting device includes an LED die disposed above a substrate that includes no electrical conductors between the top and bottom surfaces of the substrate. The device also includes a means for electrically coupling the LED die to a conductor located outside the lateral boundary of the substrate. The means contacts a landing pad disposed on the top surface of the substrate. The landing pad aligns the substrate to a contact pad on the means when the landing pad is heated. The means has a bottom surface that is coplanar with the bottom surface of the substrate. 
     After any die attach and wire bonding steps in the manufacturing of an array-based LED assembly, a layer of Highly Reflective (HR) material is deposited around the LED dice to coat the upper surface of the substrate. In one example, the HR material is deposited with precision by jetting microdots of the HR material in liquid form onto selected portions of the upper surface of the substrate, thereby forming a layer of HR material that is thick enough (at least 10 microns thick) to have a reflectivity of at least 85 percent. 
     Limits on mechanical tolerances can lead to physical differences between the LED assemblies being manufactured. LED dice may differ slightly in size, and LED dice may be placed in slightly different locations from one LED assembly to the next. In accordance with some embodiments, machine imaging is usable to detect such physical differences from LED assembly to LED assembly and to control the jetting process to adjust for such physical differences so that in each LED assembly being manufactured substantially all of the upper substrate surface that is not covered with an LED die is coated with HR material. 
     In one example, each microdot of HR material has a diameter of less than 100 microns and is typically 50-80 microns in diameter. The HR material has an adequately low viscosity (less than 1100 cP) such that it flows laterally to some degree once it reaches the substrate surface. Due to the lateral flow of the HR material, the HR material can be made (1) to flow under bridging wire bonds and to coat the substrate underneath the wire bonds, (2) to reach and to wet side edges of the LED dice, or (3) to reach and to wet the inside side edge of a phosphor retaining ring. In one example, the area of substrate between LED dice is not coated with HR material in order to reduce manufacturing time. Because the HR material is only deposited after die attach and after wire bonding, fiducial markers on the upper surface of the substrate (that would otherwise be covered and obscured by HR material were conventional screen printing used to deposit the HR material) are observable and usable during die attach and wire bonding. The depositing of the HR layer by jetting microdots of HR material results in a reduction in the amount of exposed substrate area that is not covered with HR material. Reducing the amount of exposed substrate area that is not covered with HR material serves to improve the light efficiency of the resulting LED assembly. 
     Further details and embodiments and techniques are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
         FIG. 1  (prior art) is a perspective view of an existing array product with multiple LED chips electrically connected to pads on the top side of a carrier substrate. 
         FIG. 2  is a cross sectional view of an LED system with an array of LED dies and top-side contacts disposed on the top surface of a substrate according to one embodiment of the invention. 
         FIG. 3  is a flowchart illustrating a method of fabricating an LED system with a compression-molded lens and exposed top-side contacts. 
         FIG. 4  is a cross sectional view of an LED system with a molded lens and top side contacts exposed using deflashing. 
         FIG. 5  is a flowchart illustrating a method of fabricating an LED system with a molded lens and top side contacts exposed using deflashing. 
         FIG. 6A  is a perspective view of an LED system with a molded lens, an array of LED dies and exposed top-side contacts that has been separated from a closed board and has a v-cut pattern around its entire perimeter. 
         FIG. 6B  is a cross sectional bubble view of a portion of the v-cut perimeter of the LED system of  FIG. 6A . 
         FIGS. 7A-B  shows laser-cut patterns on sides of substrates formed when a laser is used to separate an LED system from a closed board. 
         FIG. 8A  shows a saw-blade cut pattern on the side of a substrate formed by dicing a closed board using a saw blade. 
         FIG. 8B  is a cross-sectional perspective view of a punch-cut pattern formed on a substrate by punching a closed board using a punch apparatus. 
         FIG. 8C  shows a punch cut pattern on the side of a substrate formed by punching a closed board using a punch apparatus. 
         FIG. 8D  shows a substrate being cut with a water jet. 
         FIG. 8E  shows a water jetting cut pattern on the side of a substrate formed by cutting the substrate using a water jet apparatus. 
         FIG. 9  is a flowchart illustrating a method of fabricating an LED system with a molded lens and exposed top-side contacts by separating the LED system from a closed board. 
         FIG. 10  is a top view of a metal core printed circuit board (MCPCB) on which multiple arrays of LED dies are mounted. 
         FIG. 11  is a top view of the MCPCB of  FIG. 10  on which areas have been marked to show where a flash layer should be removed to expose contact pads. 
         FIG. 12  is a cross sectional view of the MCPCB of  FIG. 10  showing the flash layer that is to be removed using the novel blasting process. 
         FIG. 13  is a more detailed view of the flash layer of  FIG. 12 . 
         FIG. 14  is a flowchart of steps of a method for removing a flash layer of silicone that covers contact pads without damaging the contact pads. 
         FIG. 15  is a cross sectional view illustrating blasting particles colliding with a flash layer at a blasting site enclosed by a blasting mask. 
         FIG. 16  is a cross sectional view of the blasting sites of  FIG. 12  after the flash layer has been removed using the method of  FIG. 14 . 
         FIG. 17  is a top view of another MCPCB from which a flash layer of silicone is to be removed using the method of  FIG. 14 . 
         FIG. 18  is a top-down perspective view of a blasting site between four lenses on the MCPCB of  FIG. 17 . 
         FIG. 19  is a perspective view of a discrete light source with top-side electrical contacts from which a flash silicone layer has been removed. 
         FIG. 20  is a cross-sectional view of a novel photon building block supported by an interconnect structure. 
         FIG. 21  is a more detailed view of a contact pad connected to a landing pad as shown in  FIG. 20 . 
         FIG. 22A  is a cross-sectional view of a conductor on an interconnect structure coupled through a contact pad to a landing pad on a substrate. 
         FIG. 22B  is a perspective view of the path of the conductor of  FIG. 22A  passing through a hollow via to the contact pad. 
         FIG. 22C  is a perspective view of the conductor of  FIG. 22A  passing through and entirely covering the inside surface of a hollow via. 
         FIG. 23  is a cross-sectional view of the conductor of  FIG. 22A  passing around the rounded edge of a lip of the interconnect structure. 
         FIG. 24  shows a landing pad on the substrate bonded to a contact pad on the underside of a lip of the interconnect structure by an anisotropic conductive adhesive (ACF). 
         FIG. 25  shows a lead frame interconnect structure with a metal foil layer that functions both as a conductor of the interconnect structure and as a contact pad that bonds to a landing pad on the substrate. 
         FIG. 26  shows an interconnect structure made from a printed circuit board with a metal layer that functions both as a conductor of the interconnect structure and as a contact pad that bonds to a landing pad on the substrate. 
         FIG. 27  is a top view of a photon building block that includes four LED dice surrounded by four landing pads. 
         FIG. 28  is a top view of another implementation of a photon building block that includes four LED dice surrounded by two landing pads. 
         FIG. 29A  is a top view of two photon building blocks in an interconnect structure built into an array product. 
         FIG. 29B  is a cross-sectional view through line B-B of the array product shown in  FIG. 29A . 
         FIG. 29C  is a cross-sectional view through line C-C of the array product shown in  FIG. 29A . 
         FIG. 30A  is a more detailed view of the connection between the landing pad of the substrate and the contact pad of the interconnect structure shown in  FIG. 29A . 
         FIG. 30B  shows the contact pad  FIG. 30A  without the landing pad below. 
         FIG. 31  is a perspective view of four photon building blocks in an interconnect structure built into an array product. 
         FIG. 32  is a flowchart of steps for making both a discrete light emitter and an array product using the same standardized photon building blocks. 
         FIG. 33A  is a perspective view of another embodiment of a photon building block containing a plurality of LED dies. 
         FIG. 33B  shows another embodiment of photon building block of  FIG. 33A  in which the LED dies are not connected by wire bonds all the way to the landing pads. 
         FIG. 33C  is a perspective view of the photon building block of  FIG. 33B  that includes a micro-lens centered over each LED die. 
         FIG. 34A  is a cross-sectional view of the photon building block of  FIG. 33B  being supported by an interconnect structure solely through landing pads on the upper surface of the substrate. 
         FIG. 34B  is a cross-sectional view of the photon building block of  FIG. 33A  being supported solely through landing pads on the upper surface of the substrate. 
         FIG. 35A  is perspective view of the bottom surface of an hexagonal star-shaped molded interconnect structure. 
         FIG. 35B  is a top perspective view of the molded interconnect structure of  FIG. 35A  supporting the photon building block of  FIG. 33C . 
         FIG. 36A  is a top perspective view of a packaged LED array in which a photon building block is supported by a hexagonal molded leadframe structure. 
         FIG. 36B  is a bottom perspective view of the indentation on the bottom side of the molded leadframe structure of  FIG. 36A  into which a photon building block fits. 
         FIG. 37A  is a perspective view of a hexagonal molded interconnect structure with surface conductive paths supporting the photon building block of  FIG. 33C . 
         FIG. 37B  is a perspective view of an hexagonal molded interconnect structure with inner lead frame conductors. 
         FIG. 37C  is a perspective view of the bottom side of the molded interconnect structure of  FIG. 37B  showing contact pads formed from the leadframe conductors. 
         FIG. 38  is a perspective view of a lead frame reel with templates of conductors such as those in the molded interconnect structure of  FIG. 37C . 
         FIG. 39  (prior art) is top-down diagram of one type of conventional LED assembly. 
         FIG. 40  (prior art) is a simplified cross-sectional side view of the LED assembly of  FIG. 39 . 
         FIG. 41  (prior art) is a top-down diagram of a panel of metal core printed circuit boards (MCPCBs). 
         FIG. 42  (prior art) is a top-down diagram of the die placement area of an MCPCB of  FIG. 42  before die placement. 
         FIG. 43  (prior art) is a diagram of a screen printing mask used to apply a highly reflective (HR) material onto the die placement area of  FIG. 42 . 
         FIG. 44  (prior art) is a top-down diagram of the die placement area of  FIG. 42  after deposition of the HR material. 
         FIG. 45  (prior art) is a top-down diagram of the die placement area of  FIG. 44  after die attach has been completed. 
         FIG. 46  (prior art) is a top-down diagram of the die placement area of  FIG. 45  after wire bonding has been completed. 
         FIG. 47  (prior art) is a top-down diagram of the die placement area of  FIG. 46  after formation of a phosphor retaining ring. 
         FIG. 48  (prior art) is a top-down diagram of the die placement area of  FIG. 47  after placement of phosphor within the retaining ring. 
         FIG. 49  is a top-down diagram of a white LED assembly in accordance with one novel aspect. 
         FIG. 50  is a simplified cross-sectional side view of the white LED assembly of  FIG. 49 . 
         FIG. 51  is a top-down diagram of a panel of MCPCBs of which the MCPCB of  FIG. 50  is one. 
         FIG. 52  is a top-down diagram of the die placement area of the MCPCB of  FIG. 50 . 
         FIG. 53  is a top-down diagram of the placement area of  FIG. 52  after die attach has been completed. 
         FIG. 54  is a top-down diagram of the placement area of  FIG. 53  after wire bonding has been completed. 
         FIG. 55  is a top-down diagram of the placement area of  FIG. 54  after formation of the phosphor retaining ring. 
         FIG. 56  is a simplified cross-sectional diagram that shows the deposition of an HR layer by jetting microdots of HR material onto the substrate around and between the LED dice of the LED assembly. 
         FIG. 57  is a simplified top-down diagram of the die placement area after the jetting of the HR material has been completed. 
         FIG. 58  is a simplified top-down diagram of the die placement area after phosphor has been placed over the LED dice within the confines of the retaining ring. 
         FIG. 59  is a simplified cross-sectional diagram of a white LED assembly where the LED dice are disposed in a well. 
         FIG. 60  is a simplified cross-sectional diagram of a white LED assembly having a ceramic substrate. 
         FIG. 61  is a simplified cross-sectional diagram of a white LED assembly having a ceramic substrate, where the HR material does not touch a side edge of any of the LED dice, and is not disposed between the LED dice. 
         FIG. 62  is a flowchart of a method in accordance with a novel aspect. In a first novel aspect, an HR layer is deposited onto the substrate of an LED assembly after die attach and after wire bonding. In a second novel aspect, an HR layer is deposited by jetting microdots of HR material onto a substrate of the LED assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
     Systems and methods for manufacturing and processing LED devices using standard semiconductor packaging technologies and equipment are disclosed. The systems and methods enable LED package sizes to be shrunk to sizes that are smaller than can be made using conventional LED packaging technologies. In addition, a more efficient and less costly interface interconnect between an LED die/array and the packaging is disclosed. 
     In one embodiment, an LED is fabricated by providing a substrate with an array of LED dies and top-side contacts. One or more lenses are formed over the array of LED dies using compression molding such that one lens is formed over at least one of the LED dies. The top-side contacts are exposed by selectively removing material from areas covering the top-side contacts. Fabricating LED lens in this manner enables low cost mass production of LED dies and arrays that have an interface interconnect that makes it easy to package the LED dies and arrays. 
     In another embodiment, an LED system is fabricated by providing a substrate with an array of LED dies and top-side contacts. A lens is formed over the array of LED dies using compression molding, and the top-side contacts are exposed by selectively de-flashing material from areas covering the top-side contacts. Fabricating LED lenses in this manner also enables low cost mass production of LED dies and arrays that have an interface interconnect that makes it easy to package the LED dies and arrays. 
     In another embodiment, an LED system is fabricated by cutting a substrate that has an array of LED dies formed on it from a closed board. A molded lens is formed over the array of LED dies using compression molding, and the plurality of top-side contacts are exposed by selectively removing material from areas above the top-side contacts. When the substrate is cut, a cut pattern is formed around the entire perimeter of the substrate because the substrate is cut from a closed board. The substrate can be cut from the closed board using v-cutting, saw-blade cutting, laser cutting, punch cutting, water-jet cutting or a combination of these techniques. The cut pattern that surrounds the entire perimeter of the substrate has a v-cut pattern, a saw-blade cut pattern, a laser cut pattern, a punch cut pattern, a water-jet-cut pattern or a combination of these cut patterns. Fabricating an LED system in this manner also reduces the cost of mass production of LED dies on substrates that have an interface interconnect that makes it easy to package the substrate and LED dies. 
       FIG. 2  is a cross sectional view of an LED system  20  with an array of LED dies  21  disposed on the top surface  22  of a substrate  23 . Top-side contacts  24  are also disposed on top surface  22  of substrate  23 . A compression molded lens  25  is disposed over the LED dies  21 . 
       FIG. 3  is a flowchart illustrating steps  26 - 29  of a method of fabricating LED system  20  with compression-molded lens  25  and top-side contacts  24 . The first step  26  involves providing substrate  23  with the array of LED dies  21  disposed on top surface  22  of substrate  23 . Electrical connections to the array of LED dies  21  are made through a plurality of the top-side contacts  24 , which are disposed only on top surface  22  of substrate  23 . In step  27 , lens  25  is formed over at least one of the LED dies  21  by using compression molding to shape a material that has been disposed over substantially all of top surface  22  of substrate  23 . In one example, the material is silicone. In the embodiment of  FIG. 2 , a single lens is formed over the array of LED dies  21 . In other embodiments, however, individual micro-lenses are formed over less than the entire array, such as over individual LED dies. In step  28 , the plurality of top-side contacts  24  are exposed by selectively removing the material that forms the lens from areas covering the top-side contacts  24 . As shown in  FIG. 2 , the material need not be removed from the entire area above the contacts  24 . In step  29 , substrate  23  is detached from the closed board of which it was a part.  FIG. 2  shows substrate  23  after being detached from the closed board. 
     Further details regarding LEDs with compression molded lens and top-side contacts and methods of making them are provided below with reference to  FIGS. 10-19 . LED arrays with compression molded lens and top-side contacts can also be configured with an interface interconnect that makes it easier and more cost effective to package the LED dies as is further discussed with reference to  FIGS. 20-38 .  FIG. 2  shows an example of the interface interconnect  30 . 
       FIG. 4  is a cross sectional view of an LED system  32  with a molded lens  33  and top side contacts  34  exposed using deflashing. A substrate  35  with an array of LED dies  36  is disposed on a top surface  37  of the substrate. Electrical connections to the array of LED dies  36  are made through the top-side contacts  34 , which are disposed only on top surface  37  of substrate  35 . Molded lens  33  is formed over at least one of the LED dies  36 . The material used to make lens  33  is disposed over substantially all of top surface  37  of substrate  35  except for over the top-side contacts  34 . The material is selectively removed from the areas above the top-side contacts  34 . A plurality of solder connections  38  are formed on the plurality of top-side contacts  34 . A plurality of leads  39  are coupled to the plurality of solder connections  38 . In  FIG. 4 , one of the leads  39  is depicted as a wire. In  FIG. 2 , a lead  40  that is coupled to a solder connection  38  is depicted as a contact pad that is attached to a top-side contact  24  by the solder connection  38 . 
       FIG. 5  is a flowchart illustrating steps  41 - 46  of a method of fabricating LED system  32  with molded lens  33  and top side contacts  34  exposed using deflashing. In a step  41 , substrate  35  is provided with an array of LED dies  36  disposed on top surface  37  of the substrate. Substrate  35  is part of a closed board. Electrical connections to the LED dies  36  are made through the top-side contacts  34  that are disposed only on top surface  37 . In step  42 , molded lens  33  is formed over at least one of the LED dies  36  using a type of molding to shape a material that is disposed over substantially all of top surface  37 . In step  43 , the top-side contacts  34  are exposed by selectively de-flashing the material from areas covering the top-side contacts  34 . In step  44 , substrate  35  is detached form the closed board. In step  45 , the solder connections  38  are formed on the top-side contacts  34 . In step  46 , the leads  39  are connected to the solder connections  38  such that the LED dies  36  are connected only through the leads  39 . 
     LED arrays with molded lens and top side contacts exposed using deflashing can also be configured with an interface interconnect that makes it easier and more cost effective to package the LED dies and arrays as is further discussed with reference to  FIGS. 20-38 . 
       FIG. 6A  is a cross sectional view of an LED system  50  that has been separated from a closed board. LED system  50  has a molded lens  51 , an array of LED dies  52  and exposed top-side contacts  53 . The LED dies  52  are electrically connected only through the top-side contacts  53 , which are disposed only on the top surface  54  of a substrate  55 . LED system  50  has been separated from a closed board using a v-cutting process such that a v-cut pattern  56  is present around the entire perimeter of substrate  55 . Thus, the v-cut pattern  56  is present on each of the four sides  57 - 60  of substrate  55 . Singulation of LED system  50  from the closed board is performed by v-scribing both the top surface  54  and the bottom surface  61  and then snapping off the remaining thin portion  62  of the closed board that remains between the two v-cuts. The thin portion  62  through the middle each side  57 - 60  is rougher than the cut portions above and below because the thin middle portion has been snapped off. 
       FIG. 6B  is a bubble view of a portion of side  57  of LED system  50  showing the v-cut pattern  56  in more detail. The thin snapped portion  62  runs through the middle of the V-cut pattern  56 . 
     In another embodiment, a laser is used to separate substrate  55  from the closed board.  FIG. 7A  is a top-down view of top surface  54  showing a laser-scribed cut pattern  63  on side  57  that remains after individual laser holes are burned along the edge that is to be cut. The laser leaves the laser-scribed cut pattern  63  around the entire perimeter of substrate  55 .  FIG. 7B  shows a laser-machined cut pattern  64  that remains on side  57  after a laser beam is run along the edge of the closed board that is to be cut. Laser-machined but pattern  64  is smoother than laser-scribed cut pattern  63 . Both laser-scribed cut pattern  63  and laser-machined cut pattern  64  are shown at the same magnification. 
     In yet another embodiment, a saw blade is used to separate substrate  55  from the closed board. The saw blade leaves a saw-blade cut pattern  65  around the entire perimeter of substrate  55 , as shown in  FIG. 8A . The curved lines on the saw-blade cut pattern  65  are left by a rotating saw blade. 
     In yet another embodiment, a punch apparatus is used to separate substrate  55  from the closed board. Punching leaves a punch cut pattern  66  around the entire perimeter of substrate  55 , as shown in  FIGS. 8B-C . The punch cut pattern  66  includes substantially vertical lines generated in the direction that the punch apparatus moves to cut the substrate  55 . The punch cut pattern  66  can include a secondary pattern  67  that resembles a compression left over by the punching process. The punch cut pattern can also leave a rounded corner  68  on the side that the punch apparatus impacts substrate  55 . In the orientation of  FIG. 8B , the punch apparatus impacts substrate  55  first from the bottom. 
     In yet another embodiment, a water jetting apparatus is used to separate substrate  55  from the closed board. As illustrated in  FIG. 8D , when water jetting is used to cut substrate  55 , garnet particles dispersed in a fluid are ejected from a nozzle and follow a curved pattern through substrate  55 . The curved pattern is curved in the direction opposite to the direction of the water jet motion. Cutting substrate  55  with a water jet leaves a water-jet cut pattern  69  around the entire perimeter of substrate  55 , as shown in  FIG. 8E . The water-jet cut pattern  69  is curved from top to bottom with the top being the surface of substrate  55  that the water jet particles impact first (i.e., the side of the substrate on which the water jet is located). 
       FIG. 9  is a flowchart illustrating steps  73 - 77  of a method of fabricating LED system  50  with molded lens  51  and exposed top-side contacts  53  by separating LED system  50  from a closed board. In step  73 , molded lens  51  is formed over LED dies  52  that are disposed on top surface  54  of substrate  55 . Molded lens  51  is formed using molding to shape a material that is disposed over substantially all of top surface  54  of substrate  55 . In step  74 , the material is removed from areas above top-side contacts  53 . In step  75 , substrate  55  is cut from a closed board. The cutting of substrate  55  is performed using a technique such as v-cutting, dicing with a saw blade, laser cutting, punch cutting or water-jet cutting. In step  76 , solder connections are formed on top-side contacts  53 . In step  77 , leads are connected to the solder connections. Electrical connections to the LED dies  52  are made only through the leads and top-side contacts  53 . 
     Further details of LED systems with molded lenses and top side contacts and methods of making them from closed boards are provided below with reference to  FIGS. 10-19 and 39-62 . The LED systems can also be configured with an interface interconnect that makes it easier and more cost effective to package the arrays of LED dies is discussed below with reference to  FIGS. 20-38 . 
       FIG. 10  is a top view of a metal-core printed circuit board (MCPCB)  110  on which multiple arrays of LED dies  111  are mounted. Because MCPCB  110  has a metal core, it would be difficult to supply power to the LED dies  111  through through-hole vias that pass from the LEDs through the printed circuit board to the bottom surface of the board. Consequently, the LED dies  111  are electrically connected to contact pads on the top side of MCPCB  110 . The MCPCB  110  is then segmented to form discrete array light sources. The discrete light sources can be used as standardized photon building blocks by packaging them in a multitude of ways using a molded interconnect structure that electrically contacts the photon building blocks from the top side. How discrete light sources are packaged in a molded interconnect structure that electrically connects only from the top side to the discrete light sources is described in detail below. 
     In the embodiment of  FIG. 10 , MCPCB  110  includes a 5×12 matrix of 4×4 LED arrays. MCPCB  110  has a length of about 250 mm and a width of about 75 mm. Each LED array is later segmented into a square of the MCPCB that is 11.5 mm on a side. Thus, MCPCB  110  has a very high density of light sources per area of the printed circuit board. There are less than three millimeters of space on the board between the edge of the lens that covers the LED dies  111  and the edge of each of the segmented square light source. At each corner of the square is a contact pad  112  that is used to supply power to the array light source. The contact pads  112  are formed by exposing large triangular areas of a trace layer. The trace layer is covered by a solder mask layer  113  of hardened epoxy. Holes in solder mask layer  113  form the contact pads  112  and the locations on the trace layer below to which the LED dies  111  are wire bonded. 
     A lens is formed over each LED array using compression molding. Compression molding can be used because there are no holes or opening from the top side to the bottom side of MCPCB  110  through which high pressure molding material could escape. Thus, MCPCB  110  is a closed board. Conventional printed circuit boards used to mount LED arrays have punch-outs or etchings cuts to isolate the electrical leads of each LED array. MCPCB  110 , on the other hand, is a closed board with no punch outs, holes or etching cuts through the board. The very high density of components and the closed board of MCPCB  110  are conducive to compression molding. A single molding chamber is formed over the top of MCPCB  110  by sealing the chamber around the border  114  of MCPCB  110 . A small space is maintained between solder mask layer  113  and the mold cover to allow the molding material to flow freely between the individual cavities above the LED arrays. In the actual molding process, MCPCB  110  is inverted and lowered into the mold cover, which contains the lens cavities. The molding material is pumped into the single molding chamber under pressure and fills all of the crevices of the cavities without leaving bubbles or nonuniformities in the hardened molding material. The molding material that fills the small space between the mold cover and solder mask layer  113  forms a thin flash layer that covers the contact pads  112  that must later be electrically coupled to the interconnect packaging structure. 
     In one embodiment, the molding material is a slurry of phosphor particles in silicone. The phosphor is evenly dispersed throughout the silicone and converts a portion of the blue light generated by the LEDs into light in the yellow and red regions of the optical spectrum. The blue light from the LEDs and the yellow and red light from the phosphor combine to yield white light, which is optically spread out by the surface of the lens. After the lenses are formed using compression molding, the individual LED array light sources are segmented by cutting MCPCB  110  into squares. It is more efficient, however, first to remove the flash layer that covers the contact pads  112  before segmenting MCPCB  110  into individual LED array light sources. 
       FIG. 11  is a top view of MCPCB  110  of  FIG. 2  on which areas have been marked to show where the flash layer should be removed to expose the contact pads  112 . For a unit size of 11.5 mm by 11.5 mm for the LED array light sources of  FIG. 2 , the contact pads  112  can be cleaned of the silicone flash layer by removing silicone from 5 mm by 5 mm squares. A novel micro-bead blasting process is used to remove the silicone flash layer from the square blasting sites  115 . 
       FIG. 12  is a cross sectional view of MCPCB  110  of  FIG. 2  showing the flash layer  116  that is to be removed using the novel blasting process. MCPCB  110  has a thick solid aluminum base  117 . For example, aluminum base  117  is 1.6 mm thick. A dielectric layer  118  separates aluminum base  117  from the trace layer  119  that forms the contact pads  112 . Dielectric layer  118  has a thickness of about twenty microns (micrometers or μm). Trace layer  119  does not entirely cover dielectric layer  118 , but rather is formed by patterned traces separated by dielectric material. Solder mask layer  113  covers trace layer  119  and has openings only over the contact pads  112  and the locations at which the LED dies  111  are wire bonded to traces. 
     The molded silicone forms lenses  120  over the arrays of LED dies  111 . In the embodiment of  FIG. 12 , the diameter of lens  120  is about twice as long as each side of the 4×4 array of LED dies so as to allow most of the emitted light to reach the surface of lens  120  within the critical angle required for the light to escape from the lens. The height of the lens  120  is about 1.5 mm from solder mask layer  113 . Other embodiments have lenses of different sizes and shapes over the LED dies  111 . For example, the silicone above each LED array can have a small overall curvature that is covered by many smaller micro-structures, such as hemispheres or pyramids. Alternatively, the lens shape can have a dimple above the middle of each LED array. 
       FIG. 13  is a more detailed view of flash layer  116  of  FIG. 12 .  FIG. 13  shows that flash layer  116  is relatively thick compared to trace layer  119 . Whereas in some compression molding processes flash layer  116  has a thickness between fifty to one hundred microns, trace layer  119  can have a thickness of less than five microns. Trace layer  119  typically has three sublayers: a thicker lower layer of copper, a thinner middle layer of nickel, and a thinner upper layer of either gold or silver. Copper is less expensive than nickel, gold or silver, so the traces are comprised mostly of copper. The upper layer of gold or silver is required because it is difficult to solder the wire bonds directly to copper. The middle layer of nickel is used to attach the gold or silver to the thicker copper layer because gold and silver do not readily adhere directly to copper. The copper is typically 2-80 microns thick, the nickel is typically 1-3 microns thick, and the gold or silver is typically 1-5 microns thick. Thus, the contact pads  112  will be damaged if the gold or silver that is no thicker than five microns is removed from the upper surface of the trace layer  119 . The novel micro-bead blasting process provides a way of removing silicone flash layer that is about fifty microns thick without removing the upper layer of trace layer  119 , which is only about one tenth as thick. 
       FIG. 14  is a flowchart illustrating steps  121 - 125  of a micro-bead blasting process that removes a flash layer of silicone that covers contact pads without damaging the contact pads. The steps of the method of  FIG. 14  are described in relation to  FIG. 13 . 
     In a first step  121 , the flash layer  116  is formed over the printed circuit board  110  using compression molding. Although the flash layer  116  of  FIG. 13  results from compression molding silicone, other transparent molding materials may also be used, such as epoxy. The flash layer of silicone  116  in  FIG. 13  is disposed above two contact pads  112 . 
     In step  122 , a nozzle  127  is positioned within thirty millimeters of a top surface  128  of flash layer  116 . In order to clean a blasting site  115  that is 5 mm by 5 mm square, the method of  FIG. 14  uses a nozzle  127  that has a diameter of about two millimeters and that is placed about twenty-two millimeters above top surface  128 . A smaller nozzle diameter would be used to remove a flash layer from a smaller blasting site, in which case the nozzle would be positioned closer to the top surface of the flash layer. For example, in order to clean the flash layer from a blasting site  115  having a diameter of two millimeters located between LED arrays having unit sizes of five millimeters on a side, nozzle  127  would have a diameter of about 0.5 millimeters and would be positioned about two millimeters above the top surface  128  of flash layer  116 . The blasting site is located over the contact pads  112  that are to be cleaned of flash layer  116 . Positioning nozzle  127  farther away from top surface  128  allows the stream of air exiting the nozzle to spread out into a wider plume  129  before contacting top surface  128 . Thus, nozzle  127  must be positioned closer to top surface  128  in order to maintain the stream of air within a smaller blasting site  115 . 
     In step  123 , the flow of air that exits nozzle  127  is directed at top surface  128  of flash layer  116  within blasting site  115 . The stream of air that exits from nozzle  127  is directed towards top surface  128  at an angle that is between five and thirty degrees away from a normal angle to the top surface. The stream of air is generated by compressing the air to a pressure of more than one hundred pounds per square inch (psi) and then allowing the compressed air to escape from nozzle  127 . In order to clean a blasting site  115  that is 5 mm by 5 mm square, the flow of air is generated by compressing the air to a pressure between one hundred and one hundred forty pounds per square inch and then allowing the compressed air to escape from a nozzle that has a diameter of less than two millimeters. 
     In step  124 , blasting particles  130  of a blasting medium are added to the stream of air such that the particles are carried by the stream of air and collide into top surface  128  of flash layer  116  above contact pad  112 . The blasting particles  130  are also called micro beads, although they need not be spherically shaped. The blasting medium should have a Mohs hardness of less than three; sodium bicarbonate (NaHCO 3 ), sodium sulfate and ammonium bicarbonate (ammonium hydrogen carbonate, (NH 4 HCO 3 )) can be used. In one embodiment, the blasting particles  130  are monoclinic prisms of sodium bicarbonate that have been purified and sorted through a sieve to have a uniform particle size of about fifty microns in the longest dimension. The blasting particles  130  are stored as a powder and are added into the flow of air by a mixer  131  shortly before exiting nozzle  127 . 
     When cleaning a blasting site  115  that is 5 mm by 5 mm square, the nozzle can be placed about twenty-two millimeters above top surface  128 , which allows the blasting particles  130  to achieve their highest velocity. When the particles  130  are first added to the flow of air by mixer  131 , the inertia of the particles prevents them from immediately accelerating to the speed of the air flow. However, within about twenty-two millimeters, the particles  130  have accelerated to the speed of the stream of air and have achieved their highest velocity. At distances greater than about thirty millimeters from nozzle  127 , resistance from ambient air overcomes the thrust from the stream of air and slows down the particles  130 . At distances less than about twenty millimeters from nozzle  127 , the particles  130  have not yet accelerated to the speed of the flow of air. Thus, where particles of about fifty microns in length are used, flash layer  116  can be removed in the shortest period of time by blasting the particles from a distance of about twenty-two millimeters because the particles possess the most amount of kinetic energy at that distance from the nozzle. 
     In step  125 , the particles  130  are collided into flash layer  116  until the flash layer laterally above contact pad  112  is removed. The particles  130  have facets and edges that rip the silicone of the flash layer  116  apart. Then the air blows the ripped pieces of silicone away. Small amounts of sodium bicarbonate remain embedded in the silicone that has not been removed. When cleaning the relatively large blasting sites  115  of  FIG. 11 , nozzle  127  may be placed at about twenty-two millimeters from top surface  128  of flash layer  116 , which permits the particles  130  to acquire their maximum kinetic energy. Consequently, the flash layer in the blasting sites  115  that are squares 5 mm on a side can be removed in a relatively short 2-3 seconds. On the other hand, when cleaning the relatively small blasting site  115  having a diameter of two millimeters located between LED arrays having unit sizes of five millimeters on a side, nozzle  127  must be placed a relatively close two millimeters from top surface  128 , which does not permit the particles  130  to achieve their maximum speed. Consequently, the flash layer in a blasting site with a diameter of two millimeters can be removed only after a relatively long eight seconds of blasting. 
     The stream of air exiting nozzle  127  is not directed in step  123  towards flash layer  116  at an angle normal to top surface  128 , i.e., the stream of air is not directed orthogonally to top surface  128 . Instead, the stream of air is directed towards flash layer  116  at an angle that is between five and thirty degrees away from normal to the top surface in order to permit the particles  130  to be blown away from the blasting site. If the nozzle were to be directed orthogonally to the top surface of the flash layer, the blasting particles would bounce straight back up and collide with the particles in the stream of air. This would reduce the force by which the blasting particles collide with the flash layer. In addition, the particles would not bounce sideways after striking the top surface and therefore would not be carried out of the blasting site and would build up. On the other hand, if the nozzle were directed at a shallow angle to the top surface of the flash layer, such as an angle greater than thirty degrees from normal, then the vector of the particle speed normal to the top surface would be insufficient to remove the flash layer. The particles would tend to be deflected by the top surface and would not break into the surface. 
     Even at a steeper angle of incidence, such as ten degrees, the blasting particles  130  are more likely to bounce off of top surface  128  instead of breaking into the surface when flash layer  116  is thicker. At the beginning of the blasting process when flash layer  116  is still about fifty microns thick, the particles  130  are more likely to bounce off top surface  128  because the thicker silicone flash layer can elastically compress to absorb the impact of the particles. As flash layer  116  is eaten away and becomes thinner, the rate of silicone removal becomes faster as the kinetic energy of the particles increasingly tears the silicone as opposed to being absorbed by the silicone. 
     Current compression molding techniques specify that the thickness of a flash layer of silicone can be fifty±25% microns. It is desirable to keep the flash layer as thin as possible to save on silicone but yet allow the silicone to flow freely between the individual lens cavities to achieve high quality lens structures. Where the flash layer is thinner than thirty microns, the elasticity of the silicone layer is reduced to the point that blasting particles do not readily bounce off of the silicone but rather tear the silicone. As even thinner flash layers become possible, the flow of compressed air alone will be sufficient to remove the flash layer from between the lens structures. 
       FIG. 15  illustrates blasting particles at a blasting site that is enclosed by a blasting mask  132 . Blasting mask  132  is made of stainless steel and is about 200-500 microns thick. Mask  132  is used when the lenses are particularly close to the blasting sites  115  and must be protected from the blasting particles  130 . For example, blasting mask  132  is used for blasting sites located between LED arrays having unit sizes of five millimeters on a side. The blasting process is sped up by using a mask because the flow of air need not be turned off when moving from site to site. Each lens  120  is protected from the blasting particles  130  by mask  132  as the stream of air moves over the lens to a new blasting site. In contrast, where no blasting mask is used with larger unit sizes, such as an array unit size of 11.5 mm on a side, the flow of air is turned off as the position of the nozzle is moved from one blasting site to another in order to avoid damaging the lens structures. 
     Using a blasting mask, however, creates other complications that slow down the blasting process. The thickness of the blasting mask creates a well that both (i) obstructs the corners of the blasting site from being reached by the stream of air and (ii) hinders the blasting particles from being blown away from the blasting site. First, the blasting mask obstructs the nearest corner of the blasting site from direct blasting by the angled stream of air. Thus, the far side of the blasting site  115  is cleaned first, and then MCPCB  110  is rotated to permit the cleaning of the other side of the blasting site. The rotation and double pass of the stream of air slow the blasting process. Second, the sides  133  of the blasting mask  132  form a deep well that tends to trap the blasting particles  130 . If blasting particles  130  from the stream of air collide with other particles that previously accumulated over the surface of the blasting site  115 , then the silicone flash layer  116  will not be torn and ultimately removed. Thus, the angle of the stream of air is increased towards thirty degrees from normal to top surface  128  in order to bounce the particles  130  away from the incoming particles and out of the well. In addition, the pressure of the air used to generate the stream of air is increased towards one hundred forty pounds per square inch in order to provide the particles with enough kinetic energy to bounce out of the well. 
       FIG. 16  is a cross sectional view of the blasting sites  115  of  FIG. 12  after the flash layers  116  have been removed using the method of  FIG. 14 .  FIG. 16  shows that after the blasting process, the layer of silicone forms an edge  134  around the contact pads  112  that have been cleaned. Some of the blasting particles  130  break apart in the blasting process and form dust having particles sizes much smaller than 50 microns. Some of the dust lodges in the silicone around the blasting sites  115 . Thus, the silicone at edge  134  contains a trace amount of the blasting medium, such as sodium bicarbonate, that remains from the blasting particles  130 . The trace amount of sodium bicarbonate can be detected in the segmented LED array light sources using a gas spectrometer. 
       FIG. 17  is a top view of another MCPCB  135  from which a flash layer of silicone is removed using the method of  FIG. 14 . In  FIG. 17 , the lenses  136  and flash layer  137  have already been formed by compression molding. Like MCPCB  110  of  FIG. 2 , MCPCB  135  also includes a 5×12 matrix of LED arrays. And each LED array is later segmented into a square of the MCPCB that is 11.5 mm on a side. Unlike MCPCB  110  of  FIG. 2 , however, the contact pads  138  on MCPCB  135  are not formed by exposing areas of a trace layer that is covered by a solder mask layer. Instead, the contact pads  138  are four strips of metal that extend out from under each lens  136 . The flash layer  137  covers the metal strips. 
       FIG. 18  is a top-down perspective view of a blasting site  139  between four lenses  136  on MCPCB  135 . The micro-bead blasting process was performed using a 0.077 inch diameter nozzle positioned about 22 millimeters above flash layer  137 . A pressure of 120 psi was used to generate the stream of air that contained particles of sodium bicarbonate having a median diameter of about 50 microns. The stream of air containing the blasting particles was blasted at blasting site  139  for 1.65 seconds. The blasting removed material to various degrees progressing outwards from the center of blasting site  139 . At the center of blasting site  139 , the entire thickness of flash layer  137  has been removed, and the blasting has even removed some of the upper layer of gold from the contact pads  138 . Some of the dielectric layer was also removed from the center of blasting site  139 . Moving outwards from the center of blasting site  139 , only the silicone was removed from a large portion of the contacts pads  138  without damaging the upper layers of the contact pads  138 . This region is marked with diagonal hashes in  FIG. 18 . In the next region on each contact pad  138  outwards from the center to the blasting site, the silicone flash layer  137  was not entirely removed from the contact pad.  FIG. 18  shows areas  140  on the corners of lenses  136  that have been partially roughened by the blasting process. 
     In another embodiment, water-based jetting is used to remove a flash layer of silicone. Purified water is pressurized to a pressure of between fifty and one thousand pounds per square inch and then forced through a nozzle with an opening diameter between one hundred and one thousand microns. The exiting water beam is aimed directly at the flash layer over the electrical contact pads until the flash layer is removed. The combination of the water pressure and nozzle diameter is chosen to achieve a stream of water with enough momentum to break the silicone flash layer but yet that leaves the metal trace layer undamaged. Alternatively to using pure water, abrasive particles such as silica, aluminum oxide, or garnet particles can be added to the stream of water to allow a more efficient deflashing process at a lower water pressure compared to with pure water. 
       FIG. 19  is a perspective view of a discrete light source  141  with only top-side electrical contacts from which a flash silicone layer  116  has been removed. Discrete light source  141  was manufactured using the method of  FIG. 14 . Discrete light source  141  results from the segmentation of the arrays of LED dies  111  mounted on MCPCB  110  of  FIG. 2 . The printed circuit board (PCB) segment  142  of discrete light source  141  has a top side  143 , a bottom side  144 , and four edges  146 - 149 . A light emitting diode die  150  is disposed on the top side  143  of PCB segment  142 . A contact pad  112  is also disposed on the top side  143  of PCB segment  142 . A layer of silicone  116  is disposed over LED die  150  and extends to each of the edges  146 - 149  of PCB segment  142  except where the silicone flash layer  116  has been removed through blasting. The layer of silicone  116  is not disposed laterally above a portion of contact pad  112  at blasting site  115 . In the embodiment of  FIG. 19 , the silicone flash layer  116  has not been removed from the entire surface of contact pad  112 ; a small portion of the trace layer that forms contact pad  112  remains covered by silicone. 
     All of the electrical contacts on discrete light source  141  are on the top side  143 . Thus, PCB segment  142  has no electrical contacts on the bottom side  144 . The layer of silicone  116  forms lens  120  above LED  150 . There are less than three millimeters between the edge  145  of lens  120  and any of the edges  146 - 149  of PCB segment  142  because discrete light source  141  was segmented from a high density printed circuit board  110 . There are also less than three millimeters between the edges  146 - 149  of PCB segment  142  and any of the LED dies in the array of LED dies. There are no holes that pass from the top side  143  to the bottom side  144  of PCB segment  142 . Any punch-outs, through holes, or etching cuts in the top side  143  of discrete light source  141  would have hampered the formation of lens  120  using compression molding because the pressurized molding material would have escaped through the holes. The silicone at the edge of blasting site  115  contains a trace amount of the blasting medium that remains embedded in the silicone. 
       FIG. 20  is a cross-sectional view of a photon building block  204  supported by an interconnect structure  205 . Photon building block  204  includes a substrate  206  upon which an LED die  207  is mounted. Substrate  206  is non-conductive ceramic. In another implementation, substrate  206  is crystalline silicon. Landing pads  208  are disposed on the top surface  209  of substrate  206 . No electrical conductor passes from the top surface  209  of substrate  206  to the bottom surface  210  of substrate  206 . LED die  207  is electrically coupled to power solely through the landing pads  208 . Thermal interface materials are disposed between LED die  207  and substrate  206 . A first layer  211  of thermal interface material (TIM) is made of the same material and deposited in the same process as landing pads  208 . In one implementation, pads  208  and first layer  211  are traces made of a Cu—Ni—Au alloy or a Cu—Ni—Ag alloy. A second layer  212  of thermal interface material is deposited on first layer  211 . In one implementation, second layer  212  is a silver-filled epoxy. LED die  207  is bonded through second layer  212  and first layer  211  to top surface  209  of substrate  206 . 
     LED die  207  is electrically connected through wire bonds  213  to landing pads  208 . A thin conformal layer of a wavelength conversion material, such as a phosphor, is formed over LED die  207 . Then a clear resin encapsulant, such as silicone, is overmolded over LED die  207  and the wire bonds  213  from about the middle of a landing pad  208  on one side of upper surface  209  of substrate  206  to about the middle of a landing pad  208  on the opposite side of upper surface  209 . The silicone forms the shape of a lens  214 . Photon building block  204  includes substrate  206 , the landing pads  208  and everything encapsulated by lens  214 . 
     Interconnect structure  205  supports photon building block  204  through the landing pads  208 . The landing pads  208  are both electrically and mechanically connected to contact pads  215  disposed on the underside of a lip of the interconnect structure  205 . In one implementation, landing pads  208  are attached to contact pads  215  by a solder paste. An example of a solder paste is a SAC alloy, such as SAC  305  (96.5% Sn, 3.0% Ag, 0.5% Cu). In another implementation, landing pads  208  are attached to contact pads  215  by an adhesive. An example of an adhesive is an anisotropic conductive adhesive associated with anisotropic conductive film (ACF) technology. In the embodiment of  FIG. 20 , landing pads are electrically and mechanically connected to contact pads  215  by solder  232 . 
     In the embodiment of  FIG. 20 , contact pads  215  are electrically connected to conductive traces  216  on the top surface  217  of interconnect structure  205  by through-hole vias  218 . Thus, each conductive trace  216  is electrically coupled to LED die  207  through via  218 , contact pad  215 , solder  232 , landing pad  208  and wire bond  213 . Interconnect structure  205  has a bottom surface  219  that is substantially coplanar with bottom surface  210  of substrate  206 . 
     Photon building block  204  and interconnect structure  205  are attached over a third layer  220  of thermal interface material (TIM) to a heat sink  221 . In one implementation, third layer  220  of thermal interface material is thermal glue. In another implementation, third layer  220  is made of thermal grease, and interconnect structure  205  is attached to heat sink  221  by bolts  222 . Any small deviations of bottom surfaces  210  and  219  from being exactly coplanar are compensated by the thickness of the thermal interface material, such as the thermal grease. Bolts  222  hold interconnect structure  205  in place over heat sink  221 , and photon building block  204  is held in place by the connection between landing pads  208  and contact pads  215 . Thus, substrate  206  is thermally coupled through the third layer  220  of TIM to heat sink  221 . In one implementation, bottom surface  210  of substrate  206  is not directly connected to heat sink  221 , but is rather “floating” in the layer  220  of thermal grease. Photon building block  204  is mechanically connected to heat sink  221  only through the bonds between landing pads  208  and contact pads  215 . In contrast, carrier substrate  12  of the prior art array product  10  is attached to the heat sink only by gluing or soldering the bottom surface of substrate  12  to the heat sink. 
     Compared to a conventional discrete light emitter, a printed circuit board (PCB) and one layer of TIM have been removed from beneath novel photon building block  204 . In a conventional discrete light emitter, the carrier substrate sits on a TIM layer over a metal core PCB, which in turn sits on another TIM layer over the heat sink. Using the novel photon building blocks to make an array product is more economical than making an array product using conventional discrete light emitters because the cost of the metal core PCB and an additional TIM layer is saved. Moreover, heat generated by the LED die is more effectively transferred from the carrier substrate through one TIM layer directly to the heat sink than through an additional MCPCB and TIM layer of conventional discrete light emitters. 
     In another embodiment, photon building block  204  and interconnect structure  205  are not attached directly to heat sink  221  over third TIM layer  220 . Instead, a thermal spreader is placed between heat sink  221  and photon building block  204 . Photon building block  204  and interconnect structure  205  are then attached over third TIM layer  220  to the thermal spreader. An example of a thermal spreader is a vapor chamber. 
       FIG. 21  shows one of the contact pads  215  of  FIG. 20  in more detail and the landing pad  208  to which the contact pad is connected. Contact pad  215  is a metal trace on interconnect structure  205 . In one implementation, interconnect structure  205  is a molded interconnect device (MID). MID  205  is a three-dimensional electronic circuit carrier produced by injecting a metalized, high-temperature thermoplastic, such as liquid crystal polymer (LCP), into a mold. A laser writes the path of the trace on the surface of MID  205 . Where the laser beam oblates the thermoplastic, the metal additive in the thermoplastic forms a very thin conductor path. The metal particles on the conductor path form the nuclei for subsequent metallization. Metallization baths are used to form successive layers of copper, nickel and/or gold traces on the conductor path. For example, a layer of copper forms on the conductor path when the oblated thermoplastic is placed in a copper bath. Wherever the laser can oblate the surface of MID  205 , three-dimensional circuit traces can quickly be formed. 
     Contact pad  215  is formed on the underside of a lip  223  of MID  205  after the laser oblates the shape of the pad. Metal trace  216  is also formed on the top surface  217  of interconnect structure  205  in the same manner as contact pad  215  is formed. Either the laser is articulated so that the laser beam can be directed at both top surface  217  and the underside of a lip  223 , or two lasers can be used. In the implementation of  FIG. 21 , through-hole via  218  is filled with metal before the traces and pads are formed. The metallization baths plate the trace  216  and contact pad  215  over the ends of metal via  218 . 
     An electrical and mechanical connection is made between contact pad  215  and landing pad  208  by reflowing a solder alloy between the pads. For example, a SAC reflow process can be performed where a Sn—Ag—Cu solder alloy is placed at the edge of landing pad  208 . When the SAC solder is melted, the solder wets the metal of contact pad  215 . Then the surface tension of the molten SAC alloy pulls landing pad  208  under contact pad  215 . A bond is then formed between landing pad  208  and contact pad  215  when the SAC alloy cools and solidifies. 
       FIG. 22A  shows another implementation of how a metal trace  224  on MID  205  is electrically coupled to landing pad  208  on substrate  206 . Instead of via  218  filled with metal, as in  FIG. 21 , MID  205  of  FIG. 22A  includes a hollow tapered via  225 . Hollow via  225  is formed using a conical plug in the molding process that forms the molded interconnect device  205 . The laser oblates a conductor path across top surface  217 , around the inside surface of via  225 , and then on the underside of a lip  223  to form the shape of contact pad  215 . The conductor path and pad shape are then plated in a metallization bath.  FIG. 22B  shows the conductor path of the laser in more detail. The conductor path can be much wider than the width of the laser. The laser can make many passes to create a wide conductor path, such as the one shown in  FIG. 22C . In  FIG. 22C , the entire partially conical-shaped inside surface of hollow via  225  is oblated and will be plated in a metallization step. 
       FIG. 23  shows another implementation of how a metal trace  226  on MID  205  is electrically coupled to landing pad  208  on substrate  206 . Lip  223  of MID  205  is given a rounded edge. The laser makes a continuous conductor path across top surface  217 , around the rounded edge and then on the underside of a lip  223 . 
       FIG. 24  shows an alternative way of electrically and mechanically coupling contact pad  215  to landing pad  208  that does not involve solder. An anisotropic conductive adhesive  227  is used to connect contact pad  215  to landing pad  208  in  FIG. 24  instead of the bond formed using solder reflow as shown in  FIG. 21 . Because solder is not used, photon building block  204  does not self-align within interconnect structure  205 , but must be accurately positioned before the adhesive cured. Anisotropic conductive adhesive film (ACF) technology involves conductive balls dispersed in an adhesive. For example, Au-coated polymer balls or Ni-filled balls are dispersed in an epoxy adhesive. The surfaces being electrically coupled are then pressed together to the diameter of the balls. The adhesive is then cured, for example by heating. An electrical contact is made in those areas where the balls touch both surfaces. The anisotropic conductive adhesive  227  is not conductive in those areas where the balls are still dispersed in the cured adhesive. In  FIG. 24 , the anisotropic conductive adhesive  227  mechanically connects pad  215 , the underside of lip  223  and the entire side of MID  205  to landing pad  208  and the side of substrate  206 . However, an electrical connection is made only between those areas of contact pad  215  and landing pad  208  that were pressed together to within the diameter of the conductive balls. 
       FIG. 25  shows another implementation of how a conductor  228  on interconnect structure  205  is electrically coupled to landing pad  208  on substrate  206  using solder. Interconnect structure  205  of  FIG. 25  is a lead frame instead of a molded interconnect device. A metal foil  228  is stamped in the form of the conductors, leads and “gull wings” required for the package of the discrete light emitter or array product. Lead frame structure  205  is then made by injection molding a liquid crystal polymer (LCP)  229  around a stamped metal foil  228 . The metal foil functions both as the conductor  228  as well as the contact pad  215 . The end of the metal foil under lip  223  can be stamped in the shape of a contact pad with a shape corresponding to the shape of landing pad  208  in order to facilitate self-alignment during a solder reflow process. 
       FIG. 26  shows another implementation of a conductor  231  in interconnect structure  205  that is electrically coupled to landing pad  208  on substrate  206  using solder. Interconnect structure  205  of  FIG. 24  is a printed circuit board (PCB). For example, interconnect structure  205  is an FR-4 printed circuit board made of woven fiberglass fabric  230  with an epoxy resin binder. FR-4 PCB  205  has several metal layers. One of the metal layers  231  functions both as the conductor and as the contact pad  215 . The end of metal layer  231  under lip  223  can be formed in a shape corresponding to the shape of landing pad  208  in order to facilitate self-alignment during a solder reflow process. 
       FIG. 27  is a top view of a photon building block  234  that includes four LED dice  235 - 238 . The same material is used to make the four landing pads  239 - 242  as well as the first TIM layer  211  beneath the four LEDs. Second layer  212  of thermal interface material is deposited on first layer  211  beneath each LED die and is not visible in the view of  FIG. 27 . LED die  235  and  238  are electrically connected in series between landing pads  239  and  242 . Two wire bonds connect each LED die to a landing pad and to another LED die. For example, wire bonds  243 - 244  connect LED die  235  to landing pad  239 . The dashed circle indicates the extent to which silicone lens  214  encapsulates the components on substrate  206 . Lens  214  extends to about the middle of the landing pads  239 - 242 . The diameter of lens  214  is about twice as long as each side of the 2×2 array of LED dice so as to allow most of the emitted light to reach the surface of lens  214  within the critical angle required for the light to escape from the lens. 
     Photon building block  234  can be used to make both a discrete light emitter with a single photon building block as well as an array product with multiple photon building blocks. Interconnect structure  205  can easily be molded or configured to incorporate photon building block  234  into a plurality of different discrete light emitter products. The bolt holes through which bolts  222  attach interconnect structure  205  to heat sink  221  can easily be repositioned without changing the design of photon building block  234 . And the conductors that are electrically coupled to the LED dice can easily be retraced using a laser to write the conductive paths over the surface of the molded interconnect device. Thus, a new emitter need not be tested and qualified each time a new light emitter product is made using photon building block  234 . 
       FIG. 28  is a top view of a photon building block  245  with only two landing pads  246 - 247  that surround the four LED dice  235 - 238 . As with photon building block  234  of  FIG. 17 , the landing pads  246 - 247  and the first TIM layer  211  beneath the four LEDs are made from the same material, such as a Cu—Ni—Au alloy or a Cu—Ni—Ag alloy. The landing pads  246 - 247  have points that extend to the four corners of substrate  206 . In a SAC reflow step, the solder alloy that extends farther toward the corners of substrate  206  than with landing pads  239 - 242  can more precisely align substrate  206  beneath the contact pads of the interconnect structure  205 . The smaller surface area of landing pads  246 - 247  beneath the contact pads, however, results in a weaker mechanical connection between the landing pads and contact pads. 
       FIG. 29A  is a top view of photon building block  234  of  FIG. 17  built into an array product with another photon building block  248 . A molded interconnect device  249  holds the photon building blocks  234  and  248  in place in a 1×2 array. The area of MID  249  is denoted by cross hatching. MID  249  has six lips that extend over the corners of photon building blocks  234  and  248  and hold those corners in place. For example, a lip  223  of MID  249  extends over the upper right corner of substrate  206 , and a contact pad on the underside of lip  223  is electrically and mechanically connected to a portion of landing pad  239  using solder or an adhesive. MID  249  also has another lip  250  that extends over both the upper left corner of photon building block  234  and the upper right corner of photon building block  248 . Separate contacts pads under lip  250  are bonded to landing pad  240  of photon building block  234  and to a landing pad  251  of photon building block  248 . MID  249  has four holes  252  for the bolts  222  that attach the array product to heat sink  221 . 
       FIG. 29B  is a cross-sectional view through line B-B of the 1×2 array product shown in  FIG. 29A .  FIG. 29B  shows how contact pad  215  on the underside of lip  223  is electrically and mechanically connected to a portion of landing pad  239 .  FIG. 29B  also shows portions of the contact pads under lip  250  that bond to landing pads  240  and  251 .  FIG. 29C  is a cross-sectional view through line C-C of the 1×2 array product shown in  FIG. 29A . The contact pads of MID  249  are not visible in the cross section of  FIG. 29C . 
       FIGS. 30A-B  illustrate the connection between landing pad  239  and contact pad  215  of  FIG. 29A  in more detail. Contact pad  215  has the same outline shape as a corner of the landing pad  239  below. A solder reflow process can be performed with the contact pads on top aligning to solder on the landing pads below, or the process can be inverted. The structure of  FIG. 29B  can be inverted such that the landing pads are on top of the contact pad and align to molten solder on the contact pads. 
     In a SAC reflow process when the SAC solder on landing pad  239  is melted, the solder wets the metal of contact pad  215 . Then the surface tension of the molten SAC solder pulls contact pad  215  over the portion of landing pad  239  that has the same shape. The four landing pads at the corners of substrate  206  are thereby each pulled towards the contact pads of the same shape and align photon building block  234  within the frame of MID  249 . When the SAC solder cools and solidifies, bonds are formed between the landing pads and the contact pads. The solder bonds between the landing pads and the contact pads hold the photon building blocks in place such that the bottom surfaces of the substrates are substantially coplanar with bottom surface  219  of MID  249  even when the array product is not attached to a heat sink. The array product can be shipped unattached to any submount, such as a heat sink. The bonds between the landing pads and the contact pads are sufficiently strong to maintain the mechanical integrity of the array product despite the vibrations and bumping usually encountered in shipping. 
       FIG. 30A  also shows a conductor  253  on the top surface of MID  249  that is electrically coupled to first LED die  235 . Conductor  253  is a metal trace formed by plating a path oblated by a laser. Metal trace  253  is electrically coupled to LED die  235  through a solid metal via  254 , contact pad  215 , solder  232  or an ACF adhesive, landing pad  239  and wire bonds  243 - 244 . The dashed line designates the extent of silicone lens  214 . 
       FIG. 30B  shows contact pad  215  of  FIG. 30A  without the landing pad  239  of photon building block  234  below. The triangular cross-hatched area around contact pad  215  is lip  223  that extends over the upper right corner of substrate  206  of photon building block  234 .  FIG. 30B  also shows a lip  255  of MID  249  that extends over the lower right corner of substrate  206 . The area of MID  249  shown with a latticed pattern is filled with liquid crystal polymer from top surface  217  to bottom surface  219  of the interconnect structure. 
       FIG. 31  is a perspective view of photon building block  234  of  FIG. 17  built into an array product with three other photon building blocks. A molded interconnect device  256  holds the photon building blocks in place in a 2×2 array. The interconnect structure  256  includes bridges between the photon building blocks that support a center island  257  beneath which the contact pads attach to the inner landing pads of the four photon building blocks. As MID  256  is formed in a molding process, non-planar surfaces are easily made. MID  256  has curved walls  258  around the photon building blocks that are coated with a reflective material, such as a metal film. The curved walls can be shaped to impart a parabolic reflection to the light emitted from the photon building blocks. The conductors that connect to the contact pads (not shown in  FIG. 31 ) are drawn with a laser over the curved walls and then plated in a metallization bath. The conductors are connected to the contact pads with through hole vias or hollow vias as shown in  FIGS. 21-22 . Although  FIG. 31  depicts a 2×2 array of photon building blocks supported by an interconnect structure, arrays with other dimensions can also be made in a similar manner using bridges between the photon building blocks. 
       FIG. 32  is a flowchart illustrating steps  259 - 265  of a method of making both a discrete light emitter and an array product using the same standardized photon building blocks that have one or more LED chips mounted on a carrier substrate. The method can be used to connect photon building blocks in any configuration, such as in parallel or in series, to achieve the desired light output and power consumption of the resulting array product. The method easily connects the photon building blocks electrically, mechanically and thermally to other structures of the ultimate lighting product. The electrical connections to the power source can easily be configured. The orientation of the photon building blocks can easily be aligned with reflectors and lenses of the lighting product. The position of the bolts that mechanically connect the interconnect structure to the lighting product can easily be reconfigured without changing the photon building blocks. And the interconnect structure can easily be configured to thermally connect with a multitude of heat sinks. 
     In a first step  259 , light emitting diode die  235  is mounted on carrier substrate  206  of first photon building block  234 . Substrate  206  has no electrical conductors passing from its top surface  209  to its bottom surface  210 . LED die  235  is attached to substrate  206  using first TIM layer  211  and second TIM layer  212 . Landing pad  239  on top surface  209  of substrate  206  is made from the same material and in the same process as first TIM layer  211 . 
     In step  260 , landing pad  239  is placed under and adjacent to contact pad  215 , which is disposed on the underside of lip  223  of interconnect structure  249 . In so doing, lip  223  is placed over top surface  209  of substrate  206  and within the lateral boundary of substrate  206 . At the conclusion of step  260 , the photon building blocks are placed within interconnect structure  249 . 
     In step  261 , conductor  216  of interconnect structure  249  is electrically connecting to LED die  235  by bonding landing pad  239  to contact pad  215 . The pads are bonded by either solder or an ACF adhesive. When using solder, landing pad  239  is bonded to contact pad  215  by heating a metal alloy on landing pad  239  such that the landing pad aligns with the metal contact pad. When using anisotropic conductive adhesive film (ACF) technology to bond the pads, the photon building blocks are accurately positioned within interconnect structure  249 , and landing pad  239  is bonded to contact pad  215  when the ACF adhesive is cured by heating. After landing pad  239  is aligned with and bonded to contact pad  215 , bottom surface  210  of substrate  206  is substantially coplanar with bottom surface  219  of interconnect structure  249 . 
     In step  262 , when the method of  FIG. 32  is used to make an array product, second lip  250  of interconnect structure  249  is placed over the top surface of a second substrate, and a second landing pad  251  is placed under and adjacent to a second contact pad attached to the underside of lip  250 . The second substrate is part of second photon building block  248  and has dimensions that are substantially identical to those of the first substrate  206 . A second LED die disposed on the second substrate has dimensions that are substantially identical to those of LED die  235  on first substrate  206 . 
     In step  263 , when the method of  FIG. 32  is used to make an array product, a second conductor of interconnect structure  249  is electrically connected to the second LED die that is disposed on the second substrate by bonding second landing pad  251  to the second contact pad attached to the underside of lip  250 . For example, landing pad  251  can be bonded to the second contact pad using a SAC reflow process or by using an anisotropic conductive adhesive. After second lip  250  is placed over the top surface of the second substrate and landing pad  251  is bonded to the contact pad on the underside of lip  250 , the bottom surface of the second substrate is substantially coplanar to bottom surface  219  of interconnect structure  249 . 
     In step  264 , thermal interface material  220  is placed over the upper surface of heat sink  221 . The upper surface of heat sink  221  need not be planar except under substrate  206  and the area directly around the substrate. For example, the upper surface of heat sink  221  can be the mostly curved surface of a luminaire. Likewise, bottom surface  210  of substrate  206  and bottom surface  219  of interconnect structure  249  need not be coplanar except in the immediate vicinity of substrate  206 . 
     In step  265 , substrate  206  and interconnect structure  249  are placed over thermal interface material  220  such that thermal interface material  220  contacts both bottom surface  210  of substrate  206  and bottom surface  219  of interconnect structure  249 . When the method of  FIG. 32  is used to make an array product, the second substrate of photon building block  248  is also placed over thermal interface material  220  such that thermal interface material  220  contacts the bottom surface of the second substrate. The method of  FIG. 32  can also be used to make an array product with more than two photon building blocks, such as the array product shown in  FIG. 31 . 
       FIGS. 33A-C  are perspective views of embodiments of a photon building block  269  similar to photon building block  204  of  FIG. 20 .  FIGS. 33A-B  show photon building block  269  without a lens in order better to show the LED dies.  FIG. 33C  shows the photon building block  269  with a silicone lens structure molded over the LED dies. 
     Photon building block  269  contains nine LED dies as opposed to the single LED die of photon building block  204 . The LED dies, including labeled LED die  207 , are mounted on substrate  206  using silver epoxy. Landing pads  208  are disposed on the upper surface  209  of substrate  206 . No electrical conductor passes from the upper surface  209  of substrate  206  to the lower surface  210  of substrate  206 . The LED dies are electrically coupled to power solely through the landing pads  208 . In the embodiment of  FIG. 33A , the LED dies are electrically connected through wire bonds  271  to the landing pads  208 . The landing pads  208  are traces made of a Cu—Ni—Au alloy or a Cu—Ni—Ag alloy. In another embodiment, the landing pads  208  are traces of silver-filled epoxy. A layer  270  of a highly reflective (HR) material is disposed within a ring  272  between and around the LED dies and the wire bonds  271  as illustrated in  FIG. 33A . In the example of  FIG. 33A , layer  270  of HR material contacts the retaining ring  272  and also contacts the sides of the LED dies. 
       FIG. 33B  shows another embodiment of photon building block  269  in which the LED dies are not connected through wire bonds  271  all the way to the landing pads  208 . Instead, short bonds wires from the LED dies connect to traces on near upper surface  209  that in turn are electrically connected to the landing pads  208 . Groups of LED dies are also connected in series to each other by bond wires  271 . 
       FIG. 33C  shows a lens structure  214  that has been molded over the nine LED dies. The lens structure  214  is molded over the LED dies before the photon building blocks are segmented from the metal core printed circuit board (MCPCB) that forms substrate  206 . While the photon building blocks are still part of a single MCPCB as shown in  FIG. 2 , a thin conformal layer of a wavelength conversion material, such as a phosphor, is deposited over the LED dies. For example, a conformal layer of silicone containing yellow phosphor  273  is formed over the LED dies. Then compression molding is used to mold a clear resin encapsulant, such as silicone, over the LED dies and the wire bonds  271  such that a lens is formed over each LED die  207 . In the embodiment of  FIG. 33C , a separate micro-lens is formed over the center of each of the nine LED dies. Most of the upper surface  209  of substrate  206  can be occupied by the LED dies and the associated lens structure because the mechanical and electrical connections to a heat sink or luminaire have been removed from the photon building block and transferred to an interconnect structure that supports the photon building block. In the embodiment of  FIG. 33C , there are less than three millimeters on the upper surface  209  of substrate  206  between each edge of substrate  206  and a lens that covers one of the LED dies. 
       FIGS. 34A-B  are cross-sectional views of photon building block  269  being supported by an interconnect structure  205  solely through the landing pads  208  on the upper surface  209  of substrate  206 . The landing pads  208  are both electrically and mechanically connected to contact pads  215  disposed on the underside of a lip of the interconnect structure  205 . In one implementation, the landing pads  208  are attached to contact pads  215  by a solder paste. An example of a solder paste is a SAC alloy, such as SAC  305  (96.5% Sn, 3.0% Ag, 0.5% Cu). In a SAC reflow process that occurs in an upside down orientation to that shown in  FIGS. 34A-B , the landing pads  208  on substrate  206  self-align to the contact pads  215  on interconnect structure  205 . In a packaged LED array consisting of interconnect structure  205  and photon building block  269 , substrate  206  is electrically and mechanically connected to interconnect structure  205  only through the landing pads  208  and the contact pads  215 . Packaged LED arrays in this condition are shipped from the LED manufacturer to the luminaire manufacturer. In another implementation, the landing pads  208  are attached to contact pads  215  by an adhesive. An example of an adhesive is an anisotropic conductive adhesive associated with anisotropic conductive film (ACF) technology. 
     In the embodiment of  FIG. 34A , the conductors over the top surface  217  of interconnect structure  205  are metal traces  216 . The contact pads  215  that attach to the landing pads  208  are also metal traces. Metallization baths plate the traces  216  and contacts pad  215  over the interconnect structure  205 . A through-hole via  218  electrically couples metal trace  216  to contact pad  215 . 
     In the embodiment of  FIG. 34B , the contact pads  215  that attach to the landing pads  208  are written onto the surface of interconnect structure  205  with a laser. In addition, the conductive paths on the surface of the interconnect structure  205  are formed using the same laser process. The molded interconnect structure  205  is formed from a thermoplastic that contains a metal additive. A conductive path  226  is formed by the metal additive where the laser beam oblates the thermoplastic on the surface of the interconnect structure  205 . The metal particles in the conductive path also form nuclei for optional subsequent metallization of the conductive path. In the embodiment of  FIG. 34B , the laser has oblated a continuous conductive path  226  across top surface  217 , around the lip  223  to the underside of the lip to form contact pad  215 . The conductive path is widened on top surface  217  to form contact pads to which power and ground wires can be attached. In this manner, no vias or internal metal layers are required in the molded interconnect structure  205  of  FIG. 34B . 
       FIG. 34B  shows an implementation in which a conformal layer of silicone containing yellow phosphor  273  is formed over the LED dies. Green phosphor  274  is dispersed in the silicone that forms lenses over the LED dies. And a conformal layer of silicone containing red phosphor  275  is deposited over the lenses. 
       FIGS. 35A-B  are perspective views of the bottom and top sides, respectively, of an interconnect structure  276  that supports photon building block  269  of  FIG. 33C . Molded interconnect structure  276  has a hexagonal star shape and supports photon building block  269  by the top-side landing pads  208 . There is an opening  277  in the middle of molded interconnect  276  from which the lenses of photon building block  269  protrude.  FIG. 35A  shows the bottom surface  219  of molded interconnect structure  276  into which an indentation  278  has been formed. Indentation  278  has the shape of substrate  206  of photon building block  269 . In the orientation of molded interconnect  276  shown in  FIG. 35A , photon building block  269  is flipped over and inserted into indentation  278  such that the top-side landing pads  208  attach to the contact pads  215  that protrude out from the inner surface  279  of indentation  278 . Each contact pad  215  is the bottom of a cylindrical metal via that extends from the inner surface  279  of indentation  278  to the top surface  217  of interconnect structure  276 . The top of each cylindrical metal via is coupled to a rectangular contact pad  280  to which power and ground wires can be attached. Two of the six contact pads  280  on top surface  217  of interconnect structure  276  form redundant connections to a contact pad  215 . 
       FIG. 35B  shows a packaged LED array  281  made up of photon building block  269  being supported from its top side by hexagonal star-shaped molded interconnect structure  276 .  FIG. 35B  shows the top surface  217  of molded interconnect structure  276  and the lens structure  214  of photon building block  269  protruding through opening  277 . In the orientation of molded interconnect  276  shown in  FIG. 35B , photon building block  269  is inserted up and into indentation  278  such that top surface  209  of substrate  206  is placed under inner surface  279  of indentation  278 . In so doing, a landing pad  208  is placed under and adjacent to a contact pad  215 . The outer edges of flash layer  16  of silicone are sandwiched between top surface  209  and inner surface  279 . The contact pads  215  protrude out from the inner surface  279  of indentation  278  to bridge the width of the sandwiched flash layer  16  in order to make contact with the landing pads  208 . The landing pads  208  are then attached to the contact pads  215  using solder or a conductive adhesive. In an embodiment where flash layer  16  is about fifty microns thick, the sum of the protruding height of contact pads  215  and the solder or adhesive that connects contact pads  215  to landing pads  208  must also be fifty microns. Alternatively, the rim of inner surface  279  around opening  277  can be recessed to accommodate the thickness of flash layer  16 . Photon building block  269  is then aligned inside indentation  278  in a solder reflow step. In the inverted orientation of  FIG. 35A , molten solder on each landing pad  208  aligns over the contact pad  215  below. 
       FIG. 36A  shows a packaged LED array  282  in which photon building block  269  is supported by a hexagonal molded leadframe structure  283  that has only two of the six screw indentations  284  of the star-shaped interconnect structure  276 . Metal vias connect contact pads  285  on top surface  217  of molded leadframe structure  283  to contact pads  215  in the indentation  278  on the back side of the structure. Molded leadframe structure  283  also includes side pads  286  that are disposed at a lower level than top surface  217 . The side pads  286  are disposed on a molded shelf  287  that extends from a longer side of the hexagonal leadframe structure  283 . Power and ground wires  288  may be soldered to the side pads  286  such that the thickness of the insulated wires fits between the planes of the upper surface  217  and bottom surface  219  of molded leadframe structure  283 . The side pads  286  are electrically coupled to the contact pads  285  by conductive layers within the molded leadframe structure  283 . 
       FIG. 36B  shows the indentation  278  on the bottom side of molded leadframe structure  283  into which photon building block  269  fits. The contact pads  215  are elevated somewhat from the inner surface  279  of indentation  278  and are coupled to the contact pads  285  on top surface  217  of molded leadframe structure  283 . 
       FIG. 37A  shows a packaged LED array  289  in which photon building block  269  is supported by a hexagonal molded interconnect structure  290  that has only two of the six screw indentations  284  of the star-shaped interconnect structure  276 . Interconnect structure  290  does not have the cylindrical metal vias of molded leadframe structure  283 . Instead, the contact pads  215  in the indentation  278  and the contact pads  285  on top surface  217  are formed by writing conductive areas using a laser as illustrated in  FIG. 34B . Each contact pad  285  on top surface  217  is electrically coupled to a contact pad  215  on the bottom side of molded interconnect  290  by a conductive path  226  that extends across top surface  217 , around the rounded edge of opening  277  and then on inner surface  279  to a contact pad  215 . Interconnect structure  290  also includes the side pads  286  on molded shelf  287 . The side pads  286  are electrically coupled to the contact pads  285  by conductive paths  291  that are written using a laser across upper surface  217  and a side of the interconnect structure  290 . The laser is also used to write the side pads  286  onto molded shelf  287 . Interconnect structure  290  has no vias or internal metal layers. 
       FIGS. 37B-C  are perspective views of the top and bottom sides, respectively, of an hexagonal molded interconnect structure  292  that has been molded around lead frame conductors.  FIG. 37B  shows interconnect structure  292  supporting a photon building block  293  with a single lens that covers an array of LED dies. Together, molded interconnect  292  and photon building block  293  comprise a packaged LED array  294 . Unlike interconnect structure  290  of  FIG. 37A , interconnect structure  292  has internal metal conductors formed from a metal lead frame around which plastic has been molded. The side pads  295  on molded shelf  287  are part of the lead frame. 
       FIG. 37C  shows the indentation  278  on the bottom side of interconnect structure  292  into which photon building block  293  fits. The contact pads  215  are elevated somewhat from the inner surface  279  of indentation  278  and are part of a lead frame layer of conductors. Two contact pads  215  and one side pad  295  are part of the same lead frame conductor  296 , as shown in  FIG. 38 . The lead frame is made of a thin sheet of metal from which the lead frame conductors are stamped. For example, a 0.1 mm sheet of a copper-nickel-palladium alloy can be used to make the lead frame. The lead frame is rolled onto a reel  297  and then unrolled as individual interconnect structures are molded around each template  298  of conductors. After individual interconnect structures are formed, the connection from the lead frame reel to the side pads  295  is cut. The photon building blocks are then inserted into the indentations in a reel-to-reel process before a solder reflow step aligns the landing pads of the photon building blocks to the contact pads of the interconnect structures. 
     There are many different types of LED assemblies.  FIG. 39  (prior art) is a top-down diagram of one such LED assembly  300 . LED assembly  300  includes four laterally-contacted LED dices  302 - 305  that are mounted on a metal core substrate  306 . Substrate  306  in this case is a metal core printed circuit board (MCPCB). Areas  307 - 310  illustrated in dashed lines represent portions of a metal layer that is disposed underneath a solder mask layer  311  (see  FIG. 40 ). Reference numeral  312  identifies a portion of metal portion  307  that is exposed through a first opening in the solder mask layer  311 . Similarly, reference numeral  313  identifies a portion of metal portion  308  that is exposed through a second opening in solder mask layer  311 . These exposed portions  312  and  313  serve as bond pads. Ring structure  314  is a retaining ring of silicone. An amount of a material often referred to as phosphor  315  is disposed within the ring structure  314  over the LED dice. This phosphor actually comprises silicone and particles of phosphor that are embedded in the silicone. 
       FIG. 40  (prior art) is a simplified cross-sectional diagram of LED assembly  300  of  FIG. 39 . MCPCB  306  includes an aluminum layer  316 , a global dielectric layer  317 , a layer  318  of metallization of which metal portions  307 - 310  are parts, and solder mask layer  311 . Layer  318  of metal may involve multiple sublayers of metal including an upper layer of a very reflective metal such as silver. Metal portion  310  is a square pad of metal upon which the LED dice  302 - 305  are mounted. The LED dice  302 - 305  are fixed to pad  310  by associated amounts of silver epoxy. Amount  319  of silver epoxy is shown fixing LED die  304  to pad  310 . Amount  320  of silver epoxy is shown fixing LED die  305  of pad  310 . Reference numerals  321 - 323  identify wire bonds. 
     A layer  324  of a highly reflective (HR) material is disposed within ring  314  between and around the dice  302 - 305  and wire bonds  321 - 323  as illustrated. The diagram is simplified in that the regions of the HR material have smooth and rounded edges. Some of the light emitted by LED dice  302 - 305  may be absorbed by phosphor particles in phosphor  315 . These particles may then fluoresce and re-emit light such that this light is directed downward, rather than upward as is desired. Reference numeral  335  identifies one such particle of phosphor. A light ray  336  is emitted from the top of LED die  304  and travels up and is absorbed by particle  335 . A second light ray  337  is then emitted from particle  335  and this second light ray travels back downward as shown. HR material  324  is provided so that this light ray will be reflected so that it can pass upward and out of the assembly as light ray  338 . Particle  335  is but one such particle. There are numerous particles dispersed throughout the silicone material of phosphor  315 . Light emitted from the LED dice  302 - 305  can be emitted in various different directions including out of the sides of the LED dice. Similarly, a light ray emitted from a phosphor particle can travel away from the particle any direction. The illustration of particle  335 , of the direction of light emission from particle  335 , and of the associated light rays  336 ,  337  and  338  in  FIG. 40  are only representative of one such particle and its associated light rays. An example of an HR material is a silicone material that is commercially available from ShinEtsu Chemical Co. Ltd. of Tokyo, Japan. 
       FIGS. 41-48  (prior art) illustrate a prior art method of manufacturing the LED assembly  300  of  FIG. 39 .  FIG. 41  (prior art) is a top-down diagram of a panel  325  of MCPCBs. MCPCB  306  is one of the MCPCBs of the panel.  FIG. 42  (prior art) is a top-down diagram of the pad portion  310  of the MCPCB portion  306  of panel  325 . This pad portion  310  is exposed through an opening in the solder mask layer  311 .  FIG. 43  (prior art) is an illustration of a screen printing mask  326  used in the next step of forming the layer  324  of highly reflective (HR) material.  FIG. 44  (prior art) is a diagram that shows the result of using the screen printing mask  326  of  FIG. 43  to deposit the HR layer  324  onto panel  325 . HR material of layer  324  is deposited in the shaded circular region. This circular region is in the center of MCPCB  306 . As illustrated, there are eight windows  327 - 334  in the circular HR layer  324 .  FIG. 45  (prior art) is a diagram that shows the result of a next die attach step. Each of the four dice  302 - 305  is attached by an amount of silver epoxy in a corresponding one of the four center windows  327 - 330  in the HR layer  24 . Each of the openings  327 - 330  in the HR layer is slightly larger than its associated die in order to accommodate variations in physical dimensions and inaccuracies of the placement of the dice and wire bonds.  FIG. 46  (prior art) is a diagram that shows the result of a next step of attaching wire bonds. Only three of the wire bonds  321 - 323  are identified in the diagram with reference numerals. Some of the wire bonds extend between dice. Others of the wire bonds extend from a die to a conductive upper layer of the substrate.  FIG. 47  (prior art) shows the result of a next step of forming retaining ring  314 . Retaining ring  314  is formed so that it encircles the circular layer  324  of HR material as illustrated.  FIG. 48  (prior art) shows the result of a next step of placing the phosphor  315  over the LED dice  302 - 305  in the area bounded by retaining ring  314 . After the phosphor  315  has cured, the panel  325  is singulated to form multiple LED assemblies of which LED assembly  300  is one. 
       FIG. 49  is a simplified top-down diagram of a white LED assembly  340  in accordance with one novel aspect. LED assembly  340  includes four laterally-contacted LED dice  341 - 344  that are mounted on a substrate  345 . In the present example, the substrate is a metal core printed circuit board (MCPCB). Areas  346 - 349  illustrated in dashed lines represent portions of a metal layer  357  that is disposed underneath a solder mask layer  350  (see  FIG. 50 ). Reference numeral  351  identifies a portion of metal portion  346  that is exposed through a first opening in solder mask layer  350 . Reference numeral  352  identifies a portion of metal portion  347  that is exposed through a second opening in solder mask layer  350 . These exposed portions  351  and  352  serve as bond pads. Ring structure  353  is a retaining ring of silicone. An amount of phosphor  354  is disposed within the ring structure  353  over the LED dice. This phosphor actually comprises silicone and particles of phosphor that are embedded in the silicone. 
       FIG. 50  is a simplified cross-sectional side view of the LED assembly  50  of  FIG. 49 . MCPCB  345  includes an aluminum layer  355 , a global dielectric layer  356 , a layer  357  of metallization, and solder mask layer  350 . Metal portions  346 - 349  are parts of layer  357 . Layer  357  of metal involves multiple sublayers of metal including a lower layer of copper, a middle layer of nickel, and an upper layer of a very reflective metal such as silver. Metal portion  349  is a square pad of metal upon which the LED dice  341 - 344  are mounted. The LED dice are laterally-contacted blue LED devices whose epitaxial layers are fabricated on an insulative sapphire substrate. LED dice  341 - 344  are fixed to pad  349  by associated amounts of silver epoxy. Amount  358  of silver epoxy is shown fixing LED die  343  to pad  349 . Amount  359  of silver epoxy is shown fixing LED die  344  of pad  349 . Reference numerals  360 - 362  identify three of the wire bonds seen in top-down perspective in  FIG. 49 . 
     A layer  363  of a highly reflective (HR) material is disposed within ring  353  between and around the dice and the wire bonds as illustrated. In the example of  FIG. 50 , the layer  363  contacts the retaining ring  353  and also contacts the side edges of the LED dice  341 - 344 . 
       FIGS. 51-58  illustrate a method of manufacturing the LED assembly  340  of  FIG. 49 . 
       FIG. 51  is a top-down diagram of a panel  364  of MCPCBs. MCPCB  345  is one of the MCPCBs of the panel. 
       FIG. 52  is a top-down diagram of the pad portion  349  of the MCPCB  345  of panel  364 . This pad portion  349  is exposed through an opening in the solder mask layer  350 . The metal surfaces of the panel are plasma cleaned. The corners  349 A- 349 D serve as fiducial markers used in later assembly steps. 
       FIG. 53  shows the result of the next step of the method. LED dice  341 - 344  are placed and bonded to pad portion  349  as illustrated. Each die is bonded to pad portion  349  by an associated amount of silver epoxy. The bond line thickness (distance between the bottom of the die and the top of the substrate surface) is less than 12 microns, and it is typically about 8 microns. 
       FIG. 54  shows the result of the next step of the method. Wire bonds are attached. Some of these wire bonds extend between dice. Others of the wire bonds extend from a die to a conductive upper layer of the substrate. Reference numerals  360 - 362  identify three of the wire bonds. The wire bonds may be sections of 1 mil diameter gold wire. 
       FIG. 55  shows the result of the next step of the method. Retaining ring  353  is formed on the structure as shown. 
       FIG. 56  illustrates a next step in the method in which layer  363  of HR material is deposited. In one example, layer  363  of HR material is deposited using a jetting process. Microdots of HR material are jetted out of a jet head  365  so that the microdots travel toward the substrate  345  (MCPCB) and impact the substrate, thereby effectively painting the surface of the substrate with HR material. The liquid HR material does not flow under the LED dice due to the silver epoxy bonding material occupying this space. The jet head  365  is moved across the surface of the assembly of  FIG. 55  as microdots of HR material are shot at the substrate so that areas of the surface of the substrate around the dice, and between the dice, and within the confines of circular retaining ring  353  are painted with HR material, but such that the top surfaces of the dice and the top surfaces of the wire bonds are not painted. One of these microdots is identified with reference numeral  366  in  FIG. 56 . Arrow  367  indicates the path of its travel from jet head  365  toward the surface of the substrate. In one example, each microdot has a diameter of less than 100 microns and is typically 50-80 microns in diameter. The layer  363  is deposited to be at least 10 microns thick. Arrows  371  identify this thickness. In the illustrated example, layer  363  is fifty microns thick. The distance  369  between the bottom of the jet head  365  and the upper extent of the wire bonds is approximately 500 microns. In this example, the distance  368  between the bottom of the jet head  365  and the upper surface of metal layer  357  (including pad  349 ) is approximately 1000 microns. In this example, the distance  370  between the bottom of the jet head  365  and the upper surface of retaining ring  353  is approximately 500 microns. The HR material being jetted is made to have a predetermined and controlled viscosity such that the liquid HR material will flow laterally somewhat across the surface being painted before the HR material cures and solidifies. Due to this flowing action, microdots of liquid HR material are fired onto the substrate surface near to a wire bond. The liquid HR material once on the substrate surface then flows laterally underneath the wire bond so that after the step of depositing the HR material is completed the HR layer  363  coats the surfaces of substrate  345  (MCPCB) that are directly underneath wire bonds. At an end of a wire bond where the wire bond contacts the substrate, the entire circular circumference of the wire is contacting HR material. Similarly, due to the predetermined viscosity of the liquid HR material, the HR material flows laterally such that it reaches and wets the side edges of the LED dice  341 - 344  as illustrated. Reference numeral  372  identifies a side edge of LED die  343 . In this example, only the bottom sapphire portion of the side edge  372  is wetted. The upper epitaxial portion of the side edge  372  is not wetted. Similarly, the HR material is made to flow laterally and to wet the inside side edge of the retaining ring  353  as illustrated. Reference numeral  373  identifies the inside side edge of retaining ring  353 . The HR material is deposited with such a thickness that once it has cured and solidified it has a reflectivity of at least eighty-five percent (for example, 94 percent). 
     In one example, the HR material is the material KER-2010-DAM or material KER-2020 that is commercially available from ShinEtsu Chemical Co. Ltd. of Tokyo, Japan. The HR material may comprise silicone and a titanium dioxide powder, where the titanium dioxide powder is suspended in the silicone. The HR material is made jettable by cutting it with a solvent. In one example, the solvent is an oil-based solvent such as dimethylformamide (DMF) commercially available from ShinEtsu as DMF0.65CS. The HR material after being appropriately cut with the solvent has a viscosity less than 1100 centipois (cP) at room temperature and in this example has a viscosity of 1000 cP at room temperature. In one example, the jetting equipment used to jet the HR material is an Asymtek X1020 jetting machine available from Hordson Asmtek of 2747 Loker Avenue West, Carlsbad, Calif. 92010. The jetting machine has two jet heads. The first jet head is used to apply HR material with a first viscosity, whereas the second jet head is used to apply HR material with a second viscosity. 
       FIG. 57  shows the result of the step of depositing the HR material. Layer  363  of HR material covers substantially all the area within the confines of the retaining ring  353  other than the top surfaces of LED dice  341 - 344 . Layer  363  coats the upper surface of the substrate underneath the bridging bond wires. Whereas in the prior art example of  FIG. 47  there exists a peripheral strip of the substrate around each LED die that is not covered with HR material, in the structure illustrated in  FIG. 57  there is no such uncovered peripheral strip. Whereas in the prior art example of  FIG. 47  there are uncovered areas of the substrate in the areas where wire bonds attach to the substrate, in the structure illustrated in  FIG. 57  there are no such uncovered areas. The HR material is made to coat the upper surface of the substrate right up location where the wire bond makes contact with the substrate. The HR material is also made to coat the upper surface of the substrate right up to the side edges of the LED dice. The HR material is made to coat the upper surface of the substrate right up to the inside side edge of the retaining ring  353 . 
       FIG. 58  shows the result of the next step in the method. Phosphor  354  is deposited into the circular area bounded by the retaining ring  353  so that the phosphor  354  covers the LED dice as illustrated in  FIG. 50 . The phosphor is then allowed to cure and harden. Once the phosphor  354  has been deposited, the panel of MCPCBs is singulated, thereby forming a plurality of LED assemblies. The LED assembly structure  340  illustrated in  FIG. 49  is one of these LED assemblies. 
     The method set forth above in connection with  FIGS. 49-58  has several advantageous aspects in comparison with the prior art method set forth above in connection with  FIGS. 39-48 . First, the amount of the upper surface of the substrate that is left uncovered by HR material is reduced in comparison with the prior art screen printing method. Parts of the substrate that are not covered by HR material may and typically do absorb light or otherwise do not reflect light well, thereby reducing the light efficiency of the LED assembly. By covering more of the surface of the substrate with HR material using the jetting process, more light is reflected from the LED assembly and the light efficiency of the LED assembly is increased. In the prior art screen printing process used to deposit HR material, variations in physical sizes and imperfections in die attach and wire bonding processes required the windows in the HR layer to be so large that after die attach and wire bonding substantial areas of exposed substrate remained uncovered by HR material. In the jetting process, the HR material is applied after die placement and wire bonding, and machine vision and control techniques are used to control the jetting process so that the substrate is coated up to the edges of structures (the LED dice and the retaining ring) even if the structures are in slightly different places, from one assembly to the next. The use of laterally flowing HR material reduces the need to account for differences in die placement and wire bond locations from assembly to assembly. The HR material naturally flows laterally up to the proper structures even if the structures are not always disposed in the same location from assembly to assembly. 
     Second, the HR layer is deposited after the sensitive die attach and wire bonding process steps. In the prior art screen printing method of depositing HR material, on the other hand, the HR material is screen printed onto the substrate prior to die attach and wire bonding. The HR material is an organic material. If die attach and wire bonding are performed when organic residue is present on the substrate, then errors in die attach and wire bonding can occur and such error reduce LED assembly manufacturing yield. Accordingly, plasma cleaning is often conventionally done after the HR screen printing step in an attempt to remove all such organic residue prior to die attach and wire bonding. This plasma cleaning is, however, difficult to perform as compared to performing die attach on a plasma cleaned surface that has never been exposed to organics. Accordingly, defects due to performing die attach and wire bonding on surfaces having organic residues are reduced or eliminated using the jetting process. 
     Third, the jetted HR layer can be made to coat surfaces with relatively large steps and with different levels and sloped surfaces. In the prior art screen printing method, on the other hand, the surfaces to which the HR material is being applied must be more planar. In one example of the novel jetting process, a first HR material with less viscosity is applied to certain areas of the substrate that are relatively flat and planar so that the HR material will flow under wire bonds and will flow up to the edges of dice, whereas a second HR material with more viscosity is applied to other portions of the surface of the substrate that are more inclined or more stepped. The first HR material is applied with a first jet head of the jetting machine, whereas the second HR material is applied with a second jet head of the jetting machine. 
     Fourth, the production rate of LED assemblies is increased by not coating certain parts of the substrate with HR material in certain situations. In some examples, the area of the substrate between LED dice is small. It has been found that the benefit of coating this small inter-dice area is only slight. Accordingly, the HR material is not jetted into the inter-dice areas in order to save manufacturing time. 
     Fifth, it is generally desirable to be able to place fiducial markers on the substrate surface and to have the imaging systems of the die attach and wire bonding equipment use these fiducial markers during die attach and wire bonding processing. In the prior art screen printing process where the HR layer has been deposited prior to die attach and wire bonding, there is limited exposed substrate area available for placement of appropriate fiducial markers. Most of the upper surface of the substrate has been covered by HR material. In the novel jetting method of applying HR material, on the other hand, die attach and wire bonding occur prior to the depositing of the HR layer. Accordingly, fiducial markers (for example,  349 A- 349 D) that will later be covered over by HR material are nevertheless usable at die attach and wire bonding time by die attach and wire bonding imaging systems. 
     The deposition of an HR layer using jetting is not limited to the particular LED assembly set forth  FIG. 50 .  FIG. 59  is a diagram of another type of LED assembly  375 . In the diagrams of  FIG. 59  and  FIG. 50 , the same reference numerals are used to denote the same or similar structures. In the LED assembly of  FIG. 59 , the substrate  345  forms a well  376 . The upper surface of the substrate has a nonplanar shape. The four LED dice  341 - 344  are mounted to metal pad  349  at the bottom of the well  376  as illustrated. Jetting is used to coat the sidewalls of this well with HR material. In the specific example illustrated, substantially all of the upper surface of the substrate within the circular confines of retaining ring  353  but for the LED dice  341 - 344  is coated with HR material. The liquid HR material that is painted onto the sidewalls of the well can be a liquid HR material with a relatively higher viscosity as compared with the viscosity of the liquid HR material that is painted onto the remainder of the surface of the substrate. The resulting HR layer is conformal to the nonplanar upper surface of the substrate over the various edges and sloping surfaces of the substrate. 
       FIG. 60  is a diagram of another type of LED assembly  377 . The substrate  345  in this case includes a ceramic portion  378 . A first electrode  379  (P+ electrode), a second electrode  380  (N− electrode), and a thermal pad  381  of metal are disposed on the bottom surface of the ceramic portion  378 . A conductive via  282  couples the P+ electrode  379  to metal portion  348  on the upper surface of the ceramic portion  378 . Similarly, a conductive via  383  couples the N− electrode  380  to metal portion  346  on the upper surface of the ceramic portion  378 . The thickness of the metal layers on the top and bottom of the substrate may be large, such as eighty microns, and this large thickness makes screen printing the HR material difficult. The HR layer  363  contacts substantially all of at least one side edge of each LED die as pictured. In the illustrated example, the surface area of the substrate  345  between LED dice  341 - 344  is not covered with HR material as described above in order to reduce production times. The inter-dice distance between the LED dice  341 - 344  is less than 300 microns, and the inter-dice area is not jetted with HR material. In other examples, this inter-dice area is coated with HR material. In an example where a retaining ring is provided (not shown), the HR layer  363  may or may not extend outward all the way to the retaining ring. The HR layer  363  may contact the inside side edge of such a retaining ring, or may stop short of the retaining ring such that the HR layer  363  does not touch the inside side edge of the retaining ring. 
       FIG. 61  is a diagram of an LED assembly  384  where the substrate  345  involves a ceramic portion  378  as in  FIG. 60 , but the HR layer  363  does not contact a side edge of any of the LED dice  341 - 344 . The HR layer  363  is deposited to stop short of the LED dice so that the HR layer  363  does not contact any side edge of any LED die. In the final assembly, the LED dice appear disposed in a central window in the HR layer  363 . As compared the screen printing conventional method of applying HR material, however, the amount of exposed substrate (substrate under the phosphor  354  that is not covered by either an LED die or HR material) is much reduced in the structures of both  FIG. 60  and  FIG. 61 . 
       FIG. 62  is a flowchart of a method  385 . Initially, a substrate is cleaned (step  386 ) as necessary. In one example, the substrate  345  is part of the panel  364  of  FIG. 51 . Panel  364  is plasma cleaned to remove any organic materials from its surface. Next (step  387 ), a plurality of LED dice are attached to the substrate. In one example, the LED dice are the dice  341 - 344  that are attached using silver epoxy to the substrate  345 .  FIG. 53  shows the result of this die attach step. Next (step  388 ), wire bonding is performed as necessary. In some cases, wire bonding is not used and the die is electrically connected to the substrate without wire bonding. In an example where wire bonding is performed, the result of the wire bonding step is as shown in  FIG. 54 . Next (step  389 ), a retaining ring is formed around the LED dice as necessary. In one example where a retaining ring  353  is used, the result of the step of forming the retaining ring is as illustrated in  FIG. 55 . Next (step  390 ), a layer of an HR material is deposited onto the substrate  345  such that the HR material does not cover the LED dice.  FIG. 56  shows one example of how this HR material might be deposited in a jetting process. The HR material is jetted onto exposed portions of the upper surface of the substrate around the dice  341 - 344 , and the liquid HR material is allowed to cure and harden. Next (step  391 ), an amount of liquid phosphor (actually silicone bearing phosphor particles) is placed over the LED dice and allowed to cure. In one example, the result of this step is illustrated in  FIG. 58 . The resulting panel of LED assemblies is then singulated (segmented) to form a plurality of separate LED assemblies. In one example,  FIG. 49  is a top-down diagram of one of these separate LED assemblies. In a first novel aspect, the HR layer of the LED assembly is deposited after the die attach step and after the wire bonding step in the LED assembly process. In a second novel aspect, the HR layer of an LED assembly is deposited by jetting microdots of liquid HR material onto a substrate of the LED assembly. 
     Although certain specific embodiments are described above for instructional purposes, the teachings of this patent document have general applicability and are not limited to the specific embodiments described above. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.