# Patent

## Title
Heat spreading substrate with embedded interconnects

## Abstract

Heat spreading substrate with embedded interconnects. In an embodiment in accordance with the present invention, an apparatus includes a metal parallelepiped comprising a plurality of wires inside the metal parallelepiped. The plurality of wires have a different grain structure than the metal parallelepiped. The plurality of wires are electrically isolated from the metal parallelepiped. The plurality of wires may be electrically isolated from one another.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of U.S. patent application Ser. No. 13/399,941, filed Feb. 27, 2012, the disclosure of which is incorporated herein by reference.


FIELD OF INVENTION
Embodiments of the present invention relate to the field of integrated circuit design and manufacture. More specifically, embodiments of the present invention relate to systems and methods for a heat spreading substrate with embedded interconnects.
BACKGROUND
A variety of semiconductor devices, for example, light emitting diodes (LED), radio frequency (RF) devices, motor controllers, power semiconductors and the like, may be characterized as having high power density. For example, many LED devices may be said to run “hot.” In addition, the substrates of many such devices, e.g., comprising sapphire or Gallium arsenide (GaAs), are not good conductors of heat. Conventional mounting and heat sinking methods and structures do not cost effectively remove the heat generated by such devices.
SUMMARY OF THE INVENTION
Therefore, what is needed are systems and methods for heat spreading substrate with embedded interconnects. What is additionally needed are systems and methods for heat spreading substrate with embedded interconnects that are simple and cost effective to manufacture. A further need exists for systems and methods for heat spreading substrate with embedded interconnects that are compatible and complementary with existing systems and methods of integrated circuit design, manufacturing and test. Embodiments of the present invention provide these advantages.
In a first embodiment in accordance with the present invention, an apparatus includes a metal parallelepiped comprising a plurality of wires inside the metal parallelepiped. The plurality of wires have a different grain structure than the metal parallelepiped. The plurality of wires are electrically isolated from the metal parallelepiped. The plurality of wires may be electrically isolated from one another.
In accordance with a method embodiment of the present invention, a plurality of wires are bonded to a substrate. A volume is filled with an electrically and thermally conductive material. The volume is in contact with the substrate and includes the plurality of wires. The electrically and thermally conductive material has a different grain structure from that of the plurality of wires. The plurality of wires may (or may not) be coated with a dielectric prior to or after the bonding.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. Unless otherwise noted, the drawings are not drawn to scale.
FIGS. 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H and 1I illustrate multiple methods of manufacture of a heat spreading substrate with embedded interconnects, in accordance with embodiments of the present invention.
FIG. 2 illustrates an application of heat spreading substrate with embedded interconnects, in accordance with embodiments of the present invention.
FIG. 3 illustrates a detail of electronic assembly, in accordance with embodiments of the present invention.
FIG. 4 illustrates a detail of electronic assembly, in accordance with embodiments of the present invention.
FIG. 5 illustrates an example of an application of a light emitting diode, in accordance with embodiments of the present invention.
FIG. 6 illustrates an exemplary portable computer system 600, in accordance with embodiments of the present invention.



DETAILED DESCRIPTION
Reference will now be made in detail to various embodiments of the invention, front facing piggyback wafer assembly, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with these embodiments, it is understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the invention, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be recognized by one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the invention.
NOTATION AND NOMENCLATURE
Some portions of the detailed descriptions which follow are presented in terms of procedures, steps, logic blocks, processing, and other symbolic representations of operations on data bits that may be performed on computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. A procedure, computer executed step, logic block, process, etc., is here, and generally, conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as “attaching” or “processing” or “singulating” or “processing” or “forming” or “roughening” or “filling” or “accessing” or “performing” or “generating” or “adjusting” or “creating” or “executing” or “continuing” or “indexing” or “processing” or “computing” or “translating” or “calculating” or “determining” or “measuring” or “gathering” or “running” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.
FIGS. 1A-1I illustrate multiple methods of manufacture of a heat spreading substrate with embedded interconnects 100, in accordance with embodiments of the present invention. FIG. 1A illustrates a substrate 101 comprising a plurality of wire bond pads 110, in accordance with embodiments of the present invention. Substrate 101 should be characterized as having a high thermal conductivity, e.g., having a thermal conductivity greater than that of sapphire (α-Al2O3), 32 or 35 W ·m−1·K−1, depending on the orientation. Substrate 101 may comprise any suitable material, e.g., metal and/or a metal film, including Copper (Cu), Aluminum (Al), metal powders, particle filled materials, Silicon, metal-filled epoxy, composite materials and the like. Substrate 101 may comprise multiple layers and may further comprise routing traces, in accordance with embodiments of the present invention.
FIG. 1B illustrates the addition of a plurality of bond wires 120 applied to substrate 101, in accordance with embodiments of the present invention. Bond wires 120 may be applied via conventional wire-bonding techniques. Bond wires 120 may comprise Copper (Cu), Gold (Au), alloyed-Aluminum or any other suitable material. In accordance with embodiments of the present invention, the ball bonds 121 may touch one another. If the ball bonds 121 are in electrical contact, the ball bonds 121 may be optionally removed, as further described with respect to FIG. 1F, below.
The bond wires 120 may be substantially vertical, e.g., perpendicular to the substrate 101, or they may be formed and/or placed at an angle of up to about 30 degrees from the vertical, for example, as may occur with loop or stitch bonding.
FIG. 1C illustrates the addition of a plurality of bond wires 120 applied to substrate 101, in accordance with embodiments of the present invention. In FIG. 1C, bond wires 120 are applied via loop or stitch bonding.
In accordance with embodiments of the present invention, wires 120 may comprise conductive wires 120A coated with a dielectric 120B, e.g., an electrophoretically deposited polymer or Silicon nitride. Alternatively, “bare” wires 120A may be coated with a dielectric 120B after wire bonding. FIG. 1D illustrates bonded conductors 120A coated with a dielectric 120B, in accordance with embodiments of the present invention.
FIG. 1E illustrates metal 130 electroplated over substrate 101 and encompassing wires 120 and ball bonds 121, in accordance with embodiments of the present invention. In an alternative embodiment in accordance with the present invention, the volume of metal 130 may be filled by any suitable process utilizing any suitable material, e.g., a fill metal, electrically conductive epoxy, powdered metal and/or a metal-filled material.
Metal 130 generally forms a regular solid, e.g., a cuboid or parallelepiped. It is to be appreciated, however, that metal 130 is not completely solid, as it comprises gaps formed by the wires 120. It is to be further appreciated that metal 130, whether electroplated as illustrated in the embodiments of FIG. 1E, or formed via other methods, as described below, will have a different grain structure from the bond wires 120A, which are typically drawn wires.
FIG. 1F illustrates a first embodiment of a heat spreading substrate with embedded interconnects 100, in accordance with embodiments of the present invention. In FIG. 1F, the substrate 101 is optionally removed, in accordance with embodiments of the present invention. In addition, the top surface is optionally polished, exposing the conductive portion of the wire bond, 120A, exposed on both the top and bottom surfaces of metal 130. For example, if the wires 120A comprise loop bonding, top surface polishing may eliminate the loop in the wire, electrically isolating the remaining wires.
FIG. 1F also illustrates optional cut/polish extent line 107. In accordance with embodiments of the present invention, substrate 101 and/or metal 130 may be cut and/or polished to cut/polish line 107 to remove ball bonds 121. In this novel manner, the wires 120 may be placed closer together, e.g., without a need to physically separate ball bonds 121 from one another, and heat spreading substrate with embedded interconnects 100 may achieve a denser interconnect structure with a finer pitch, in comparison to a technique requiring wires and balls to be electrically isolated. It is to be appreciated that cut/polish line 107 is well suited to all embodiments in accordance with the present invention.
FIG. 1G illustrates a second embodiment of a heat spreading substrate with embedded interconnects 100, in accordance with embodiments of the present invention. In FIG. 1G, a substrate 101 comprising a metal film is optionally patterned to electrically isolate the wire bond pads 110, wires 120A and/or the ball bonds 121 from the metal 130. For example, a gap 135 is formed in film substrate 101.
FIG. 1H illustrates a third embodiment of a heat spreading substrate with embedded interconnects 100, in accordance with embodiments of the present invention. FIG. 1H illustrates an alternative method of manufacture of heat spreading substrate with embedded interconnects 100, in accordance with embodiments of the present invention. Starting with the configuration of FIG. 1D, metal 131 is laminated to the substrate or film 101. Metal 131 comprises holes 132 that have been pre-drilled, perforated or otherwise formed. Holes 132 fit over wires 120 and ball bonds 121. After lamination of metal 131 to substrate 101, the remaining volume of the holes 132 may be filled in, e.g., plated.
FIG. 1I illustrates a fourth embodiment of a heat spreading substrate with embedded interconnects 100, in accordance with embodiments of the present invention. FIG. 1I illustrates an alternative method of manufacture of heat spreading substrate with embedded interconnects 100, in accordance with embodiments of the present invention. Starting with the configuration of FIG. 1D, metal 133 is laminated to the substrate or film 101. Metal 133 comprises holes 134 that have been pre-drilled or otherwise formed. Holes 134 fit over wires 120A and ball bonds 121. It is to be appreciated that wires 120A may not be coated with dielectric. After lamination of metal 133 to substrate 101, the remaining volume of the holes 134 may be filled with dielectric 125.
FIG. 2 illustrates an application of heat spreading substrate with embedded interconnects 100, in accordance with embodiments of the present invention. In FIG. 2, a plurality of electronic devices 210, 211 have been functionally mounted to heat spreading substrate with embedded interconnects 100 to form electronic assembly 200. Embodiments in accordance with the present invention are well suited to a variety of electronic devices, including, for example, light emitting diodes (LED), radio frequency (RF) devices, motor controllers, power semiconductors and the like.
The plurality of electronic devices 210, 211 need not be of the same design, in accordance with embodiments of the present invention. For example, electronic device 210 may be an LED, whereas electronic device 211 may comprise power and control electronics for LED 210.
FIG. 3 illustrates a detail of electronic assembly 200, in accordance with embodiments of the present invention. In FIG. 3, a first device contact (on the bottom of device 210, not shown) is electrically coupled to the wire 120A via first bond 301, and a second device contact (not shown) is electrically coupled to the conductive body of heat spreading substrate with embedded interconnects 100, e.g., metal 130, 131 or 133, via second bond 302. Bonds 301 and 302 may comprise a variety of bonding types, including, for example, solder balls, controlled chip collapse connections (C4), conductive epoxy and/or eutectic solder. It is to be appreciated that dielectric 120B electrically isolates first lead 301 and wire 120A from second lead 302 and the metal body, e.g., metal 130. Device 210 may be surface mounted to heat spreading substrate with embedded interconnects 100. Alternatively, device 210 may comprise short leads, and such leads may be mounted to heat spreading substrate with embedded interconnects 100.
In accordance with embodiments of the present invention, a plurality of electronic devices, e.g., 210, 211 (FIG. 2) may be surface mounted to a heat spreading substrate with embedded interconnects 100. It is to be appreciated that dielectric 120B may form a solder mask to prevent wicking of solder across contacts of the heat spreading substrate with embedded interconnects 100.
FIG. 4 illustrates a detail of electronic assembly 200, in accordance with embodiments of the present invention. In FIG. 4, a first contact 401 is electrically coupled to the end or face of wire 120A via wire bond 411, and a second lead 302 is electrically coupled to the conductive body of heat spreading substrate with embedded interconnects 100, e.g., metal 130, 131 or 133, via wire bond 412. It is to be appreciated that dielectric 120B electrically isolates first contact 401 and wire 120A from second contact 402 and the metal body, e.g., metal 130.
In accordance with embodiments of the present invention, the plurality of electronic devices mounted on heat spreading substrate with embedded interconnects 100 may be individualized or singulated. For example, heat spreading substrate with embedded interconnects 100 may be sawed or otherwise cut between electronic devices.
In accordance with alternative embodiments of the present invention, some contacts of an electronic device may be functionally coupled to heat spreading substrate with embedded interconnects 100 via surface mount methods, while other contacts of the same electronic device may be functionally coupled to heat spreading substrate with embedded interconnects 100 via wire bond techniques. For example, a contact on the bottom of electronic device 210 may be functionally coupled to heat spreading substrate with embedded interconnects 100 via a surface mount connection, while a contact on the top of electronic device 210 may be functionally coupled to heat spreading substrate with embedded interconnects 100 via a wire bond connection. It is to be appreciated that light emitting diodes frequently have electrical terminals at opposite ends of their layer stack. Embodiments in accordance with the present invention are well suited to such applications.
Alternatively, a plurality of electronic devices, e.g., an array or matrix, of similar and/or dissimilar electronic devices may be operated while mounted together on a common instance of heat spreading substrate with embedded interconnects 100. For example, if many of the plurality of electronic devices are light emitting diodes (LED), the assembly may provide more light than a single LED is capable of providing. Alternatively, the array/matrix of LEDs may provide a variety of spectral colors, by combining the light output of multiple, single-color, LEDs.
In accordance with embodiments of the present invention, a plurality of electronic devices may be assembled onto a heat spreading substrate with embedded interconnects 100, as illustrated in FIG. 2. These assemblies are commonly referred to in terms of the electronic device. For example, the combination of one or more light emitting diodes, e.g., 210, 211 (FIG. 2) assembled onto a heat spreading substrate may be referred to itself as a light emitting diode (LED). Similarly, an individual LED mounted on heat spreading substrate with embedded interconnects 100, may also be referred to as an LED.
In this novel manner, heat generated from electronic devices 210, 211 (FIG. 2) is efficiently and cost effectively conducted through the metal 130, 131 or 133 and to any additional heat sinking structures. For example, heat flows “down” in the perspective of FIG. 2. In addition, heat spreading substrate with embedded interconnects 100 may also conduct electrical signals, e.g., voltage and ground, to electronic devices 210, 211.
FIG. 5 illustrates an example of an application of a light emitting diode, in accordance with embodiments of the present invention. Light source 500 is well suited to a variety of lighting applications, including domestic, industrial and landscape lighting. Light source 500 is also well suited to stage or theatrical lighting. Light source 500 comprises a base 510. As illustrated, base 510 is an Edison type base. It is appreciated that embodiments in accordance with the present invention are well suited to other types of bases, including, for example, GU, bayonet, bipin, wedge, stage pin or other types of bases.
Light source 500 additionally comprises a body portion 520 that houses power conditioning electronics (not shown) that convert 110V AC input electrical power (or 220 V AC, or other selected input electrical power) to electrical power suitable for driving a plurality of light emitting diode devices 540. Body portion 520 may also comprise, or couple to, optional heat sink features (not shown).
Light source 500 additionally comprises optional optics 530. Optics 530 comprise diffusers and/or lenses for focusing and/or diffusing light from the plurality of light emitting diode devices 540 into a desired pattern.
Light source 500 comprises a plurality of light emitting diode devices (LEDs) 540. Individual LEDs of plurality of light emitting diode devices 540 may correspond to assemblies previously described herein. For example, plurality of light emitting diode devices 540 may include instances of devices 210, 211 (FIG. 2). It is appreciated that not all instances of plurality of light emitting diode devices 540 need be identical.
It is to be further appreciated that plurality of light emitting diode devices 540 may include a single heat spreading substrate comprising multiple light emitting devices. For example, a single instance of plurality of light emitting diode devices 540 may comprise a plurality of individual, different, LED devices mounted on a common heat spreading substrate. For example, one instance of an electronic device may be a blue light emitting diode comprising a sapphire substrate. Another instance of an electronic device may be a green light emitting diode comprising a Gallium phosphide (GaP) substrate. Another instance of an electronic device may be a red light emitting diode comprising a Gallium arsenide (GaAs) substrate. The three instances of electronic devices may be arranged in an array on heat spreading substrate with embedded interconnects 100 such that the light from such three colors may be combined to produce a variety of spectral colors. For example, a plurality of light emitting diode devices may operate in combination to produce a “white” light output.
In accordance with embodiments of the present invention, plurality of light emitting diode devices 540 may include additional electronics associated with the LED devices, e.g., as previously described with respect to FIG. 2. In one exemplary embodiment, such additional electronics may comprise circuits to implement a white balance among tri-color LEDs.
FIG. 6 illustrates an exemplary portable computer system 600, in accordance with embodiments of the present invention. Portable computer system 600 may be a mobile phone or smart phone, email device, tablet, laptop or netbook computer, personal digital assistant or the like. A bus 601 functionally couples the various functional blocks of system 600. Bus 601 may comprise multiple busses, and any such bus may be a single conductor.
Portable computer system 600 comprises a processor 610. Processor 610 may be any type of processor for executing software, and may comprise multiple distinct processors, including central processing units and graphical processing units. Processor 610 may also be a multi-core device. Processor 610 generally controls the operation of portable computer system 600, and may operate a graphical user interface. For example, processor 610 accepts input, e.g., from touch sensor 650 and/or optional RF communications 640, and may produce output, e.g., to display 670 and/or RF communications 640. Processor 610 may access random access memory (RAM) 620 for programs and/or data, and may also access read only memory (ROM) for programs and/or data.
Portable computer system 600 optionally comprises a radio-frequency (RF) communications subsystem 640. RF communications system 640 is well suited to operate on a variety of radio communication protocols, including, for example, data and/or telephony networks, e.g., Bluetooth, WiFi, TDMA, CDMA, GSM, AMPS and the like. RF communications system 640, if present, operates to communicate voice, image and/or data to and from portable communication system 600.
Portable computer system 600 comprises a touch sensor subsystem 650. Touch sensor 650 may operate as a resistive or capacitive device, and generally functions to accept input to system 600 in the form of a touch, e.g., from a finger and/or a stylus. Touch sensor 650 is generally strongly associated with a display device. For example, a user of system 600 may perceive touching a “screen” rather than a separate touch sensor.
Portable computer system 600 also comprises a display device 670. Display 670 may be any suitable technology, including, for example, an STN or TFT LCD display device Display 670 functions to output images and/or alpha-numeric information from system 600
Portable computer system 600 further includes a light 680 to illuminate display 670. For example, most LCD devices do not directly produce light; rather such devices filter light from another source, e.g., light 680. Alternatively, light 680 may provide supplemental illumination when ambient light is insufficient for viewing display 670.
In accordance with embodiments of the present invention, light 680 comprises a plurality of light emitting diodes. Individual LEDs of plurality of light emitting diode devices 680 may correspond to assemblies previously described herein. For example, plurality of light emitting diode devices 680 may include instances of electronic devices 210, 211 (FIG. 2). It is appreciated that not all instances of plurality of light emitting diode devices 680 need be identical.
Light 680 may illuminate display 670 from the front and/or the back and/or the sides of display 670, and may be referred to as a front light, back light and/or side light. Light from light 680 may be coupled to the display by a diffuser in front of or behind display 670.
Embodiments in accordance with the present invention provide systems and methods for heat spreading substrate with embedded interconnects. In addition, embodiments in accordance with the present invention provide systems and methods for heat spreading substrate with embedded interconnects that are simple and cost effective to manufacture. Further, embodiments in accordance with the present invention provide systems and methods for heat spreading substrate with embedded interconnects that are compatible and complementary with existing systems and methods of integrated circuit design, manufacturing and test.
Various embodiments of the invention are thus described. While the present invention has been described in particular embodiments, it should be appreciated that the invention should not be construed as limited by such embodiments, but rather construed according to the below claims.

## Claims

1. A method comprising:
wire bonding a plurality of wires to a substrate, said plurality of wires being a plurality of bond wires;
filling a volume with an electrically and thermally conductive material, wherein said volume is in contact with said substrate and comprises said plurality of wires,
wherein said electrically and thermally conductive material comprises a different grain structure from that of said plurality of wires.

2. The method of claim 1 further comprising coating said plurality of wires with a dielectric prior to said bonding.

3. The method of claim 1 further comprising placing a plurality of contacts on said substrate.

4. The method of claim 1 further comprising polishing a surface of said electrically and thermally conductive material to expose ends of said plurality of wires.

5. The method of claim 4 wherein said polishing electrically isolates at least two of said plurality of wires.

6. The method of claim 1 wherein said plurality of wires are electrically isolated from said electrically and thermally conductive material.

7. The method of claim 2 further comprising mounting an electronic device on a surface of said electrically and thermally conductive material.

8. The method of claim 7 wherein said electronic device comprises:
first and second differentiated electrical contacts;
wherein said first differentiated electrical contact is electrically coupled to one of said plurality of wires; and
wherein said second differentiated electrical contact is electrically coupled to said electrically and thermally conductive material.

9. The method of claim 8 further comprising:
wire bonding said first differentiated electrical contact to one of said plurality of wires.

10. The method of claim 8 further comprising:
surface mounting said second differentiated electrical contact to said electrically and thermally conductive material.

11. The method of claim 1 wherein said filling comprises placing an electrically and thermally conductive material on said substrate, wherein said electrically and thermally conductive material has pre-existing holes to accommodate ball bonds of said plurality of wires.