PATENT DOCUMENT

Publication Number: US-8946566-B2
Application Number: US-201213646610-A
Country: US
Kind Code: B2

Title: Heterogeneous encapsulation

Abstract:
An improved method for producing a PCB assembly requiring at least two different encapsulants is disclosed. The PCB assembly may have two or more separate regions in which electronic devices are attached. In each region, a unique encapsulant with different mechanical, electrical, physical and or chemical properties is used according to the particular requirements of the electronic devices in that region.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 a substrate having first and second non-overlapping regions; 
 at least a first electronic component attached to the first region of the substrate, wherein the first electronic component is sealed with a first encapsulant that is an epoxy material; 
 a second encapsulant formed over the second region of the substrate, the second encapsulant having mechanical, electrical and/or chemical properties different from mechanical, electrical and/or chemical properties of the first encapsulant; and 
 at least a second electronic component attached to the second region and sealed with the second encapsulant; 
 wherein the second encapsulant is applied over a plurality of leads extending out of a receptacle connector and electrically attached to circuitry on the substrate. 
 
     
     
       2. The electronic device set forth in  claim 1  wherein the second encapsulant is a silicone material. 
     
     
       3. The electronic device set forth in  claim 2  wherein the epoxy material is curable with ultra-violet light and the silicone material is curable using both heat and moisture. 
     
     
       4. The electronic device set forth in  claim 1  wherein the first electronic component is an integrated circuit. 
     
     
       5. The electronic device set forth in  claim 4  wherein the second encapsulant seals an edge of a body of the receptacle connector to the substrate and covers the circuitry. 
     
     
       6. The electronic device set forth in  claim 5  wherein the second encapsulant is a silicone material that is more compliant than the epoxy material. 
     
     
       7. An electronic device comprising:
 a substrate having first and second non-overlapping regions; 
 at least a first electronic component attached to the first region of the substrate, wherein the first electronic component is sealed with a first encapsulant; 
 a second encapsulant formed over the second region of the substrate, the second encapsulant having mechanical, electrical and/or chemical properties different from mechanical, electrical and/or chemical properties of the first encapsulant; and 
 at least a second electronic component attached to the second region and sealed with the second encapsulant; 
 wherein the first electronic component is an integrated circuit and the second electronic component is an electrical connector; 
 wherein the electrical connector is bonded to circuitry formed on the substrate and the second encapsulant seals an edge of a body of the connector to the substrate and covers the circuitry; 
 wherein the first encapsulant is an epoxy material and the second encapsulant is a silicone material that is more compliant than the epoxy material; and 
 wherein the second encapsulant is applied on first and second opposing sides of the substrate and extends between the body of the connector and an edge of the substrate. 
 
     
     
       8. An electronic device comprising:
 a printed circuit board; 
 circuitry formed on the printed circuit board; 
 a first plurality of electronic components attached to a first region of the printed circuit; 
 a first encapsulant covering the first region of the printed circuit board including the first plurality of electronic components; 
 an electronic connector having a housing and a plurality of leads that extend from the housing attached to the circuitry, wherein an exterior surface of the housing of the electronic connector is spaced apart from a second region of the printed circuit board different than the first region; and 
 a second encapsulant extending between the exterior surface of the housing to the second region of the printed circuit board and covering the plurality of leads attached to the circuitry, wherein the second encapsulant is more compliant than the first encapsulant. 
 
     
     
       9. The electronic device set forth in  claim 8  wherein the first encapsulant is a silicone material. 
     
     
       10. The electronic device set forth in  claim 9  wherein the silicone material is curable using both heat and moisture. 
     
     
       11. The electronic device set forth in  claim 9  wherein the second encapsulant is an epoxy material that is less compliant than the silicone material. 
     
     
       12. The electronic device set forth in  claim 11  wherein the epoxy material is curable with ultra-violet light. 
     
     
       13. The electronic device set forth in  claim 8  further comprising second circuitry formed on the printed circuit board and a second connector coupled to the second circuitry by a flex cable. 
     
     
       14. The electronic device set forth in  claim 8  wherein the second circuitry and an end portion of the flex cable are covered by the second encapsulant. 
     
     
       15. The electronic device set forth in  claim 8  further comprising a conductive dam bar attached to the flex cable. 
     
     
       16. The electronic device set forth in  claim 8  further comprising a metal shield that surrounds the printed circuit board. 
     
     
       17. The electronic device set forth in  claim 8  further comprising a second connector that is incompatible with the first connector. 
     
     
       18. An adapter for providing a communication path between first and second electronic devices, the adapter comprising:
 a printed circuit board having non-overlapping first, second and third regions; 
 first circuitry formed in the second region of the printed circuit board; 
 second circuitry formed in the third region of the printed circuit board; 
 a plurality of electronic components attached to the printed circuit in the first region; 
 a first electrical connector having a housing and a plurality of leads that extend from the housing attached to the first circuitry, wherein an exterior surface of the housing of the electronic connector is spaced apart from the second region of the printed circuit board; 
 a second electrical connector attached to the printed circuit board; 
 a flex cable coupled between the second electrical connector and the second circuitry; 
 an epoxy encapsulant covering the first region of the printed circuit board including the first plurality of electronic components; and 
 a silicone encapsulant covering the second and third regions of the printed circuit board including the first and second circuitry. 
 
     
     
       19. The adapter set forth in  claim 18  wherein:
 the first connector is a receptacle connector having a body that is spaced apart from the printed circuit board; 
 the plurality of leads extend from the body over an edge of the printed circuit board to the first circuitry; and 
 the silicone encapsulant extends from the second region of the printed circuit board to the body covering the edge of the printed circuit board. 
 
     
     
       20. A method of forming a substrate assembly comprising:
 attaching a plurality of electronic components to a substrate; 
 sealing a first region of the substrate with a first encapsulant; and 
 sealing a second region of the substrate with a second encapsulant that has mechanical and chemical properties different from mechanical and chemical properties of the first encapsulant; 
 wherein the substrate is a printed circuit board; and 
 wherein the first encapsulant is a relatively hard and rigid epoxy encapsulant that is applied over one or more of the electronic components attached to the printed circuit board and the second encapsulant is a relatively compliant silicone encapsulant that is applied between an electrical connector and the printed circuit board and covers a plurality of leads that extend out of the connector and are electrically attached to circuitry on the printed circuit board. 
 
     
     
       21. A method of forming a substrate assembly comprising:
 attaching a plurality of electronic components to a substrate; 
 sealing a first region of the substrate with a first encapsulant; 
 sealing a second region of the substrate with a second encapsulant that has mechanical and chemical properties different from mechanical and chemical properties of the first encapsulant; and 
 attaching a metallic shield around at least a portion of the printed circuit board and filling space between the shield and the printed circuit board with an injection molded plastic; 
 wherein the substrate is a printed circuit board.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to techniques of encapsulating integrated circuits and other electronic components on a substrate, such as a printed circuit board, to to mechanically, electrically and/or chemically protect the encapsulated components. 
     Many electronic devices include multiple electronic components attached to a substrate, such as a printed circuit board (PCB). The PCB or other type of substrate provides a base that supports the electronic components, including integrated circuits, electronic subassemblies, capacitors, resistors and the like, and provides connection paths that electrically connect the various components together to form various electrical circuits that are required for a properly functioning electronic device. 
     In some electronic devices the electronic components are encapsulated with a protective cover that mechanically, electrically and/or chemically protects the encapsulated components. For example, in some electronic devices various electronic components may be encapsulated with an epoxy encapsulant to protect the encapsulated components from environmental hazards including moisture and various chemicals that they may otherwise be exposed to. While a number of different encapsulation techniques have been developed, improvements are desirable. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the invention employ two or more different types of encapsulant to mechanically, electrically and/or chemically protect various electronic components attached to a substrate, such as a printed circuit board, in an electronic device. The different encapsulants may have different mechanical, electrical and physical properties that better protect different components depending on the location of the components on substrate or better protect different portions of the substrate itself. For example, a surface mount connector may have multiple leads that physically and electrically couple the connector to a printed circuit board. The body of the connector may be positioned off the printed circuit board while the leads are soldered to bonding pads on the circuit board. Encapsulant may be used to seal the interface between the connector and the printed circuit board to prevent the ingress of moisture or various chemicals, but the connector may need to be mechanically compliant with the circuit board for one or more reasons. Embodiments of the invention may use a compliant or relatively soft encapsulant, such as a silicone-based encapsulant, to provide the desired seal and environmental protection in this area. In a different area of the printed circuit board, however, a precise pattern of encapsulant may be needed to cover various closely spaced electronic components while leaving other areas of the printed circuit board uncovered with encapsulant. Embodiments of the invention may use an epoxy encapsulant that can be applied with a jet dispenser to provide the intricate encapsulation pattern required. 
     One embodiment of the invention pertains to an electronic device that includes a substrate and at least first and second electronic components attached to the substrate. The first electronic component is sealed with a first encapsulant and the second electronic component is sealed with a second encapsulant that has mechanical, electrical and/or chemical properties different from mechanical, electrical and/or chemical properties of the first encapsulant. In some embodiments the first encapsulant is a relatively hard and rigid epoxy encapsulant and the second encapsulant is a relatively compliant silicone encapsulant. In some embodiments the substrate can be a printed circuit board, the second component can be an electrical connector and the second encapsulant can extend between a portion of the body of the electrical connector and the printed circuit board. 
     Another embodiment of the invention pertains to an electronic device that includes at least a first electronic component attached to a first region of the substrate and sealed with a first encapsulant. A second encapsulant that has mechanical, electrical and/or chemical properties different from mechanical, electrical and/or chemical properties of the first encapsulant is formed over a second region of the substrate. In some embodiments the second encapsulant protects the substrate itself or the overall assembly. In other embodiments the second encapsulant protects one or more electronic components attached to the substrate in the second region. 
     Another embodiment of the invention pertains to an electronic device that includes a printed circuit board, a first set of bonding pads formed on the printed circuit board and a plurality of electronic components attached to a first region of the printed circuit. A first encapsulant covers the first region of the printed circuit board including the first plurality of electronic components. The electronic device further includes an electronic connector that has a housing and a plurality of leads that extend from the housing and are attached to the first set of bonding pads. The connector is positioned off of and attached to the printed circuit board such that an exterior surface of the housing of the electronic connector is spaced apart from a second region of the printed circuit board different than the first region. A second encapsulant that is more compliant than the first encapsulant extends between the exterior surface of the housing to the second region of the printed circuit board and covers the plurality of leads attached to the first plurality of bonding pads. In some embodiments the first encapsulant is an epoxy material and the second encapsulant is a silicone material. 
     Additional embodiments of the invention pertain to methods of assembling a substrate or printed circuit board assembly. According to one such embodiment, electronic components are attached to a printed circuit board or other type of substrate. A first region of the printed circuit board is sealed with a first encapsulant and a second region of the printed circuit board is sealed with a second encapsulant that has mechanical and chemical properties different from mechanical and chemical properties of the first encapsulant. In some embodiments the first encapsulant is a relatively hard and rigid epoxy encapsulant that is applied over one or more of the electronic components attached to the printed circuit board and the second encapsulant is a relatively compliant silicone encapsulant that is applied between an electrical connector and the printed circuit board and covers a plurality of leads that extend out of the connector and are electrically attached to bonding pads on the printed circuit board. In some embodiments the first encapsulant is an epoxy material and the second encapsulant is a silicone material. 
     To better understand the nature and advantages of the present invention, reference should be made to the following description and the accompanying figures. It is to be understood, however, that each of the figures is provided for the purpose of illustration only and is not intended as a definition of the limits of the scope of the present invention. Also, as a general rule, and unless it is evident to the contrary from the description, where elements in different figures use identical reference numbers, the elements are generally either identical or at least similar in function or purpose. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram that illustrates a top plan view of a PCB assembly  100  in accordance with an embodiment of the invention; 
         FIG. 2  is a diagram that illustrates a cross-sectional view of PCB assembly  100  shown in  FIG. 1 ; 
         FIG. 3  is a diagram that illustrates a top plan view of a PCB assembly  150  in accordance with another embodiment of the invention in a first partial state of assembly; 
         FIG. 4  is a diagram that illustrates a top plan view of PCB assembly  150  shown in  FIG. 3  in a second partial state of assembly; 
         FIG. 5  is a diagram that illustrates a top plan view of PCB assembly  150  shown in  FIG. 3  in a third partial state of assembly; 
         FIG. 6  is a simplified cross-sectional view of PCB assembly  150  in accordance with one embodiment of the invention; 
         FIG. 7  is a simplified cross-sectional view of PCB assembly  150  shown in  FIG. 6  when connector  140  is subject to a lateral force; 
         FIG. 8  is a simplified cross-sectional view of a portion of PCB assembly  150  showing an underfill encapsulant applied beneath an electronic component  119  according to an embodiment of the invention; 
         FIG. 9  is a diagram that illustrates a cross-sectional view of a PCB assembly  180  in accordance with another embodiment of the invention; 
         FIG. 10  is a diagram that illustrates a cross-sectional view of a PCB assembly  190  in accordance with yet another embodiment of the invention; and 
         FIG. 11  is a process by which a PCB assembly using two or more encapsulants can be made in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain embodiments of the present invention relate to substrate assemblies having electronic components attached thereto and encapsulated with a protective encapsulant. The substrate assemblies may be employed in portable electronic devices, such as portable media players, cellular telephones, tablet computers, laptop computers and the like including accessories for such devices, or may be employed in electronic devices that are not traditionally thought of as portable devices such as desktop computers and video displays, among other devices. The substrate employed in the assembly may include any type of substrate used for attaching integrated circuits including a ceramic substrate, a glass substrate, a silicon substrate, a polyimide substrate or a printed circuit board (PCB) among others. Some embodiments of the invention to substrate assemblies, such as PCB assemblies, for electronic devices that include different types of encapsulates, each having different mechanical, electrical and/or chemical properties, on the same PCB assembly as described in more detail below. 
     Certain embodiments of the present invention relate to PCB assemblies employed in electronic devices. Many electronic devices such as smart-phones, media players, tablet computers, and connector adapters may have PCB assemblies containing encapsulated electronic components.  FIG. 1  is simplified a top schematic view of an exemplary PCB assembly  100  in accordance with one embodiment of the invention. PCB assembly  100  includes a printed circuit board  105  comprised of, for example, epoxy/glass-fiber/metal, ceramic/metal, polyamide film/metal. PCB  105  may have a portion of outer surfaces that are metallic and designed for the electrical attachment of exemplary electronic components  110  and  119 , which may be attached to the PCB in regions  111  and  112 , respectively. Attachment of electronic components  110 ,  119  to PCB  105  may be performed with any electrically conductive material including, for example, solder alloys and conductive adhesive. Myriad processes may be employed to perform the attachment, for example, convective solder reflow, wave soldering and epoxy dispensing/placement/curing. Electronic components  110 ,  119  may include integrated circuits, electronic subassemblies, electrical connectors, capacitors, resistors and the like. 
     After electronic components  110 ,  119  are attached to PCB  105 , one or more encapsulants may be dispensed on top of the electronic components, forming a protective barrier around the components. In some embodiments, it may be desirable to encapsulate electronic components  110  in region  111  with an encapsulant that has different mechanical, chemical and/or electrical properties than the encapsulant used to encapsulate electronic components  119  in region  112 . For example, electronic components  110  mounted in region  111  of PCB  105  may require different protection than electronic components  119  mounted in region  112 . To provide the required protection, two different encapsulants may be employed where region  111  uses a first encapsulant  130  and region  112  uses a second encapsulant  135 . The different encapsulants may have different mechanical, electrical and/or chemical properties designed to protect the electronic components  110 ,  119  and the areas  111 ,  112  differently. The different mechanical, electrical, chemical and physical properties of encapsulants  130 ,  135  and exemplary benefits thereof, will be discussed in more detail below. 
     PCB assembly  100  may have one or more regions, such as regions  116  and  117  shown in  FIG. 1 , designated as keep out regions where the encapsulant must be kept out of altogether or must not enter until a later stage of assembly. In one embodiment, keep out region  116  may be a feature attached to PCB  105 , such as a vertical stand-off that helps keep separation between PCB  105  and an exterior shield or housing of an electronic device that the PCB assembly  100  is positioned within, while region  117  may contain a plurality of bonding pads  125  that need to remain exposed for a subsequent step in which a cable, a flex circuit or other component is bonded to the bonding pads. Thus, in some embodiments, encapsulants  130 ,  135  may be required to be dispensed carefully and may have the necessary properties to not run or bleed into keep out regions  116  and  117 . 
     While  FIG. 1  is a top view only of PCB assembly  100  and thus shows only one of the two major sides of PCB  105 , the PCB assembly may include electronic components attached to the opposing side of PCB  105  as well.  FIG. 2 , which is a simplified cross-sectional view of PCB  100  shown in  FIG. 1 , depicts electronic components formed on each such side and depicts that encapsulants  130 ,  135  may or may not entirely cover all of electronic components  110 ,  119 . In some embodiments, encapsulants  130 ,  135  may cover the entirety of all the electronic components  110 ,  119 , whereas in other embodiments the encapsulants may only cover the periphery of the electronic components. Further, encapsulants  130 ,  135  may be disposed on either or both sides of PCB  105  as shown in  FIG. 2 . 
       FIG. 3  is a simplified top schematic view of a PCB assembly  150  according to another embodiment of the invention at a partial stage of manufacture. PCB assembly  150  can be used in an electronic accessory that is an adapter that allows two electronic devices that include otherwise incompatible connectors to be electrically connected with each other to exchange information. Specifically, the adapter may provide an electrical communication path between first and second electronic devices that could otherwise only communicate via a wireless means. An example of such an adapter is described in U.S. patent application Ser. No. 13/607,519, filed on Sep. 7, 2012, which is hereby incorporated by reference in its entirety. 
     As shown in  FIG. 3 , PCB assembly  150  includes two different encapsulants  152  and  154  along with a surface mount receptacle connector  140  with leads  145  that may be attached to a first set of bonding pads  148  on PCB  105 . More specifically, surface mount connector  140  may have multiple leads  145  that physically and electrically couple the connector to PCB  105 . As shown in  FIG. 3 , connector  140  is a 30-pin connector that includes thirty leads  145 ( 1 ) . . .  145 ( 30 ) and PCB  105  includes a corresponding number of first bonding pads  148 ( 1 ) . . .  148 ( 30 ). In other embodiments of the invention, PCB assembly  150  may include a connector  140  with a different number of leads, fewer or more than thirty, and include a set of bonding pads  148  with a number of bonding pads equal to or different than the number of leads. 
     Connector  140  further includes a body  142  that has a surface spaced apart from PCB  105  in a vertical, horizontal or both vertical and horizontal direction. Body  142  defines a cavity in which a plurality of contact structures are positioned. Each contact structure has a contact tip exposed within the cavity to make electrical connection to a corresponding contact in a mating plug connector and a lead that extends out of the housing and is bonded to one of the plurality of bonding pads as described above. In some embodiments, each contact structure includes a beam portion and an anchor portion (neither of which are shown) between the contact tips and leads. 
     In the embodiment depicted in  FIG. 4 , the body of connector  140  is positioned off of and spaced apart from PCB  105  in the horizontal direction while leads  145 ( 1 ) . . .  145 ( 30 ) may be soldered to bonding pads  148 ( 1 ) . . .  148 ( 30 ) on the PCB. Encapsulant  152  may be used to seal the interface between connector  140  and PCB  105  to prevent the ingress of moisture or various chemicals, to strengthen the mechanical connection between the connector PCB  105  and/or to distribute stress or strain. Towards this end encapsulant  152  may extend from a portion of PCB  105  to a surface of connector  140  and may do so from both sides of the PCB as shown in  FIG. 6 . Some embodiments of the invention allow the connector to remain mechanically compliant relative to the PCB and may use a compliant or relatively soft encapsulant  152  in region  117 , such as, for example, a silicone encapsulant which is not easily separable from PCB  105  or connector  140 , to provide the desired seal and environmental protection in this area. In other embodiments, encapsulant  152  may be used in any location where, through use of the electronic device that PCB assembly  150  is incorporated into, mechanical forces can be imparted to the assembly to possibly separate one or more components from PCB  105 . In the case of PCB assembly  150  and connector  140 , such separation may result in dendryte growth on the contacts due to sugars and salts that may travel through cracks in the encapsulant, which in turn may result in thermal failures. 
     As shown in  FIG. 3 , in one embodiment PCB  105  includes a second set of bonding pads  125  in a region  117  that must be initially kept free of encapsulant. In this embodiment, encapsulant  152  may first be applied to extend from first and second edge portions  122   a  and  122   b  on opposing sides of region  117  to the body of connector  140 , covering a portion of an edge  105   a  of PCB  105  as well as some of leads  145  and bonding pads  148 . While bonding pads  125  and  148  are shown as being on the same side of PCB  105  in  FIG. 3 , in other embodiments of the invention bonding pads  125  and  148  can be on opposite sides of the PCB. 
     PCB assembly  150  also includes a second type of encapsulant  154  to environmentally seal electronic components  110  and  119 . Encapsulant  154  may be an epoxy encapsulant that is harder than and relatively rigid compared to encapsulant  152 . The use of a relatively rigid non-compliant encapsulant may be beneficial in particular regions of PCB assembly  150 . In some embodiments, encapsulant  154  is a jet dispensable material so that it can be applied with a jet dispenser in a precise pattern to cover certain electronic components while leaving other portions of PCB  105  free from encapsulant. Also, in some embodiments, encapsulant  154  is curable with ultra-violet radiation and heat, is UV fluorescent and does not allow outgassing of halogen elements. In some embodiments, encapsulant  154  has a hardness value of medium hard or higher on the Shore D scale while encapsulant  152  has a hardness value of medium soft or less on the Shore A scale. 
     As shown in  FIG. 3A , PCB assembly  150  includes at least one zone  117  which is kept free of encapsulant. As discussed above, bonding pads  125 ( 1 ) . . .  125 ( 11 ) are positioned in zone  117 . The bonding pads  125  are kept free of encapsulant at this stage of assembly so that a flex cable (cable  156  shown in  FIG. 4 ) can be bonded to the bonding pads using a hot bar or other suitable bonding operation. Referring now to  FIG. 4 , which is a simplified top plan view of PCB assembly  150  at a second stage of assembly after the first stage, PCB assembly  150  may include a second, plug connector  142  that physically incompatible with receptacle connector  140  and is attached to PCB  105  using a flexible mount (not shown) that enables connector  142  to flex or bend in multiple dimensions. Further details of a suitable flexible mount can be found in U.S. patent application Ser. No. 13/607,598, filed on Sep. 7, 2012, which is hereby incorporated by reference in its entirety. 
     Flex cable  156  extends from connector  142  to bonding pads  125 ( 1 ) . . .  125 ( 11 ). The end of flex cable  156  opposite connector  142  includes a plurality of connector pads (not shown) that correspond in number and are bonded to bonding pads  125 ( 1 ) . . .  125 ( 11 ). In one embodiment, the connector pads and bonding pads are bonded in a hot bar process. Flex cable  156  also includes a conductive spacer  158  that includes a conductive elastomer material and extends upwards from cable  156  in the vertical direction. Conductive spacer  158  can be electrically connected to an outer shield (shield  170  shown in  FIG. 8 ) and provides a dam for additional encapsulant  160  that can be applied in a subsequent assembly step as described below. 
       FIG. 5 , which is a simplified top plan view of PCB assembly  150  at a third stage of assembly after the second stage, shows additional encapsulant  160  applied over bonding pads  125 ( 1 ) . . .  125 ( 11 ) and an end portion of flex cable  156  as well as over any remaining leads  145  and bonding pads  146  not previously covered by encapsulant  152 . In one embodiment, encapsulant  160  is a compliant silicone encapsulant and is identical to encapsulant  152 . 
     In some embodiments, compliant encapsulants  152  and  160  may improve the reliability of the electronic device, as illustrated in  FIG. 7 . More specifically, connector  140  may be subjected to an exemplary force depicted by “F” and the associated arrow. Thus, connector  140  may be required to flex relative to PCB  105 . If a rigid, hard encapsulant were used as encapsulants  152  and/or  160  in this area, PCB  105  or connector  140  may break or crack creating a potential path for the ingress of moisture or various chemicals or the solder connections to leads  145  may crack or break, any of which may in turn cause a subsequent failure of the electronic device. 
     Some embodiments of the invention include an underfill encapsulant for some or all of electronic components  110  and  119  in addition to the two or more different encapsulants such as encapsulants  152 ,  154  and  160  described above. To better understand this aspect of embodiments of the invention, reference is made to  FIG. 8 , which is a cross-sectional view of an exemplary electronic component  119 . In  FIG. 8  electronic component  119  may be a flip-chip integrated circuit with electronic leads  161  that may be attached to PCB  105 . Encapsulant  154  is depicted as covering the entirety of electronic device  119 . An optional underfill encapsulant  165  is also shown between electronic component  119  and PCB  105 . Other electronic components  110  and  119  may have a similar underfill encapsulant applied under them. In one embodiment, encapsulants  154 ,  165  both have a relatively high modulus of elasticity and a coefficient of thermal expansion that may be roughly close to the coefficient of thermal expansion of electronic component  119 . However, in other embodiments, the encapsulants may have different mechanical properties, for example, their mechanical properties may more closely match those of the PCB  105 . Encapsulants  135 ,  165  may strengthen, stiffen and restrict flexure of PCB  105  in the local region of electronic component  119 . Encapsulants  135 ,  165  may also add environmental or electrical protection to electronic component  119 . In some regions of PCB  105  some embodiments of the invention include underfill encapsulant  165  without covering component  119  with another encapsulant. 
     Further embodiments, depicted in  FIG. 9 , may involve placing a metallic shield  170  over at least a portion of a PCB assembly  180 . Metallic shield  170  may have interference regions  182  where the shield may interfere or come in contact with encapsulant  152 ,  160 . In some embodiments encapsulant  152 ,  160  may be compliant, easily deforming when shield  170  is engaged. In other embodiments, encapsulant  152 ,  160  may be designed with a relatively slow curing rate that may allow it to be in a partially cured state having a low modulus of elasticity and a higher modulus of elasticity after fully curing. Such an encapsulant provides a window in which shield  170  can be assembled and attached to PCB assembly  180  prior to encapsulant  152 ,  160  being fully cured. This, in turn, allows the encapsulant to be pressed towards PCB  105  by the shield in interference regions  182  further improving the seal between the shield and the encapsulant. Thus, in some embodiments, encapsulant  152 ,  160  may have a slower curing rate than encapsulant  154  used on PCB  105 . 
     In some embodiments, shield  170  may have a ground connection (not shown) that may interface with keep out region  116  (see  FIG. 3 ). More specifically, region  116  may be required to be completely free of any encapsulant, for the ground connection to make contact with this region. Certain PCB regions such as  112  (see  FIG. 3 ) that are encapsulated may be close to keep out regions. These areas may require encapsulant  154  to be dispensed with precision, which may require encapsulant  154  to have different properties than other encapsulants used on PCB assembly  100 . More specifically, some encapsulant dispense processes, for example, jet dispensing, may provide improved control of the encapsulant. However, jet dispensing may require the encapsulant to have a particular formulation of viscosity, thixotropic index and other properties. Further, certain encapsulants, even if dispensed with a syringe and needle, may need to be formulated to minimize bleeding and running to ensure they remain contained in encapsulant regions  111 ,  112  (see  FIG. 3 ) and do not enter keep out regions  116 ,  117 . Thus, to achieve the required control of the dispensed encapsulants, certain encapsulants may require different formulations as compared to other encapsulants used on PCB assembly  100 . 
     Further embodiments, depicted in  FIG. 10 , may involve a final step of filling some or all of the space between shield  170  and the PCB assembly with a material  185 . In some embodiments, an injection molding process may be used where an injection moldable plastic such as, for example, nylon, ABS or PBT may be used. In other embodiments, an injection molding process may be used where an injection moldable mold compound is used such as a phenol-aralkyl type epoxy resin filled with 70% fused silica. In other embodiments, an encapsulant may be used as described above. An encapsulant differs from the injection molding embodiments wherein an encapsulant does not employ injection molding die and the encapsulant is typically dispensed with, for example, a syringe, a jet dispenser, an ultrasonic dispenser, or other similar dispensers. 
     An exemplary simplified process for manufacturing a PCB assembly comprising electronic components encapsulated with two different materials, in accordance with embodiments described herein, is depicted in  FIG. 10 . In step  205  one or more electronic components are attached to a PCB or other type of substrate. The electronic components may include integrated circuits, electronic subassemblies, electrical connectors, capacitors, resistors, and the like may be attached, for example, with a solder or a conductive adhesive. The PCB assembly may be cleaned, or may not be cleaned depending on the requirements of the encapsulant and the PCB assembly. In step  215 , a first encapsulant with particular chemical, physical, mechanical and electrical properties is dispensed in one or more regions of the PCB and on one or both sides of the PCB to environmentally seal a portion or portions of the PCB. Depending on where the first encapsulant is applied it may cover various electronic components attached to the PCB or it may extend between a component and the PCB to cover an area of potential separation between the two. The encapsulant may then be cured, according to its particular requirements. In step  220 , a second encapsulant with different particular chemical, physical, mechanical and electrical properties as compared to the first encapsulant is dispensed in one or more other regions of the PCB on one or both sides of the PCB to environmentally seal another portion or portions of the PCB. Depending on where the second encapsulant is applied it may cover various electronic components attached to the PCB or it may extend between a component and the PCB to cover an area of potential separation between the two. The second encapsulant may then be cured, according to its particular requirements. Additional encapsulants, different from either the first or second encapsulant, may also be applied as appropriate in steps after step  220  or after any of the subsequently described steps prior to the completion of the PCB assembly. 
     Next, in step  225  a component such as flex cable  160  is bonded to bonding pads on the PCB that were purposefully left uncovered by encapsulant in steps  215  and  220 . The component (flex cable) can then be encapsulated with the same encapsulant used to encapsulate other portions of the receptacle connector. In step  235 , shield  170  can be attached to the PCB assembly as shown in  FIG. 9  and in step  240  the assembly of PCB assembly can be completed and it may be installed in an appropriate electronic device. 
     In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. While a number of specific embodiments and examples were disclosed with specific features, a person of ordinary skill in the art will recognize instances where the features of one embodiment can be combined with the features of other embodiments. Also, myriad encapsulants comprising different mechanical, physical, chemical and electrical properties may be used in PCB assembly  100  without departing from the invention. For example, some embodiments may use encapsulants that comprise silicone and may be moisture cured while others may be cured using ultra-violet light. Some embodiments may use encapsulants that comprise an epoxy that may be heat, light or catalyst cured. Some embodiments may use encapsulants that may comprise a filler such as silica, or a ceramic to increase mechanical modulus, reduce the coefficient of thermal expansion and or to increase thermal conductivity. Other embodiments may use encapsulants with high surface free energy designed to wick into small crevices such as between a flip-chip and a PCB. Other embodiments may comprise a combination of encapsulants such as dam and fill where a viscous encapsulant is used to build a dam and a lower viscosity encapsulant is used to fill. Some encapsulants may comprise special formulations to chemically bond to particular components within PCB assembly  105 . The sole and exclusive indicator of the scope of the invention, and what is intended by the applicants to be the scope of the invention, is the literal and equivalent scope of the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction.

Metadata:
Filing Date: 20121005
Publication Date: 20150203
Grant Date: 20150203
Priority Date: 20121005
Inventors: BAKER JOHN J.
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K3/284", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K2201/09972", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10189", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T29/49146", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10356", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10446", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1476", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10356", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/284", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K2201/10446", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09972", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10189", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1327", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1327", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1476", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T29/49146", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 50432507