PATENT DOCUMENT

Publication Number: US-10966321-B2
Application Number: US-202016894463-A
Country: US
Kind Code: B2

Title: System-in-package including opposing circuit boards

Abstract:
System-in-package structures and methods of assembly are described. In an embodiment, a system-in-package includes opposing circuit boards, each including mounted components overlapping the mounted components of the opposing circuit board. A gap between the opposing circuit boards may be filled with a molding material, that additionally encapsulates the overlapping mounted components. In some embodiments, the opposing circuit boards are stacked on one another using one or more interposers that may provide mechanical or electrical connection.

Claims:
What is claimed is: 
     
       1. A system-in-package comprising:
 a circuit board; 
 a plurality of components mounted on the circuit board; 
 one or more interposers mounted on the circuit board laterally adjacent to the plurality of components; 
 wherein a first interposer of the one or more interposers includes one or more lateral tunnels extending from a laterally exterior side to a laterally interior side of the first interposer; and 
 a molding material that laterally surrounds the plurality of components and the one or more interposers, and at least partially fills the one or more lateral tunnels for the first interposer. 
 
     
     
       2. The system-in-package of  claim 1 , wherein each of the one or more interposers comprises an insulating material and a plurality of metal traces extending from a bottom side to a top side of the corresponding interposer. 
     
     
       3. The system-in-package of  claim 2 , wherein the plurality of traces is a plurality of vias. 
     
     
       4. The system-in-package of  claim 1 , wherein the one or more interposers is arranged laterally around the plurality of components. 
     
     
       5. The system-in-package of  claim 4 , wherein the one or more interposers is arranged adjacent a periphery of the circuit board. 
     
     
       6. The system-in-package of  claim 4 , further comprising an additional component mounted on the circuit board outside the one or more interposers. 
     
     
       7. The system-in-package of  claim 6 , wherein the molding material does not laterally surround the additional component. 
     
     
       8. The system-in-package of  claim 1 , wherein the one or more interposers is solder bonded to the circuit board. 
     
     
       9. The system-in-package of  claim 1 , wherein the one or more lateral tunnels extends through a top side or a bottom side of the first interposer. 
     
     
       10. The system-in-package of  claim 1 , wherein the one or more lateral tunnels extends through a bottom side of the first interposer. 
     
     
       11. The system-in-package of  claim 1 , wherein the one or more lateral tunnels includes a first lateral tunnel that extends through a top side of the first interposer and a second lateral tunnel that extends through a bottom side of the first interposer. 
     
     
       12. The system-in-package of  claim 11 , wherein the first lateral tunnel is located directly over the second lateral tunnel. 
     
     
       13. The system-in-package of  claim 1 , wherein the one or more lateral tunnels extends through a center section of the first interposer. 
     
     
       14. The system-in-package of  claim 1 , wherein the one or more lateral tunnels comprises one or more first lateral tunnels extending through a top side or a bottom side of the first interposer, and one or more intermediate lateral tunnels extending through a center section of the first interposer, wherein the one or more first lateral tunnels are not connected to the one or more intermediate lateral tunnels. 
     
     
       15. The system-in-package of  claim 1 , wherein the one or more interposers laterally surrounds a subsystem of the plurality of components. 
     
     
       16. The system-in-package of  claim 1 , wherein the one or more interposers includes a passive device. 
     
     
       17. The system-in-package of  claim 1 , wherein the circuit board comprises a rigid substrate and conductive traces that electrically connect the plurality of components. 
     
     
       18. The system-in-package of  claim 1 , wherein:
 each of the one or more interposers comprises an insulating material, and a plurality of metal traces extending from a bottom side to a top side of the corresponding interposer; and 
 the one or more lateral tunnels includes a first group of lateral tunnels that extends through a top side of the first interposer and a second group of lateral tunnels that extends through a bottom side of the first interposer. 
 
     
     
       19. The system-in-package of  claim 18 , wherein the one or more interposers is arranged laterally around the plurality of components. 
     
     
       20. The system-in-package of  claim 1 , wherein:
 each of the one or more interposers comprises an insulating material, and a plurality of metal traces extending from a bottom side to a top side of the corresponding interposer; and 
 the one or more lateral tunnels includes a first lateral tunnel that extends through a top side of the first interposer and a second lateral tunnel that extends through a bottom side of the first interposer, wherein the first lateral tunnel is located directly over the second lateral tunnel.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/426,443, filed May 30, 2019, which is a continuation of U.S. patent application Ser. No. 15/939,097 filed Mar. 28, 2018, now U.S. Pat. No. 10,356,903, which is herein incorporated by reference. 
    
    
     BACKGROUND 
     Field 
     Embodiments described herein relate to electronic packaging, and more particularly to printed circuit board assembly. 
     Background Information 
     The trend in consumer electronics is to make products smaller, with the exception of display size, for a range of product categories including phones, computers, portable music players, earbuds, audio systems, etc. Hence there is a drive for minimization for all the parts inside these products. 
     The main logic board (MLB) is a common part in almost all of the consumer electronics. Industry has been working to utilize smaller and thinner dies, packages and components. The spacings between the components are also made smaller and smaller. Industry is also trying to add more and more smart functions in all the portable electronics including smart phones, watches, etc. These new functions require new hardware. To accomplish hardware like camera module, alerts, charging, batteries, biosensors, etc. the MLBs may become constrained to certain volume with restrictions on areas, heights, or shapes. 
     SUMMARY 
     System-in-package structures and methods of assembly are described. In an embodiment, a system-in-package structure includes a first circuit board having a first side and a second side opposite the first side, one or more second side components mounted on at least the second side of the first circuit board, a second circuit board having a first side and a second side opposite the first side, and one or more first side components are mounted on at least the first side of the second circuit board. In accordance with embodiments, the first side of the second circuit board faces the second side of the first circuit board, and a gap between the first circuit board and the second circuit board is filled with molding material. 
     The opposing circuit boards may be stacked using one or more interposers, which may provide mechanical and optionally electrical connection. In an embodiment, the interposers include one or more lateral tunnels extending from a laterally exterior side to a laterally interior side of the interposer. 
     Assembly of the system-in-package in accordance with embodiments may include stacking the first circuit board on the second circuit board, and then molding to stacked circuit boards to fill the gap between the circuit boards with a molding material. In some embodiments, the molding material flows through the one or more lateral tunnels extending through the one or more interposers. The molding material may remain in the lateral tunnels in the final system-in-package structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart illustrating a method of assembling a system-in-package in accordance with an embodiment. 
         FIGS. 2A-2E  are cross-sectional side view illustrations of a sequence of assembling a system-in-package in accordance with an embodiment. 
         FIG. 3  is a schematic cross-sectional side view illustration of stacked interposers mounted between two circuit boards in accordance with an embodiment. 
         FIG. 4  is a schematic top layout view of circuit board components and interposers on a circuit board in accordance with embodiments. 
         FIGS. 5A-5B  are schematic cross-sectional side view illustrations of interposers including lateral tunnels in accordance with embodiments. 
         FIGS. 6A-6D  are cross-sectional side view illustrations of a sequence of assembling a system-in-package using sacrificial supports in accordance with an embodiment. 
         FIGS. 7A-7B  are schematic top layout views of sacrificial supports mounted on a circuit board in accordance with embodiments. 
         FIGS. 8A-8C  are cross-sectional side view illustrations of a sequence of assembling a system-in-package with double side surface mounted circuit boards in accordance with an embodiment. 
         FIGS. 9A-9D  are cross-sectional side view illustrations of a sequence of assembling a system-in-package with a pre-molded circuit board in accordance with an embodiment. 
         FIGS. 10A-10C  are cross-sectional side view illustrations of a sequence of assembling a system-in-package with pre-molded circuit boards in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe system-in-package (SiP) structures and methods of assembly in which opposing circuit boards are stacked on top of one another, with a gap between the stacked boards being filled with a molding material. In addition, interposer structures can be arranged between the circuit boards to provide mechanical support to the stacked structure, as well as electrical interconnection between the circuit boards. Embodiments described herein may be applicable to a variety of circuit boards, such as printed circuit boards and MLBs. 
     In one aspect, it has been observed that due to open face designs of traditional circuit board arrangements, such as with main logic boards (MLBs), there can be increasing yield losses, reliability failures, and performance degradations as component density increases. Industry has commonly looked to underfill materials to make the whole circuit boards more robust. Though underfill materials and tools can be expensive. In accordance with embodiments, alternative structures and processes are described which may achieve target reliability and performance function. 
     In accordance with embodiments, two circuit boards are stacked together as opposed to using a single open faced board. As a result, the overall x, y size for the system may be smaller. The two circuit boards may be connected with interposers. There can be interposers on both sides (e.g. stacked and bonded), or one single interposer on one of the boards. In accordance with embodiments, the interposers electrically connect the two circuit boards, and physically connect the two circuit boards. For example, the interposers include vias for signal and power transmission between the circuit boards. A molding design with a molding material, such as an epoxy molding compound (EMC), can additionally be included to fill the gap between the two circuit boards. For example, a film assisted transfer molding process may be able to fill gaps of several tens of microns. In some embodiments, this may allow for the elimination of underfilling the board components. The molded design may also be mechanically robust, particularly compared to open face designs or hollow board stacks. Additionally, the molded structure may be water proof. Furthermore, due to stacked design, component layout on the circuit boards may be more flexible for improved signal integrity. 
     The interposers in accordance with embodiments, may include through vias, for signal and power connections, and optionally include active or passive components such as integrated circuits, resistors, capacitors (e.g. electrostatic discharge (ESD) decoupling capacitors), etc. The interposers may additionally provide electromagnetic interference (EMI) shielding. In some embodiments, the interposers are arranged along the edge, or outline of the circuit boards. In some embodiments, the interposers include lateral tunnels, or spaces to assist with the molding operation. These lateral tunnels may be partially or completely filled with the molding compound used to fill the gap between opposing circuit boards. 
     In various embodiments, description is made with reference to figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions and processes, etc., in order to provide a thorough understanding of the embodiments. In other instances, well-known semiconductor processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the embodiments. Reference throughout this specification to “one embodiment” means that a particular feature, structure, configuration, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The terms “over”, “to”, “between”, “spanning” and “on” as used herein may refer to a relative position of one layer with respect to other layers. One layer “over”, “spanning” or “on” another layer or bonded “to” or in “contact” with another layer may be directly in contact with the other layer or may have one or more intervening layers. One layer “between” layers may be directly in contact with the layers or may have one or more intervening layers. 
     Referring now to  FIG. 1  a cross-sectional side view illustration is provided of a method of assembling a system-in-package in accordance with an embodiment. In interest of clarity and conciseness, the following discussion of  FIG. 1  is made concurrently with the description of the sequence illustrated in  FIG. 2A-2E . It is to be appreciated however, that embodiments are not so limited, and variations of structure and sequence are contemplated. For example, various structural and sequence variations are provided in  FIGS. 3-10C  that follow. 
     In accordance with embodiments, the illustrated processing sequences begin with circuit boards that have been populated with components, and optionally interposers, with SMT assembly. This may have been done at the panel level, followed by singulation of the populated circuit boards. In certain variations, the circuit boards can be populated on a single side or both sides, or also molded on a single side or both side, or not yet molded. Thus, the processing sequences described herein in accordance with embodiments may be compatible with a variety of different circuit board designs. These circuit boards may then be stacked and molded, which can be performed at a re-constituted panel process, followed by singulation of stacked circuit boards. A final SMT assembly may be optionally be performed, before or after singulation, to add any additional desired components to the stacked circuit boards. 
     In an embodiment, at operation  110  a first circuit board  210  is stacked on a second circuit board  240  to form a circuit board stack  280 . As shown in  FIGS. 2A-2B , the first circuit board  210  may include a first side  212  and a second side  214  opposite the first side, and one or more second side components  220  mounted on at least the second side  214  (e.g. bottom side) of the first circuit board  210 . The second circuit board  240  may include a first side  242  and a second side  244  and one or more first side components  250  mounted on at least the first side  212  (e.g. top side) of the second circuit board  240 . In accordance with embodiments, a gap  281  exists between the first circuit board  210  and the second circuit board  240 , as well as the associated components as shown in  FIG. 2B . Thus, the gap  281  is also between the components  220 ,  250  that overlap each other (e.g vertically, as opposed to laterally). 
     As shown in  FIG. 2B  and the close up illustration in  FIG. 3 , interposers  230 ,  260  can also be mounted on either or both of the circuit boards  210 ,  240  and extend between and connect the first circuit board  210  and the second circuit board  240 . The connection may be physical, and may additionally be an electrical connection between the circuit boards. Thus, there may be a single interposer mounted on one of the circuit boards  210 ,  240  that connects the circuit boards  210 ,  240  after stacking. Alternatively, as illustrated, there may be an interposer mounted on each circuit board, and stacking the circuit boards includes stacking the interposers  230 ,  260  to form an interposer stack  270 . The one or more interposers  230 ,  260  in accordance with embodiments are located laterally adjacent the one or more components  220 ,  250  on their respective circuit boards  210 ,  240 . 
     The circuit boards  210 ,  240  can be substrates with one more layers of conductive traces or routing inside them. For example, the circuit boards  210 ,  240  may include a rigid substrate  211 ,  241  with conductive traces  215 ,  245  for attachment of various components, interposers, etc. Conductive traces  215 ,  245  may be contained wholly or partially within the rigid substrates  211 ,  241 , and may also be formed on surfaces of the substrates  211 ,  241 . In some configurations, a substantial portion of the conductive traces  215 ,  245  are contained within multiple metal layers in the substrates  211 ,  241 , with limited routing of the conductive traces  215 ,  245  on top of the substrates  211 ,  241 . In an embodiment, each interposer  230 ,  260  is bonded to a conductive trace  215 ,  245  on a substrate  211 ,  241  of a respective circuit board  210 ,  240 . The substrates  211 ,  241  may be formed of a variety of materials, including traditional substrates such as FR-2 (a phenolic paper impregnated with resin), FR-4 (a woven fiberglass impregnate with resin), ABF (Ajinomoto Build-up Film) metal or metal core substrates, silicon core substrates, ceramics, polymers, etc. In some embodiments, the substrates may be flexible. Conductive traces  215 ,  245  may be formed of suitable materials, such as copper, etc. In an embodiment, the first conductive traces  215  additionally electrically connect the one or more second side components  220  mounted on the second side  214  of the first circuit board  210 , and the second conductive traces  245  additionally electrically connect the one or more first side components  250  mounted on the first side  242  of the second circuit board  240 . 
     Still referring to  FIG. 3 , the one or more components  220 ,  250  and one or more interposers  230 ,  260  may be mounted on their corresponding circuit boards using SMT techniques such as flip chip, with solder bumps  350 . Alternative techniques may additionally be used, including conductive films, pins, wire bonding, etc. In the embodiment illustrated, the stacked interposers  230 ,  260  are bonded to one another. In application where the interposers  230 ,  260  provide primarily structural support, any suitable bonding technique may be used. Where the interposers  230 ,  260  additionally provide electrical connection, the bonding technique may support the electrical connections. For example, conductive pastes, films, and solder bumps  350  may be suitable bonding methods. In order to facilitate electrical connections the interposers  230 ,  260  may include one or more metal traces  310 , such as vias, extending from a bottom side to a top side of the interposers. The metal traces  310  may be contained within one or more layers of insulating material(s)  302 . Thus, interposers  230 ,  260  are not limited to configurations with through vias, and metal traces  310  may be formed in multiple metal layers and layers of insulating material  302 . The interposers  230 ,  260  may optionally include top side routing  330  or bottom side routing  320  to facilitate electrical connections. 
     Referring now to  FIG. 2C , at operation  120  the circuit board stack  280  can be placed onto a carrier substrate  290 . This may be performed at the panel level, where a plurality of circuit board stacks  280  are placed on the carrier substrate  290 . A variety of carrier substrates maybe suitable such as glass or metal carriers. Placement may be aided by the addition of an adhesive tape layer. The carrier substrate  290  may be a rigid substrate to support handling, and subsequent molding and singulation operations. 
     The circuit board stack(s)  280  may then may be molded at operation  130  to fill the gap  281  between the first circuit board  210  and the second circuit board  240  with a molding material  295 . As shown in  FIG. 2D , the molding operation may be performed at the panel level, with a plurality of molding cavities corresponding to the plurality of circuit board stacks  280 . In an embodiment, the molding operation is a film assisted transfer molding process. Such a process may be capable of filling gaps of several tens of microns. In one aspect, this may allow for the omission of underfill materials for any of the components  220 ,  250  or interposers  230 ,  260 . The circuit board stack may then be singulated at operation  140 . Singulating in accordance with embodiments may cut through only one of the circuit boards (e.g. second circuit board  240 ), or through both circuit boards  210 ,  240  and the molding material  295  in the gap  281 . 
     In accordance with embodiments, additional processing and SMT mounting of various components can be performed before or after singulation.  FIG. 2E  is a schematic cross-sectional side view illustration of a singulated system-in-package  200  in accordance with an embodiment. As shown in the singulated structure the components  220  overlap components  250 . Additionally, the gap between the circuit boards  210 ,  240  and additionally between the components  220 ,  250  is filled with the molding material  295 . In accordance with embodiments, the first circuit board  210  includes a plurality of interposers  230  laterally adjacent to the one or more components  220  on the first circuit board, and the second circuit board  240  includes a plurality of interposers  260  laterally adjacent to the one or more components  250  on the second circuit board, and stacking the first circuit board on the second circuit board includes bonding the first plurality of interposers to the second plurality of interposers to form interposer stacks  270 . 
     In accordance with embodiments, the final surface mount operation can optionally place components  222  on the first side  212  of the first circuit board  210 , and/or place components  290 ,  292  on the first side  242  of the second circuit board  240 . As shown, second circuit board  240  may have more area (e.g. increased length or width) than the first circuit board  210  to accommodate additional components  290 ,  292 . In other embodiments, the sequence of final surface mount of components and singulation may be reversed. 
     Referring now to both and  FIG. 4  and  FIGS. 5A-5B ,  FIG. 4  is a schematic top layout view of circuit board components and interposers in a system-in-package in accordance with embodiments, and  FIGS. 5A-5B  are schematic cross-sectional side view illustrations of interposers including lateral tunnels  410  in accordance with embodiments. In interest of clarity, the schematic top layout view of  FIG. 4  is made with regard to the components  220  and interposers  230  relative to a single circuit board  210  within the circuit board stack. 
     The interposers in accordance with embodiments have already been described as providing mechanical support between the stacked circuit boards and electrical connection between the circuit boards. In accordance with embodiments, the interposers may also be utilized to provide shielding, such as electromechanical interference (EMI) shielding. Thus, the interposers may be arranged in a variety of different ways. In some embodiments, the interposers are dispersed to provide mechanical support or electrical connections at specified locations. The interposers may be spaced apart, or closely together. When utilized for EMI shielding the interposers may be arranged closely together, and may surround one or more components. As shown in  FIG. 4 , a plurality of the interposers  230 / 270  may be arranged laterally around one or more of the components  220  (as well as components  250 ) in a configuration where the interposers  230 / 270  are arranged adjacent a periphery of one of the circuit boards  210  (or  240 ). This may be a uniform configuration entirely around the periphery of the circuit board(s), or a non-uniform arrangement where denser spacing is placed nearer specific components, and wider spacing may be allowed nearer other components. In another embodiment also illustrated in  FIG. 4 , a plurality of the interposers  230 / 270  may be arranged in a smaller scale, and among the components  220 , yet surround one or more specific components  220 . In both examples, the interposers  230 / 270  may surround, or be more densely arranged (spacing between), a subsystem of specific passive components  220 P in order to shield them from other components, such as wireless components  220 W outside the subsystem within the stacked system-in-package, or outside the system-in-package. 
     In some embodiments, while a dense arrangement of interposers may be provided, this may potentially affect flow of the molding compound during the molding operation. Thus, the interposers  230 ,  260  may include lateral tunnels  410  that extend from a laterally exterior side  422  of the interposer to a laterally interior side  424  of the interposer, through which the molding compound can flow during molding. 
     In an embodiment, molding the circuit board stack  280  includes flowing a molding compound through lateral tunnels  410  of a plurality of interposers  230  and/or  260  connecting the bottom side of the first circuit board  210  to the top side of the second circuit board  240 , where the plurality of interposers  230  and/or  260  are laterally adjacent to the one or more components  220  on the first circuit board  210  and the one or more components  250  on the second circuit board  240 . 
     Referring now to  FIGS. 5A-5B , various configurations are illustrated for providing lateral tunnels  410 . It is understood that these configurations are exemplary, and embodiments envision alternative arrangements. As shown, the interposers  230 ,  260  may include a top side  332 , a bottom side  322 , and a plurality of metal traces  310  extending from the bottom side  322  to the top side  332  of the interposer. One or more lateral tunnels  410  may extend from a laterally exterior side  422  to a laterally interior side  424  of the interposer. Additionally, the interposer may optionally include a top side routing layer  330  and a bottom side routing layer  320  (as shown in  FIG. 3 ). In some embodiments, a metallic shielding layer may be formed on exterior the exterior side  422  of the interposer, particularly for EMI shielding application. In some embodiments, the interposers  230 ,  260  can include additional active or passive components, such as an integrated circuit, resistor, capacitor (e.g. electrostatic discharge decoupling capacitor), etc. embedded in the interposer. 
     Both of the particular embodiments illustrated in  FIGS. 5A-5B  provide one or more lateral tunnels  410  extending through the top side  332  of the interposer. For example, these may resemble notches formed in the insulating material(s)  302 . Similarly, one or more lateral tunnels  410  (e.g. notches) may extend through the bottom side  322  of the interposer. In addition, or alternatively, one or more intermediate lateral tunnels  410  can extend through a center section of the interposer. Such intermediate lateral tunnels  410  are fully enclosed (e.g. are not open at the top or bottom sides).  FIG. 5A  in particular is illustrative of an example of an interposer including columns of metal traces  310  (e.g. vias). In the embodiment illustrated in  FIG. 5B , the interposer may include multiple, staggered columns of metal traces  310 . In such an embodiment, the number of lateral tunnels  410  may be reduced, or spacing increased to accommodate additional columns of metal traces  310 . 
     The interposers in accordance with embodiments may remain between the circuit boards in the system-in-package structure. The lateral tunnels  410  may provide a pathway for molding compound flow during the molding operation. In accordance with some embodiments, the lateral tunnels  410  may remain fully filled with the molding material  295  in the final structure. 
     In the following description of  FIGS. 6A-10C  several process flow variations are provided. While illustrated and described separately, it is understood that many of these several process flows can be combined together, as well as with the description related to  FIGS. 1-5B . 
       FIGS. 6A-6D  are cross-sectional side view illustrations of a sequence of assembling a system-in-package using sacrificial supports in accordance with an embodiment.  FIGS. 7A-7B  are schematic top layout views of sacrificial supports mounted on a circuit board in accordance with embodiments. It is envisioned that mold flash onto a non-molded side of a circuit board is possible during a film assisted molding operation of the circuit board stacks. In an embodiment, sacrificial supports  600  may be utilized to mitigate this potential. In such an embodiment, both circuit boards  210 ,  240  can optionally be cut to slightly larger than end-product size. The sacrificial supports  600  may then be mounted in the enlarged portion of the one or both of the circuit boards, for example, around the perimeter. The supports can be mounted on selective areas of the circuit boards, such as at all corners, as illustrated in  FIG. 7A . The sacrificial supports  600  may also be a frame with enough holes for mold flow, as illustrated in  FIG. 7B . 
     The the sacrificial supports  600  may allow the circuit board stack  280  to be stronger during the molding operation, with less resulting deformation of the circuit board stack  280 . Additionally, this may allow for pressure on the circuit boards to be increased, and mold flash or bleed avoided. In the process sequence illustrated in  FIG. 6A , the sacrificial supports may be mounted on one or both of the circuit boards. Circuit board  240  is selected for illustrational purposes. The circuit boards are then stacked and molded, as shown in  FIG. 6B . Following the molding operation, the stacked circuit boards can be singulated as shown in  FIG. 6C  to remove the sacrificial supports  600 , followed by an optional final surface mount of components  222  as shown in  FIG. 6D . Alternatively, the order of the final surface mount of components  222  and singulation can be reversed. In some embodiments, the singulation operation may create singulated edges  299  spanning sides of the first circuit board  210 , sides of the second circuit board  240 , and sides of the molding compound  295 . 
       FIGS. 8A-8C  are cross-sectional side view illustrations of a sequence of assembling a system-in-package with double side surface mounted circuit boards in accordance with an embodiment. While embodiments described and illustrated thus far have focused on stacking of single side mounted circuit boards  210 ,  240 , embodiments are not so limited. Thus, the SMT processes on either or both circuit boards  210 ,  240  may be done before stacking, or molding. As shown, the first circuit board  210  may include components  220 ,  222  mounted on opposite sides, and the second circuit board  240  may include components  250 ,  252  mounted on opposite sides. The double side mounted circuit boards may then be stacked and molded, as illustrated in  FIG. 8C . 
       FIGS. 9A-9D  are cross-sectional side view illustrations of a sequence of assembling a system-in-package with a pre-molded circuit board in accordance with an embodiment. In the process variation illustrated in  FIGS. 9A-9D , one of the circuit boards (second circuit board  240 ) already includes molded components  252  on the second side  244 , and encapsulated in molding material  254 . SMT mounting for both circuit boards illustrated in  FIG. 9A  can be performed at the panel level, and singulated to unit circuit boards  210 ,  240  before stacking at  FIG. 9B . Additionally, the sequence of final SMT mounting of components  222  in  FIG. 9D  and singulation in  FIG. 9C  can be switched as previously described. 
       FIGS. 10A-10C  are cross-sectional side view illustrations of a sequence of assembling a system-in-package with pre-molded circuit boards in accordance with an embodiment. The process flow of  FIGS. 10A-10C  includes a process variation in that both SMT component mounting and molding operations are performed for both circuit boards  210 ,  240  prior to stacking. As shown in  FIG. 10A-10B , a molding operation such as film assisted molding is done with surfaces of the interposers  230 ,  260  remaining exposed for electrical connection. A final stacking operation is performed as shown in  FIG. 10C  to create the circuit board stack  280 . During the final stacking operation, an adhesive layer such as epoxy glue or thermal sensitive adhesive may be used between circuit boards  210 ,  240  to enhance mechanical rigidity and hold the molding materials  296 ,  297  together. Interposers  230 ,  260  may be bonded using suitable methods as previously described, such as conductive pastes, films, and solder bumps  350 . 
     In utilizing the various aspects of the embodiments, it would become apparent to one skilled in the art that combinations or variations of the above embodiments are possible for forming a system in package including stacked circuit boards. Although the embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the appended claims are not necessarily limited to the specific features or acts described. The specific features and acts disclosed are instead to be understood as embodiments of the claims useful for illustration.

Metadata:
Filing Date: 20200605
Publication Date: 20210330
Grant Date: 20210330
Priority Date: 20180328
Inventors: CHEN, YANFENG
PENNATHUR, Shankar
PAINAIK, MANDAR
HOANG, LAN
LEE, MENG CHI
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K1/144", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L21/561", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L24/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2225/06575", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/32", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/284", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L23/3121", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L24/97", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2225/06537", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/0097", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L25/0652", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K3/0097", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K3/284", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2924/00014", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/144", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L25/50", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K3/4611", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L24/97", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2225/06572", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2225/0652", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L25/117", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/144", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L24/48", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/181", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2224/13101", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/0097", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L25/117", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/181", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L24/97", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K3/284", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K3/4611", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/144", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 67220297