PATENT DOCUMENT

Publication Number: US-11552053-B2
Application Number: US-202016912000-A
Country: US
Kind Code: B2

Title: Miniaturization of optical sensor modules through wirebonded ball stacks

Abstract:
Optical sensor modules and methods of fabrication are described. In an embodiment, an optical component is mounted on a module substrate. In an embodiment, a pillar of stacked wireballs adjacent the optical component is used for vertical connection between the module substrate and a top electrode pad of the optical component.

Claims:
What is claimed is: 
     
       1. An optical sensor module comprising:
 a module substrate including a landing pad; 
 an optical component mounted on the landing pad; 
 a pillar of stacked wireballs adjacent the optical component; 
 a molding compound layer laterally surrounding the pillar and the optical component on the module substrate; and 
 a metal wire that is looped above a top surface of the molding compound layer and connecting the pillar and a top electrode pad of the optical component. 
 
     
     
       2. The optical sensor module of  claim 1 , further comprising a transparent encapsulation material over the metal wire and the optical component. 
     
     
       3. The optical sensor module of  claim 1 , wherein the module substrate comprises an embedded controller chip. 
     
     
       4. The optical sensor module of  claim 1 , wherein the stacked wireballs and the metal wire are formed of a same material. 
     
     
       5. The optical sensor module of  claim 1 , wherein a lateral stand-off distance between the pillar and the optical component is less than 30 μm. 
     
     
       6. The optical sensor module of  claim 1 , wherein the pillar is greater than 200 μm tall. 
     
     
       7. The optical sensor module of  claim 1 , wherein the optical component is a photodetector (PD), and further comprising:
 an emitter mounted on a second landing pad of the module substrate; 
 a second pillar of stacked wireballs adjacent the emitter, wherein the molding compound layer laterally surrounds the emitter and the second pillar; and 
 a second metal wire over the molding compound layer and connecting the second pillar and a second top electrode pad of the emitter. 
 
     
     
       8. The optical sensor module of  claim 1 , wherein the optical component is mounted adjacent an opening in a housing of portable electronic device. 
     
     
       9. An optical sensor module comprising:
 a module substrate including a landing pad; 
 a photodetector (PD) mounted on the landing pad; 
 an emitter mounted on a second landing pad of the module substrate; 
 a pillar of stacked wireballs adjacent the PD; 
 a second pillar of stacked wireballs adjacent the emitter; 
 a molding compound layer laterally surrounding the pillar, the second pillar, and the PD, and the emitter on the module substrate; 
 a wiring layer over the molding compound layer and connecting the pillar and a top electrode pad of the PD; and 
 a second wiring layer over the molding compound layer and connecting the second pillar and a second top electrode pad of the emitter. 
 
     
     
       10. The optical sensor module of  claim 9 , wherein a lateral stand-off distance between the pillar and the PD is less than 30 μm. 
     
     
       11. The optical sensor module of  claim 9 , wherein the pillar is greater than 200 μm tall. 
     
     
       12. The optical sensor module of  claim 9 , wherein the PD is mounted adjacent an opening in a housing of portable electronic device. 
     
     
       13. An optical sensor module comprising:
 a module substrate including a landing pad; 
 an optical component mounted on the landing pad; 
 a pillar of stacked wireballs adjacent the optical component; 
 wherein a lateral stand-off distance between the pillar and the optical component is less than 30 μm; 
 a molding compound layer laterally surrounding the pillar and the optical component on the module substrate; and 
 a wiring layer over the molding compound layer and connecting the pillar and a top electrode pad of the optical component. 
 
     
     
       14. The optical sensor module of  claim 13 , wherein the pillar is greater than 200 μm tall. 
     
     
       15. The optical sensor module of  claim 13 , wherein the optical component is mounted adjacent an opening in a housing of portable electronic device. 
     
     
       16. An optical sensor module comprising:
 a module substrate including a landing pad and an embedded controller chip; 
 an optical component mounted on the landing pad; 
 a pillar of stacked wireballs adjacent the optical component; 
 a molding compound layer laterally surrounding the pillar and the optical component on the module substrate; and 
 a wiring layer over the molding compound layer and connecting the pillar and a top electrode pad of the optical component. 
 
     
     
       17. The optical sensor module of  claim 16 , further comprising a transparent encapsulation material over the wiring layer and the optical component. 
     
     
       18. The optical sensor module of  claim 16 , wherein the pillar is greater than 200 μm tall. 
     
     
       19. The optical sensor module of  claim 16 , wherein the optical component is mounted adjacent an opening in a housing of portable electronic device.

Description:
BACKGROUND 
     Field 
     Embodiments described herein relate to microelectronic packaging, and more specifically to optical module packages. 
     Background Information 
     As microelectronic devices become increasingly smaller and more portable, sensors are increasingly being incorporated in order to detect the environment or context associated with use of the devices. Among such sensors include light sensors or proximity sensors, which can detect ambient light or proximity to a target object such as a user&#39;s ear or face. In one implementation a proximity sensor can include a light source and photodetector (PD). In application, the PD may detect proximity to a target object by measuring the amount of light from the light source. 
     SUMMARY 
     Optical sensor modules and methods of fabrication are described in which a pillar of stacked wireballs adjacent an optical component is used for vertical connection between a module substrate and a top electrode pad of the optical component. In an embodiment, an optical sensor module includes a module substrate including a landing pad, an optical component (e.g. PD, emitter) mounted on the landing pad, and a pillar of stacked wireballs on the module substrate and adjacent the optical component. A molding compound layer can be formed on the module substrate to laterally surround the pillar and the optical component on the module substrate, and a wiring layer is formed over the molding compound layer to connect the pillar and a top electrode pad of the optical component. The wiring layer can be formed using various techniques that may achieve a low z height profile, including low loop wire bonding and deposition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic cross-sectional side view illustration of an optical sensor module including pillars of stacked wireballs in accordance with an embodiment. 
         FIG.  2    is a schematic cross-sectional side view illustration showing x-y width and z height associated with a wire bond connection. 
         FIG.  3    is a schematic cross-sectional side view illustration showing x-y width associated with a PCB bar connection. 
         FIG.  4    is a flow diagram for a method of assembling an optical sensor module in accordance with an embodiment. 
         FIGS.  5 A- 5 H  are schematic cross-sectional side view illustrations of a method of forming an optical sensor module in accordance with an embodiment. 
         FIGS.  6 A- 6 B  are schematic side view illustrations of an earbud in accordance with an embodiment. 
         FIG.  7    is a schematic side view illustration of an earpiece in accordance with an embodiment. 
         FIG.  8    is a schematic side view illustration of a mobile phone in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe optical sensor modules and methods of fabrication. In particular, the optical sensor modules may be incorporated as light sensors or proximity sensors in portable electronic devices. In one aspect, the optical sensor modules in accordance with embodiments embed a controller chip along with one or more photodetectors (PDs) and one or more emitters in a single module. For example, the photodetectors may be photodiodes, and the emitters may be light emitting diodes. The controller chip may function to control operation of the one or more PDs and emitters. For example, the controller chip can be an application specific integrated circuit (ASIC) or field-programmable gate array (FPBA). 
     In one aspect the optical sensor module packages and methods of fabrication in accordance with embodiments provide an alternative layout and form factor compared to traditional optical sensor modules. For example, it has been observed that traditional optical sensor modules for proximity sensors mount the PD and light source onto a flex circuit. This end of the flex circuit can be mounted to a housing, while the opposite end of the flex circuit is routed to a controller on a circuit board located elsewhere in the housing. It has been observed that such a configuration can be particularly susceptible to mechanical shock, and also take up considerable space. 
     In accordance with embodiments, the optical sensor modules may utilize wire bonded ball stacks, also referred to as pillars of stacked wireballs, to reduce volume of the optical sensor modules as part of miniaturization. Furthermore, the pillars of stacked wireballs may provide additional x-y width and z height saving compared to traditional connection techniques such as wirebonding or printed circuit board (PCB) bars. The pillars of stacked wireballs can also be formed to match optical component (e.g. PD, emitter) height and avoid exposure to harmful chemicals associated with formation of pillars using alternative pillar (via) first or pillar (via) last approaches. This reduction may create space for adding more modules and functionalities when integrated into portable and wearable electronics, for example, where space can be limited. 
     Mechanical shock can also be mitigated in accordance with embodiments by embedding the multiple components into a single module, rather than having multiple components connected on opposite ends of a flex circuit. Furthermore, the optical sensor module packages in accordance with embodiments may be considered a system-in-package which allows for standalone testing and calibration. 
     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 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 “above”, “over”, “to”, “between”, and “on” as used herein may refer to a relative position of one layer with respect to other layers. One layer “above”, “over”, 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 an optical sensor module  100  in accordance with an embodiment. As shown, the optical sensor module  100  may include a module substrate  110  including one or more dielectric layers  112  and routing layers  114  and vias  115 . Module substrate  110  may be a variety of suitable substrates, such as a printed circuit board (PCB), which may be rigid or flexible, cored or coreless. The module substrate  110  may include a top side  111  with a plurality of landing pads  120 ,  122 , and a bottom side  113  with a plurality of landing pads  124 . In an embodiment, the bottom side landing pads  124  may be ball grid array (BGA) pads, for example, to accept solder balls  129 , for example for subsequent mounting to another component, such as motherboard. The top side landing pads  120 ,  122  may be surface mount (SMT) pads, for example. 
     In the illustrated embodiment, the module substrate  110  may optionally include an embedded controller chip  125  to control operation of the one or more PDs and emitters. For example, the controller chip  125  can be an application specific integrated circuit (ASIC) or field-programmable gate array (FPBA). As shown, the controller chip  125  may be mounted face up in the module substrate  110  with contact pads  126  on a front side  127  of the controller chip  125  facing the optical components. The back side  128  of the controller chip  125  may optionally not include any contact pads. As shown, the contact pads  126  may be connected to routing layers  114  or vias  115  within the module substrate  110 . 
     Still referring to  FIG.  1   , one or more PDs  130  and one or more emitters  140  can be mounted onto landing pads  120 . Additionally, one or more pillars  160  of stacked wireballs  162  can be formed on landing pads  122  adjacent to the corresponding landing pads  120 . The pillars  160  of stacked wireballs  162  can be formed of a variety of materials, including typical wire materials (e.g. including metals, and metal alloys) for wirebonding such as copper, aluminum, gold, silver, platinum, and various alloys thereof, etc. Sizing of the pillars stacked wireballs  162  may depend upon width/diameter of the bond wire selected. In an illustrative example, the individual stacked wireballs  162  have a width of 50-100 μm, or more specifically approximately 100 μm, and thickness/height of 25-100 μm, or more specifically approximately 50 μm. In an embodiment, the optical components and corresponding pillars have approximately a same height, and may be greater than 200 μm tall in some embodiments. 
     The one or more pillars  160  and optical components (e.g. PD(s)  130 , emitter(s)  140 ) can then be encapsulated in a molding compound layer  170 , which can be any suitable molding compound material. As shown, the molding compound layer  170  laterally surrounds the pillar(s)  160  and the optical component(s) on the module substrate  110 . Wiring layers  180  may then be used to connect the pillars  160  to the corresponding top electrode pads  132 ,  142  of the corresponding optical components. The wiring layers  180  may be metal bond wires, or deposited layers. For example, wiring layer  180  can be formed by wire bonding a bond wire to the pillar  160  and top electrode pad  132 ,  142 . This may be visualized with terminal stud bumps  182 . The bond wire forming wiring layer  180  may be formed of the same material as the stacked wireballs  162 , though they may be different materials. Where wire bonding is utilized, the metal bond wire can be looped above a top surface  172  of the molding compound layer  170 . This may be a low loop structure, with less z height compared to a traditional wire loop. In an embodiment, the metal wire for the low loop structure can also be partially formed on the top surface  172  of the molding compound layer  170 . Alternatively, the wiring layer  180  may be formed using a deposition technique, such as a physical deposition technique or application of conductive spray, slurry, or paste followed by heating to drive off residual liquid. Heating may also be used to anneal, coalesce deposited conductive particles in the wiring layer  180 . In such a fabrication method, the wiring layer may be formed on (e.g. directly on) the top surface  172  of the molding compound layer  170  if no intervening layers are present. 
     An opaque material  190 , such as a black matrix material, may optionally be formed on top of the molding compound layer  170  laterally between the optical components (e.g. between the PD  130  and emitter  140 ). For example, this can mitigate cross-talk between the PD(s)  130  and emitter(s)  140 . A transparent encapsulation material  192  can then be formed over the wiring layer  180  and the optical components, and optionally the opaque material  190 . In the embodiment illustrated, a single transparent encapsulation material  192  layer is formed, though separate layers may be formed. 
     In accordance with embodiments, the pillars  160  may be formed with a stand-off distance (Sd) of less than 50 μm from an adjacent optical component, or more specifically less than 30 μm. Furthermore, the pillars  160  can be stand-alone structures that are not encapsulated other than with the molding compound layer  170 . This can contribute to overall module x-y area reduction. Furthermore, the pillars  160  can be formed to have an approximately equivalent height as the adjacent optical component. Furthermore, the ability to use low-loop wirebonding or deposition techniques for the formation of the wiring layer  180  can further contribute to a reduction of z height. Thus, the pillars  160  and wiring layers  180  can be formed to necessary height, without exposing the module components to harmful chemicals and processes, with overall x-y area and z-height reduction. This is illustrated in  FIGS.  2 - 3   .  FIG.  2    is a schematic cross-sectional side view illustration showing x-y width and z height associated with a wire bond connection. As shown, a typical wire  202  used to connect the top electrode pad  132 ,  142  of an optical component to landing pad  122  may have an increase in both x-y area, and z height compared to the electrical connection in accordance with embodiments.  FIG.  3    is a schematic cross-sectional side view illustration showing x-y width associated with a PCB bar  300  connection. As shown, such a PCB bar  300  may include a vertical via  315  within an insulating layer  312 , which contributes to overall x-y width. Furthermore, placement tolerances and insulating layer  312  may also contribute to an increased stand-off distance between the via  315  and optical component compared to the electrical connection in accordance with embodiments. 
       FIG.  4    is a flow diagram for a method of assembling an optical sensor module such as that illustrated in  FIG.  1    in accordance with an embodiment.  FIGS.  5 A- 5 H  are schematic cross-sectional side view illustrations of a method of forming an optical sensor module such as that illustrated in  FIG.  1    in accordance with an embodiment. In interest of clarity and conciseness, the structures and process flow of  FIGS.  4  and  5 A -H are described together in the following description. 
     Referring to  FIG.  5 A , the process sequence can begin with the module substrate  110 , which may optionally include an embedded controller chip  125  as described with regard to  FIG.  1   . At operation  4010  the optical components, including one or more PDs  130  and one or more emitters  140  are attached to, or mounted on, the module substrate  110  as shown in  FIG.  5 B . Specifically, the optical components may include bottom electrodes that are mounted on, and in electrical contact with the landing pads  120  of the module substrate  110 . 
     Referring now to  FIG.  5 C , the pillars  160  of stacked wireballs  162  are then formed at operation  4020 . In an embodiment this includes sequentially forming each stacked wireball  162  of the stacked wireballs from a first wire. For example, the first wire (e.g. metal) may be formed of copper, aluminum, gold, silver, platinum, and various alloys thereof, etc. In the particular sequence illustrated the pillars  160  are formed after the placement of the optical components. This may be attributed to the pillars  160  being a more fragile structure. However, it is contemplated pillars  160  could be formed prior to placement of the optical components. 
     Once the optical components have been placed, and pillars  160  are formed, they are then encapsulated in a molding compound layer  170  at operation  4030 , as illustrated in  FIG.  5 D . As shown, the molding process may leave the top sides  161  of the pillars  160  exposed, and top sides  131 ,  141  of the optical components exposed, including top electrode pads  132 ,  142 . Wiring layers  180  are then formed between the exposed pillars  160  and optical components at operation  4040 , as illustrated in  FIG.  5 E . In the particular embodiment illustrated, wiring layers  180  are shown as a low loop formation, in which a metal wire is looped above the top surface  172  of the molding compound layer  170 . For example, the metal wire may be substantially straight between terminal stud bumps  182  formed of the metal wire on the top sides  161  of the pillars  160  and on the top electrode pads  132 ,  142 . The metal wire may optionally partially rest on the top surface  172  of the molding compound layer  170 . The metal wire may be formed of the same material (e.g. metal, alloy) as the wire used to form the pillars  160 , or may be formed of a different material, which can be any of the materials from which the first wire (used to form the pillars  160 ) is made. 
     In accordance with embodiments, the wiring layers  180  can be formed using a deposition technique, such as a physical deposition technique or application of conductive spray, slurry, or paste followed by heating to drive off residual liquid. Heating may also be used to anneal, coalesce deposited conductive particles in the wiring layer  180 . In such a fabrication method, the wiring layer may be formed on (e.g. directly on) the top surface  172  of the molding compound layer  170  if no intervening layers are present. 
     An opaque material  190 , such as a black matrix material, may then optionally be formed on top of the molding compound layer  170  laterally between the optical components (e.g. between the PD  130  and emitter  140 ) as shown in  FIG.  5 F , followed by formation of a transparent passivation material  192  over the wiring layers  180  and optical components at operation  4050 , as shown in  FIG.  5 G . This may include a single transparent passivation material  192  layer over the wiring layers  180 , one or more PDs  130  and one or more emitters  140 , or may include separate transparent passivation material  192  layers, for example for each pillar  160  and optical component pair. Solder balls  129  may then be applied to the bottom side landing pads  124 , for subsequent mounting. 
       FIGS.  6 A- 8    illustrate various portable electronic devices in which the various embodiments can be implemented.  FIGS.  6 A- 6 B  are schematic side view illustrations of an earbud in accordance with an embodiment that includes a housing  602  and one or more openings  610  to which the optical components (e.g. PD, emitter) of the optical sensor modules  100  described herein can be aligned adjacently.  FIG.  7    is a schematic side view illustration of an earpiece in accordance with an embodiment that includes a housing  702  including an opening  710  to which the optical components (e.g. PD, emitter) of the optical sensor modules  100  described herein can be aligned adjacently.  FIG.  8    is a schematic side view illustration of a mobile phone in accordance with an embodiment including a housing  802  including an opening  810  to which the optical components (e.g. PD, emitter) of the optical sensor modules  100  described herein can be aligned adjacently. These illustrations are intended to be exemplary and non-exhaustive implementations. 
     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 an optical sensor module. 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: 20200625
Publication Date: 20230110
Grant Date: 20230110
Priority Date: 20200625
Inventors: KANI, BILAL MOHAMED IBRAHIM
RENJAN, KISHORE N.
KIM, KYUSANG
VADEENTAVIDA, MANOJ
LUPO, PIERPAOLO
CHANDRAN, PRAVEESH
Assignee: APPLE INC
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Family ID: 79031820