PATENT DOCUMENT

Publication Number: US-9446941-B2
Application Number: US-201414568845-A
Country: US
Kind Code: B2

Title: Method of lower profile MEMS package with stress isolations

Abstract:
MEMS packages, modules, and methods of fabrication are described. In an embodiment, a MEMS package includes a MEMS die and an IC die mounted on a front side of a surface mount substrate, and a molding compound encapsulating the IC die and the MEMS die on the front side of the surface mount substrate. In an embodiment, a landing pad arrangement on a back side of the surface mount substrate forms and anchor plane area for bonding the surface mount substrate to a module substrate that is not directly beneath the MEMS die.

Claims:
What is claimed is: 
     
       1. A module comprising:
 a module substrate; 
 a surface mount substrate bonded to a top side the module substrate with an arrangement of conductive bumps including all conductive bumps bonding the surface mount substrate to the module substrate; 
 wherein the arrangement of conductive bumps corresponds to an anchored area of the surface mount substrate directly over the module substrate, and the surface mount substrate includes a hanging area that laterally extends from the anchored area in which a conductive bump is not formed directly beneath the hanging area of the surface mount substrate; 
 an integrated circuit (IC) die mounted on a front side of the surface mount substrate in the anchored area of the surface mount substrate; 
 a micro-electro-mechanical systems (MEMS) die mounted on the front side of the surface mount substrate in the hanging area of the surface mount substrate; 
 a molding compound encapsulating the IC die and the MEMS die on the front side of the surface mount substrate. 
 
     
     
       2. The module of  claim 1 , further comprising a trench in a top surface of the molding compound between the IC die and the MEMS die. 
     
     
       3. The module of  claim 1 , further comprising a metal trace on the top side of the module substrate directly underneath the hanging area of the surface mount substrate, and a solder mask directly over the metal trace directly underneath the hanging area of the surface mount substrate. 
     
     
       4. The module of  claim 1 , further comprising a metal trace on a back side of the surface mount substrate directly in the hanging area of the surface mount substrate, and a solder mask directly on the metal trace directly in the hanging area of the surface mount substrate. 
     
     
       5. The module of  claim 1 , wherein the molding compound is formed directly on the surface mount substrate. 
     
     
       6. The module of  claim 1 , further comprising a plurality of components bonded to the top side the module substrate, wherein the plurality of components are encapsulated in a second molding compound on the top side of the module substrate. 
     
     
       7. The module of  claim 6 , wherein a top surface of the molding compound encapsulating the IC die and the MEMS die is below a top surface of the second molding compound encapsulating the plurality of components. 
     
     
       8. The module of  claim 1 , wherein the molding compound encapsulating the IC die and the MEMS die does not cover a top surface of the MEMS die. 
     
     
       9. The module of  claim 1 , further comprising:
 a bumper on the front side of the module substrate directly beneath the hanging area of the surface mount substrate; and 
 an air gap directly between a back side of the surface mount substrate and the bumper. 
 
     
     
       10. The module of  claim 1 , further comprising:
 a bumper on a back side of the surface mount substrate directly beneath the hanging area of the surface mount substrate; and 
 an air gap directly between a front side of the module substrate and the bumper. 
 
     
     
       11. The module of  claim 1 , further comprising an opening in the surface mount substrate between the IC die and the MEMS die. 
     
     
       12. The module of  claim 1 , further comprising a trench in a top surface of the molding compound between the IC die and the MEMS die, wherein a bottom surface of the trench is below a top surface of the MEMS die.

Description:
BACKGROUND 
     1. Field 
     Embodiments described herein relate to semiconductor packaging. More particularly embodiments relate to MEMS packages, modules, and methods of fabrication. 
     2. Background Information 
     As electronic products are becoming increasingly sophisticated and the size of the overall packages is reduced to meet market needs, these advances are associated with various packaging challenges to reduce cost and form factor of the packages. In addition as the market drives thinner package profiles, it becomes more difficult to manage strain induced performance drift. 
     Micro-electro-mechanical systems (MEMS) die can be formed from customized integrated circuits, and have become a significant growth area in consumer space. MEMS are often used to sense environmental characteristics or act as a user input for electronic products. However, MEMS devices such as gyroscopes, accelerometers, microphones, pressure sensors, environmental sensors and magnetometers are all sensitive to strain induced performance drift and can have unique packaging and mounting requirements compared to some general purpose integrated circuit (IC) die. 
     SUMMARY 
     MEMS packages, modules, and methods of formation are described. In an embodiment, a MEMS package includes an IC die mounted on a front side of a surface mount substrate, and a MEMS die mounted on the front side of the surface mount substrate laterally adjacent to the IC die. The MEMS die and IC die can be mounted on the surface mount substrate using a variety of methods, including a die attach film with wire bonding or flip chip bonding. A molding compound encapsulates the IC die and the MEMS die on the front side of the surface mount substrate. The molding compound may be formed directly on the surface mount substrate. The molding compound may be formed directly over the MEMS die, or alternatively may not cover a top surface of the MEMS die, for example, so that the MEMS die is exposed to ambient environment. In an embodiment, a landing pad arrangement, including all landing pads on a back side of the surface mount substrate, surrounds a periphery of the IC die on the front side of the surface mount substrate and does not surround a periphery of the MEMS die on the front side of the surface mount substrate. A plurality of conductive bumps (e.g. solder balls) may be placed on the landing pads, with each landing pad having corresponding conductive bump. 
     In an embodiment, a trench is in a top surface of the molding compound between the IC die and the MEMS die. In an embodiment, one or more openings are formed in the surface mount substrate between the IC die and the MEMS die. The size and shape of the trench and opening(s) may be used for isolating the MEMS die from package and module stress. In an embodiment, a bottom surface of the trench is below a top surface of the MEMS die. 
     In an embodiment, a module includes a module substrate, and the MEMS package bonded to the module substrate. In an embodiment, the arrangement of conductive bumps corresponds to an anchored area of the surface mount substrate directly over the module substrate. A hanging area of the surface mount substrate laterally extends from the anchored area of the surface mount substrate, and a conductive bump is not formed directly beneath the hanging area of the surface mount substrate. In such a configuration an air gap may exist directly between a back side of the surface mount substrate and the module substrate. Various configurations are described that may protect the hanging portion from flexing to the point that the conductive bumps fracture. For example, one or more bumpers may optionally be formed on the module substrate directly beneath the hanging area of the surface mount substrate. An air gap may exist directly between the back side of the surface mount substrate and the bumper(s). One or more bumpers may optionally be formed on a back side of the surface mount substrate directly beneath the hanging area of the surface mount substrate. An air gap may exist directly between the bumper(s) and the front side of the module substrate. Other structural features may be used to provide mechanical protection. For example, a metal trace, and or solder mask can be formed on either or both of the back side of the surface mount substrate and the front side of the module substrate directly beneath the hanging area. In an embodiment, the solder mask covers the metal trace. In this manner, height of the metal traces and/or solder mask layers can form protruding structures for protecting against excessive bending of the hanging area. 
     In an embodiment, a plurality of other components are bonded to the top side of the module substrate, and encapsulated in a second molding compound on the top side of the module substrate. For example, the plurality of other components and the second molding compound may correspond to a mold array package (MAP) configuration. In an embodiment, a top surface of the molding compound encapsulating the IC die and the MEMS die is below a top surface of the second molding compound encapsulating the plurality of other components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional side view illustration of a module including a MEMS package with a stacked die configuration. 
         FIG. 2  is a cross-sectional side view illustration of a module including a MEMS package a side-by-side die configuration in accordance with an embodiment. 
         FIG. 3  is schematic back side view illustration of a MEMS package in accordance with an embodiment. 
         FIG. 4A  is a cross-sectional side view illustration of a MEMS package in accordance with an embodiment. 
         FIG. 4B  is a cross-sectional side view illustration of a MEMS package in accordance with an embodiment. 
         FIG. 5  is a close up cross-sectional side view illustration of a MEMS package bonded to a module substrate in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view illustration of a strained MEMS module in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe MEMS packages, modules, and methods of fabrication. 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. 
     In one aspect, embodiments describe MEMS packages, modules, and manners of fabrication which may address MEMS package and module stress. It has been observed that MEMS devices are sensitive to stress. For example, stress transfer to a MEMS die from an underlying substrate (such as surface mount substrate and module substrate) can cause MEMS device/sensor output shift. In addition, stress impact to device/sensor output change may become more serious when MEMS package thickness and form factor are further reduced to meet market needs. 
     In another aspect, embodiments describe MEMS packages, modules, and manners of fabrication which may enable reduced MEMS package profile and overall module profile. In an embodiment, a MEMS die and integrated circuit (IC) die are mounted side-by-side on a surface mount substrate. In such an arrangement, MEMS die thickness may be maintained without sacrificing the strain sensitivity of the MEMS die. It has been observed that thicker MEMS die may be less sensitive to strain then thinner MEMS die. Thus, as consumer devices, particularly mobile and wearable devices, continue to become thinner with increased functionality, further reduction in MEMS die thickness may be met with a tradeoff of increased strain induced performance drift. A side-by-side configuration may also allow for a reduced MEMS package height and resulting module height, particularly where a MEMS die component thickness is a significant barrier to z-height profile reduction of the MEMS package and module. Thus, while a side-by-side configuration may possibly increase the footprint of a MEMS package, in accordance with some embodiments, MEMS die thickness can be maintained at a sufficient thickness for reduced susceptibility to strain. 
     In another aspect, embodiments describe a MEMS packages and modules with low profiles, low strain susceptibility, and low temperature coefficient of offset (TCO) for a contained MEMS device. The offset error of a device/sensor due to temperature is due to TCO. This parameter is the rate of change of the offset when the device/sensor is subject to temperature. Where TCO is high, the device/sensor may require offset calibration. Lower TCO may allow for higher resolution devices/sensors and less offset calibration. In accordance with embodiments, MEMS packages and modules are described that may include low profiles, and specific structures for stress management or isolation resulting in improved TCO and MEMS device or sensor operation. 
     In an embodiment, an air gap technique is described in order to alleviate the impact of stress transfer from underlying substrates to MEMS devices. In an embodiment, a MEMS die and IC die are mounted side-by-side on a surface mount substrate, which in turn is bonded to a module substrate such as a printed circuit board (PCB). In an embodiment, the surface mount substrate is anchored to the module substrate with an arrangement of conductive bumps such that a portion of the package substrate includes an anchored area directly over the PCB, and a hanging area. In an embodiment, the MEMS die is mounted on the surface mount substrate in the hanging area of the surface mount substrate. For example, the surface mount substrate may be bonded to a module substrate in a cantilever-type configuration. Additional features may be included for additional stress isolation, and reduced strain susceptibility of the MEMS die. In an embodiment a partial cut or trench is created in a top surface of a molding compound that encapsulates the side-by-side MEMS die and IC die, with the partial cut or trench located between the MEMS die and the IC die. In an embodiment, one or more slots or holes are formed in the surface mount substrate between the side-by-side MEMS die and IC die. 
     As used herein, “encapsulating” does not require all surfaces to be encased within a molding compound. For example, referring briefly to  FIG. 5  the lateral sides of MEMS die  302  are encased in molding compound  310 , while the molding compound is not formed over the top surface of the MEMS die  302 . As will become apparent in the following description, the height of the molding compound  310  may contribute to the overall z-height of the MEMS package and module. Accordingly, in some embodiments, the amount of molding compound is controlled to achieve a specified height. In accordance with embodiments, MEMS devices such as pressure sensors, microphones, and environmental sensors for sensing temperature, humidity, and gas can have unique packaging and mounting requirements since the MEMS devices often require exposure to an ambient external environment, such as an ambient environment of a user using the electronic product having the MEMS device. In some embodiments, an amount of the molding compound  310  is controlled in order to expose the top surface of the MEMS die  302  so that it is exposed to ambient environment. However, it is not required that that the top surface of the MEMS die  302  is exposed in all embodiments, and the molding compound  310  may cover the top surface of the die  302 . For example, it may not be required for MEMS devices such as accelerometers, magnetometers, and gyroscopes to be exposed to the ambient environment. 
     A variety of surface mount substrates can be used in accordance with embodiments, such as land grid array (LGA), ball grid array (BGA), quad flat no-leads QFN, or ceramic substrates. In an embodiment, flip chip bonding is used as the surface mount interconnection method for electrically connecting the surface mount substrate to the module substrate. 
     Referring now to  FIG. 1 , a cross-sectional side view illustration is provided of a module including a MEMS package  300  with a stacked die configuration. As illustrated the module includes a MEMS package  300  bonded to a module substrate  100  with conductive bumps  316 . A plurality of additional components, illustrated as  202 ,  204 , and  206  are also bonded to the module substrate and encapsulated within a molding compound  210  on the module substrate. For example, the module substrate  100  may be a printed circuit board (PCB), ceramic panel, leadframe, or wafer. The components  202 ,  204 ,  206  can be any combination of numerous passive or active components. The assembled components  202 ,  204 ,  206  may be arranged on the module substrate  100  in a mold array package (MAP) configuration in which each of the components  202 ,  204 ,  206  is encapsulated within a single molding compound  210  on a top side  101  of the module substrate  100 . Together, the components  202 ,  204 ,  206  and molding compound  210  may be considered as a MAP  200 . The molding compound  210  may cover a top surface of each of the components  202 ,  204 ,  206 . 
     As illustrated in  FIG. 1 , a MEMS package  300  is bonded to a top side  101  of the module substrate  100  outside the area reserved for the MAP  200 . For example, this may aid in stress isolation and operation of the MEMS die  302 . The particular MEMS package  300  illustrated in  FIG. 1  includes a stacked-die arrangement in which a MEMS die  302  is stacked onto an IC die  304 . As shown, the MEMS die  302  includes a base substrate  302 A and a cap  302 B. The particular arrangement is meant to be exemplary, and non-limiting. The exemplary MEMS package  300  includes a surface mount substrate  312 , an IC die  304 , such as an application specific integrated circuit (ASIC) die, attached to the surface mount substrate  312  with a die attach film  308 , and a MEMS die  302  attached to the IC die  304  with a die attach film  306 . Wire bonds  314  are used to provide electrical connection between the MEMS die  302 , IC die  304 , and surface mount substrate  312 . A molding compound  310  of a molding compound encapsulates the die and wire bonds on the surface mount substrate  312 . 
     In the particular configuration illustrated in  FIG. 1 , the profile height of the MEMS package  300  is illustrated as being greater than a profile height of the MAP  200  on the same side of the module substrate  100 . The height difference (+h) between the top surface  311  of the MEMS package  300  and the top surface  211  of the MAP  200  may be attributed to the thickness of the MEMS die  302  or die stacking within the MEMS package  300 . It has been observed that thicker MEMS die  302  may be less sensitive to strain than thinner MEMS die. Thus, as consumer devices, particularly mobile and wearable devices, continue to become thinner with increased functionality, further reduction in MEMS die  302  and MEMS package  300  thickness may be met with a tradeoff of increased strain induced performance drift. 
     Referring now to  FIG. 2 , in accordance with embodiments a MEMS package  400  is illustrated including a MEMS die  302  and IC die  304  mounted on a front side of a surface mount substrate  312  in a side-by-side configuration. In the embodiment illustrated in  FIG. 2 , MEMS die  302  thickness may be maintained at a sufficient thickness for reduced susceptibility to strain. In the embodiment illustrated, surface mount substrate  312  is bonded to the module substrate  100  with an arrangement of conductive bumps  316  including all of the conductive bumps bonding the surface mount substrate  312  to the module substrate  100 . The arrangement of conductive bumps  316  corresponds to an anchored area  330  of the surface mount substrate directly over the module substrate. The surface mount substrate  312  additionally includes a hanging area  332  that laterally extends from the anchored area  330  in which a conductive bump  316  is not formed directly underneath the hanging area  332  of the surface mount substrate  312 . Still referring to  FIG. 2 , the IC die  304  (e.g. ASIC die) is mounted on the front side  313  of the surface mount substrate  312  in the anchored area  330  of the surface mount substrate, and the MEMS die  302  is mounted on the front side  313  of the surface mount substrate  312  in the hanging area  332  of the surface mount substrate  312 . In the exemplary MEMS package  400 , the IC die  304  is mounted on the surface mount substrate with a die attach film  308 , and the MEMS die  302  is mounted on the surface mount substrate with a die attach film  306 . Wire bonds  314  are used to provide electrical connection between the MEMS die  302 , IC die  304 , and surface mount substrate  312  in the illustrated embodiment. Wire bonds  314  can also be used for die-to-die interconnection between MEMS die  302  and IC die  304 . In another embodiment, the IC die  304  and/or the MEMS die  302  may be mounted on the surface mount substrate, for example as a flip chip attachment with no wire bonds. Such a configuration is illustrated in  FIG. 4B . A variety of alternative attachment method may be used for mounting the MEMS die and IC die on the surface mount substrate. In accordance with embodiments, molding compound  310  (e.g. epoxy) encapsulates the IC die  304  and the MEMS die  302  on the front side  313  of the surface mount substrate  312 . The molding compound  310  may be formed directly on the front side  313  of the surface mount substrate. In the particular embodiment illustrated, the molding compound  310  does not cover the top surface of the MEMS die  302 , and is illustrated as being flush with the top surface of the MEMS die  302 . For example, this may allow the MEMS die  302  to be exposed to the ambient atmosphere. The molding compound  310  may alternatively cover the top surface of the MEMS die  302 . 
     As shown in  FIG. 2 , the profile height of the MEMS package  400  is illustrated as being less than a profile height of the MAP  200  on the same side of the module substrate  100 . The height difference (−h) between the top surface  311  of the MEMS package  400  and the top surface  211  of the MAP  200  may be attributed to the side-by-side arrangement of MEMS die  302  and IC die  304 . The side-by-side arrangement, may additionally allow for a thicker MEMS die  302 , which may be less sensitive to strain than thinner MEMS die. For example, the MEMS die  302  illustrated in  FIG. 2  could be made thicker for improved performance, with a total thickness increase equivalent to (−h) without affecting the overall module thickness. In an embodiment, the profile height of the MEMS package  400  on the module substrate  100  is approximately the same as the profile height of the MAP  200  on the same side of the module substrate  100 . 
     In an embodiment, the surface mount substrate  312  is bonded to the module substrate  100  in a cantilever-type configuration, in which the anchored area  330  corresponds to a fixed end of the cantilever and the hanging area  332  corresponds includes a free end opposite the fixed end. In an embodiment, an air gap  324  exists between the back side  317  of the surface mount substrate  312  and the module substrate  100 . In an embodiment, one or more bumpers  320  are formed on the module substrate  100  directly beneath the hanging area  332  of the surface mount substrate to protect the bonded area between the surface mount substrate and module substrate (corresponding to the conductive bumps  316 ) from breaking. Alternatively, or in addition to, one or more bumpers  320  may be formed on the back side  317  of the surface mount substrate  312  in the hanging area  332  to protect the bonded area between the surface mount substrate and module substrate from breaking. For example, the one or more bumpers  320  may aid in drop and shock resistance of the bonded MEMS package  400 . In an embodiment, the one or more bumpers  320  are formed of an elastomeric material. In an embodiment, the air gap  324  is also directly between the one or more bumpers  320  and either the surface mount substrate or module substrate, depending on location of the one or more bumpers. Additional structures for providing mechanical protection to the bonded area are described below with regard to  FIG. 5  in accordance with embodiments. 
     Still referring to  FIG. 2 , in an embodiment a trench  322  is located in the top surface  311  of the molding compound  310  (which also corresponds to the top surface of the MEMS package  400  in  FIG. 2 ) between the IC die  304  and the MEMS die  302 . The trench  322  may be formed during the molding process. Trench  322  may also be formed after the molding process, for example by using a mechanical blade or laser. In an embodiment, the depth, length, and width of the trench is designed to achieve mechanical integrity for handling and stress isolation. For example, the trench may isolate the MEMS die  302  from induced stress transfer from the underlying substrates (surface mount substrate and/or module substrate) including mechanical stress, thermal mechanical stress, and hygroscopic stress. For example, the trench may isolate stress transfer from mechanical stress in the surface mount substrate and/or module substrate (e.g. from screws in the module substrate), thermal mechanical stress (e.g. associated with a higher coefficient of thermal expansion (CTE) of the module substrate), or hygroscopic stress (e.g. associated with moisture absorption by the module substrate). In an embodiment, a bottom surface  323  of the trench  322  is below a top surface  303  of the MEMS die  302 . 
     In an embodiment, one or more openings  340  are optionally formed in the surface mount substrate  312  between the IC die  304  and the MEMS die  302 . In an embodiment, the one or more openings  340  extend entirely through the surface mount substrate  312 . Openings  340  may be in the form of slots or holes, for example. In an embodiment, the size of the openings  340  isolate the MEMS die  302  from induced stress transfer from the surface mount substrate and/or module substrate including mechanical stress, thermal mechanical stress, and hygroscopic stress. 
     Referring now to  FIG. 3  a schematic back side view illustration is provided of a MEMS package  400  in accordance with an embodiment. In the particular illustration provided in  FIG. 3 , only certain features are included in order to illustrate the relationship of specific features.  FIGS. 4A-4B  are cross-sectional side view illustrations of MEMS packages  400  in accordance with embodiments. For example, in  FIG. 4A  the IC die  304  and MEMS die  302  are illustrated as being bonded to the surface mount substrate  312  with die attach films  308 . In  FIG. 4B  the IC die  304  and MEMS die  302  are illustrated as being flip chip bonded to the surface mount substrate  312  with conductive bumps  316 . In accordance with embodiments, a number of combinations of bonding methods may be used for bonding the IC die and MEMS die to the surface mount substrate, and it is not required for the same bonding method to be used for both the IC die and MEMS die. In the following description, features in any or all  FIGS. 3-4B  are discussed concurrently. As shown in  FIGS. 3-4B , an arrangement of landing pads  318  is on a back side  317  of the surface mount substrate  312 . Conductive bumps  316  (e.g. solder balls) may optionally be placed on landing pads  318  for bonding to a module substrate. In an embodiment, the landing pad  318  arrangement surrounds a periphery of the IC die  304  on the front side  313  of the surface mount surface and does not surround a periphery of the MEMS die  302  on the front side of the surface mount substrate. In an embodiment, the landing pad  318  arrangement does not overlap the periphery of the MEMS die  302 . The peripheries of the IC die  304  and MEMS die  302  are illustrated as dotted lines in  FIG. 3 . As illustrated, the landing pads  318  are offset such that they are located only underneath a proximity of the IC die area, rather than underneath the MEMS die area. 
     As described above, the dimensions of the trench  322  and/or opening  340  may be designed to achieve mechanical integrity for handling and isolation of the MEMS die  302  from induced stress transfer. In an embodiment, at least one x-y dimension of the trench  322  is smaller than an x-y dimension of the molding compound  310 . In the embodiment illustrated in  FIG. 3  the trench  322  is formed entirely across the width of the molding compound  310  between the IC die  304  and MEMS die  302 . Location and dimensions of the trench  322  may be adjusted so that wires  314  are not exposed, if present. In the embodiment illustrated, a width of the slot shaped opening  340  is greater than a width of the MEMS die  302  in the same direction. Width and length, and potentially depth, of the one or more openings  340  may be adjusted to accommodate routing within the surface mount substrate  312 . In an embodiment, a plurality of openings  340  are formed through the surface mount substrate between the IC die  304  and MEMS die  302 . In an embodiment, the openings  340  are located in an area of the outside of the landing pad  318  arrangement in the hanging area  332  of the surface mount substrate. 
       FIG. 5  is a close up cross-sectional side view illustration of a MEMS package bonded to a module substrate in accordance with an embodiment. As described above, it is not required for the molding compound  310  to cover the top surface of the MEMS die  302 . For example, as shown in  FIG. 5  a vent hole  305  in the top surface of the cap  302 B is exposed to allow exposure of the MEMS device within the IC die to ambient atmosphere. 
     As described above, various structures may be included to provide mechanical protection to the bonded area corresponding to conductive bumps  316  that bonded to the landing pads  118 ,  318  on the module substrate  100  and surface mount substrate  312 . In an embodiment, one or more bumpers  320  are formed on the back side  317  of the surface mount substrate  312  and/or top side  101  of the module substrate  100 . In an embodiment, a metal trace  118 ,  318  (e.g., Cu) and/or solder mask  152 ,  352  can be formed on either or both of the back side of the surface mount substrate and the front side of the module substrate directly beneath the hanging area. Solder masks  152 ,  352  may be formed of any suitable material such as, but not limited to, epoxy or polyimide. In an embodiment, an exemplary standoff height for conductive bumps  316  may be approximately 20-50 p.m. In an embodiment, metal traces  118 ,  318  may be approximately 5-15 μm thick. Thus, by tailoring the thickness of the conductive bumps  316 , metals traces, and/or solder masks  152 ,  352  and appropriate air gap  324  thickness can be provided directly underneath the hanging area  332  for protecting against excessive bending of the hanging area. Height of optional bumpers  320  can similarly be determined. In an embodiment, a bumper  320  is formed directly over a solder mask  152 ,  352 , and may be formed directly on a solder mask. 
     Referring now to  FIG. 6 , a cross-sectional side view illustration is provided of a strained MEMS module in accordance with an embodiment. For example, the module substrate  100  may be warped due to thermal expansion or hygroscopic stress. In the particular embodiment illustrated, the module substrate  100  has a “cry” shape. In such a configuration, the bottom surface of the module substrate may be under compressive strain with the top surface onto which the MEMS package  400  is bonded under tensile strain. The particular strain relationship illustrated in  FIG. 6  is exaggerated to illustrate immunity to bending strain that may be achieved in accordance with embodiments. As shown, as the module substrate  100  is bent, stress is transferred directly into the anchored area  330 . The transferred stress may also result in strain in the anchored area  330  of the surface mount substrate  312 , and potentially bending of the surface mount substrate in the anchored area  330 . This stress is transferred to components mounted in this region of the surface mount substrate. In accordance with embodiments, since the hanging area  332  is not directly attached to the module substrate  100  less strain is transferred to the hanging area  332 , and consequently to any components mounted in the hanging area. Thus, the hanging area may exhibit less bending, and stress transfer to the MEMS die  302 . 
     In the embodiment illustrated in  FIG. 6 , the back side  317  of the surface mount substrate  312  in the anchored area  330  may be under compressive stress caused by the module substrate  100 . Similarly, the top surface  311  of the molding compound may be under tensile stress. In accordance with embodiments, the trench  322  may reduce the transfer of tensile stress across the hanging area  332 . Similarly, the one or more openings  340  may reduce the transfer of stress (e.g. compressive) from the surface mount substrate  312  across the hanging area  332 . Thus, in accordance with embodiments the hanging area  332 , trench  322 , and opening  340  may isolate the MEMS die  302  from mechanical stress. 
     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 MEMS package and 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: 20141212
Publication Date: 20160920
Grant Date: 20160920
Priority Date: 20141212
Inventors: JIANG TONGBI
ZHAO JIE-HUA
HARTWELL PETER G.
Assignee: APPLE INC
CPC Classifications: [{"code": "B81B2207/012", "inventive": false, "first": false, "tree": "[]"}, {"code": "B81C3/001", "inventive": true, "first": false, "tree": "[]"}, {"code": "B81B2207/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "B81B7/0048", "inventive": true, "first": true, "tree": "[]"}, {"code": "B81C2203/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "B81B2207/99", "inventive": false, "first": false, "tree": "[]"}, {"code": "B81C2203/035", "inventive": false, "first": false, "tree": "[]"}, {"code": "B81B7/0058", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 56110474