Abstract:
The present invention relates to a surface mount package for a silicon condenser microphone and methods for manufacturing the surface mount package. The surface mount package uses a limited number of components which simplifies manufacturing and lowers costs, and features a substrate that performs functions for which multiple components were traditionally required, including providing an interior surface on which the silicon condenser die is mechanically attached, providing an interior surface for making electrical connections between the silicon condenser die and the package, and providing an exterior surface for surface mounting the package to a device&#39;s printed circuit board and for making electrical connections between package and the device&#39;s printed circuit board.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/732,265, filed Dec. 31, 2012, which is a continuation of U.S. patent application Ser. No. 13/286,558 (now U.S. Pat. No. 8,358,004), filed Nov. 1, 2011, which is a continuation of U.S. patent application Ser. No. 13/111,537 (now U.S. Pat. No. 8,121,331), filed May 19, 2011, which is a continuation of U.S. patent application Ser. No. 11/741,881 (now U.S. Pat. No. 8,018,049), filed Apr. 30, 2007, which is a divisional of U.S. patent application Ser. No. 10/921,747 (now U.S. Pat. No. 7,434,305), filed Aug. 19, 2004, which is a continuation-in-part of U.S. patent application Ser. No. 09/886,854 (now U.S. Pat. No. 7,166,910), filed Jun. 21, 2001, which claims the benefit of U.S. Provisional Patent Application No. 60/253,543, filed Nov. 28, 2000. U.S. patent application Ser. No. 13/668,035, filed Nov. 2, 2012, U.S. patent application Ser. No. 13/668,103, filed Nov. 2, 2012, U.S. patent application Ser. No. 13/732,120, filed Dec. 31, 2012, U.S. patent application Ser. No. 13/732,179, filed Dec. 31, 2012, U.S. patent application Ser. No. 13/732,205, filed Dec. 31, 2012, and U.S. patent application Ser. No. 13/732,232, filed Dec. 31, 2012, are also continuations of U.S. patent application Ser. No. 13/286,558 (now U.S. Pat. No. 8,358,004). These applications are hereby incorporated by reference herein in their entireties for all purposes. 
    
    
     TECHNICAL FIELD 
     This patent relates generally to a housing for a transducer. More particularly, this patent relates to a silicon condenser microphone including a housing for shielding a transducer. 
     BACKGROUND OF THE INVENTION 
     There have been a number of disclosures related to building microphone elements on the surface of a silicon die. Certain of these disclosures have come in connection with the hearing aid field for the purpose of reducing the size of the hearing aid unit. While these disclosures have reduced the size of the hearing aid, they have not disclosed how to protect the transducer from outside interferences. For instance, transducers of this type are fragile and susceptible to physical damage. Furthermore, they must be protected from light and electromagnetic interferences. Moreover, they require an acoustic pressure reference to function properly. For these reasons, the silicon die must be shielded. 
     Some shielding practices have been used to house these devices. For instance, insulated metal cans or discs have been provided. Additionally, DIPs and small outline integrated circuit (SOIC) packages have been utilized. However, the drawbacks associated with manufacturing these housings, such as lead time, cost, and tooling, make these options undesirable. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a silicon condenser microphone package that allows acoustic energy to contact a transducer disposed within a housing. The housing provides the necessary pressure reference while at the same time protects the transducer from light, electromagnetic interference, and physical damage. In accordance with an embodiment of the invention a silicon condenser microphone includes a transducer and a substrate and a cover forming the housing. The substrate may have an upper surface with a recess formed therein allowing the transducer to be attached to the upper surface and to overlap at least a portion of the recess thus forming a back volume. The cover is placed over the transducer and includes an aperture adapted for allowing sound waves to reach the transducer. 
     Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a first embodiment of a silicon condenser microphone of the present invention; 
         FIG. 2  is a cross-sectional view of a second embodiment of a silicon condenser microphone of the present invention; 
         FIG. 3  is a cross-sectional view of a third embodiment of a silicon condenser microphone of the present invention; 
         FIG. 4  is a cross-sectional view of the third embodiment of the present invention affixed to an end user circuit board; 
         FIG. 5  is a cross-sectional view of the third embodiment of the present invention affixed to an end user circuit board in an alternate fashion; 
         FIG. 6  is a plan view of a substrate to which a silicon condenser microphone is fixed; 
         FIG. 7  is a longitudinal cross-sectional view of a microphone package of the present invention; 
         FIG. 8  is a lateral cross-sectional view of a microphone package of the present invention; 
         FIG. 9  is a longitudinal cross-sectional view of a microphone package of the present invention; 
         FIG. 10  is a lateral cross-sectional view of a microphone package of the present invention; 
         FIG. 11  is a cross-sectional view of a top portion for a microphone package of the present invention; 
         FIG. 12  is a cross-sectional view of a top portion for a microphone package of the present invention; 
         FIG. 13  is a cross-sectional view of a top portion for a microphone package of the present invention; 
         FIG. 14   a  is a cross-sectional view of a laminated bottom portion of a housing for a microphone package of the present invention; 
         FIG. 14   b  is a plan view of a layer of the laminated bottom portion of  FIG. 14   a;    
         FIG. 14   c  is a plan view of a layer of the laminated bottom portion of  FIG. 14   a;    
         FIG. 14   d  is a plan view of a layer of the laminated bottom portion of  FIG. 14   a;    
         FIG. 15  is a cross-sectional view of a bottom portion for a microphone package of the present invention; 
         FIG. 16  is a cross-sectional view of a bottom portion for a microphone package of the present invention; 
         FIG. 17  is a cross-sectional view of a bottom portion for a microphone package of the present invention; 
         FIG. 18  is a cross-sectional view of a bottom portion for a microphone package of the present invention; 
         FIG. 19  is a plan view of a side portion for a microphone package of the present invention; 
         FIG. 20  is a cross-sectional view of a side portion for a microphone package of the present invention; 
         FIG. 21  is a cross-sectional view of a side portion for a microphone package of the present invention; 
         FIG. 22  is a cross-sectional view of a side portion for a microphone package of the present invention; 
         FIG. 23  is a cross-sectional view of a microphone package of the present invention; 
         FIG. 24  is a cross-sectional view of a microphone package of the present invention; 
         FIG. 25  is a cross-sectional view of a microphone package of the present invention; 
         FIG. 26  is a cross-sectional view of a microphone package of the present invention; 
         FIG. 27  is a cross-sectional view of a microphone package of the present invention with a retaining ring; 
         FIG. 28  is a cross-sectional view of a microphone package of the present invention with a retaining wing; 
         FIG. 29  is a cross-sectional view of a microphone package of the present invention with a retaining ring; 
         FIG. 30  is a plan view of a panel of a plurality of microphone packages; and 
         FIG. 31  is a plan view of a microphone pair. 
     
    
    
     DETAILED DESCRIPTION 
     While the invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail several possible embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated. 
     The present invention is directed to microphone packages. The benefits of the microphone packages disclosed herein over microphone packaging utilizing plastic body/lead frames include the ability to process packages in panel form allowing more units to be formed per operation and at much lower cost. The typical lead frame for a similarly functioning package would contain between 40 and 100 devices connected together. The present disclosure would have approximately 14,000 devices connected together (as a panel). Also, the embodiments disclosed herein require minimal “hard-tooling” This allows the process to adjust to custom layout requirements without having to redesign mold, lead frame, and trim/form tooling. 
     Moreover, many of the described embodiments have a better match of thermal coefficients of expansion with the end user&#39;s PCB, typically made of FR-4, since the microphone package is also made primarily of FR-4. These embodiments of the invention may also eliminate the need for wire bonding that is required in plastic body/lead frame packages. The footprint is typically smaller than that would be required for a plastic body/lead frame design since the leads may be formed by plating a through-hole in a circuit board to form the pathway to the solder pad. In a typical plastic body/lead frame design, a (gull wing configuration would be used in which the leads widen the overall foot print. 
     Now, referring to  FIGS. 1-3 , three embodiments of a silicon condenser microphone package  10  of the present invention are illustrated. Included within silicon microphone package  10  is a transducer  12 , e.g. a silicon condenser microphone as disclosed in U.S. Pat. No. 5,870,482 which is hereby incorporated by reference and an amplifier  16 . The package itself includes a substrate  14 , a back volume or air cavity  18 , which provides a pressure reference for the transducer  12 , and a cover  20 . The substrate  14  may be formed of FR-4 material allowing processing in circuit board panel form, thus taking advantage of economies of scale in manufacturing.  FIG. 6  is a plan view of the substrate  14  showing the back volume  18  surrounded a plurality of terminal pads. 
     The back volume  18  may be formed by a number of methods, including controlled depth drilling of an upper surface  19  of the substrate  14  to form a recess over which the transducer  12  is mounted ( FIG. 1 ); drilling and routing of several individual sheets of FR-4 and laminating the individual sheets to form the back volume  18 , which may or may not have internal support posts ( FIG. 2 ); or drilling completely through the substrate  14  and providing a sealing ring  22  on the bottom of the device that will seal the back volume  18  during surface mounting to a user&#39;s “board”  28  ( FIGS. 3-5 ). In this example, the combination of the substrate and the user&#39;s board  28  creates the back volume  18 . The back volume  18  is covered by the transducer  12  (e.g., a MEMS device) which may be “bumpbonded” and mounted face down. The boundary is sealed such that the back volume  18  is operably “air-tight.” 
     The cover  20  is attached for protection and processability. The cover  20  contains an aperture  24  which may contain a sintered metal insert  26  to prevent water, particles and/or light from entering the package and damaging the internal components inside; i.e. semiconductor chips. The aperture  24  is adapted for allowing sound waves to reach the transducer  12 . The sintered metal insert  26  will also have certain acoustic properties, e.g. acoustic damping or resistance. The sintered metal insert  26  may therefore be selected such that its acoustic properties enhance the functional capability of the transducer  12  and/or the overall performance of the silicon microphone  10 . 
     Referring to  FIGS. 4 and 5  the final form of the product is a silicon condenser microphone package  10  which would most likely be attached to an end user&#39;s PCB  28  via a solder reflow process.  FIG. 5  illustrates a method of enlarging the back volume  18  by including a chamber  32  within the end user&#39;s circuit board  28 . 
     Another embodiment of a silicon condenser microphone package  40  of the present invention is illustrated in  FIGS. 7-10 . In this embodiment, a housing  42  is formed from layers of materials, such as those used in providing circuit boards. Accordingly, the housing  42  generally comprises alternating layers of conductive and non-conductive materials  44 ,  46 . The non-conductive layers  46  are typically FR-4 board. The conductive layers  44  are typically copper. This multi-layer housing construction advantageously permits the inclusion of circuitry, power and ground planes, solder pads, ground pads, capacitance layers and plated through holes pads within the structure of the housing itself. The conductive layers provide EMI shielding while also allowing configuration as capacitors and/or inductors to filter input/output signals and/or the input power supply. 
     In the embodiment illustrated, the housing  42  includes a top portion  48  and a bottom portion  50  spaced by a side portion  52 . The housing  42  further includes an aperture or acoustic port  54  for receiving an acoustic signal and an inner chamber  56  which is adapted for housing a transducer unit  58 , typically a silicon die microphone or a ball grid array package (BGA). The top, bottom, and side portions  48 ,  50 ,  52  are electrically connected, for example with a conductive adhesive  60 . The conductive adhesive may be provided conveniently in the form of suitably configured sheets of dry adhesive disposed between the top, bottom and side portions  48 ,  50  and  52 . The sheet of dry adhesive may be activated by pressure, heat or other suitable means after the portions are brought together during assembly. Each portion may comprise alternating conductive and non-conductive layers of  44 ,  46 . 
     The chamber  56  may include an inner lining  61 . The inner lining  61  is primarily formed by conductive material. It should be understood that the inner lining may include portions of non-conductive material, as the conductive material may not fully cover the non-conductive material. The inner lining  61  protects the transducer  58  against electromagnetic interference and the like, much like a faraday cage. The inner lining  61  may also be provided by suitable electrically coupling together of the various conductive layers within the top, bottom and side portions  48 ,  50  and  52  of the housing. 
     In the various embodiments illustrated in  FIGS. 7-10  and  23 - 26 , the portions of the housing  42  that include the aperture or acoustic port  54  further include a layer of material that forms an environmental barrier  62  over or within the aperture  54 . This environmental barrier  62  is typically a polymeric material formed to a film, such as a polytetrafluoroethylene (PTFE) or a sintered metal. The environmental barrier  62  is supplied for protecting the chamber  56  of the housing  42 , and, consequently, the transducer unit  58  within the housing  42 , from environmental elements such as sunlight, moisture, oil, dirt, and/or dust. The environmental barrier  62  will also have inherent acoustic properties, e.g. acoustic damping/resistance. Therefore the environmental barrier  62  is chosen such that its acoustic properties cooperate with the transducer unit  58  to enhance the performance of the microphone. This is particularly true in connection with the embodiments illustrated in  FIGS. 24 and 25 , which may be configured to operate as directional microphones. 
     The environmental barrier layer  62  is generally sealed between layers of the portion, top  48  or bottom  50  in which the acoustic port  54  is formed. For example, the environmental barrier may be secured between layers of conductive material  44  thereby permitting the layers of conductive material  44  to act as a capacitor (with electrodes defined by the metal) that can be used to filter input and output signals or the input power. The environmental barrier layer  62  may further serve as a dielectric protective layer when in contact with the conductive layers  44  in the event that the conductive layers also contain thin film passive devices such as resistors and capacitors. 
     In addition to protecting the chamber  56  from environmental elements, the barrier layer  62  allows subsequent wet processing, board washing of the external portions of the housing  42 , and electrical connection to ground from the walls via thru hole plating. The environmental barrier layer  62  also allows the order of manufacturing steps in the fabrication of the printed circuit board-based package to be modified. This advantage can be used to accommodate different termination styles. For example, a double sided package can be fabricated having a pair of apertures  54  (see  FIG. 25 ), both including an environmental barrier layer  62 . The package would look and act the same whether it is mounted face up or face down, or the package could be mounted to provide directional microphone characteristics. Moreover, the environmental barrier layer  62  may also be selected so that its acoustic properties enhance the directional performance of the microphone. 
     Referring to  FIGS. 7 ,  8 , and  11 - 13  the transducer unit  58  is generally not mounted to the top portion  48  of the housing. This definition is independent of the final mounting orientation to an end user&#39;s circuit board. It is possible for the top portion  48  to be mounted face down depending on the orientation of the transducer  58  as well as the choice for the bottom portion  50 . The conductive layers  44  of the top portion  48  may be patterned to form circuitry, ground planes, solder pads, ground pads, capacitors and plated through hole pads. Referring to  FIGS. 1-13  there may be additional alternating conductive layers  44 , non-conductive layers  46 , and environmental protective membranes  62  as the package requires. Alternatively, some layers may be deliberately excluded as well. The first non-conductive layer  46  may be patterned so as to selectively expose certain features on the first conductive layer  44 . 
       FIG. 11  illustrates an alternative top portion  48  for a microphone package. In this embodiment, a connection between the layers can be formed to provide a conduit to ground. The top portion of  FIG. 11  includes ground planes and/or pattern circuitry  64  and the environmental barrier  62 . The ground planes and or pattern circuitry  64  are connected by pins  65 . 
       FIG. 12  illustrates another embodiment of a top portion  48 . In addition to the connection between layers, ground planes/pattern circuitry  64 , and the environmental barrier  62 , this embodiment includes conductive bumps  66  (e.g. Pb/Sn or Ni/Au) patterned on the bottom side to allow secondary electrical contact to the transducer  58 . Here, conductive circuitry would be patterned such that electrical connection between the bumps  66  and a plated through hole termination is made. 
       FIG. 13  illustrates yet another embodiment of the top portion  48 . In this embodiment, the top portion  48  does not include an aperture or acoustic port  54 . 
     Referring to  FIGS. 7 ,  8  and  14 - 18 , the bottom portion  50  is the component of the package to which the transducer  58  is primarily mounted. This definition is independent of the final mounting orientation to the end user&#39;s circuit board. It is possible for the bottom portion  50  to be mounted facing upwardly depending on the mounting orientation of the transducer  58  as well as the choice for the top portion  48  construction Like the top portion  48 , the conductive layers  44  of the bottom portion  50  may be patterned to form circuitry, ground planes, solder pads, ground pads, capacitors and plated through hole pads. As shown in  FIGS. 14-18 , there may be additional alternating conductive layers  44 , non-conductive layers  46 , and environmental protective membranes  62  as the package requires. Alternatively, some layers may be deliberately excluded as well. The first non-conductive layer  46  may be patterned so as to selectively expose certain features on the first conductive layer  44 . 
     Referring to  FIGS. 14   a  through  14   d , the bottom portion  50  comprises a laminated, multi-layered board including layers of conductive material  44  deposited on layers of non-conductive material  46 . Referring to  FIG. 14   b , the first layer of conductive material is used to attach wire bonds or flip chip bonds. This layer includes etched portions to define lead pads, bond pads, and ground pads. The pads would have holes drilled through them to allow the formation of plated through-holes. 
     As shown in  FIG. 14   c , a dry film  68  of non-conductive material covers the conductive material. This illustration shows the exposed bonding pads as well as an exposed ground pad. The exposed ground pad would come in electrical contact with the conductive epoxy and form the connection to ground of the side portion  52  and the base portion  50 . 
     Referring to  FIG. 14   d , ground layers can be embedded within the base portion  50 . The hatched area represents a typical ground plane  64 . The ground planes do not overlap the power or output pads, but will overlap the transducer  58 . 
     Referring to  FIG. 15 , an embodiment of the bottom portion  50  is illustrated. The bottom portion  50  of this embodiment includes a solder mask layer  68  and alternating layers of conductive and non-conductive material  44 ,  46 . The bottom portion further comprises solder pads  70  for electrical connection to an end user&#39;s board. 
       FIGS. 16 and 17  illustrate embodiments of the bottom portion  50  with enlarged back volumes  18 . These embodiments illustrate formation of the back volume  18  using the conductive/non-conductive layering. 
       FIG. 18  shows yet another embodiment of the bottom portion  50 . In this embodiment, the back portion  50  includes the acoustic port  54  and the environmental barrier  62 . 
     Referring to  FIGS. 7-10  and  19 - 22 , the side portion  52  is the component of the package that joins the bottom portion  50  and the top portion  48 . The side portion  52  may include a single layer of a non-conductive material  46  sandwiched between two layers of conductive material  44 . The side portion  52  forms the internal height of the chamber  56  that houses the transducer  58 . The side portion  52  is generally formed by one or more layers of circuit board material, each having a routed window  72  (see  FIG. 19 ). 
     Referring to  FIGS. 19-22 , the side portion  52  includes inner sidewalls  74 . The inner sidewalls  74  are generally plated with a conductive material, typically copper, as shown in  FIGS. 20 and 21 . The sidewalls  74  are formed by the outer perimeter of the routed window  72  and coated/metallized with a conductive material. 
     Alternatively, the sidewalls  74  may be formed by may alternating layers of non-conductive material  46  and conductive material  44 , each having a routed window  72  (see  FIG. 19 ). In this case, the outer perimeter of the window  72  may not require coverage with a conductive material because the layers of conductive material  44  would provide effective shielding. 
       FIGS. 23-26  illustrate various embodiments of the microphone package  40 . These embodiments utilize top, bottom, and side portions  48 ,  50 , and  52  which are described above. It is contemplated that each of the top, bottom, and side portion  48 ,  50 ,  52  embodiments described above can be utilized in any combination without departing from the invention disclosed and described herein. 
     In  FIG. 23 , connection to an end user&#39;s board is made through the bottom portion  50 . The package mounting orientation is bottom portion  50  down. Connection from the transducer  58  to the plated through holes is be made by wire bonding. The transducer back volume  18  is formed by the back hole (mounted down) of the silicon microphone only. Bond pads, wire bonds and traces to the terminals are not shown. A person of ordinary skilled in the art of PCB design will understand that the traces reside on the first conductor layer  44 . The wire bonds from the transducer  58  are be connected to exposed pads. The pads are connected to the solder pads via plated through holes and traces on the surface. 
     In  FIG. 24 , connection to the end user&#39;s board is also made through the bottom portion  50 . Again, the package mounting orientation is bottom portion  50 . Connection from the transducer  58  to the plated through holes are made by wire bonding. The back volume is formed by a combination of the back hole of the transducer  58  (mounted down) and the bottom portion  50 . 
     In  FIG. 25 , connection to the end user&#39;s board is also made through the bottom portion  50 . Again, the package mounting orientation is bottom portion  50 . Connection from the transducer  58  to the plated through holes are made by wire bonding. With acoustic ports  54  on both sides of the package, there is no back volume. This method is suitable to a directional microphone. 
     In  FIG. 26 , connection to the end user&#39;s board is made through the top portion  48  or the bottom portion  53 . The package mounting orientation is either top portion  48  down or bottom portion  50  down. Connection from the transducer  58  to the plated through holes is made by flip chipping or wire bonding and trace routing. The back volume  18  is formed by using the air cavity created by laminating the bottom portion  50  and the top portion  48  together. Some portion of the package fabrication is performed after the transducer  58  has been attached. In particular, the through hole formation, plating, and solder pad definition would be done after the transducer  58  is attached. The protective membrane  62  is hydrophobic and prevents corrosive plating chemistry from entering the chamber  56 . 
     Referring to  FIGS. 27-29 , the portion to which the transducer unit  58  is mounted may include a retaining ring  84 . The retaining ring  84  prevents wicking of an epoxy  86  into the transducer  58  and from flowing into the acoustic port or aperture  54 . Accordingly, the shape of the retaining ring  84  will typically match the shape of the transducer  58  foot print. The retaining ring  84  comprises a conductive material (e.g., 3 mil. thick copper) imaged on a non-conductive layer material. 
     Referring to  FIG. 27 , the retaining ring  84  is imaged onto a nonconductive layer. An epoxy is applied outside the perimeter of the retaining ring  84 , and the transducer  58  is added so that it overlaps the epoxy  86  and the retaining ring  84 . This reduces epoxy  86  wicking up the sides of the transducer&#39;s  58  etched port (in the case of a silicon die microphone). 
     Alternatively, referring to  FIG. 28 , the retaining ring  84  can be located so that the transducer  58  does not contact the retaining ring  84 . In this embodiment, the retaining ring  84  is slightly smaller than the foot print of the transducer  58  so that the epoxy  86  has a restricted path and is, thus, less likely to wick. In  FIG. 29 , the retaining ring  84  is fabricated so that it contacts the etched port of the transducer  58 . The following tables provide an illustrative example of a typical circuit board processing technique for fabrication of the housing of this embodiment. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Materials 
               
             
          
           
               
                 Mate- 
                   
                   
                   
               
               
                 rial 
                 Type 
                 Component 
                 Note 
               
               
                   
               
               
                 1 
                 0.5/0.5 oz. DST 
                 Bottom Portion (Conductive 
                   
               
               
                   
                 Cu 5 core FR-4 
                 Layers Non-Conductive Layer 1) 
                   
               
               
                 2 
                 0.5/0.5 oz. DST 
                 Bottom Portion (Conductive 
                   
               
               
                   
                 Cu 5 core FR-4 
                 Layers 3 and 4; Non-Conductive 
                   
               
               
                   
                   
                 Layer 2) 
                   
               
               
                 3 
                 106 pre-preg 
                   
                 For  
               
               
                   
                   
                   
                 Laminating 
               
               
                   
                   
                   
                 Material 1 and 
               
               
                   
                   
                   
                 Material 2 
               
               
                 4 
                 0.5/0.5 oz. DST 
                 Side Portion 
                 Metallized 
               
               
                   
                 Cu 40 Core FR-4 
                   
                 Afterward 
               
               
                 5 
                 Bare/0.5 oz. Cu 2 
                 Top Portion (Each Piece 
                   
               
               
                   
                 core FR-4 (2 
                 Includes 1 Conductive and 1 
                   
               
               
                   
                 pieces) 
                 Non-Conductive Layer) 
                   
               
               
                 6 
                 Expanded PTFE 
                 Environmental Barrier 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Processing of Materials (Base Portion Material 1) 
               
             
          
           
               
                 Step 
                 Type 
                 Description 
                 Note 
               
               
                   
               
               
                 1 
                 Dry Film 
                   
                   
               
               
                   
                 Conductive Layers 
                   
                   
               
               
                 2 
                 Expose 
                 Mask Material 1 (Upper 
                 Forms Ground 
               
               
                   
                   
                 Conductive Layer) 
                 Plane on Lower 
               
               
                   
                   
                   
                 Conductive Layer 
               
               
                 3 
                 Develop 
                   
                   
               
               
                 4 
                 Etch Cu 
                   
                 No Etching on 
               
               
                   
                   
                   
                 Upper Conductive 
               
               
                   
                   
                   
                 Layer 
               
               
                 5 
                 Strip Dry Film 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Processing of Materials (Bottom Portion Material 2) 
               
             
          
           
               
                 Step 
                 Type 
                 Description 
                 Note 
               
               
                   
               
               
                 1 
                 Dry Film 
                   
                   
               
               
                   
                 Conductive 
                   
                   
               
               
                   
                 Layers 
                   
                   
               
               
                 2 
                 Expose 
                 Mask Material 2 (Upper 
                 Forms Ground 
               
               
                   
                   
                 Conductive Layer) 
                 Plane on Upper 
               
               
                   
                   
                   
                 Conductive Layer 
               
               
                 3 
                 Develop 
                   
                   
               
               
                 4 
                 Etch Cu 
                   
                 No Etching on Upper 
               
               
                   
                   
                   
                 Conductive 
               
               
                   
                   
                   
                 Layer 
               
               
                 5 
                 Strip Dry Film 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Processing of Materials 1, 2, and 3 (Form Bottom Portion) 
               
             
          
           
               
                 Step 
                 Type 
                 Description 
                 Note 
               
               
                   
               
             
          
           
               
                 1 
                 Laminate 
                 Materials 1 and 2 
                   
               
               
                   
                   
                 Laminated Using 
                   
               
               
                   
                   
                 Material 3 
                   
               
               
                 2 
                 Drill Thru Holes 
                 Drill Bit = 0.025 in. 
                   
               
               
                 3 
                 Direct 
                 Plates Thru Holes 
                   
               
               
                   
                 Metallization/Flash 
                   
                   
               
               
                   
                 Copper 
                   
                   
               
               
                 4 
                 Dry Film (L1 and 
                   
                   
               
               
                   
                 L4) 
                   
                   
               
               
                 5 
                 Expose 
                 Mask Laminated 
                 Forms Traces and Solder 
               
               
                   
                   
                 Materials 1 and 2 
                 Pads 
               
               
                   
                   
                 (Upper and Lower 
                   
               
               
                   
                   
                 Conductive Layers) 
                   
               
               
                 6 
                 Develop 
                   
                   
               
               
                 7 
                 Electrolytic Cu 
                 1.0 mil 
                   
               
               
                 8 
                 Electrolytic Sn 
                 As Required 
                   
               
               
                 9 
                 Strip Dry Film 
                   
                   
               
               
                 10 
                 Etch Cu 
                   
                   
               
               
                 11 
                 Etch Cu 
                   
                   
               
               
                 12 
                 Insert Finishing 
                 NG Option (See 
                 NG Option for Proof 
               
               
                   
                 Option Here 
                 Table Below) 
                 of Principle 
               
               
                 13 
                 Dry Film (cover 
                 2.5 mil 
                 Minimum Thickness 
               
               
                   
                 lay) on Upper 
                   
                 on Upper Conductive 
               
               
                   
                 Conductive Layer 
                   
                 Layer 
               
               
                   
                 Only 
                   
                   
               
               
                 14 
                 Expose 
                 Mask Laminated 
                 This mask defines an 
               
               
                   
                   
                 Materials 1 and 2 
                 area on the upper 
               
               
                   
                   
                 (upper and lower) 
                 conductive layer that 
               
               
                   
                   
                   
                 will receive a dry film 
               
               
                   
                   
                   
                 solder mask (cover 
               
               
                   
                   
                   
                 lay). The bottom layer 
               
               
                   
                   
                   
                 will not have dry film 
               
               
                   
                   
                   
                 applied to it. The 
               
               
                   
                   
                   
                 plated through holes 
               
               
                   
                   
                   
                 will be bridged over by 
               
               
                   
                   
                   
                 the coating on the top. 
               
               
                 15 
                 Develop 
                   
                   
               
               
                 16 
                 Cure 
                   
                 Full Cure 
               
               
                 17 
                 Route Panels 
                 Route Bit = As 
                 Forms 4″ × 4″ pieces. 
               
               
                   
                   
                 Required 
                 Conforms to finished 
               
               
                   
                   
                   
                 dims 
               
               
                   
               
             
          
         
       
     
     Table 5 describes the formation of the side portion  52 . This process involves routing a matrix of openings in FR-4 board. However, punching is thought to be the cost effective method for manufacturing. The punching may done by punching through the entire core, or, alternatively, punching several layers of no-flow pre-preg and thin core c-stage which are then laminated to form the wall of proper thickness. 
     After routing the matrix, the board will have to be electroless or DM plated. Finally, the boards will have to be routed to match the bottom portion. This step can be done first or last. It may make the piece more workable to perform the final routing as a first step. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Processing of Material 4 (Side Portion) 
               
             
          
           
               
                 Step 
                 Type 
                 Description 
                 Note 
               
               
                   
               
               
                 1 
                 Route/Punch 
                 Route Bit = 0.031 in. 
                 Forms Side Portion 
               
               
                   
                 Matrix of 
                   
                   
               
               
                   
                 Openings 
                   
                   
               
               
                 2 
                 Direct 
                 0.25 mil minimum 
                 Forms Sidewalls 
               
               
                   
                 Metallization/ 
                   
                 on Side Portion 
               
               
                   
                 Flash Cu 
                   
                   
               
               
                 3 
                 Route Panels 
               
               
                   
               
             
          
         
       
     
     Table 6 describes the processing of the top portion. The formation of the top portion  48  involves imaging a dry film cover lay or liquid solder mask on the bottom (i.e. conductive layer forming the inner layer. The exposed layer of the top portion  48  will not have a copper coating. It can be processed this way through etching or purchased this way as a one sided laminate. 
     A matrix of holes is drilled into the lid board. Drilling may occur after the imaging step. If so, then a suitable solder mask must be chosen that can survive the drilling process. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Processing of Top Portion 
               
             
          
           
               
                 Step 
                 Type 
                 Description 
                 Note 
               
               
                   
               
               
                 1 
                 Dry Film 
                 Conductive Layer 
                   
               
               
                 2 
                 Expose 
                 Mask Bare Layer 
                 Form Conduction Ring 
               
               
                 3 
                 Develop 
                   
                   
               
               
                 4 
                 Cure 
                   
                   
               
               
                 5 
                 Drill Matrix of 
                 Drill Bit 0.025 in. 
                 Acoustic Ports 
               
               
                   
                 Holes 
                   
                   
               
               
                 6 
                 Laminate 
                 PTFE (Environmental 
                 Forms Top Portion 
               
               
                   
                   
                 Barrier) Between 2 Pieces 
                   
               
               
                   
                   
                 of Material 5 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Processing of Laminated Materials 1 and 2 with Material 4 
               
             
          
           
               
                 Step 
                 Type 
                 Description 
                 Note 
               
               
                   
               
               
                 1 
                 Screen 
                   
                   
               
               
                   
                 Conductive 
                   
                   
               
               
                   
                 Adhesive on 
                   
                   
               
               
                   
                 Material 4 
                   
                   
               
               
                 2 
                 Laminate 
                 Bottom Portion with Side 
                 Forms Bottom 
               
               
                   
                   
                 Portion 
                 Portion with Side 
               
               
                   
                   
                   
                 Portion (spacer) 
               
               
                 3 
                 Add Transducer 
                 Silicon Die Microphone 
                   
               
               
                   
                 Assembly 
                 and Integrated Circuit 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 Processing of Laminated Materials 1, 2, and 4 with Material 5 
               
             
          
           
               
                 Step 
                 Type 
                 Description 
                 Note 
               
               
                   
               
               
                 1 
                 Screen 
                   
                   
               
               
                   
                 Conductive 
                   
                   
               
               
                   
                 Adhesive on 
                   
                   
               
               
                   
                 Top Portion 
                   
                   
               
               
                 2 
                 Laminate 
                 Bottom Portion and Side 
                 Forms Housing 
               
               
                   
                   
                 Portion with Top Portion 
                   
               
               
                 3 
                 Dice 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 Finishing Option NG (Nickel/Gold) 
               
             
          
           
               
                 Step 
                 Type 
                 Description 
                 Note 
               
               
                   
               
               
                 1 
                 Immersion Ni 
                   
                   
               
               
                   
                 (40-50 μ-in) 
                   
                   
               
               
                 2 
                 Immersion Au 
                   
                   
               
               
                   
                 (25-30 μ-in) 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 Finishing Option NGT (Nickel/Gold/Tin) 
               
             
          
           
               
                 Step 
                 Type 
               
               
                   
               
               
                 1 
                 Mask L2 (using thick dry film or high tack dicing tape) 
               
               
                 2 
                 Immersion Ni (40-50 μ-in) 
               
               
                 3 
                 Immersion Au (25-30 μ-in) 
               
               
                 4 
                 Remove Mask on L2 
               
               
                 5 
                 Mask L1 (using thick dry film or high tack dicing tape) 
               
               
                   
                 bridge over cavity created by wall 
               
               
                 6 
                 Immersion Sn (100-250 μ-in) 
               
               
                 7 
                 Remove Mask on L1 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
           
               
                 TABLE 11 
               
             
             
               
                   
               
               
                 Finishing Option ST (Silver/Tin) 
               
             
          
           
               
                 Step 
                 Type 
               
               
                   
               
               
                 1 
                 Mask L2 (using thick dry film or high tack dicing tape) 
               
               
                 2 
                 Immersion Ag (40-50 μ-in) 
               
               
                 3 
                 Remove Mask on L2 
               
               
                 4 
                 Mask L1 (using thick dry film or high tack dicing tape) 
               
               
                   
                 bridge over cavity created by wall 
               
               
                 5 
                 Immersion Sn (100-250 μ-in) 
               
               
                 6 
                 Remove Mask on L1 
               
               
                   
               
             
          
         
       
     
       FIG. 30  is a plan view illustrating a panel  90  for forming a plurality of microphone packages  92 . The microphone packages  92  are distributed on the panel  90  in a 14×24 array, or 336 microphone packages total. Fewer or more microphone packages may be disposed on the panel  90 , or on smaller or larger panels. As described herein in connection with the various embodiments of the invention, the microphone packages include a number of layers, such as top, bottom and side portions of the housing, environmental barriers, adhesive layers for joining the portions, and the like. To assure alignment of the portions as they are brought together, each portion may be formed to include a plurality of alignment apertures  94 . To simultaneously manufacture several hundred or even several thousand microphones, a bottom layer, such as described herein, is provided. A transducer, amplifier and components are secured at appropriate locations on the bottom layer corresponding to each of the microphones to be manufactured. An adhesive layer, such as a sheet of dry adhesive is positioned over the bottom layer, and a sidewall portion layer is positioned over the adhesive layer. An additional dry adhesive layer is positioned, followed by an environmental barrier layer, another dry adhesive layer and the top layer. The dry adhesive layers are activated, such as by the application of heat and/or pressure. The panel is then separated into individual microphone assemblies using known panel cutting and separating techniques. 
     The microphone, microphone package and method of assembly herein described further allow the manufacture of multiple microphone assembly, such as microphone pairs. In the simplest form, during separation two microphones may be left joined together, such as the microphone pair  96  shown in  FIG. 31 . Each microphone  98  and  100  of the microphone pair  96  is thus a separate, individually operable microphone in a single package sharing a common sidewall  102 . Alternatively, as described herein, conductive traces may be formed in the various layers of either the top or bottom portion thus allowing multiple microphones to be electrically coupled. 
     While specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying Claims.