MEMS microphone package

In one embodiment a micro-electro-mechanical system (MEMS) microphone package includes a multiple layer substrate, an upper acoustic port formed through a plurality of upper layers of the multiple layer substrate and exposing an upper surface of a membrane portion, a lower acoustic port formed through a plurality of lower layers of the multiple layer substrate and exposing a lower surface of the membrane portion, a ring trench formed through at least one of the plurality of upper layers and exposing a metal ring, a MEMS die located above the ring trench, a copper pillar ring extending between the metal ring and the MEMS die, and a solder pillar ring positioned on a first surface of the copper pillar ring, the copper pillar ring and solder pillar ring attaching the MEMS die to the metal ring.

FIELD OF THE DISCLOSURE

The present disclosure relates to microphones and in particular to MEMS microphones.

BACKGROUND

A MEMS device (micro-electro-mechanical system) is a miniaturized device which integrates mechanical and electrical functions in a chip or die of semiconductor material, for example of silicon. MEMS devices offer many advantages including miniaturization, and low manufacturing costs. These advantages are realized using micro-manufacturing lithographic techniques. The final assembled device is typically made of the silicon die wherein the MEMS device is integrated and, optionally, of integrated circuits for specific applications mounted on a substrate using conventional assembling processes.

A cover or cap, fixed to the substrate is typically formed by overmolding the MEMS device and any other devices mounted on the substrate, forming a casing which protects the MEMS device against external physical stresses.

Many types of sensors can be produced in a MEMS platform. One such sensor is a microphone. Many applications incorporate MEMS microphones including cellular telephones, laptops, etc. The attraction of MEMS microphones is the ability to provide a lightweight and small form factor microphone. Because of the low manufacturing costs and small footprint, MEMS microphones are increasingly replacing electric condenser microphones (ECMs). Additionally, a MEMS microphone has an inherent advantage of low power consumption (160 μA), which is approximately ⅓ of that of the ECM. For mobile phone and laptop applications with limited power storing capacity, the power savings available using MEMS microphones is significant.

One limitation of known MEMS microphones, however, is their susceptibility to damage from moisture. For example, in order to function properly, the sensor portion of the MEMS microphone must be configured to react to sound waves. By providing access for sound waves, however, an access is also provided for moisture.

What is needed, therefore, is MEMS microphone which provides protection to the sensor area against moisture. A need also exists for a MEMS microphone which provides a defined front volume that is compatible with epoxy overmold processes such as are common to standard semiconductor packages

SUMMARY

In one embodiment a micro-electro-mechanical system (MEMS) microphone package includes a multiple layer substrate, an upper acoustic port formed through a plurality of upper layers of the multiple layer substrate and exposing an upper surface of a membrane portion, a lower acoustic port formed through a plurality of lower layers of the multiple layer substrate and exposing a lower surface of the membrane portion, a ring trench formed through at least one of the plurality of upper layers and exposing a metal ring, a MEMS die located above the ring trench, a copper pillar ring extending between the metal ring on the substrate and the MEMS die, and a solder pillar ring positioned on a first surface of the copper pillar ring, the copper pillar ring and solder pillar ring attaching the MEMS die to the metal ring located on the substrate.

In one or more embodiments the membrane portion comprises a water resistant membrane portion.

In one or more embodiments the first surface is a lower surface of the copper pillar ring.

In one or more embodiments a MEMS microphone package includes a back cavity defined within the MEMS die and enclosed on an upper end portion by a cap positioned on an upper surface of the MEMS die.

In one or more embodiments the plurality of upper layers includes a first upper metal layer and an upper solder mask on an upper surface of the first upper metal layer, and a plastic overmold is positioned on an upper surface of the upper solder mask encasing the MEMS die.

In one or more embodiments the plastic overmold extends within the ring trench but does not pass beyond the copper seal ring connecting the MEMs die and substrate.

In one or more embodiments a MEMS microphone package includes at least one well extending through the upper solder mask, and at least one input/output post extending downwardly from the MEMS die into that well, the input/output post including an upper copper post portion soldered within the corresponding well using a solder post portion positioned on a lower surface of the upper copper post portion.

In one or more embodiments the plurality of upper layers comprises a middle Pre-preg organic layer, and a lower metal layer, the middle Pre-preg organic layer is located between the upper metal layer and the lower metal layer, a respective contact pad formed in the upper metal layer is located within each the described wells, and the corresponding input/output post is soldered to the respective contact pad located in the well.

In one or more embodiments a MEMS microphone package includes a metal acoustic seal ring positioned in the lower acoustic port.

In one or more embodiments a method of forming a MEMS microphone package includes forming an upper acoustic port through a plurality of upper layers of a multiple layer substrate to expose an upper surface of a membrane portion, forming a lower acoustic port through a plurality of lower layers of the multiple layer substrate to expose a lower surface of the membrane portion, forming a ring trench through at least one of the plurality of upper Pre-preg layers to expose a metal ring, positioning a MEMS die above the ring trench, and attaching the MEMS die to the metal ring using a copper pillar ring extending between the metal ring and the MEMS die, and using a solder pillar ring positioned on a first surface of the copper pillar ring.

In one or more embodiments forming the upper acoustic port includes forming the upper acoustic port through the plurality of upper layers of the multiple layer substrate to expose an upper surface of a water resistant membrane portion.

In one or more embodiments the method of forming a MEMS microphone package includes inserting the solder pillar ring into the ring trench, and reflowing the solder pillar ring.

In one or more embodiments the method of forming a MEMS microphone package includes defining a back cavity within the MEMS die, and enclosing an upper end portion of the back cavity with a cap.

In one or more embodiments the method of forming a MEMS microphone package includes providing the multiple layer substrate with a first upper metal layer and an upper solder mask on an upper surface of the first upper metal layer, and forming a plastic overmold on an upper surface of the upper solder mask thereby encasing the MEMS die.

In one or more embodiments forming the plastic overmold includes flowing the plastic overmold within the ring trench up to but not beyond the copper seal ring connecting the MEMs device to the substrate.

In one or more embodiments the method of forming a MEMS microphone package includes forming at least one well through the upper solder mask, and positioning at least one input/output post extending downwardly from the MEMS die into the described well, the described input/output post including an upper copper post portion and a lower solder post portion, and reflowing the lower solder post portion within the described well.

In one or more embodiments the method of forming a MEMS microphone package includes forming at least one pad within the upper metal layer, wherein forming the at least one well includes exposing the at least one pad.

In one or more embodiments providing the multiple layer substrate further includes providing a multiple layer substrate with a middle Pre-preg organic layer, and a lower metal layer, the middle Pre-preg organic layer located between the upper metal layer and the lower metal layer.

In one or more embodiments forming a lower acoustic port includes exposing a metal acoustic seal ring positioned on a lower pre-preg organic layer.

DESCRIPTION

FIG. 1depicts a MEMS microphone assembly100. The MEMS microphone assembly100includes a MEMS die102supported on a water resistant substrate104and encased in a plastic overmold106. A cap108is positioned over a back-cavity110of the MEMS die102. The MEMS die102further includes a downwardly extending copper pillar ring112shown in additional detail inFIGS. 2-5. At a lower distal end of the copper pillar ring112a solder pillar ring114is provided on a lower surface of the copper pillar ring112. In some embodiments, the solder pillar ring is positioned at an upper surface of the copper pillar ring. The solder pillar ring114is used to attach the MEMS die102to the substrate104as discussed in further detail below.

The MEMS die102further includes four I/O posts116,118,120, and122. Each of the I/O posts116,118,120, and122includes an upper copper post126,128,130, and132and a lower solder post136,138,140, and142. The I/O posts116,118,120, and122provide for electrical connection points between the MEMS die102and the substrate104. In different embodiments, more or fewer I/O posts are included.

Returning toFIG. 1, above the water resistant membrane160, a pair of metal layers166and168sandwich an upper Pre-preg organic layer170. An upper solder mask layer172is located on the upper surface of the metal layer168. Each of the upper layers172,166,168and170are perforated to form an upper acoustic port174which terminates at the water resistant membrane160. The upper acoustic port174is aligned with the lower acoustic port158.

With reference toFIG. 7, four wells180,182,184, and186are formed through the upper solder mask layer172to expose portions of I/O pads188,190,192, and194formed in the metal layer168. A ring trench196is also formed through the upper solder mask layer172and the metal layer168to expose a ring of the Pre-preg organic layer170and form a metal ring171.

Fabrication of the MEMS microphone assembly100is substantially accomplished using any desired fabrication processes. For example, electrical connections for the I/O pads164and the I/O pads188,190,192, and194can be provided within the substrate104by the drilling of vias that are then filled with conductive epoxy or lined and plated using standard PCB via plating techniques. Likewise, the layers of the substrate104are sandwiched using any desired process. In at least one embodiment, however, the substrate104includes the water resistant membrane160. The water resistant membrane160is an acoustically transparent breathable material which restricts the passage of moisture therethrough. In one embodiment, the water resistant membrane160is formed from Polytetrafluoroethylene (PTFE). Accordingly, fluid is hindered from moving into the MEMS die102through the acoustic ports158and174.

One difference from known devices is the formation of the metal ring171using the ring trench196through the upper solder mask layer172and the metal layer168. The ring171is configured to attach to the copper pillar ring112using the solder pillar ring114as depicted inFIG. 1during a flip-chip assembly process. The copper pillar ring112and solder pillar ring114are formed, for example, using a modification of a process described in U.S. Pat. No. 6,681,982 which issued on Jan. 27, 2004. The modified '982 patent process is used in one embodiment to form the copper pillar ring112with a 80 μm height while the solder pillar ring114has a 20 μm height. The copper pillar ring112and the solder pillar ring114both have a 75 μm diameter. The I/O posts116,118,120, and122are each formed in like manner to the copper pillar ring112and solder pillar ring114.

Accordingly, when the MEMS die102is positioned on the substrate104during the flip-chip process, the lower solder posts136,138,140, and142are positioned through the respective wells180,182,184, and186and into contact with the respective I/O pad188,190,192, and194. Additionally, the solder pillar ring114is positioned through the ring trench196and into contact with the ring171. The lower solder posts136,138,140, and142are then connected to the respective I/O pad188,190,192, and194using a reflow process. The solder pillar ring114is also connected to the ring171during the reflow process. The copper pillar ring112thus forms the microphone front volume in the finished assembly.

The cap108is then positioned on the upper end of the MEMS die102(seeFIG. 1) and the plastic overmold is overmolded onto the MEMS die102and the upper solder mask layer172. In some embodiments, the ring trench196is sufficiently larger than the copper pillar ring112so as to allow some of the plastic overmold106to flow into the well to provide increased bonding as depicted inFIG. 1.

The MEMS microphone assembly100thus provides a water proof seal between the MEMS die and the substrate, which may further include a water proof membrane integrated into a substrate such that an acoustic port that is water proof/resistant may be implemented at the package level. This is achieved by bonding two substrate cores that have pre-drilled acoustic port holes over a water proof breathable membrane. In some embodiments, the water proof breathable membrane is provided in the form of an insert.

By way of example,FIG. 8depicts a substrate198which is used in the MEMS microphone assembly100in place of the substrate104. The substrate198is a multiple layer substrate. The bottom layer of the substrate198is a solder mask layer200. A metal layer202is located on an upper surface of the solder mask layer200. A Pre-preg organic layer204is located between the metal layer202and another metal layer206. Each of the layers200,202,204, and206are perforated to form a lower acoustic port208which terminates at a water resistant membrane210. The opening in the solder mask layer200and the metal layer202are larger than the openings in the other layers204and206to allow for a metal acoustic seal ring (pad)212located on the lower surface of the Pre-preg organic layer204.

Above the water resistant membrane210, a pair of metal layers216and218sandwich an upper Pre-preg organic layer220. An upper solder mask layer222is located on the upper surface of the metal layer218. Each of the layers216,218,220and222are perforated to form an upper acoustic port224which terminates at the water resistant membrane210. The upper acoustic port224is aligned with the lower acoustic port208. A ring trench226is formed through the upper solder mask layer222to expose a metal ring227, and wells, vias, and I/O ports (not shown) are also provided. The substrate198is thus substantially the same as the substrate104, and is assembled to the MEMS die102in like manner as the substrate104. The main difference is that instead of a membrane layer, the water resistant membrane210is formed as an insert within a substrate core228.

Both lower substrates allow for the provision of electrical connection between the top and bottom substrates in any desired manner such as by laser or mechanical drilling of vias that are then filled with conductive epoxy or lined and plated using standard PCB via plating techniques. The MEMS microphone assembly100further incorporates a copper pillar ring plated onto the MEMs die forms. This ring forms a barrier for subsequent processes when the die has been bonded to the substrate/chip carrier. Specifically, the ring forms an epoxy barrier during overmold processing of the microphone assembly.

The MEMS microphone assembly100thus provides a new semiconductor package form factor that incorporates wafer proof/resistant characteristics and allows for overmolded package construction. The package design in some embodiments further addresses a need for integrating a water-proof membrane into the porthole of a MEMs microphone package to prevent moisture damage. Additionally, the MEMS microphone assembly100provides a method for using a copper pillar seal ring to create a defined front volume that is compatible with epoxy overmold processes that are common to standard semiconductor packages.