Patent Application
20150041931
This application relates to acoustic devices and, more specifically, to protecting these devices from pressure and vacuum transients.
Different types of acoustic devices have been used through the years. One type of device is a microphone. In a microelectromechanical system (MEMS) microphone, a MEMS die includes a diagram and a back plate. The MEMS die is supported by a substrate and enclosed by a housing (e.g., a metal can or cover with walls). A sound inlet or acoustic port may extend through the substrate (for a bottom port device) or through the top of the housing (for a top port device). In any case, sound energy traverses through the port, moves the diaphragm and creates a changing potential of the back plate, which creates an electrical signal. Microphones are deployed in various types of devices such as personal computers or cellular phones.
MEMS microphones are susceptible to diaphragm and back plate damage when the microphone port is subjected to transient variations in pressure or vacuum. In particular, pressures during drop testing can generate pressure impulses on an order of approximately 100-1000 psi. Such high pressures exceed the mechanical strength of typical back plate and diaphragm structures resulting in the catastrophe failures of these devices. Previous attempts at solving this problem have not been successful leading to user dissatisfaction with previous approaches.
For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein:
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.
Approaches are provided that protect microphones from pressure or vacuum differentials (transients) that occur between the interior of the microphone and the exterior of the microphone. The approaches provided are scalable and cost effective to implement, and are effective at negating the potential consequences of pressure transients in MEMS devices. In one example, pressure or vacuum transients of approximately 760 to 25 Torr will cause the embedded diaphragm to seal the port of the microphone and thereby prevent damage from occurring to the microphone as a result of a pressure or vacuum transient.
In one aspect, the approaches provided herein utilize a diaphragm (e.g., a metal or polymer sheet) which is approximately 0.5 mil (or thinner) and that is embedded within printed circuit board (PCB) layers of the substrate or base of the microphone. This configuration forms a diaphragm, with passage(s) along the perimeter, in the direct sound path of the acoustic port. This embedded diaphragm is, in fact, a second diaphragm that is deployed in addition to the diaphragm associated with a MEMS device (that is internal to the microphone and associated with the MEMS device of the microphone).
The embedded diaphragm is either tensioned or simply supported such that when it deflects in the presence of a pressure pulse or vacuum pulse (e.g., 100 to 1000 psi or 760 to 25 Torr, respectively), it makes contact with the outer surface of the acoustic port, thereby intermittently blocking flow through an acoustic port of the microphone (that under normal conditions would allow sound to enter from the exterior of the microphone to the interior of the microphone). One advantage of the present approaches is that they provide protection against both pressure and vacuum transients. Pressure and/or vacuum transients can result in MEMS back plate and diaphragm damage.
The embedded valve microphone has opening so that when a pressure transient does not occur, sound energy can move from the exterior of the microphone to the interior of the microphone. In one example, the embedded diaphragm has an opening that is generally a “C” shaped with one support provided. In yet another example, three openings and three supports are provided. Other types and shapes of openings may be provided in the embedded diaphragm.
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The base 102 is constructed of multiple layers of materials that form a printed circuit board (PCB). A first passivation layer 152 is disposed on the top of the base 102. A metal layer 154 is disposed under the layer 152. A first core 156, a first adhesive layer 158, a second core 160, a second adhesive layer 162, an embedded micro valve diaphragm 164 that is constructed of polyimide for example, a third adhesive layer 166, a third core 168, a fourth adhesive layer 170, a fourth core 172, a second metal layer 174, and a second passivation layer 176 form the substrate 102. It will be appreciated that this is one possible substrate configuration and that other configurations are possible. In other words, the number and types of layers may vary as long as one of the layers is an embedded micro valve diaphragm layer.
The first passivation layer 152 and the second passivation layer 176 are constructed of a material such as solder resist or other suitable polymer. The purpose of the first passivation layer 152 and the second passivation layer 176 are to protect against oxidation and to prevent solder bridging.
The metal layer 154 and the second metal layer 174 may be constructed of a metal such as ENIG plated copper. The purpose of the first metal layer 154 and the second metal layer 174 are to provide electrical pathways that are wire bondable and solderable.
The first core 156, second core 160, third core 168, and fourth core 172 are constructed of FR-4 material, although other materials such as BT epoxy or flexible polyimide may also be used. The purpose of the first core 156, second core 160, third core 168, and fourth core 172 are to electrically insulate metal layers and to provide structural support to the finished PCB.
The first adhesive layer 158, second adhesive layer 162, third adhesive layer 166, and fourth adhesive layer 170 are constructed of low flow thermoset resin or B-stage epoxy. The purpose of the first adhesive layer 158, second adhesive layer 162, third adhesive layer 166, and fourth adhesive layer 170 is to secure adjacent layers of the base 102 together.
In one aspect, the embedded micro valve diaphragm 164 is constructed of a thin metal or semi-rigid polymer sheet which is approximately 0.5 mil (or thinner), for example. Other dimensions and materials may also be used. The diaphragm 164 deflects upward in the direction of the arrow labeled 161 when the interior pressure is greater than the exterior pressure (the pressure transient) exceeds a predetermined value. The diaphragm 164 will deflect downward in the direction indicated by the arrow labeled 163 when the interior pressure is greater than the exterior pressure (the pressure transient) by a predetermined threshold. In either deflection, the diaphragm 164 blocks air flow through the port 110 from the exterior to the interior or from the interior to the exterior of the microphone. Pressure differentials of a predetermined value cause the diaphragm 164 to move (upward or downward depending upon the direction of the differential). When this pressure differential does not exist, then the diaphragm 164 no longer blocks the port 110 and sound reaches the MEMS device 106.
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Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.
This patent claims benefit under 35 U.S.C. § 119 (e) to United States Provisional Application No. 61864829 entitled “Embedded Micro valve in Microphone” filed Aug. 12, 2013, the content of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61864829 | Aug 2013 | US |
