Patent Grant
11082774
Micro-electromechanical system (“MEMS”) microphone packages include an acoustic port for acoustic waves to enter the package housing where they cause deflections (e.g. vibrations) of a membrane. These deflections cause variations in an electrical signal output of the microphone package indicative of the acoustic wave. In some MEMS microphone packages, the package housing might be at least partially sealed for performance or environmental purposes.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
Methods and systems are described in this disclosure for verification of an environmental seal provided by an encapsulant coating of a bottom-ported MEMS microphone package. A purposeful acoustic leak is provided on an upper surface of a package housing and a sealing material is applied to an outer surface of the package housing. A properly applied encapsulant coating will completely seal the purposeful acoustic leak on the upper surface of the package housing. However, the placement of the purposeful acoustic leak on the upper surface of the package housing will have a significant, detectable effect on the acoustic frequency response of the microphone if it is not completely sealed by the encapsulant coating. Accordingly, the environmental seal provided by the encapsulant coating is verified by confirming, based on the acoustic frequency response testing, that the encapsulant coating has effectively sealed the purposeful acoustic leak on the upper surface of the package housing.
In some implementations, this disclosure provides a method of verifying the environmental seal provided by an encapsulant coating applied to a MEMS microphone package by testing the acoustic frequency response to confirm that the encapsulant coating has effectively sealed the purposeful acoustic leak on the upper surface of the package housing. In other implementations, the disclosure provides an electronic device including a bottom-ported MEMS microphone package coupled to a printed circuit board (PCB) and sealed with an encapsulant coating, wherein the bottom-ported MEMS microphone package includes an additional acoustic port formed in an upper surface of a package housing of the MEMS microphone package. The environmental seal provided by the encapsulant coating can be verified by analyzing the frequency response of the bottom-ported microphone package to determine whether the additional acoustic port provides an acoustic leak.
The MEMS microphone package 103 of the device 101 is communicatively coupled to a test system 113 through an audio output component (e.g., additional printed circuit board component 109) configured to output an electrical signal indicative of mechanical deflections/vibrations of the MEMS microphone membrane 105. Alternatively, in some implementations, the electrical output signal may be provided to the test system 113 through the device controller 111 or the test system 113 might be directly coupled to the MEMS microphone package 103 to receive the electrical output signal.
The test system 113 includes a test system controller 115 that is communicatively coupled to a test system memory 117. The test system memory 117 is a non-transitory, computer readable memory configured to store computer-executable instructions that are accessed and executed by the test system controller 115. The test system controller 115 includes, for example, an electronic processor configured to execute the computer-executable instructions from the test system memory 117. The test system controller 115 is also configured to receive the electrical output signal from the MEMS microphone package 103 and to analyze the electrical output signal including, for example, performing an acoustic frequency response testing. In some implementations where the electrical output signal from the MEMS microphone package 103 is received by the test system 113 as an analog signal, the test system controller 115 may also include an analog-to-digital converter to convert the analog electrical output signal into digital data that is then analyzed by the electronic processor of the test system controller 115. In other implementations, the test system 113 includes a separate analog-to-digital converter (not pictured) configured to receive the analog electrical output signal from the MEMS microphone package 103, convert the analog electrical output signal to a digital output signal, and provide the digital output signal to the test system controller 115.
In still other implementations, the test system controller 115 include a signal comparator configured to receive the electrical output signal from the MEMS microphone package 103 and a reference signal (e.g., from a reference signal generator (not pictured)), and to generate an output indicative of a difference between the electrical output signal from the MEMS microphone package 103 and the reference signal.
In the example of
In some implementations, the test system 113 also includes a test system user interface 123 including, for example, a display screen and a user input device (e.g., a touch-screen display, a keyboard, a mouse, etc.). In some implementations, the test system controller 115 is configured to initiate and control a testing routine (e.g., acoustic frequency response testing) based on a user input received through the test system user interface 123. The test system controller 115 may also be configured to cause the test system user interface 123 to display output information (e.g., graphically or textually) indicative of the results of the testing procedure performed on the device 101. For example, the test system 113 may be configured to output on the test system user interface 123 a graph of the acoustic frequency response of the MEMS microphone package 103 of the device 101 and/or an indicative of whether the MEMS microphone package 103 of the device 101 has passed a particular testing routine (e.g., whether the acoustic frequency response testing has verified the application of an encapsulant seal to the MEMS microphone package 103 as described in further detail below).
In some implementations, the device 101 may be designed and configured to position the MEMS microphone package 103 on or at a superficial boundary of the device 101 (i.e., an outer layer of environmental exposure). This placement of the MEMS microphone package 103 reduces length/distance of the acoustic path within the device 101 and thereby reduces undesirable acoustic resonances. This preserves a flat, wide-band acoustic sensitivity of the MEMS microphone package 103 that is beneficial, for example, for speech recognition and noise cancellation applications. However, placement of the MEMS microphone package 103 as close as possible to an exposed outer surface of the device 101 seemingly conflicts with the need to protect the MEMS microphone from environmental factors such as, for example, water ingress. Such remote mounting requirements make it difficult for the superficial boundary of the device 101 to protect the body of the MEMS microphone package 103 and any peripheral electrical components (e.g., additional printed circuit board component(s) 109) from environmental exposure. And so, in some implementations, this protection is provided instead, by applying a sealing material to an exterior surface of the MEMS microphone package 103 to encapsulate the MEMS microphone package 103 in a protective encapsulant.
The MEMS microphone package 103 is communicatively coupled to other electrical components on the printed circuit board 201 (e.g., additional printed circuit board component 109) by one or more solder bond points 215 coupling electrical circuit output pads of the MEMS microphone package 103 to printed electrical traces on the printed circuit board 201 that extend to electrical contact pins of the other electrical components on the printed circuit board 201.
An additional acoustic port 217 is also formed in the cap 205 on an upper surface of the package housing of the bottom-ported MEMS microphone package 103. As discussed in further detail below, the additional acoustic port 217 is a purposeful acoustic leak that is incorporated in the structure of the bottom ported MEMS microphone package 103 for verification testing of an environmental seal. In some implementations, the cap 205 is formed of a continuous solid barrier of sheet metal and serves as the “back-side” acoustic enclosure that tightly establishes the back-volume for the MEMS microphone membrane 105. Accordingly, the creation of the purposeful acoustic leak provided by the additional acoustic port 217 in the package housing will significantly degrade the sensitivity response of the MEMS microphone membrane 105. An example of a purposeful acoustic leak provided by an additional acoustic port 217 formed in the cap 205 portion of the package housing is also illustrated in
As illustrated in
In some implementations (such as in the example of
For example,
As demonstrated by the graph of
In some implementations, the sealing material 251 is selected based on its viscosity, thixotropic, and/or surface tension properties as well as the surface energy properties of the package housing of the MEMS microphone package 103 and the printed circuit board 201 to ensure appropriate coverage and sealing coupling. Furthermore, in some implementations, the sealing material 251 and the size of the additional acoustic port 217 are selected to ensure that the sealing material 251 will cover the additional acoustic port 217 without fully penetrating the additional acoustic port 217. Accordingly, the viscosity, thixotropic, and/or surface tension properties can be leveraged to ensure that the sealing material does not partially or entirely fill the internal volume of the MEMS microphone package 103 when it is deposited as the conformal encapsulant.
Furthermore, in some implementations, the properties of the sealing material can be selectively tuned during the dispensing process. For example, the viscosity of the sealing material can be regulated or changed by controlling or adjusting a temperature of the sealing material (e.g., using heating elements incorporated into the dispensing system). Additionally or alternatively, the thixotropic properties of the sealing material can be regulated by applying a vibrational force to the sealing material prior to or during the dispensing process. In some implementations, the sealing material 251 is a two-part epoxy. However, in other implementations, the sealing material may include other types of material including, for example, silicone or putty.
As discussed above, the performance of a MEMS microphone can be improved by more closely positioning the MEMS microphone on or at an exterior of the electronic device. For electronic devices in which an environmental seal is necessary (e.g., “ruggedized” and/or waterproof electronic devices), the environmental seal provided by the encapsulant 251 to the bottom-ported MEMS microphone package 103 allows the bottom-ported MEMS microphone package 103 to be positioned external to a sealed interior volume of the electronic device 101.
In the example of
For example, an audio output of the device may be selectively coupled to an audio input of a test system 113 (as illustrated in
In some implementations, the reference signal is indicative of a frequency response of a microphone package that does not have an additional acoustic port 217 formed in the package housing (or a microphone package where the additional acoustic port 217 has been sealed by the encapsulant). In some such implementations, the test system 113 verifies the applied encapsulant coating (i.e., the device passes the test) if the electrical output signal received by the test system 113 from the MEMS microphone package 103 matches the reference signal (or one or more particular metrics of the reference signal) within a defined tolerance threshold. Conversely, the device under test has “failed” the test (indicating an incomplete or otherwise flawed encapsulant coating) when the difference between the electric output signal and the reference signal exceeds the defined tolerance threshold.
Additionally or alternatively, in some implementations, the reference signal is indicative of the frequency response of a MEMS microphone package where the additional acoustic port 217 is not sealed by an encapsulant coating. In some such implementations, the test system 113 is configured to determine that the encapsulant coating of the device under test has “failed” the test if the electrical output signal received by the test system 113 from the MEMS microphone package 103 matches the reference signal (or one or more particular metrics of the reference signal) within a defined tolerance threshold. Accordingly, the environmental seal of the microphone package is verified by the test system if the test is not failed (i.e., when a difference between the electrical output signal and the reference signal exceeds the defined tolerance threshold).
If the device 101 passes the frequency response testing (step 409), then the test system 113 is able to confirm that the encapsulant sealing has been applied to the MEMS microphone package 103 effectively (step 411). If the device 101 does not pass the frequency response testing (step 409), then the test system 113 indicates a failure of the encapsulant seal (step 413).
Although the examples described above discuss primarily a frequency response-based testing procedure, in some implementations, other types of verification testing may be performed on the device and/or the MEMS microphone package in addition to or instead of a frequency response-based test. For example, it may be desirable to perform other tests on the MEMS microphone package to verify other aspects of the microphone performance before the MEMS microphone package is mounted to the printed circuit board. In some such implementations, the presence of the additional acoustic port 217 on the package housing may also negatively affect the results of those other tests. Accordingly, in some implementations, a temporary seal is applied to the package housing to seal the additional acoustic port 217. This temporary seal is then removed before the sealing material is dispensed to form the conformal encapsulant coating.
Returning now to the example of
As discussed above, the installation and configuration of the MEMS microphone package 103 as illustrated in the example of
Accordingly, the systems and methods described in the examples of this disclosure provide a process for applying an environmental seal to a back-side of a MEMS microphone package, a MEMS microphone package that is specifically designed for a testing procedure to verify the proper application of the back-side environmental seal, and a method for testing a device to verify the proper application of a back-side environmental seal to a MEMS microphone package.
In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings.
The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “has,” “having,” “includes,” “including,” “contains,” “containing” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a,” “has . . . a,” “includes . . . a,” or “contains . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially,” “essentially,” “approximately,” “about” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1% and in another embodiment within 0.5%. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed.
It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or “processing devices”) such as microprocessors, digital signal processors, customized processors and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the method and/or apparatus described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used.
Moreover, an embodiment can be implemented as a computer-readable storage medium having computer readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory) and a Flash memory. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.
The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.
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| Number | Date | Country | |
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| 20210195341 A1 | Jun 2021 | US |
