MEMS Microphone Packaging Structure and Electronic Device

Abstract

The present invention discloses a MEMS microphone packaging structure and electronic device. The package structure includes: a packaging shell, the packaging shell including a cover and a PCB board, the cover being disposed on the PCB board, forming a cavity within the cover and the PCB board; a diaphragm assembly disposed within the cavity, the diaphragm assembly being flip-mounted on the PCB board, the diaphragm assembly including a vibrating membrane suspended above the PCB board, a back plate disposed on the PCB board opposite the vibrating membrane, the vibrating membrane and the back plate forming a capacitor, a guard electrode disposed on the PCB board, the guard electrode surrounding the back plate and spaced apart from the back plate; and an ASIC chip, the ASIC chip including a source follower, the back plate connected to the gate of the source follower, and the guard electrode connected to the source of the source follower.

Description

Technical Field

[0001] The present invention relates to the technical field of acoustic-electric conversion, and more particularly, to a MEMS microphone packaging structure and an electronic device. Background Art

[0002] A MEMS microphone packaging structure generally includes a packaging housing and a MEMS microphone chip and an ASIC chip disposed in the packaging housing. The MEMS microphone chip includes a substrate and a double-layer plate capacitor disposed on the substrate. Two electrode plates of the double-layer plate capacitor are connected to the ASIC chip. The MEMS microphone chip can be mounted on the packaging housing in a flip-chip or face-up manner and is electrically connected to other components through the packaging housing.

[0003] In some technical solutions, a double-layer plate capacitor is formed by a vibrating diaphragm and a metal layer on the PCB board of the packaging housing. In this technical solution, in order to ensure a high signal-to-noise ratio (SNR), the requirement for the leakage resistance of the PCB board is high. In view of factors such as possible moisture, contamination, and even increased leakage of the high-temperature end PCB board during the use of the packaging structure, such solutions either have a very low yield or have no guarantee of reliability, greatly limiting their application fields.

[0004] Therefore, a new technical solution is needed to solve the above technical problems. Summary of the Invention

[0005] An object of the present invention is to provide a new technical solution for a MEMS microphone packaging structure.

[0006] According to a first aspect of the present invention, there is provided a MEMS microphone packaging structure. The packaging structure includes: a packaging housing, the packaging housing including a cover body and a PCB board, the cover body being disposed on the PCB board, and a cavity being formed inside the cover body and the PCB board; a diaphragm assembly, the diaphragm assembly being disposed in the cavity, the diaphragm assembly being flip-chip mounted on the PCB board, the diaphragm assembly including a vibrating diaphragm, the vibrating diaphragm being suspended above the PCB board, a back plate being disposed at a position on the PCB board opposite to the vibrating diaphragm, the vibrating diaphragm and the back plate constituting a capacitor, a protection electrode being disposed on the PCB board, the protection electrode surrounding the back plate, the protection electrode being spaced apart from the back plate; and an ASIC chip, the ASIC chip including a source follower, the back plate being connected to the gate of the source follower, and the protection electrode being connected to the source of the source follower.

[0007] Optionally, the protection electrode is connected to the source of the source follower through a metal layer embedded in the PCB board.

[0008] Optionally, the protection electrode is connected to the metal layer through a metallized via, and the source of the source follower is connected to the metal layer through a metallized via.

[0009] Optionally, the diaphragm assembly includes a substrate and a conductive isolator. A back cavity is formed in the middle of the substrate. The vibrating diaphragm is disposed on the substrate, covering the back cavity. The conductive isolator is disposed on the substrate and / or the vibrating diaphragm, surrounding the back cavity. The conductive isolator is connected to the PCB board. The protection electrode is located inside the conductive isolator and is spaced apart from the conductive isolator.

[0010] Optionally, the conductive isolator is fixed on the corresponding metal pad of the PCB board by a thermosonic or eutectic bonding process.

[0011] Optionally, the protection electrode is located outside the projection area of the back cavity on the PCB board.

[0012] Optionally, the protection electrode is annular.

[0013] Optionally, the ASIC chip is located inside the cavity or embedded in the PCB board.

[0014] Optionally, the gap height between the back plate and the vibrating diaphragm is 5 μm - 10 μm.

[0015] According to another aspect of the present disclosure, there is provided an electronic device. The electronic device includes the above-mentioned MEMS microphone packaging structure.

[0016] According to an embodiment of the present disclosure, the back plate of the MEMS microphone chip, i.e., the high-impedance end, is connected to the gate of the source follower. The gate of the source follower (i.e., the G pole) serves as the input end of the ASIC chip. The high-impedance end and the source follower perform impedance conversion (for example, the unit gain is 0 dB). The source of the source follower (i.e., the S pole) connected to the protection electrode is the low-impedance end. Due to the function of the source follower, the back plate and the protection electrode are at the same potential. Therefore, by setting the protection electrode, the leakage path of the PCB board can be eliminated. That is, it is equivalent to the leakage resistance R of the PCB board PCB infinity.

[0017] In this way, the protection electrode can effectively protect the back plate, thereby avoiding the interference of the leakage current on the signal output of the back plate. This significantly improves the signal-to-noise ratio (SNR) of the MEMS microphone packaging structure.

[0018] Other features and advantages of the present invention will become clear from the following detailed description of the exemplary embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings incorporated in and forming a part of the specification illustrate embodiments of the present invention and, together with the description thereof, are used to explain the principles of the present invention.

[0020] Figure 1 It is a schematic structural diagram of a MEMS microphone packaging structure according to an embodiment of the present disclosure.

[0021] Figure 2 It is a partial schematic diagram of a PCB board according to an embodiment of the present disclosure.

[0022] Figure 3 It is a schematic diagram of a diaphragm assembly and a PCB board according to another embodiment of the present disclosure.

[0023] Figure 4 It is a circuit diagram of a MEMS microphone packaging structure according to an embodiment of the present disclosure.

[0024] Description of reference numerals:

[0025] 100, PCB board; 101, first pad; 102, second pad; 103, third pad; 106, protection electrode; 107, metallized via; 109, cover; 110, ground terminal; 111, fourth pad; 112, fifth pad; 113, bonding wire; 114, bonding ring; 115, welding ring; 200, ASIC chip; 201, input terminal; 202, output terminal; 203, bias voltage terminal; 204, source follower; 205, charge pump; 206, source; 300, diaphragm assembly; 301, vibrating membrane; 302, substrate; 303, back cavity; 304, conductive isolator; 305, protrusion; 306, fold; 307, back plate; 308, sound hole; 309, connection pad; 310, column. Detailed Description of the Invention

[0026] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions and values set forth in these embodiments do not limit the scope of the present invention.

[0027] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present invention, its application, or its use.

[0028] Techniques, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered as part of the specification.

[0029] In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments may have different values.

[0030] It should be noted that like reference numerals and letters denote like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.

[0031] According to an embodiment of the present disclosure, a MEMS microphone packaging structure is provided. As Figure 1 , Figure 4 shown. The packaging structure includes: a packaging housing, a diaphragm assembly 300, and an ASIC chip 200.

[0032] Specifically, the packaging housing includes a cover body 109 and a PCB board 100. The cover body 109 is disposed on the PCB board 100. A cavity is formed inside the cover body 109 and the PCB board 100. For example, the cover body 109 is a metal cover body 109 with one end open. The PCB board 100 is fixed at the open end by bonding, welding, etc.

[0033] Alternatively, the cover body 109 includes a PCB circuit board frame. The middle part of the PCB circuit board frame is a hollow structure. Two PCB boards 100 are respectively fixed at the two open ends of the circuit board frame. The packaging structure is a three-layer board structure.

[0034] The cavity inside the packaging structure is an acoustically sealed cavity to facilitate the entry of sound. Sound holes 308 are provided on the cover body 109 and / or the PCB board 100.

[0035] The diaphragm assembly 300 is disposed inside the cavity. The diaphragm assembly 300 is flip-chip mounted on the PCB board 100. The diaphragm assembly 300 includes a vibrating membrane 301. The vibrating membrane 301 is suspended above the PCB board 100. A back plate 307 is provided at a position on the PCB board 100 opposite to the vibrating membrane 301. The vibrating membrane 301 and the back plate 307 form a capacitor. A protection electrode 106 is provided on the PCB board 100. The protection electrode 106 is disposed around the back plate 307. The protection electrode 106 is spaced apart from the back plate 307.

[0036] The diaphragm assembly 300 and a part of the PCB board 100 together form a MEMS microphone chip.

[0037] The diaphragm 301 is arranged in parallel with the backplate 307 to serve as the two electrodes of the capacitor respectively. A gap is provided between the diaphragm 301 and the backplate 307 to allow the diaphragm 301 to vibrate. Flip-chip refers to the way of mounting the substrate 302 of the diaphragm assembly 300 facing away from the PCB board 100. The flip-chip method can reduce the gap between the diaphragm 301 and the backplate 307, so that the vibration sensitivity of the diaphragm 301 is higher than that of the right-side-up mounting method. The protection electrode 106 is made of a conductive material, for example, metal, semiconductor, etc. The protection electrode 106 and the backplate 307 are located on the same layer of the PCB board 100, such as the surface layer of the PCB board 100.

[0038] The ASIC chip 200 includes a source follower 204. The backplate 307 is connected to the gate (i.e., G pole) of the source follower. The protection electrode 106 is connected to the source (i.e., S pole) of the source follower 204. In this example, the output terminal Vout of the ASIC chip 200 is connected to the first pad 101 through a lead, for example. The first pad 101 is connected to the fifth pad 112 located outside the PCB board 100 through a metallized via 107. The low-impedance terminal 206 of the ASIC chip 200 is connected to the second pad 102 through a lead, for example. The second pad 102 is connected to the protection electrode 106. The input terminal 201 of the ASIC chip 200 is connected to the third pad 103 through a lead, for example. The third pad 103 is connected to the backplate 307. The bias voltage terminal Vmic203 of the ASIC chip 200 is connected to the fourth pad 111 through a lead, for example. The bias voltage Vmic is connected to the charge pump inside the ASIC chip. The fourth pad 111 is connected to the diaphragm 301.

[0039] In this example, as Figure 4 shown, the backplate 307 of the MEMS microphone chip, that is, the high-impedance terminal, is connected to the gate (i.e., G pole) of the source follower 204. The gate (i.e., G pole) of the source follower serves as the input terminal Vin of the ASIC chip 200. The high-impedance terminal performs impedance conversion with the source follower 204 (for example, the unit gain is 0 dB). The source (i.e., S pole) of the source follower 204 connected to the protection electrode 106 is the low-impedance terminal. Due to the function of the source follower 204, the backplate 307 and the protection electrode 106 are at the same potential. Therefore, by setting the protection electrode 106, the leakage path of the PCB board 100 can be eliminated. That is, it is equivalent to the leakage resistance R of the PCB board 100 PCB being infinite.

[0040] In this way, the protection electrode 106 can effectively protect the backplate 307, thereby avoiding the interference of the leakage current on the signal output of the backplate 307. This significantly improves the signal-to-noise ratio (SNR) of the MEMS microphone packaging structure.

[0041] In addition, since the protection electrode 106 is disposed around the back plate 307, the protection electrode 106 can shield the adverse effects of the parasitic capacitance on the bias voltage terminal 203, thereby ensuring the high sensitivity and high signal-to-noise ratio of the MEMS microphone packaging structure.

[0042] In one example, the protection electrode 106 is connected to the source 206 of the source follower 204 of the ASIC chip 200 through a metal layer embedded in the PCB board 100.

[0043] As Figure 1 shown, the metal layer is embedded inside the PCB board 100. Compared with the method of connecting the protection electrode 106 to the ASIC chip 200 through a metal wire, due to the shielding effect of the PCB board 100 in this example, the interference of external signals to the protection electrode 106 can be effectively avoided. In this way, the signal-to-noise ratio of the MEMS microphone packaging structure can be further improved.

[0044] In one example, the protection electrode 106 is connected to the metal layer through a metallized via 107. The source 206 of the source follower 204 is connected to the metal layer through a metallized via 107.

[0045] As Figure 1 shown, metallized vias 107 are provided at positions corresponding to the protection electrode 106 on the PCB board 100. Metallized vias 107 are provided at positions corresponding to the second pad 102 on the PCB board 100. The lower ends of the two metallized vias 107 are both connected to the metal layer. In this way, the conductors for connecting the protection electrode 106 and the second pad 102 are all located inside the PCB board 100, which enables the protection electrode 106 to be more effective in resisting electromagnetic signal interference.

[0046] In one example, as Figure 1 shown, the diaphragm assembly 300 includes a substrate 302 and a conductive isolator 304. A back cavity 303 is formed in the middle of the substrate 302. The vibrating diaphragm 301 is disposed on the substrate 302. The vibrating diaphragm 301 covers the back cavity 303. The conductive isolator 304 is disposed on the substrate 302 and / or the vibrating diaphragm 301. The conductive isolator 304 is disposed around the back cavity 303. The conductive isolator 304 is connected to the PCB board 100. The protection electrode 106 is located inside the conductive isolator 304. The protection electrode 106 is spaced apart from the conductive isolator 304.

[0047] As Figure 1As shown, for example, the material of the substrate 302 is silicon, silicon nitride, silicon carbide, etc. An acoustic back cavity 303 is formed in the middle of the substrate 302 by etching. The vibrating diaphragm 301 is disposed opposite to the acoustic back cavity 303. Sound holes 308 are provided on the PCB. The sound holes 308 penetrate through the back electrode plate 307. For example, there are multiple sound holes 308. The multiple sound holes 308 are all disposed opposite to the acoustic back cavity 303.

[0048] The conductive isolator 304 has an annular structure. The conductive isolator 304 can conduct electricity. For example, the conductive isolator 304 is made of materials such as metal and polysilicon. The vibrating diaphragm 301 is connected to the fourth pad 111 through the conductive isolator 304 to output an electrical signal to the ASIC chip 200. In this example, the conductive isolator 304 is disposed around the outer edge of the vibrating diaphragm 301. In other examples, the conductive isolator 304 can also cover the vibrating diaphragm 301 or cover both the vibrating diaphragm 301 and the substrate 302.

[0049] The height of the conductive isolator 304 determines the height of the gap between the vibrating diaphragm 301 and the back electrode plate 307. The conductive isolator 304 is fixed on the PCB board 100 by bonding. As Figure 2 shown, a bonding ring 114 is provided on the PCB board 100, and the conductive isolator 304 is fixed on the bonding ring 114 through a bonding wire 113. The bonding wire 113 and the bonding ring 114 are both made of metal, and a metallized via 107 is provided under the bonding ring 114, so as to realize the transmission of the electrical signal of the vibrating diaphragm 301.

[0050] In addition, connection pads 309 are also provided on the PCB board 100. For example, there are four connection pads 309, and the four connection pads 309 correspond to the four corners of the diaphragm assembly. The overall diaphragm assembly 300 is in a cuboid shape. A column 310 is provided at each of the four corners of the side of the diaphragm assembly 300 facing the PCB board 100. The height of the column 310 is the same as the height of the conductive isolator 304. The column 310 can also play a role in conduction. The formation method of the column 310 is as described below. The connection between the column 310 and the connection pad 309 can increase the connection strength between the diaphragm assembly and the PCB board 100. The four columns 310 can make the positioning of the diaphragm assembly 300 on the PCB board 100 accurate and ensure that the gap height between the vibrating diaphragm 301 and the back electrode plate 307 is consistent.

[0051] The protection electrode 106 is annular. The protection electrode 106 is located inside the conductive isolator 304 and is spaced from the conductive isolator 304. The annular protection electrode 106 can save the space of the PCB board 100.

[0052] In one example, the conductive isolator 304 is fixed on the corresponding metal pad of the PCB board 100 by thermosonic or eutectic bonding process.

[0053] The conductive isolation layer 304 can be a conductive metal and alloy composite layer with a set thickness (for example, an annular electroplated gold (Au) layer with a thickness of 5 μm to 20 μm). The conductive isolation layer 304 is bonded to the corresponding metal pads on the PCB board 100 by using a thermalsonic or eutectic bonding process, so that the diaphragm assembly 300 is flip-chip mounted on the PCB board 100. In this case, since the conductive isolation layer 304 is an annular narrow metal-alloy ring, the parasitic capacitance of the MEMS microphone chip can be minimized and the manufacturing cost can be further reduced.

[0054] In addition, the diaphragm assembly 300 can further include a protrusion 305 formed by protruding outward from the vibrating diaphragm 301. The protrusion 305 can prevent the vibrating diaphragm 301 from adhering to the backplate 307.

[0055] In addition, the column 310 and the corresponding connection pad 309 can also be fixed together by a thermalsonic or eutectic bonding process.

[0056] In one example, an annular fold 306 is provided at the edge of the vibrating diaphragm 301. The ratio of the depth of the fold 306 to the thickness of the vibrating diaphragm 301 (i.e., the depth-to-thickness ratio) is greater than or equal to 5:1, and the wall of the fold 306 is inclined at an angle within the range of 80° to 100° with respect to the surface of the vibrating diaphragm 301. The annular fold 306 is one or a plurality of concentrically arranged ones.

[0057] Since the performance of the sensitivity of the MEMS microphone chip with the vibrating diaphragm 301 having folds 306 with a high depth-to-thickness ratio is not sensitive to the initial stress of the vibrating diaphragm 301, consistent and optimal sensitivity can be obtained in this example, and thus the reproducibility and reliability can be improved.

[0058] In one example, the protection electrode 106 is located outside the projection area of the back cavity 303 on the PCB board 100.

[0059] As Figure 2 shown, the dashed line is the projection of the edge of the back cavity 303 on the PCB board 100. The annular protection electrode 106 is located outside this projection. In this way, the formation of parasitic capacitance between the protection electrode 106 and the vibrating diaphragm 301 can be reduced or even avoided.

[0060] In one example, the ASIC chip 200 is located inside the cavity or embedded in the PCB board 100.

[0061] As Figure 1 shown, the ASIC chip 200 is located inside the cavity. The processing technology in this way is simple and the yield is high.

[0062] As shown Figure 3 in FIG. 1, the ASIC chip 200 is embedded in the PCB board 100. In this example, the PCB board 100 can effectively shield the interference of external electromagnetic waves to the ASIC chip 200.

[0063] In one example, the gap height between the back plate 307 and the vibrating diaphragm 301 is 5 μm - 10 μm. Within this range, the MEMS microphone chip has high sensitivity.

[0064] The height of the gap is controlled by the conductive spacer 304. The conductive spacer 304 is a metal material or a composite material of metal and non-metal. When it is a composite material, the metal layer is attached to the surface of the non-metal substrate so that the conductive spacer 304 can conduct electricity.

[0065] For example, during preparation, first, materials (such as SiO2, Si3N4, PolySi, PSG, BPSG, SOG, BCB, PBO, PI, SU8, PMMA, photoresist, etc.) are raised to the required height by using metal stacks or other common MEMS processes to form the conductive spacer 304.

[0066] Then, the metal layer (such as Au, Cu, Al, etc.) on the surface of the conductive spacer is bonded to the metal on the PCB board, such as Au - Au thermosonic bonding.

[0067] In this way, the conductive spacer 304 can precisely control the gap height and can play a role in conducting electricity to realize the electrical connection between the vibrating diaphragm 301 and the bias voltage terminal 203Vmic of the ASIC chip. As Figure 4 shown in FIG. 2, the bias voltage terminal 203Vmic is electrically connected to the charge pump built in the ASIC chip. The charge pump is used to provide a bias voltage to the MEMS microphone chip.

[0068] In other examples, it can also be that the solder (such as solder paste) is heated, and the molten solder flows laterally under the drive of surface tension and wets the pads of the large-area vibrating diaphragm assembly 310, so that the inverted vibrating diaphragm assembly 300 is set at a preset and fixed height of the column 310 position and a limiting mechanism is formed to realize the set gap height.

[0069] The above methods can all control the height of the gap within the above range.

[0070] In other examples, the gap height is 10 μm - 50 μm. Within this range, the MEMS microphone chip also has high sensitivity.

[0071] According to another embodiment of the present disclosure, an electronic device is provided. The electronic device includes the above-mentioned MEMS microphone packaging structure.

[0072] For example, the electronic device may be, but is not limited to, a mobile phone, a tablet computer, a smart speaker, a smart display, a laptop computer, a telephone, a walkie-talkie, a smart watch, a smart bracelet, headphones, a VR device, an AR device, etc.

[0073] The electronic device has the characteristics of excellent sound pickup effect.

[0074] In the above embodiments, the differences between the embodiments are mainly described. As long as the different optimization features between the embodiments are not contradictory, they can be combined to form a better embodiment. For the sake of brevity, they will not be elaborated here.

[0075] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and not for limiting the scope of the present invention. Those skilled in the art should understand that the above embodiments can be modified without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A MEMS microphone packaging structure, characterized in that, include: A packaging shell, the packaging shell comprising a cover and a PCB board, the cover being disposed on the PCB board, and a cavity being formed inside the cover and the PCB board; A diaphragm assembly is disposed in the cavity and is inverted on the PCB. The diaphragm assembly includes a diaphragm, the diaphragm is suspended above the PCB, a back plate is disposed on the PCB at a position opposite to the diaphragm, the diaphragm and the back plate form a capacitor, and a protective electrode is disposed on the PCB, the protective electrode is disposed around the back plate, and the protective electrode is spaced apart from the back plate. as well as The ASIC chip includes a source follower, the back plate is connected to the gate of the source follower, and the protection electrode is connected to the source of the source follower.

2. The MEMS microphone packaging structure according to claim 1, wherein: The protection electrode is connected to the source of the source follower through a metal layer embedded in the PCB board.

3. The MEMS microphone packaging structure according to claim 2, wherein The protection electrode is connected to the metal layer through a metallized through-hole, and the source of the source follower is connected to the metal layer through a metallized through-hole.

4. The MEMS microphone packaging structure according to claim 1, wherein: The diaphragm assembly includes a substrate and a conductive insulator, a back cavity is formed in the middle of the substrate, the diaphragm is arranged on the substrate, the diaphragm covers the back cavity, the conductive insulator is arranged on the substrate and / or the diaphragm, the conductive insulator is arranged around the back cavity, the conductive insulator is connected to the PCB board, the protective electrode is located inside the conductive insulator, and the protective electrode is separated from the conductive insulator.

5. The MEMS microphone packaging structure according to claim 4, characterized in that: The conductive insulator is fixed to the corresponding metal pad of the PCB board through a thermoacoustic wave or eutectic bonding process.

6. The MEMS microphone packaging structure according to claim 4, characterized in that: The protection electrode is located outside the projection area of the back cavity on the PCB board.

7. The MEMS microphone packaging structure according to any one of claims 1 to 6, wherein: The protective electrode is ring-shaped.

8. The MEMS microphone packaging structure according to any one of claims 1 to 6, wherein: The ASIC chip is located in the cavity or embedded in the PCB board.

9. The MEMS microphone packaging structure according to any one of claims 1 to 6, characterized in that: The gap height between the back plate and the vibration membrane is 5 μm-10 μm.

10. An electronic device, characterized in that, The MEMS microphone packaging structure comprises the MEMS microphone packaging structure according to any one of claims 1 to 9.

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