High-rigidity ultrathin MEMS microphone substrate and its fabrication method

Abstract

This invention discloses a high-rigidity ultrathin MEMS microphone substrate and its processing method, comprising: fabricating inner layer circuitry on two thin copper layers of a buried capacitor substrate, and laminating copper foil overlays on the inner layer circuitry to form an intermediate plate A; fabricating slots A and B on the intermediate plate A; depositing a seed layer on the entire board followed by via electroplating to form a conductive structure filling slot B and a copper layer A not filling slot A; plating a non-copper functional layer and copper layer B on copper layer A to obtain a reinforced structure filling slot A and the intermediate plate B; fabricating sound holes and reinforcing holes on the intermediate plate B, and filling the reinforcing holes with metal base material to form reinforcing pillars, wherein the reinforcing pillars and the reinforced structure are mutually independent or adjacent; and fabricating outer layer circuitry on the two copper foil overlays. This processing method is reasonable, simple, and easy to implement. The resulting MEMS microphone substrate has the characteristics of thinness, high rigidity, and strong anti-interference capability, meeting the packaging requirements of MEMS microphones.

Description

Technical Field

[0001] This invention relates to the field of MEMS microphone technology, and in particular to a high-rigidity ultrathin MEMS microphone substrate and its processing method. Background Technology

[0002] To meet the demand for thinner designs in smartphones, true wireless stereo (TWS) earphones, and smart wearable devices, the substrate thickness of MEMS microphones is also decreasing, currently reaching approximately 0.15mm. However, as the substrate thickness decreases, the following problems are prone to occur during the packaging process of MEMS microphones:

[0003] ① As the substrate thickness decreases, its rigidity will inevitably decrease significantly. Therefore, during MEMS microphone packaging, the substrate is easily affected by factors such as the negative pressure of the mounting nozzle, the pushing force of the die bond / wire bonding pin, and the internal stress of the potting compound, which can easily cause defects such as warping, bending, or even cracking, thus greatly affecting the packaging quality of the MEMS microphone.

[0004] ②Since the substrate is an important component of the acoustic cavity, when the substrate becomes thinner and its rigidity is insufficient, the damping of the acoustic cavity will be insufficient. External environmental noise (such as mechanical vibration) can easily be transmitted to the diaphragm through the substrate, causing acoustic crosstalk, reducing the signal-to-noise ratio by 2-5 dB, and thus reducing the anti-interference ability.

[0005] ③ Copper foil circuitry on ultra-thin substrates is prone to micro-deformation due to substrate deformation, resulting in parasitic inductance / capacitance fluctuations, noise and delays in high-frequency signals, and reduced signal integrity. Furthermore, the limited thickness of the grounding / shielding layer on ultra-thin substrates can also reduce electromagnetic shielding effectiveness, making them susceptible to external radio frequency interference (such as mobile phone signals), and causing noise in the output signal; etc.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] To overcome the above-mentioned defects, the present invention provides a high-rigidity ultra-thin MEMS microphone substrate and its processing method. The processing method is reasonable, simple and easy to operate and implement, and the resulting MEMS microphone substrate has the characteristics of thinness, high rigidity and strong anti-interference ability, which well meets the packaging requirements of MEMS microphones.

[0008] The technical solution adopted by this invention to solve its technical problem is: a method for processing a high-rigidity ultrathin MEMS microphone substrate, comprising:

[0009] A buried capacitor substrate is provided, wherein the buried capacitor substrate has two thin copper layers and a capacitor layer sandwiched between the two thin copper layers;

[0010] An intermediate board A is obtained by fabricating inner layer circuits on two thin copper layers and laminating copper foil layers on the two inner layer circuits respectively; wherein, each of the two inner layer circuits is provided with a part A for cooperating in the fabrication of a reinforcing structure and a part B for cooperating in the fabrication of a conductive structure.

[0011] A groove A is machined on the obtained intermediate plate A, which opens onto the surface of the copper foil layer and has the portion A adjacent to the copper foil layer as the bottom of the groove; and a groove B is machined on the surface of the copper foil layer, which opens onto the surface of the copper foil layer and has the portion B adjacent to and / or far from the copper foil layer as the bottom of the groove.

[0012] After the seed layer is deposited on the whole board, the through-hole electroplating is performed to form a conductive structure that fills the groove B and is flush with the surface of the copper foil layer, as well as a copper layer A that does not fill the groove A.

[0013] A non-copper functional layer and a copper layer B are sequentially plated on the copper layer A to obtain a reinforced structure that fills the groove A and is flush with the surface of the copper foil layer; thus, an intermediate plate B is obtained.

[0014] Sound holes and reinforcing holes that penetrate the two layers of copper foil reinforcement are machined on the obtained intermediate plate B, and the reinforcing holes are filled with metal base material to form reinforcing columns. The reinforcing columns and the reinforcing structure are mutually independent or adjacent.

[0015] Outer layer circuitry is fabricated on the two copper foil overlays.

[0016] As a further improvement of the present invention, the thickness direction of the obtained intermediate board A is defined as the up and down direction; the portions A on the two inner layer circuits are arranged vertically opposite each other, and the slots A are configured as multiple, namely multiple first slots A with the slot opening facing upwards and multiple second slots A with the slot opening facing downwards; and the multiple first slots A and the multiple second slots A are arranged in a one-to-one vertical correspondence.

[0017] As a further improvement of the present invention, a plurality of first slots A and a plurality of second slots A are respectively arranged in an array, and the spacing between any two adjacent first slots A and the spacing between any two adjacent second slots A are controlled to be between 0.1 and 0.3 mm.

[0018] As a further improvement of the present invention, the groove depth of the groove A in the vertical direction is not greater than the groove depth of the groove B in the vertical direction, and the cross-sectional area of ​​the groove A is greater than the cross-sectional area of ​​the groove B.

[0019] As a further improvement of the present invention, the material of the non-copper functional layer is selected from at least one of nickel, manganese and zinc.

[0020] As a further improvement of the present invention, before electroplating to form the copper layer B, the non-copper functional layer is first subjected to surface modification treatment to form a micron-level rough surface on the surface of the non-copper functional layer.

[0021] As a further improvement of the present invention, the reinforcing hole is close to the acoustic hole, and the metal base material is also selected from at least one of nickel, manganese and zinc.

[0022] As a further improvement of the present invention, the thickness of both thin copper layers is no greater than 18 μm, and the thickness of the capacitor layer is 6 μm.

[0023] Accordingly, the inner layer circuitry is fabricated on the two thin copper layers in sequence.

[0024] As a further improvement of the present invention, after the outer layer circuit is obtained, conventional outer layer anti-drying, surface treatment, molding, finished product electrical testing, and finished product inspection processes are performed in sequence to obtain a MEMS microphone substrate with a board thickness of no more than 0.12 mm.

[0025] The present invention also provides a high-rigidity ultra-thin MEMS microphone substrate, which is fabricated using the high-rigidity ultra-thin MEMS microphone substrate processing method described in the present invention.

[0026] The beneficial effects of this invention are as follows: Compared with the prior art, the processing method of the high-rigidity ultra-thin MEMS microphone substrate provided by this invention has the following advantages: ① Through process innovation, this invention embeds multiple composite reinforcing structures within the ultra-thin MEMS microphone substrate. These reinforcing structures have good rigidity and shielding functions, which can improve the overall structural rigidity of the MEMS microphone substrate while effectively blocking electromagnetic interference from external sources (such as mobile phone radio frequency and circuit board electromagnetic radiation) to the microphone chip, diaphragm, etc., thereby improving the microphone's anti-interference capability. Particularly noteworthy is that this invention also optimizes the positional layout of the multiple reinforcing structures to form multiple reinforcing units with a cross-section approximately in the shape of a grid. Through these specially shaped grid-shaped reinforcing units, a mesh-like group of reinforcing units can be formed within the MEMS microphone substrate, thereby achieving optimal rigidity of the ultra-thin MEMS microphone substrate and effectively ensuring the packaging quality of the MEMS microphone. ② Through process innovation, this invention also embeds reinforcing pillars within the MEMS microphone substrate to further improve the structural rigidity and shielding performance (i.e., anti-interference capability) of the MEMS microphone substrate. ③ The processing method of the MEMS microphone substrate provided by the present invention is reasonable, the process flow is simple, and it is easy to operate and implement. Attached Figure Description

[0027] Figure 1 This is a flowchart of the processing method for the high-rigidity ultra-thin MEMS microphone substrate described in Embodiment 1 of the present invention;

[0028] Figure 2 This is a schematic cross-sectional view of the embedded capacitor substrate described in Example 1;

[0029] Figure 3 This is a schematic cross-sectional view of the intermediate plate A obtained in Example 1;

[0030] Figure 4 This is a schematic diagram of the cross-sectional structure after grooves A and B are machined on the obtained intermediate plate A in Example 1;

[0031] Figure 5 This is a schematic diagram of the cross-sectional structure of the conductive structure and copper layer A formed after the hole-filling electroplating in Example 1.

[0032] Figure 6 This is a schematic cross-sectional view of the intermediate plate B obtained in Example 1;

[0033] Figure 7 This is a schematic diagram of the cross-sectional structure after the sound holes and reinforcing holes are machined on the obtained intermediate plate B in Example 1;

[0034] Figure 8 This is a schematic cross-sectional view of the reinforcing column formed by filling the obtained reinforcing hole with metal-based material in Example 1.

[0035] Figure 9 This is a schematic cross-sectional view of the substrate semi-finished product obtained after the outer layer circuitry is fabricated in Example 1.

[0036] Figure 10 This is a schematic cross-sectional view of the high-rigidity ultrathin MEMS microphone substrate obtained in Example 1.

[0037] Figure 11 This is a schematic diagram of the cross-sectional structure after the sound holes and reinforcing holes are machined on the obtained intermediate plate B in Example 2;

[0038] Figure 12 This is a schematic cross-sectional view of the high-rigidity ultra-thin MEMS microphone substrate obtained in Example 2.

[0039] Referring to the accompanying drawings, the following explanations are provided:

[0040] 1. Embedded capacitor substrate; 10. Thin copper layer; 11. Capacitor layer; 12. Inner layer circuitry; 120. Part A; 121. Part B; 20. Insulating layer; 21. Copper foil layer; 30a. First recess A; 30b. Second recess A; 31. Recess B; 4. Conductive structure; 5. Reinforcing structure; 50. Copper layer A; 51. Non-copper functional layer; 52. Copper layer B; 6. Acoustic aperture; 7. Reinforcing hole; 8. Reinforcing pillar; 9. Outer layer circuitry; 13. Solder resist layer; 14. Surface treatment layer. Detailed Implementation

[0041] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0042] Example 1:

[0043] Please see the appendix Figure 1 To be continued Figure 10 As shown, this embodiment 1 provides a method for fabricating a high-rigidity ultra-thin MEMS microphone substrate, including the following fabrication steps:

[0044] S1: Provide embedded capacitor substrate 1, please refer to the appendix. Figure 2 As shown, the embedded capacitor substrate 1 has two thin copper layers 10 and a capacitor layer 11 sandwiched between the two thin copper layers 10. According to the processing design requirements of the MEMS microphone substrate, the thickness of the two thin copper layers 10 is no more than 18μm. The capacitor layer 11 is made of an insulating material with a high dielectric constant (such as epoxy resin, polyimide resin, etc.), and the thickness of the capacitor layer 11 is about 6μm.

[0045] Additional explanation: Regarding the material of the capacitor layer 11, in addition to using an insulating material with a high dielectric constant as the main material, ceramic fillers (such as barium titanate) can also be added to further improve the dielectric performance.

[0046] S2: Because the embedded capacitor substrate 1 is relatively thin, this embodiment performs circuit fabrication and lamination layering operations on the two thin copper layers 10 in a sequential (i.e., step-by-step) manner. Specifically: In this embodiment, an inner layer circuit 12 is first fabricated on one of the thin copper layers 10, and an insulating layer 20 and a copper foil layer 21 are laminated on the inner layer circuit 12. Then, an inner layer circuit 12 is fabricated on the other thin copper layer 10, and an insulating layer 20 and a copper foil layer 21 are laminated on the inner layer circuit 12, thereby obtaining the intermediate board A; see attached document for details. Figure 3 As shown.

[0047] Furthermore, based on the thickness of the thin copper layer 10, this embodiment employs the mSAP process to fabricate the circuit of the thin copper layer 10. Specifically, the thin copper layer 10 is subjected to the following pretreatments in sequence: pre-coating treatment (i.e., roughening, cleaning, and drying of the thin copper layer 10), coating with resist photosensitive film (i.e., applying the resist photosensitive dry film onto the thin copper layer 10 using a vacuum laminator), exposure (i.e., exposing the resist photosensitive dry film using an LDI exposure machine according to preset exposure data), and development (i.e., developing the unexposed resist with a developing solution). After processes such as photosensitive dry film removal, pattern electroplating (i.e., using pattern electroplating to plate the inner layer circuit pattern prototype on the thin copper layer 10 and the area exposed outside the photosensitive dry film), film removal (i.e., using a stripping solution to remove the photosensitive dry film), baking, and flash etching (i.e. using an alkaline / or acidic etching solution to etch away the thin copper layer not covered by the inner layer circuit pattern prototype), the inner layer circuit 12 with a line width of 10-40 μm and a line spacing of 10-25 μm can be obtained; it is understood that the inner layer circuit 12 belongs to fine circuits.

[0048] For further details, please refer to the appendix. Figure 3 As shown, according to the processing design requirements of the MEMS microphone substrate (such as interlayer conductivity, structural rigidity requirements, etc.), both inner layer circuits 12 are provided with a portion A120 for cooperating in the fabrication of the reinforcing structure 5 and a portion B121 for cooperating in the fabrication of the conductive structure 4. The positional layout of portions A120 and B121 on the two inner layer circuits 12 is optimally designed as follows: Please refer to the appendix. Figure 3 As shown, if the thickness direction of the obtained intermediate board A is defined as the vertical direction, the two inner layer circuits 12 are arranged vertically, and each of the two inner layer circuits 12 is provided with at least one of the portions A120, and the portions A120 on the two inner layer circuits 12 are arranged vertically opposite each other; each of the two inner layer circuits 12 is provided with multiple portions B121, and the portions B121 on the two inner layer circuits 12 are arranged vertically opposite each other and / or vertically staggered.

[0049] Furthermore, after the inner layer circuit 12 is fabricated, it is subjected to AOI optical inspection to ensure the processing quality of the inner layer circuit.

[0050] Furthermore, after each inner layer circuit 12 is fabricated, this embodiment employs an electrothermal pressing method for lamination and layering. The preferred processing parameters for this electrothermal pressing method are: a heating rate of 3–4 °C / min, a material temperature > 190 °C, a pressing pressure of 350–490 Psi (i.e., the high pressure at a material temperature of 70–80 °C), and a pressing time > 120 min. Understandably, through the above lamination and pressing, the resulting intermediate board A exhibits very high structural strength.

[0051] Furthermore, the insulating layer 20 can be, but is not limited to, a prepreg or a pure adhesive film, with a pure adhesive film being preferred as it can improve the quality of subsequent laser drilling. The thickness of the insulating layer 20 is not limited and is determined according to the processing and design requirements of the MEMS microphone substrate. In addition, the thickness of the copper foil layer 21 is no greater than 18 μm.

[0052] S3: According to the processing design requirements of the MEMS microphone substrate, a groove A is processed on the obtained intermediate board A by using laser technology (including laser windowing and laser drilling / grooving technology), which opens onto the surface of the copper foil layer 21 and has the portion A120 adjacent to the copper foil layer 21 as the groove bottom. A groove B31 is also processed on the surface of the copper foil layer 21, which opens onto the surface of the copper foil layer 21 and has the portion B121 adjacent to and / or far away from the copper foil layer 21 as the groove bottom.

[0053] Furthermore, based on the aforementioned positional layout of portions A120 and B121, the positional layout of slot A and slot B31 is optimized as follows: (See attached diagram) Figure 4 As shown, the slot A is configured as multiple slots, namely multiple first slots A30a with their openings facing upwards and multiple second slots A30b with their openings facing downwards; that is to understand, the multiple first slots A30a open onto the surface of the upper copper foil layer 21 and have the portion A120 on the upper inner layer circuit 12 as their bottom, and the multiple second slots A30b open onto the surface of the lower copper foil layer 21 and have the portion A120 on the lower inner layer circuit 12 as their bottom, and the multiple first slots A30a and the multiple second slots A30b are also arranged in a one-to-one vertical correspondence. The slots B31 are configured in multiple ways, with some of the slots B31 opening onto the surface of an upper (or lower) copper foil layer 21 and having a portion B121 on an upper (or lower) inner layer circuit 12 as the slot bottom. The remaining slots B31 open onto the surface of an upper (or lower) copper foil layer 21 and have a portion B121 on a lower (or upper) inner layer circuit 12 as the slot bottom.

[0054] Furthermore, to better improve the rigidity of the MEMS microphone substrate, this embodiment further optimizes the positional layout of the slot A as follows: multiple first slots A30a and multiple second slots A30b are arranged in an array, and the spacing between any two adjacent first slots A30a and the spacing between any two adjacent second slots A30b are controlled within 0.1 to 0.3 mm. The specific reasons are as follows.

[0055] In addition, to meet the processing requirements of the reinforcing structure 5 described below, this embodiment also optimizes the dimensions of the groove A. Specifically, the groove depth of the groove A (including the first groove A30a and the second groove A30b) in the vertical direction is not greater than the groove depth of the groove B31 in the vertical direction. However, the cross-sectional area of ​​the groove A is much larger than the cross-sectional area of ​​the groove B31. The specific reasons are as follows.

[0056] Furthermore, in this embodiment, during the laser drilling / grooving operation, the processing parameters are optimized as follows: a CO2 laser is used, with 1 to 3 laser shots of 1.5–2.5 mJ laser energy and 5–7 μs pulse width, and 1 to 3 laser shots of 1.5–2.5 mJ laser energy and 1–3 μs pulse width. That is, this embodiment uses two laser parameters alternately for grooving; the mask size is 1.4 mm. Understandably, based on the above laser drilling / grooving operation, the processing accuracy of the resulting grooves A and B31 can be ensured to be very high, providing good technical support and guarantee for the subsequent processing to obtain high-precision reinforcing structure 5 and conductive structure 4.

[0057] In addition, regarding laser windowing, conventional processing techniques can be used, and this embodiment does not impose any restrictions.

[0058] S4: First, deposit a seed layer with a thickness of 0.5-1 μm on the entire board. Then, perform fill electroplating on the groove A and the groove B31 to form a conductive structure 4 that fills the groove B31 and is flush with the surface of the copper foil reinforcement layer 21, as well as a copper layer A50 that does not fill the groove A. For details, please refer to the appendix. Figure 5 As shown. Understandably, because the cross-sectional area of ​​the groove A is much larger than that of the groove B31, during the above-mentioned hole-filling electroplating, the groove B31 will be quickly filled with copper, while the groove A (including the first groove A30a and the second groove A30b) will be in an unfilled state, reserving filling space for the non-copper functional layer 51 and the copper layer B52 described below. Furthermore, it is understood that the above-mentioned precise control of the dimensions of the groove A and the groove B31 can well meet the processing requirements of the conductive structure 4 and the reinforcing structure 5.

[0059] Furthermore, in this S4, the seed layer can be processed using one of the following processes: PVD, CVD, and flash plating. These are conventional techniques in the field of circuit board manufacturing and will not be described in detail here.

[0060] Furthermore, in this S4, the preferred processing parameters for the hole-filling electroplating are: a monovalent chloride ion concentration of 40–60 ppm, a divalent copper ion concentration of 18–22 g / L, a sulfuric acid concentration of 170–190 g / L, and a plating solution temperature of 23–26°C. The hole-filling electroplating process is divided into an impact stage and a filling stage. In the impact stage, the current density is 2–2.5 ASD and the plating time is 3–5 min, which allows the electroplated copper layer to quickly cover the bottom of the tank. In the filling stage, the current density is 1.2–1.8 ASD, which allows the electroplated copper layer to be densely filled. The plating efficiency is 0.45–0.5 μm / min. It is understandable that this S4 adopts a segmented plating method. On the one hand, it can quickly fill the embedded tanks B31 and A, thereby effectively overcoming the problem of long cycles in traditional low-current electroplating and significantly improving plating efficiency / production efficiency. On the other hand, it can ensure the density of the electroplated copper layer and improve the filling quality.

[0061] Furthermore, in this S4, after the hole-filling electroplating operation is completed, the surface of the copper foil layer 21 and the end face of the conductive structure 4 need to be corrected by mechanical grinding (such as grinding with a ceramic brush wheel) to ensure that the two are flush and connected, while also ensuring that the thickness of the copper foil layer 21 is maintained at the set copper thickness. In addition, a cleaning process is performed after grinding is completed.

[0062] S5: Using a through-hole plating technique, a non-copper functional layer 51 and a copper layer B52 are sequentially plated onto the copper layer A50 to obtain a reinforcing structure 5 that fills the groove A and is flush with the surface of the copper foil reinforcement layer 21. It can be understood that the reinforcing structure 5 is composed of the stacked copper layer A50, the non-copper functional layer 51, and the copper layer B52; thus, an intermediate plate B is obtained. For details, please refer to the appendix. Figure 6 As shown.

[0063] Furthermore, the material of the non-copper functional layer 51 can be selected from at least one of nickel, manganese and zinc (with nickel being the best) so that the reinforcing structure 5 has good rigidity and shielding function, thereby improving the overall structural rigidity of the MEMS microphone substrate while effectively blocking electromagnetic interference from external sources (such as mobile phone radio frequency and circuit board electromagnetic radiation) to the microphone chip, diaphragm, etc., and improving the microphone's anti-interference ability.

[0064] Furthermore, based on the material of the non-copper functional layer 51, the processing and forming method of the non-copper functional layer 51 is optimized as follows: firstly, a photosensitive anti-plating film with a processing opening is applied to the board obtained in S4 using a film pattern transfer process, so as to achieve that only the groove A is exposed outside the processing opening, and the rest of the board is covered and protected by the photosensitive anti-plating film; then, the non-copper functional layer 51 with a thickness of 3 to 12 μm is plated on the copper layer A50 using a hole-filling electroplating technology; subsequently, the photosensitive anti-plating film is removed using a stripping solution.

[0065] Note: The above-mentioned film pattern transfer process includes sequentially performing pre-coating treatment (i.e., roughening, cleaning and drying the board) on the board obtained in S4, coating with resist photosensitive film (i.e., coating the resist photosensitive wet film onto the surface of the board), exposure (exposing the preset area of ​​the resist photosensitive wet film using an LDI exposure machine), development (removing the unexposed areas on the resist photosensitive wet film using a developer) and baking (baking and curing the resist photosensitive wet film) to obtain a resist photosensitive film with a processing port.

[0066] In addition, based on the material of the non-copper functional layer 51, after the non-copper functional layer 51 is prepared, it is subjected to plasma surface modification treatment to remove foreign matter while forming a micron-level rough surface on the surface of the non-copper functional layer 51. That is, an "anchoring structure" is formed on the surface of the non-copper functional layer 51 to ensure that the subsequent copper layer B52 can be embedded in the rough surface of the non-copper functional layer 51, so that the copper layer B52 is firmly bonded to the non-copper functional layer 51.

[0067] Furthermore, when performing the above-mentioned plasma surface modification treatment, the preferred processing parameters are: using plasma formed by pure argon (Ar), or using plasma formed by a mixture of argon (Ar) and hydrogen (H2) (with hydrogen accounting for 5% to 15% of the volume); a vacuum degree of 1 to 5 Pa, a processing power of 50 to 300 W, and a processing time of 2 to 4 min. It is understood that through the above-mentioned optimized plasma surface modification treatment, the surface of the non-copper functional layer 51 can be formed into a micron-level rough surface.

[0068] Furthermore, after completing the plasma surface modification treatment described above, the copper layer B52 is fabricated using the same via-filling electroplating process as S4 described above. Understandably, after obtaining the copper layer B52, it is also necessary to correct the surface of the copper foil augmentation layer 21 and the end face of the copper layer B52 through mechanical grinding (using a ceramic brush wheel) to ensure that the two are flush and connected, while also ensuring that the thickness of the copper foil augmentation layer 21 remains at the set copper thickness.

[0069] Furthermore, based on the positional layout of the slots A, namely: multiple first slots A30a and multiple second slots A30b are arranged in an array, and the multiple first slots A30a and multiple second slots A30b are arranged in a one-to-one vertical correspondence; it can be concluded that: the resulting intermediate plate B contains two vertically arranged reinforcing packages, each of which is composed of multiple composite structures arranged in an array, and the multiple reinforcing structures 5 in the two reinforcing packages are also arranged in a one-to-one vertical correspondence; in particular, any two pairs of reinforcing structures 5 belonging to different reinforcing packages and simultaneously satisfying the condition of "adjacent in the same pair and vertically corresponding in different pairs", and the two parts A120 corresponding to them, together constitute a reinforcing unit with a cross-section approximately "grid-shaped" as shown in the appendix. Figure 6 The part enclosed in red dotted lines; understandably, by means of the above-mentioned specially shaped "grid-shaped" reinforcement units, a mesh-like reinforcement unit group is formed in the obtained intermediate plate B and even the MEMS microphone substrate (understandably, the reinforcement unit group is composed of multiple "grid-shaped" reinforcement units), thereby enabling the obtained intermediate plate B and even the MEMS microphone substrate to have excellent / extremely high rigidity.

[0070] S6: Based on the processing design requirements of the MEMS microphone substrate, laser technology (refer to S3 above) is used to process sound holes 6 and reinforcing holes 7 that penetrate the two copper foil reinforcement layers 21 on the obtained intermediate board B. The reinforcing holes 7 are spaced apart from the sound holes 6 and the reinforcement structure 5, and are also close to the sound holes 6. For details, please refer to the appendix. Figure 7 As shown; then, the reinforcing holes 7 are filled with metal base material using a hole-filling electroplating technique to form reinforcing pillars 8. It is understood that the reinforcing pillars 8 and the reinforcing structure 5 / reinforcing unit have an independent relationship; see the appendix for details. Figure 8 As shown.

[0071] Furthermore, the metal base material can also be selected from at least one of nickel, manganese, and zinc, with nickel being the most preferred. Understandably, by providing the reinforcing pillars 8, the structural rigidity and shielding performance (i.e., anti-interference capability) of the MEMS microphone substrate can be further improved.

[0072] Furthermore, based on the aforementioned metal-based material, before performing the hole-filling electroplating operation in S6, a photosensitive anti-plating film with a processing opening needs to be applied to the obtained intermediate plate B using a film pattern transfer process (refer to S5 above). This ensures that only the reinforcing hole 7 is exposed outside the processing opening, while the remaining parts of the obtained intermediate plate B are covered and protected by the photosensitive anti-plating film. Additionally, after the reinforcing post 8 is formed, the end face of the reinforcing post 8 needs to be ground and corrected, and the photosensitive anti-plating film needs to be removed using a stripping solution.

[0073] S7: Based on the thickness of the copper foil augmentation layer 21, outer layer circuitry 9 can be selectively fabricated on the two copper foil augmentation layers 21 using mSAP or subtractive processing methods; thereby obtaining a substrate semi-finished product. For details, please refer to the appendix. Figure 9 As shown.

[0074] Specifically, when the copper foil augmentation layer 21 is a thin copper layer, the outer layer circuit is fabricated using the mSAP process (refer to the inner layer circuit 12 fabrication method in S2 above). When the copper foil augmentation layer 21 is a thick copper layer, the outer layer circuit can be fabricated using a subtractive process. Further, the subtractive process includes: performing pre-coating treatment (i.e., roughening, cleaning, and drying the copper foil augmentation layer 21), coating with a photoresist film (i.e., applying the photoresist film onto the copper foil augmentation layer 21 using a vacuum laminator), exposure (exposing the photoresist film using an LDI exposure machine according to exposure data), development (removing the unexposed portions of the photoresist film using a developer), etching (etching away the areas of the copper foil augmentation layer 21 exposed outside the photoresist film using an alkaline etching solution), and stripping to obtain the outer layer circuit 9.

[0075] In addition, after the outer layer circuit 9 is fabricated, AOI optical inspection is performed on the outer layer circuit 9 to ensure the processing quality of the outer layer circuit.

[0076] S8: The substrate semi-finished product obtained in S7 is subjected to conventional processes such as outer layer solder resist (i.e., setting solder resist layer 13 at a preset position on the outer layer circuit 9), surface treatment (i.e., setting surface treatment layer 14 on the outer layer circuit 9, the surface treatment layer 14 can be, but is not limited to, electroplated soft gold layer, electroless nickel-palladium-gold layer, or electroless nickel-gold layer), molding, finished product electrical testing, finished product inspection, shipment inspection, and packaging and shipping, thereby obtaining a MEMS microphone substrate with a board thickness of no more than 0.12mm; for details, please refer to the appendix. Figure 10 As shown.

[0077] As can be seen from the above, compared with the prior art, the processing method of the high-rigidity ultra-thin MEMS microphone substrate provided in this embodiment 1 has the following advantages: ① Through process innovation, this embodiment achieves the embedding of multiple composite reinforcing structures 5 within the ultra-thin MEMS microphone substrate. The reinforcing structures 5 have good rigidity and shielding functions, which can improve the overall structural rigidity of the MEMS microphone substrate while effectively blocking electromagnetic interference from external sources (such as mobile phone radio frequency and circuit board electromagnetic radiation) to the microphone chip, diaphragm, etc., thereby improving the microphone's anti-interference capability. In particular, this embodiment also optimizes the position layout of the multiple reinforcing structures 5 to form multiple reinforcing units with a cross-section approximately "grid-shaped". Through these specially shaped "grid-shaped" reinforcing units, a mesh-like reinforcing unit group can be formed in the MEMS microphone substrate, thereby achieving the optimal rigidity of the ultra-thin MEMS microphone substrate and effectively ensuring the packaging quality of the MEMS microphone. ② This embodiment, through process innovation, also embeds reinforcing pillars 8 within the MEMS microphone substrate to further enhance the structural rigidity and shielding performance (i.e., anti-interference capability) of the MEMS microphone substrate. ③ The processing method for the MEMS microphone substrate provided in this embodiment is reasonable, the process flow is simple, and it is easy to operate and implement.

[0078] Example 2:

[0079] This embodiment 2 also provides a processing method for a high-rigidity ultra-thin MEMS microphone substrate. Compared with embodiment 1, the difference in the processing method of the MEMS microphone substrate provided in this embodiment 2 is that the reinforcing hole 7 processed on the obtained intermediate plate B in this embodiment 2 penetrates the reinforcing structure 5, and the reinforcing post 8 and the reinforcing structure 5 are adjacent to each other.

[0080] Specifically, in this embodiment 2, after the intermediate plate B is prepared according to the processing method provided in embodiment 1 (see S1 to S5 in embodiment 1), laser technology is first used to process acoustic holes 6 and reinforcing holes 7 that penetrate the two layers of copper foil reinforcement layers 21 on the obtained intermediate plate B. The reinforcing holes 7 are spaced apart from the acoustic holes 6 and close to the acoustic holes 6. The reinforcing holes 7 also penetrate at least one pair of reinforcing structures 5 that are arranged vertically in correspondence. For details, please refer to the appendix. Figure 11 As shown; then, using a hole-filling electroplating technique, the reinforcing holes 7 are filled with a metal base material to form reinforcing pillars 8. It is understood that the reinforcing pillars 8 and the reinforcing structure 5 (further, "grid-shaped" reinforcing units) are adjacent to each other. For details, please refer to the appendix. Figure 12 As shown, this can significantly improve the structural rigidity of the MEMS microphone substrate.

[0081] After the reinforcing post 8 is fabricated, this embodiment 2 will then fabricate a MEMS microphone substrate with a thickness of no more than 0.12 mm according to the contents of S7 to S8 provided in embodiment 1.

[0082] Understandably, the processing method of the MEMS microphone substrate provided in this embodiment 2 is reasonable, the process flow is simple, and it is easy to operate and implement. The resulting MEMS microphone substrate has the advantages of thinness, high rigidity, and strong anti-interference ability, which well meets the packaging requirements of MEMS microphones.

[0083] Example 3:

[0084] This embodiment 3 provides a high-rigidity ultra-thin MEMS microphone substrate, which is fabricated using the high-rigidity ultra-thin MEMS microphone substrate processing method described in embodiment 1 or embodiment 2 above.

[0085] Specifically, the MEMS microphone substrate includes a board body, which has an inner layer circuit 12 and an outer layer circuit 9 located outside the inner layer circuit 12 and electrically connected to the inner layer circuit 12 through a conductive structure 4. The board body has a sound hole 6 penetrating its opposite sides, and a plurality of reinforcing structures 5 and reinforcing pillars 8 are also embedded in the board body. The reinforcing structure 5 is a composite structure composed of a copper layer A50, a non-copper functional layer 51 and a copper layer B52 stacked in sequence. The reinforcing pillars 8 penetrate the opposite sides of the board body and are close to the sound hole 6. The materials of the non-copper functional layer 51 and the reinforcing pillars 8 are selected from at least one of nickel, manganese and zinc, respectively.

[0086] As can be seen from the above, by using the high-rigidity ultra-thin MEMS microphone substrate processing method provided in this application, the MEMS microphone substrate obtained in this embodiment 3 has high structural rigidity and strong shielding performance (i.e., strong anti-interference ability), which well meets the packaging requirements of MEMS microphones.

[0087] Finally, the prefixes "first," "second," etc. (such as first groove A, second groove A, etc.) in the component names in this patent specification, as well as the suffixes "A," "B," etc. (such as part A, part B, etc.) in the component names, are only for ease of description and are not intended to limit the scope of implementation of this patent.

[0088] Many specific details have been set forth in the foregoing description to provide a thorough understanding of the present invention. However, the above description is merely a preferred embodiment of the present invention, and the present invention can be implemented in many other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed above. Furthermore, any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, using the methods and techniques disclosed above, without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for fabricating a high-rigidity ultrathin MEMS microphone substrate, characterized in that: include: An embedded capacitor substrate (1) is provided, wherein the embedded capacitor substrate (1) has two thin copper layers (10) and a capacitor layer (11) sandwiched between the two thin copper layers (10). Inner layer circuits are fabricated on the two thin copper layers (10) respectively, and copper foil extension layers (21) are laminated on the two inner layer circuits respectively to obtain an intermediate board A; wherein, the two inner layer circuits are provided with a part A (120) for cooperating in the fabrication of a reinforcing structure and a part B (121) for cooperating in the fabrication of a conductive structure. A groove A is formed on the obtained intermediate plate A, which opens onto the surface of the copper foil layer (21) and has the portion A (120) adjacent to the copper foil layer (21) as the bottom of the groove. A groove B (31) is formed on the intermediate plate A, which opens onto the surface of the copper foil layer (21) and has the portion B (121) adjacent to and / or far away from the copper foil layer (21) as the bottom of the groove. After the seed layer is deposited on the whole board, the hole-filling electroplating is performed to form a conductive structure (4) that fills the groove B (31) and is flush with the surface of the copper foil superposition layer (21), as well as a copper layer A (50) that does not fill the groove A. A non-copper functional layer (51) and a copper layer (52) are sequentially plated on the copper layer A (50) to obtain a reinforced structure (5) that fills the groove A and is flush with the surface of the copper foil reinforcement layer (21); thus, an intermediate plate B is obtained. Sound holes (6) and reinforcing holes (7) that penetrate the two layers of copper foil reinforcement (21) are processed on the obtained intermediate plate B, and the reinforcing holes (7) are filled with metal base material to form reinforcing pillars (8). The reinforcing pillars (8) and the reinforcing structure (5) are mutually independent or adjacent. Outer layer circuits (9) are fabricated on the two copper foil overlays (21).

2. The processing method of the high-rigidity ultra-thin MEMS microphone substrate according to claim 1, characterized in that: The thickness direction of the obtained intermediate board A is defined as the up and down direction; the portions A (120) on the two inner layer circuits are arranged vertically opposite each other, and the slots A are configured as multiple, namely multiple first slots A (30a) with the slot opening facing upwards and multiple second slots A (30b) with the slot opening facing downwards; and the multiple first slots A (30a) and the multiple second slots A (30b) are arranged vertically in a one-to-one correspondence.

3. The processing method of the high-rigidity ultra-thin MEMS microphone substrate according to claim 2, characterized in that: The plurality of first slots A (30a) and the plurality of second slots A (30b) are arranged in an array, and the spacing between any two adjacent first slots A (30a) and the spacing between any two adjacent second slots A (30b) are controlled to be between 0.1 and 0.3 mm.

4. The processing method of the high-rigidity ultra-thin MEMS microphone substrate according to claim 2, characterized in that: The groove depth of groove A in the vertical direction is not greater than the groove depth of groove B (31) in the vertical direction, and the cross-sectional area of ​​groove A is greater than the cross-sectional area of ​​groove B (31).

5. The processing method of the high-rigidity ultrathin MEMS microphone substrate according to claim 1, characterized in that: The material of the non-copper functional layer (51) is selected from at least one of nickel, manganese and zinc.

6. The processing method of the high-rigidity ultrathin MEMS microphone substrate according to claim 5, characterized in that: Before electroplating to form the copper layer B (52), the non-copper functional layer (51) is first subjected to surface modification treatment to form a micron-level rough surface on the surface of the non-copper functional layer (51).

7. The processing method of the high-rigidity ultra-thin MEMS microphone substrate according to claim 1, characterized in that: The reinforcing hole (7) is close to the acoustic hole (6), and the metal base material is also selected from at least one of nickel, manganese and zinc.

8. The processing method of the high-rigidity ultrathin MEMS microphone substrate according to claim 1, characterized in that: The thickness of both thin copper layers (10) is no greater than 18 μm, and the thickness of the capacitor layer (11) is 6 μm. Accordingly, the inner layer circuits are fabricated on the two thin copper layers (10) in sequence.

9. The processing method of the high-rigidity ultra-thin MEMS microphone substrate according to claim 1, characterized in that: After the outer circuit (9) is obtained, conventional outer layer anti-drying, surface treatment, molding, finished product electrical testing and finished product inspection processes are carried out in sequence to obtain a MEMS microphone substrate with a thickness of no more than 0.12mm.

10. A high-rigidity ultrathin MEMS microphone substrate, characterized in that: It is manufactured using the processing method of any one of claims 1-9 for a high-rigidity ultra-thin MEMS microphone substrate.

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