Packaging process of MEMS acoustic device structure

Abstract

The invention discloses a packaging process of an MEMS acoustic device structure. The process comprises the following steps: packaging a first device: packaging the first device and exposing an electrical interface, electroplating a rewiring layer connected with the electrical interface on a packaging surface, electroplating a conductive block on a part of the rewiring layer, continuously packaging and exposing the top surface of the conductive block, and forming a packaging body; interconnection of a second device: electrically interconnecting the second device with the conductive block, and stacking and interconnecting the second device and the first device up and down; mounting the substrate ring: mounting the substrate ring on the packaging body to surround the second device; and cover plate packaging: the cover plate is pasted to seal the substrate ring, and a sound hole of the cover plate is aligned with the middle part of a vibrating diaphragm of the second device. The second device is welded on the first device, so that vertical stacking of the two device structures is realized, a routing process is not needed, the stacking space is saved, and the whole structure is higher in integration level, smaller in size and good in structural stability; and line transmission is more stable and reliable.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and particularly relates to a packaging process for a MEMS acoustic device structure. Background Art

[0002] MEMS (Micro-Electro-Mechanical System) technology is the most popular sensor manufacturing technology today and an important driving force for the miniaturization, intelligence, and low energy consumption of sensors. MEMS technology has promoted the great development of sensors. MEMS mainly uses microelectronic technology to shape the mechanical structure of sensors in a micro-nano volume. A MEMS sensor is a device formed by packaging a second device and a dedicated integrated circuit chip (the first device) together. The second device converts sound into signal changes such as capacitance and resistance, and the first device converts signal changes such as capacitance and resistance into electrical signals, thereby realizing the function of the MEMS sensor - converting external signals into electrical signals. MEMS acoustic sensors mainly refer to silicon microphones, ultrasonic sensors, etc.

[0003] In existing acoustic sensors, the second device and the first device are arranged flatly, and the electrodes of the second device are above the substrate. Metal wires are connected between the second device and the first device through a wire bonding process to achieve their electrical connection. This structural arrangement results in an overly large size of the sensor.

[0004] Chinese Patent Publication No. CN221319324U discloses a MEMS packaging structure and a MEMS acoustic sensor including the same. The MEMS packaging structure includes: a third substrate; a first substrate with a sound inlet hole formed thereon; a second substrate in a hollow ring shape, sandwiched between the first substrate and the third substrate; wherein, within the device installation space, the second device is fixed on the first substrate with its back cavity facing the sound inlet hole; the first device is fixed on the third substrate; an electrical signal guide column for signal transmission is formed longitudinally inside the second substrate, and the induction signal of the second device is transmitted to the first device through the electrical signal guide column, eliminating the traditional wire bonding process and still being able to achieve signal interconnection between chips and between chips and the substrate. In this way, the volume of the packaged device is greatly reduced, meeting the requirements of higher circuit integration. However, in this technology, three substrates are required, and circuits need to be provided in each substrate. The second device still needs a wire bonding process to achieve electrical connection with the circuit inside the substrate, and the first device and its electrical structure are exposed, affecting the service life, with a complex process and low integration. Summary of the Invention

[0005] To solve the above problems in the prior art, the present invention provides a packaging process for a MEMS acoustic device structure.

[0006] To achieve the above object, a packaging process for a MEMS acoustic device structure proposed by the present invention includes the following steps: First device encapsulation: Encapsulate the first device and expose the electrical interface. Electroplate a redistribution layer connected to the electrical interface on the encapsulation surface, electroplate conductive blocks on a part of the redistribution layer, and continue to encapsulate and expose the top surface of the conductive blocks to form an encapsulation body. Second device interconnection: Electrically interconnect the second device with the conductive blocks, and stack and interconnect the second device and the first device vertically. Substrate ring mounting: Mount the substrate ring on the encapsulation body to enclose the second device. Cover plate encapsulation: Mount the cover plate to seal the substrate ring, and align the sound holes of the cover plate with the middle part of the diaphragm of the second device.

[0007] Further, in the first device encapsulation step, the first device is placed on a carrier plate. Before electroplating the redistribution layer on the encapsulation top surface that exposes the electrical interface after encapsulating the first device, vertically etch the encapsulant to the bottom of the drill hole to expose the carrier plate, and electroplate metal pillars to completely fill the drill hole.

[0008] Furthermore, in the first device encapsulation step, the top end of the metal pillar is electrically connected to another part of the redistribution layer, the bottom end of the metal pillar contacts the carrier plate, and the electricity of the first device is transmitted from the electrical interface through the redistribution layer to the bottom end of the metal pillar.

[0009] Further, in the first device encapsulation step, the bottom end of the metal pillar is flush with and exposed on the bottom surface of the encapsulation body. Electroplate external pins on the bottom surface of the exposed metal pillar outside the encapsulation body, and the bottom end of the metal pillar is electrically connected to part of the external pins.

[0010] Further, in the first device encapsulation step, after encapsulating with the encapsulant, respectively perform horizontal mechanical grinding on the encapsulation surface to expose the electrical interface and the conductive blocks.

[0011] Furthermore, in the second device interconnection step, an electrode is covered above the substrate of the second device, and a diaphragm is covered above the electrode.

[0012] Furthermore, in the second device interconnection step, the distance between the diaphragm and the electrode is 1 - 5 μm.

[0013] Furthermore, in the second device interconnection step, the material of the substrate is selected from one or more of flexible materials, glass, and semiconductor materials.

[0014] Furthermore, in the second device interconnection step, the material of the diaphragm is selected from one or more of polysilicon, silicon nitride, and metal.

[0015] Further, in the second device interconnection step, the middle part of the substrate of the second device is etched through to form a back cavity, which is located directly below the diaphragm. A circuit is provided inside the substrate of the second device, and solder pads are provided at the bottom of the substrate. The top end of the circuit is electrically interconnected with the electrode, and the bottom end of the circuit is electrically interconnected with the solder pad.

[0016] Further, in the second device interconnection step, the solder pads of the second device are soldered to the top surface of the exposed conductive block outside the package by reflow soldering to form a single body.

[0017] Further, in the second device interconnection step, the diaphragm of the second device generates mechanical vibration, causing a change in the electrical value, and sequentially transmits the signal to the first device through the electrode, circuit, solder pad, conductive block, and redistribution layer for processing.

[0018] Further, in the first device encapsulation step, the first device is an ASIC chip.

[0019] Further, in the second device interconnection step, the second device is a MEMS chip.

[0020] The beneficial effects of the present invention are as follows: 1. By leading the electrical connection of the second device from the electrode on its front surface to the solder pad on its back surface, the MEMS chip has good mounting flexibility.

[0021] 2. Encapsulating the first device prolongs the service life of the ASIC chip. The back surface of the first device is exposed outside the package through the adhesive, enhancing the heat dissipation performance.

[0022] 3. The first device and the second device are separately processed and then mounted and stacked together, making the entire processing process more efficient.

[0023] 4. By soldering the solder pads of the second device to the conductive block on the package body of the first device, the two devices are stacked without using the wire bonding process, saving stacking space. The entire structure has high integration, smaller size, good structural stability, and more stable and reliable line transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figures 1-7 It is a cross-sectional schematic diagram of the manufacturing steps of the second device in a packaging process of a MEMS acoustic device structure; Figures 8-14 It is a cross-sectional schematic diagram of the encapsulation step of the first device in a packaging process of a MEMS acoustic device structure of the present invention; Figure 15 It is a cross-sectional schematic diagram of the mounting of the first device and the second device in a packaging process of a MEMS acoustic device structure of the present invention; Figures 16-17 It is a cross-sectional schematic diagram of the mounting of the substrate ring and the cover plate encapsulation in a packaging process of a MEMS acoustic device structure of the present invention; Figure 18 Cross-sectional view of a package structure obtained by a packaging process for a MEMS acoustic device structure according to the present invention; Figure 19 Cross-sectional view of a second device obtained by a packaging process for a MEMS acoustic device structure according to the present invention.

[0025] In the figure: 1. First device; 2. Redistribution layer; 3. Conductive block; 4. Package body; 5. Metal post; 6. External pin; 7. Second device; 8. Solder pad; 9. Substrate; 10. Circuit; 11. Back cavity; 12. Diaphragm; 13. Substrate ring; 14. Cover plate; 15. Sound hole. Detailed implementation manners

[0026] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative efforts based on the embodiments in the present invention belong to the scope of protection of the present invention; the content of the present invention will be described below in conjunction with specific implementation manners, and examples of the implementation manners are shown in the accompanying drawings, where the same or similar reference numerals indicate the same or similar components or components with the same or similar functions throughout.

[0027] Terms such as "first" and "second" in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments described here can be implemented in an order different from that shown or described here; the directional terms mentioned in the present invention, such as: up, down, left, right, front, back, inside, outside, front side, back side, side, etc., are only references to the directions in the accompanying drawings. The implementation manners and the directional terms used below by referring to the accompanying drawings are exemplary and are only used to explain the present invention and cannot be construed as a limitation to the present invention. In addition, for various specific examples of processes and materials provided by the present invention, those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0028] To better understand the objectives, structure and functions of the present invention, a packaging process for a MEMS acoustic device structure proposed by the present invention will be further described in detail below with reference to the accompanying drawings. The process includes the following steps: Mounting and encapsulating the first device 1: Mount the first device 1 on a carrier board, encapsulate the first device 1 and grind the encapsulation surface until the electrical interface is exposed; Electrical lead-out of the first device 1: The electroplated redistribution layer 2 is laid flat on the package cover. The redistribution layer 2 is electrically connected to the exposed electrical interface of the first device 1, and the conductive block 3 is electroplated on a part of the redistribution layer 2. Then, continue the encapsulation and grinding to expose the top surface of the conductive block 3. The encapsulant forms an encapsulation body 4. Mounting and interconnection of the second device 7: The second device 7 is electrically interconnected with the conductive block 3 through the bottom solder feet 8 of the substrate. The second device 7 and the first device 1 are stacked vertically. Mounting of the substrate ring 13: The substrate ring 13 is mounted on the encapsulation body 4 to enclose the second device 7. Cover plate 14 encapsulation: The cover plate 14 is mounted on the substrate ring 13 to seal the substrate ring 13. The sound holes on the cover plate 14 are aligned with the middle position of the diaphragm 12 of the second device 7.

[0029] Generally speaking, the above steps of this process can be summarized into the following five steps: manufacturing of the second device 7, encapsulation of the first device 1 (such as mounting and encapsulation of the first device 1 and electrical lead-out of the first device 1), mounting of the first device 1 and the second device 7 (mounting and interconnection of the second device 7), mounting of the substrate ring 13, and encapsulation of the cover plate 14.

[0030] Among them, the second device 7 is a MEMS chip, and the manufacturing steps of the second device 7 are specifically as follows: S1: Provide a carrier board, which can be a resin board commonly used in the art. Place the original substrate 9 for manufacturing the second device 7 on the carrier board (as Figure 1 shown); the substrate 9 can be one or more of flexible materials, glass, semiconductor materials, usually silicon. Silicon has good mechanical properties, thermal stability, and good compatibility with microfabrication processes. The substrate 9 is located at the bottom layer of the second device 7, serving as the mechanical support of the entire structure, providing structural stability, and serving as the substrate for other components such as electrodes and the back cavity 11.

[0031] S2: Cover a layer of electrodes on the upper surface of the substrate 9 (as Figure 2 shown). The electrodes of the MEMS acoustic sensor are divided into fixed electrodes and movable electrodes. The fixed electrodes are located above or below the diaphragm 12 and are parallel to the diaphragm 12, fixed on the substrate 9, while the movable electrodes are directly integrated on the surface of the diaphragm 12. The diaphragm 12 itself can serve as an electrode. In this application, the electrodes cover the upper surface of the substrate 9.

[0032] S3: Continue to cover a layer of diaphragm 12 on the electrodes (as Figure 3As shown in the figure, in the present invention, the electrode is disposed below the diaphragm 12. The electrode is a fixed electrode, and the fixed electrode is designed as a porous structure to reduce air damping and allow sound waves to pass through. The distance between the diaphragm 12 and the electrode is about 1-5 μm to form a variable capacitor. The diaphragm 12 is directly exposed to the external sound field. The material of the diaphragm 12 is selected from polysilicon. The polysilicon film has excellent characteristics such as high mobility like single-crystalline silicon material, compatibility with amorphous silicon thin film growth process, easy to achieve large-area growth, and low preparation cost, and is widely used in technical fields such as microelectronic devices. In addition, the polysilicon film structure is also commonly used in microelectromechanical systems (MEMS), especially as the basic vibration structure of sensor devices. The material of the diaphragm 12 can also be one or more of silicon nitride or metal, etc. The thickness of the diaphragm 12 on the second device is extremely thin, with a thickness ranging from nanometers to micrometers, sensitive to sound pressure, and its vibration displacement is proportional to the sound pressure, which is the core sensitive element of the sensor.

[0033] S4: Peel the substrate 9 from the carrier plate, turn it upside down and remount it on the carrier plate. At this time, the diaphragm 12 contacts the carrier plate, and the bottom of the substrate 9 faces upward (as Figure 4 shown).

[0034] S5: Etch at the middle position of the substrate 9 to expose the electrode, making the substrate 9 into an annular structure with a hollow middle. The hollow part is the back cavity 11 of the substrate 9. The back cavity 11 is located directly below the diaphragm 12. The back cavity 11 is generally cylindrical or rectangular. In the present invention, the cylindrical shape is taken as an example. The depth of the back cavity 11 is determined by the acoustic sensitivity and frequency response requirements of specific products. The structure of the back cavity 11 allows the diaphragm 12 to vibrate freely under the action of sound pressure, avoids air damping, and can balance the pressures on both sides of the diaphragm 12; and at the same time etch the remaining cylindrical ring of the substrate 9 to also expose the electrode (as Figure 5 shown). Since the substrate 9 can be one or more of flexible materials, glass, semiconductor materials, usually silicon, when etching, a protective film is coated on the surface of the substrate 9 to be etched, and the position to be etched is not coated with the film for protection. In this application, anisotropic etching perpendicular to the surface of the substrate 9 is used, and the etching penetrates from the surface of the substrate 9 to the upper surface of the electrode, exposing the electrode surface.

[0035] Etching can be carried out by laser etching, dry etching or other etching methods. Vertical through holes are formed on the substrate by etching, and the through holes are used for vertical interconnection in multi-layer stacked packaging, such as electroplated circuits. In the present invention, laser etching (Laser Ablation) is taken as an example. Its principle is: using a high-energy laser beam to directly ablate the material, without a mask, and controlling the etching situation by adjusting parameters such as the laser irradiation frequency.

[0036] S6: After etching the cylindrical ring of the substrate 9, the holes formed by etching are filled through an electroplating process. The electroplated metal constitutes the circuit 10. The bottom end of the circuit 10 is integrally connected to the electrode, and the electroplated solder feet 8 are extended along the surface of the substrate 9 at the top of the electroplating (as Figure 6 shown). In the process of manufacturing the second device 7, after covering the electrode and the diaphragm 12, etching the back cavity of the substrate 9 is the normal process for manufacturing the second device 7. Since the diaphragm 12 is very thin, protective measures need to be taken to protect the diaphragm 12 during the process, such as covering a polymer protective layer on the surface of the diaphragm 12 to prevent contamination or mechanical damage. This invention will not elaborate further. After peeling off the carrier plate, the manufacturing of the second device 7 is completed (as Figure 7 shown). The diaphragm 12 generates mechanical vibrations under the impact of sound waves, causing changes in capacitance or other electrical values. The electrode transmits the changed electrical values to the solder feet 8 through the circuit.

[0037] During the manufacturing process of the second device 7, electroplating the circuit 10 and the solder feet 8 is added after etching the substrate 9. The electrical property of the second device 7 is led from the electrode on its front side (the side where the diaphragm 12 is located) to the solder feet 8 on its back side. The second device 7 is mounted through the solder feet 8 to achieve electrical connection. The MEMS chip has better mounting flexibility. Instead of wire bonding, the internal circuit of the substrate is used, and the structure is compact, meeting the requirements of device miniaturization.

[0038] Through the above manufacturing steps of the second device 7, a MEMS chip packaging structure of an acoustic device, that is, the second device 7 (MEMS chip), can be obtained. As Figure 19 shown, Figure 19 is a cross-sectional view of the packaging structure, including the substrate 9. The material of the substrate 9 is selected from one or more of flexible materials, glass, and semiconductor materials. It also includes: An electrode and a diaphragm 12. The electrode is arranged above the substrate 9. The electrode is a porous structure. The diaphragm 12 is arranged above the electrode. The distance between the diaphragm 12 and the electrode is about 1 - 5 μm. The material of the diaphragm 12 is selected from one or more of polysilicon, silicon nitride, or metal; A back cavity 11. The back cavity 11 is formed by etching through the middle position of the surface of the substrate 9 away from the electrode, exposing the electrode. The back cavity 11 is located directly below the diaphragm 12 and the electrode; A circuit 10. Circuit holes are formed by etching through other parts of the substrate 9, and the circuit holes are filled with electroplated metal to form the circuit 10. One end of the circuit 10 is electrically connected to the electrode, and the other end of the circuit 10 is flush with the surface of the substrate 9 and exposed. The electroplated solder feet 8 are extended on the surface of the substrate 9 of the exposed circuit 10. The solder feet 8 are electrically connected to the circuit 10.

[0039] The diaphragm 12 generates mechanical vibrations under the impact of sound waves, causing changes in capacitance or other electrical values. The electrode transmits the changed electrical values to the solder feet 8 through the circuit 10.

[0040] Among them, the first device 1 is an ASIC chip, and the ASIC chip is encapsulated in the package body 4. The manufacturing steps of the first device 1 are specifically as follows: S1: Provide a carrier board, which can be a resin board commonly used in the art. Place the first device 1 on the carrier board (as Figure 8 shown). The front of the first device 1 has electrical interfaces, and the back of the first device 1 is mounted on the carrier board.

[0041] S2: Use encapsulant to encapsulate the first device 1 on the carrier board, and horizontally grind the top surface of the encapsulation by mechanical grinding until the front electrical interfaces of the first device 1 are exposed (as Figure 9 shown).

[0042] S3: Vertically etch the encapsulant at the corresponding position on the top surface of the encapsulation to form a drill hole until the surface of the carrier board is exposed (as Figure 10 shown).

[0043] S4: Electroplate metal posts 5 to fill the drill holes through electroplating process. The bottom ends of the metal posts 5 are in contact with the carrier board, and horizontally lay electroplated redistribution layers 2 on the top surface of the encapsulation. The redistribution layers 2 are respectively connected to the exposed electrical interfaces of the first device 1, and electroplate conductive blocks 3 on a part of the redistribution layers 2 (as Figure 11 shown). The other part of the redistribution layers 2 is electrically connected to the top ends of the metal posts 5. The electricity of the first device 1 is transmitted from the electrical interfaces through the redistribution layers 2 to the bottom ends of the metal posts 5. The electricity of the first device 1 is electrically connected by the electrical interfaces, redistribution layers 2 and conductive blocks 3.

[0044] S5: Continue to use encapsulant to encapsulate on the top surface of the encapsulation in S2, encapsulate each redistribution layer 2, conductive block 3, and metal post 5 in the encapsulant, and horizontally grind the top surface of the new encapsulation in the same way of mechanical grinding until the top surface of the conductive block 3 is exposed (as Figure 12 shown). The conductive block 3 serves as the electrical connection end between the first device 1 and the second device 7, and its quantity and layout are set according to the electrical connection relationship between the second device 7 and the first device 1 of the actual product.

[0045] S6: Peel the whole encapsulation from the carrier board, turn it upside down and remount it on the carrier board. At this time, the exposed conductive block 3 is in contact with the carrier board, and the bottom ends of the exposed metal posts 5 are exposed. Electroplate external pins 6 at the corresponding positions on this surface of the whole encapsulation, and part of the external pins 6 are electrically connected to the exposed metal posts 5 (as Figure 13 shown).

[0046] S7: After electroplating, peel the whole encapsulation from the carrier board to obtain the package body 4 of the first device 1 (as Figure 14As shown in the figure, for mounting multiple first devices 1 on a carrier board at one time and processing multiple first devices 1 simultaneously in the process flow, a cutting process is finally required, that is, cutting the encapsulant at the cutting lane position in the safe area of the overall encapsulation, so as to separate the encapsulation body 4 of each first device 1 into product units. In the present invention, the encapsulation case of one first device 1 is taken as an example for processing.

[0047] The first device 1 is encapsulated in the encapsulation body 4, so that the ASIC chip is protected from the external environment and its service life is extended. The back surface of the first device 1 is exposed outside the encapsulation body 4 through an adhesive, enhancing the heat dissipation performance.

[0048] The specific mounting steps of the first device 1 and the second device 7 are as follows: S1: The encapsulation body 4 is re-placed on the carrier board through the external pins 6, and the solder feet 8 of the second device 7 are stacked with the exposed conductive blocks 3 of the encapsulation body 4 (as Figure 15 shown). The solder feet 8 of the second device 7 are soldered to the exposed conductive blocks 3 of the encapsulation body 4 through reflow soldering to form an integrated body, and the two devices are electrically connected. The diaphragm 12 of the second device 7 generates mechanical vibration under the impact of sound waves, causing a change in capacitance or other electrical values. The electrodes transmit the changed electrical values to the solder feet 8 through the circuit 10. The solder feet 8 are transmitted to the first device 1 through the conductive blocks 3 and the redistribution layer 2 for processing, such as signal amplification, filtering, and analog-to-digital conversion (ADC), etc. According to the specific product structure and its functions, the electrical connection relationship between the first device 1 and the second device 7 is laid out, and the circuit 10 and solder feet 8 of the second device 7, as well as the number and positions of the conductive blocks 3 and the redistribution layer 2 of the first device 1 are correspondingly laid out. For example, to increase the clock or synchronization signal performance, the ASIC needs to synchronously sample (such as a digital microphone), and may provide a clock signal to the MEMS to coordinate the work. An electrical connection relationship to implement this function needs to be added between the first device 1 and the second device 7. All the figures are cross-sectional views, only showing the electrical connection relationship presented by this cross-sectional view. Other necessary electrical connection relationships between the ASIC chip and the MEMS chip are also within the protection scope of the present invention.

[0049] In the present invention, the first device 1 and the second device 7 are processed separately and then mounted and stacked together. The first device 1 and the second device 7 can be pre-fabricated separately without affecting each other, and the overall processing efficiency is higher. In the present invention, the second device 7 is processed first and the first device 1 is processed later as an example; by soldering the solder feet 8 of the second device 7 to the conductive blocks 3 of the encapsulation body 4 of the first device 1, the two devices are stacked without using a wire bonding process, saving stacking space, with a high integration degree of the whole structure, smaller size, good structural stability, and more stable and reliable line transmission.

[0050] There are often significant differences in the structural dimensions between MEMS chips and ASIC chips. By electroplating the redistribution layer 2 and the conductive block 3 in the package 4, the electrical interfaces of the ASIC chip are repositioned to adapt to the size of the MEMS chip, ensuring that the MEMS chip is stacked and mounted on the conductive block 3 of the ASIC chip through the bottom solder feet 8 of the substrate 9 to achieve electrical interconnection. The size of the entire sensor meets the miniaturization requirements, with a compact structure and reasonable layout.

[0051] The specific steps for mounting the substrate ring 13 and encapsulating the cover plate 14 are as follows: S1: The substrate ring 13 is mounted on the package 4 to enclose the second device 7 therein (as Figure 16 shown). The side surface of the substrate ring 13 is flush with the side surface of the package 4 of the second device 7. The substrate ring 13 is arranged along the surface shape of the package 4. The substrate ring 13 is a printed circuit board (PCB). The reason for using a PCB is that on the one hand, its cost is relatively low and the process is relatively mature. On the other hand, it is convenient to directly connect the PCB to the package 4, and connection and mounting can be achieved through an adhesive or the like. The height of the substrate ring 13 is higher than the height of the second device 7, and the second device 7 can be enclosed within the substrate ring 13.

[0052] S2: The cover plate 14 is mounted on the substrate ring 13, and the side surface of the cover plate 14 is also flush with the side surface of the substrate ring 13 (as Figure 17 shown). The cover plate 14 and the substrate ring 13 can be connected and mounted through an adhesive or the like to seal the substrate ring 13. Sound holes 15 are provided on the cover plate 14. The sound holes 15 are aligned with the middle position of the diaphragm 12 of the second device 7. The diaphragm 12 is aligned with the middle position of the back cavity 11 of the second device 7. The three are arranged vertically. The diaphragm 12 communicates with the external environment through the sound holes 15.

[0053] The working principle of MEMS (Micro-Electro-Mechanical System) acoustic sensors (such as MEMS microphones) is based on the conversion between mechanical vibration and electrical signals. Its core is to convert acoustic waves (sound signals) into electrical signals through a micro-mechanical structure. The core of the MEMS acoustic sensor is a micron-scale diaphragm 12 suspended above the back cavity 11. There are electrodes between the diaphragm 12 and the substrate 9, and the electrodes form a capacitive structure. The substrate ring 13 and the cover plate 14 encapsulate and protect the MEMS chip. The cover plate 14 has sound holes 15, and the sound holes 15 are vertically aligned with the middle of the diaphragm 12 of the MEMS chip. When acoustic waves (air vibrations) act on the diaphragm 12 through the sound holes 15, the diaphragm 12 will undergo mechanical vibration with the change of sound pressure. The back cavity 11 of the substrate 9 provides a vibration space and acoustic damping to adjust the mechanical response of the diaphragm 12. The mechanical vibration of the diaphragm 12 causes the distance between the electrodes and the substrate 9 to change, and the electrical property value of the electrodes changes, such as the capacitance value C. The capacitance value C is determined by the formula C = εA / d (where ε is the dielectric constant, A is the electrode area, and d is the plate spacing, and the plates refer to the electrodes and the substrate 9). The change in the electrical property value of the electrodes is transmitted to the ASIC chip through the circuit 10, the solder pad 8, the conductive block 3, and the redistribution layer 2. The present invention sets these structures and can also reduce or increase corresponding components. As long as the electrical connection relationship between the ASIC chip and the MEMS chip can be achieved, it also belongs to the protection scope of the present invention. The application-specific integrated circuit (ASIC) integrated in the sensor is responsible for processing these changes in electrical property values. The ASIC chip is integrated inside the sensor, which can reduce noise interference and improve sensitivity. The ASIC chip provides a bias voltage (DC voltage) for the capacitive structure to convert the capacitance change into a charge change, and converts the weak charge into a voltage signal through a charge amplifier, and then converts the analog voltage signal into a digital signal for output. The ASIC chip does not need to directly interact with the environment and is encapsulated in the package 4. The plastic encapsulant is used to protect it from moisture, dust, and mechanical stress. No additional protective structure is required after encapsulation, and the overall integration of the sensor is higher. The ASIC chip leads out its electrical properties to the outside of the package 4 through the redistribution layer 2, the metal posts 5, and the external pins 6. The external pins 6 serve as a connection bridge between the electrical properties outside the working area of the sensor and the electrical properties inside the ASIC chip in the package 4. Of course, other structures for realizing the internal electrical connection of the package 4 also belong to the protection scope of the present invention.

[0054] Through the above-mentioned packaging process of the MEMS acoustic device structure, a MEMS acoustic device packaging structure can be obtained. As Figure 18 shown, Figure 18 is a cross-sectional view of the packaging structure, including a first device 1 and a second device 7, and further including: A package 4, the first device 1 is encapsulated in the package 4, and the first device 1 is an ASIC chip; The redistribution layer 2 and the conductive block 3 are provided. Inside the package 4, the redistribution layer 2 electrically connected to the electrical interface of the first device 1 is electroplated in a tiled manner, and the conductive block 3 is electroplated on a part of the redistribution layer 2. The top surface of the conductive block 3 is flush with the top surface of the package 4 and exposed. The structural sizes of the MEMS chip and the ASIC chip often have large differences. By electroplating the redistribution layer 2 and the conductive block 3 inside the package 4, the electrical interface of the ASIC chip is re-layouted to adapt to the size of the MEMS chip, ensuring that the MEMS chip is stacked and mounted on the conductive block 3 of the ASIC chip through the bottom solder pads 8 of the substrate 9, realizing electrical interconnection. The size of the entire sensor meets the miniaturization requirements, with a compact structure and a reasonable layout.

[0055] Before electroplating the redistribution layer 2 inside the package 4, the encapsulant is vertically etched to the bottom surface of the package 4, and the metal pillars 5 are electroplated to completely fill the drilled holes. The top end of the metal pillar 5 is electrically connected to another part of the redistribution layer 2. The electricity of the first device 1 is transmitted from the electrical interface through the redistribution layer 2 to the bottom end of the metal pillar 5. The bottom end of the metal pillar 5 is flush with the bottom surface of the package 4 and exposed. External pins 6 are electroplated on the bottom surface of the exposed metal pillars 5 of the package 4. The bottom end of the metal pillar 5 is electrically connected to a part of the external pins 6. The external pins 6 serve as the connection bridge between the external electricity in the working area of the sensor and the internal electricity of the ASIC chip inside the package 4.

[0056] The second device 7 is mounted on the exposed conductive block 3 of the package 4 through the bottom solder pads 8 of the substrate 9, realizing the vertical stacking and electrical interconnection of the second device 7 and the first device 1. An electrode is covered above the substrate 9 of the second device 7, and a diaphragm 12 is covered above the electrode. The material of the substrate 9 of the second device 7 is selected from one or more of flexible materials, glass, and semiconductor materials. The substrate 9 is located at the bottommost layer of the second device 7, serving as the mechanical support of the entire structure, providing structural stability, and serving as the substrate for other components such as electrodes and the back cavity 11. The material of the diaphragm 12 is selected from one or more of polysilicon, silicon nitride, or metal. The thickness of the diaphragm 12 is extremely thin, ranging from nanometers to micrometers, sensitive to sound pressure, and its vibration displacement is proportional to the sound pressure. It is the core sensitive element of the sensor.

[0057] The middle part of the substrate 9 of the second device 7 is etched through to form a back cavity 11. The back cavity 11 is located directly below the diaphragm 12. The structure of the back cavity 11 allows the diaphragm 12 to vibrate freely under the action of sound pressure, avoiding air damping, and can balance the pressures on both sides of the diaphragm 12. A circuit 10 is provided inside the substrate 9 of the second device 7. The top end of the circuit 10 is interconnected with the electrode, and the bottom end of the circuit 10 is electrically interconnected with the bottom solder pads 8 of the substrate 9. The solder pads 8 of the second device 7 are welded to the top surface of the exposed conductive block 3 of the package 4 by reflow soldering to form an integrated body.

[0058] By adding electroplated circuit 10 and solder feet 8 after etching the substrate 9 during the manufacturing process of the second device 7, the electrical connection of the second device 7 is led from the electrodes on its front side (the side where the diaphragm 12 is located) to the solder feet 8 on its back side, resulting in better flexibility in mounting the second device 7 and a more compact structure.

[0059] The diaphragm 12 generates mechanical vibrations, causing changes in electrical values, which are then transmitted through the electrodes, circuit 10, solder feet 8, conductive block 3, and redistribution layer 2 to the first device 1 for signal processing in sequence. The second device 7 is a MEMS chip.

[0060] Substrate ring 13, the substrate ring 13 is mounted on the package body 4 to enclose the second device 7.

[0061] Cover plate 14, the cover plate 14 is mounted on the substrate ring 13 to seal the substrate ring 13. The sound holes 15 on the cover plate 14 are aligned with the middle position of the diaphragm 12 of the second device 7. The substrate ring 13 and the cover plate 14 are bonded with adhesive.

[0062] In this structure, the substrate ring 13 and the cover plate 14 encapsulate and protect the MEMS chip. The cover plate 14 has sound holes 15 that are vertically aligned with the middle of the diaphragm 12 of the MEMS chip. When sound waves (air vibrations) act on the diaphragm 12 through the sound holes 15, the diaphragm 12 will undergo mechanical vibrations with changes in sound pressure. The back cavity 11 of the substrate 9 provides a vibration space and acoustic damping to adjust the mechanical response of the diaphragm 12. The mechanical vibrations of the diaphragm 12 cause changes in the distance between the electrodes and the substrate 9, resulting in changes in the electrical values of the electrodes. The changes in the electrical values of the electrodes are transmitted through the circuit 10, solder feet 8, conductive block 3, and redistribution layer 2 to the ASIC chip. The ASIC chip processes the changes in electrical values such as capacitance values and amplifies the signals. The ASIC chip is integrated inside the sensor and is encapsulated within the package body 4, and is encapsulated with molding compound to protect it from moisture, dust, and mechanical stress. The ASIC chip leads out its electrical connection to the outside of the package body 4 through the redistribution layer 2, metal posts 5, and external pins 6.

[0063] The beneficial effects of the present invention are as follows: 1. By adding electroplated circuit 10 and solder feet 8 after etching the substrate 9 during the manufacturing process of the second device 7, the electrical connection of the second device 7 is led from the electrodes on its front side (the side where the diaphragm 12 is located) to the solder feet 8 on its back side, resulting in better flexibility in mounting the second device 7.

[0064] 2. Encapsulating the first device 1 within the package body 4 protects the ASIC chip from the external environment, extending its service life. The back side of the first device 1 is exposed outside the package body 4 through adhesive, enhancing the heat dissipation performance.

[0065] 3. The first device 1 and the second device 7 are processed separately and then mounted and stacked together. The first device 1 and the second device 7 can be pre-fabricated separately without affecting each other, and the overall processing efficiency is higher.

[0066] 4. By soldering the pins 8 of the second device 7 onto the conductive block 3 of the package body 4 of the first device 1, the stacking of the two devices is achieved without using the wire bonding process, saving stacking space. The overall structure has high integration, smaller size, good structural stability, and more stable and reliable line transmission.

[0067] In all the encapsulation steps of the present invention, the encapsulating material used is a plastic encapsulant, and the specific material can be epoxy resin, cyanate ester, polyimide, etc. It has low cost and good curing performance. The encapsulation process plays an important role in the semiconductor manufacturing field, mainly reflected in aspects such as protection, connection, support, reliability, and promotion of technological progress; the encapsulation method is the commonly used molding and injection molding methods in the art.

[0068] In all the post-encapsulation grinding processes of the present invention, a commonly used grinding machine in this technical field is used to perform surface treatment on the encapsulation surface, that is, horizontal mechanical grinding on the top surface of the encapsulation. Finally, after grinding, the grinding surface is horizontal and flat, and the outer surface of the entire encapsulation structure is smooth.

[0069] In all the steps using the electroplating process of the present invention, first, a photoresist film is used to form electroplating protection on the surface through the photolithography techniques of exposure and development, protecting the areas that do not need electroplating with the photoresist film and exposing the areas that need electroplating. Then, a metal seed layer is formed in the area to be electroplated through a suitable method such as sputtering or copper deposition. The metal seed layer is made of copper or other metal materials. The metal seed layer is to ensure the bonding force between the subsequent electroplated metals, between the metal and the encapsulating material, and at the same time provide a surface for the attachment of conductive ions for electroplating to ensure the electroplating effect. The entire process and the materials used during electroplating are also common technical knowledge in the art. In all the electroplating processes of the present invention, the electroplated metal is made of copper.

[0070] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent substitutions can be made to these features and embodiments. Additionally, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present invention belong to the scope protected by the present invention.

Claims

1. A packaging process for a MEMS acoustic device structure, characterized in that: The following steps are involved: First device encapsulation: encapsulating the first device and exposing the electrical interface, electroplating a redistribution layer connected to the electrical interface on the encapsulation surface, electroplating a conductive block on a portion of the redistribution layer, and continuing to encapsulate and expose the top surface of the conductive block to form a package; Second device interconnection: the second device is electrically interconnected with the conductive block, and the second device is stacked and interconnected with the first device; Substrate ring mounting: A substrate ring is mounted on the package to surround the second device; Cover packaging: The cover is mounted on the sealing substrate ring, and the sound hole of the cover is aligned with the middle of the diaphragm of the second device.

2. The packaging process of the MEMS acoustic device structure according to claim 1, characterized in that: In the first device encapsulation step, the first device is placed on a carrier, and before the redistribution layer is electroplated on the top surface of the encapsulation to expose the electrical interface after the first device is encapsulated, the encapsulation material is vertically etched to the bottom of the drilled hole to expose the carrier, and the metal column is electroplated to completely fill the drilled hole.

3. The packaging process of the MEMS acoustic device structure according to claim 2, characterized in that: In the first device encapsulation step, the top of the metal column is electrically connected to another part of the redistribution layer, the bottom of the metal column is in contact with the carrier, and the first device electrical property is transferred from the electrical interface to the bottom of the metal column through the redistribution layer.

4. The packaging process of the MEMS acoustic device structure according to claim 3, characterized in that: In the first device encapsulation step, the bottom end of the metal column is flush with the bottom surface of the package body and exposed, external pins are electroplated on the bottom surface of the exposed metal column outside the package body, and the bottom end of the metal column is electrically connected to some of the external pins.

5. The packaging process of the MEMS acoustic device structure according to claim 1, characterized in that: In the first device encapsulation step, after encapsulation with an encapsulation material, mechanical grinding is performed at the encapsulation surface level to expose the electrical interface and the conductive block.

6. The packaging process of the MEMS acoustic device structure according to claim 1, characterized in that: In the second device interconnection step, the substrate of the second device is covered with electrodes, and the electrodes are covered with a diaphragm.

7. The packaging process of the MEMS acoustic device structure according to claim 6, characterized in that: In the second device interconnection step, the distance between the diaphragm and the electrode is 1-5 μm.

8. The packaging process of the MEMS acoustic device structure according to claim 6, characterized in that: In the second device interconnection step, the material of the substrate is selected from one or more of flexible materials, glass, and semiconductor materials.

9. The packaging process of the MEMS acoustic device structure according to claim 6, characterized in that: In the second device interconnection step, the material of the diaphragm is selected from one or more of polysilicon, silicon nitride or metal.

10. The packaging process of the MEMS acoustic device structure according to claim 6, characterized in that: In the second device interconnection step, the middle of the substrate of the second device is etched through to form a back cavity, the back cavity is located directly below the diaphragm, a circuit is provided inside the substrate of the second device, a solder pin is provided at the bottom of the substrate, the top of the circuit is electrically interconnected with the electrode, and the bottom of the circuit is electrically interconnected with the solder pin.

11. The packaging process of the MEMS acoustic device structure according to claim 10, characterized in that: In the second device interconnection step, the second device soldering feet are soldered to the top surface of the conductive block exposed outside the package body through reflow soldering.

12. The packaging process of the MEMS acoustic device structure according to claim 10, characterized in that: In the second device interconnection step, the diaphragm of the second device generates mechanical vibration, causing an electrical value change, which is transmitted to the first device for signal processing through electrodes, circuits, solder feet, conductive blocks, and redistribution layers in sequence.

13. The packaging process of the MEMS acoustic device structure according to claim 1, characterized in that: In the first device encapsulation step, the first device is an ASIC chip.

14. The packaging process of the MEMS acoustic device structure according to claim 1, characterized in that: In the second device interconnection step, the second device is a MEMS chip.

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