A MEMS acceleration sensor packaging structure and a packaging process thereof

Abstract

The application discloses a MEMS acceleration sensor packaging structure and a packaging process thereof, and belongs to the technical field of MEMS device packaging. The packaging structure comprises a composite stress isolation base, a gradient thermal matching bonding system and a multi-dimensional limiting anti-vibration assembly. The rigid support frame of the composite stress isolation base forms point contact support with the ceramic packaging tube shell through the point support boss, greatly reduces the transmission contact area of thermal stress and thermal deformation, cooperates with the elastic deformation of the flexible support beam to absorb the thermal deformation of the tube shell, and gradually releases the thermal stress through the modulus gradient bonding structure of the gradient thermal matching bonding system. The chip-level flexible damping limiting boss of the multi-dimensional limiting anti-vibration assembly and the packaging-level elastic buffer column form omnidirectional limiting and buffering in the plane and in the normal direction. Without interfering with the detection accuracy of the MEMS chip, the high-temperature interface peeling and thermal stress drift caused by the mismatch of the thermal expansion coefficients of the silicon-based MEMS chip and the ceramic packaging tube shell are solved.

Description

Technical Field

[0001] This invention belongs to the field of MEMS device packaging technology, and in particular relates to a high-temperature resistant and vibration-resistant MEMS accelerometer packaging structure and its packaging process. Background Technology

[0002] MEMS sensors are widely used in aerospace, automotive electronics, and industrial measurement and control due to their advantages of miniaturization, low power consumption, and high integration. Among them, MEMS chips with resonant sensitive structures and sandwich capacitive triangular electrode arrays have significant advantages in acceleration and vibration detection scenarios due to their high sensitivity and wide measurement range. These chips have a large inertial mass block at the center, making them extremely sensitive to thermal stress, mechanical shock, and ambient temperature. The difference in thermal expansion coefficients between the silicon substrate and the ceramic package is large, and conventional packaging structures cannot meet their usage requirements in harsh environments with high temperature and high vibration.

[0003] In existing technologies, packaging solutions for this type of MEMS chip mostly focus on optimizing the chip's structure, improving its vibration resistance through beam structure design. However, these solutions do not address the issues of high-temperature interface delamination and thermal stress drift caused by the large difference in thermal expansion coefficients between the silicon-based chip and the ceramic package. Existing low-stress packaging technologies often employ multi-layer adhesive structures to achieve stress isolation, but these are only general-purpose packaging solutions and are not tailored to the high sensitivity and stress-sensitive characteristics of large-mass MEMS chips. They cannot simultaneously meet the dual requirements of thermal stress isolation and high-g impact protection. Therefore, it is still necessary to improve the high-temperature resistance and vibration resistance of the MEMS accelerometer packaging structure. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a MEMS accelerometer packaging structure and packaging process, which solves the problems that existing packaging solutions cannot solve the high-temperature failure and thermal stress drift caused by the mismatch of thermal expansion coefficients between silicon-based chips and ceramic shells, and cannot simultaneously take into account thermal stress isolation and high impact protection.

[0005] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0006] In a first aspect, the present invention provides a MEMS accelerometer packaging structure, comprising a ceramic package shell, a MEMS chip disposed within the inner cavity of the ceramic package shell, and a metal sealing cover plate covering the opening end of the ceramic package shell, wherein the inner cavity of the ceramic package shell further comprises: The composite stress isolation base includes a central support platform, a rigid support frame, and a flexible support beam. The rigid support frame forms a point-contact support with the bottom of the inner cavity of the ceramic encapsulation shell through a support boss on its lower surface, and there is a gap between the rigid support frame and the side wall of the inner cavity of the ceramic encapsulation shell. The central support platform is connected to the internal area of ​​the rigid support frame through the flexible support beam, and forms a gap with the bottom of the inner cavity of the ceramic encapsulation shell. The gradient thermal matching bonding system includes at least three bonding structures arranged sequentially along the thermal stress transmission direction. The three bonding structures are configured as follows: the first bonding layer located between the MEMS chip and the central support stage provides rigid fixation for the MEMS chip; the second bonding layer covering the sidewall of the MEMS chip provides flexible buffering; and the third bonding layer filling the lower surface of the rigid support frame and the bottom of the inner cavity of the ceramic package provides thermal expansion coefficient transition matching. The multi-dimensional limiting and vibration-damping components include a chip-level flexible damping limiting protrusion set on the upper surface of the central support platform and located outside the MEMS chip, and a package-level elastic buffer column set on the lower surface of the metal sealing cover and facing the upper part of the central support platform. A redistribution layer is disposed on the upper surface of the central support platform, through which the external pins of the MEMS chip and the ceramic package are electrically connected.

[0007] The flexible support beam comprises multiple sets of symmetrically distributed cantilever beams, each set of cantilever beams arranged in an E-shape.

[0008] Optionally, the chip-level flexible damping limiting protrusion is a photosensitive polyimide, and its height is higher than the upper surface of the MEMS chip; the distance between the inner wall of the chip-level flexible damping limiting protrusion and the outer wall of the MEMS chip is 5μm~20μm. The encapsulation-grade elastic buffer pillar is made of fluorosilicone rubber and has an embedded helical spring skeleton inside; The distance between the lower end face of the encapsulation-grade elastic buffer post and the upper surface of the central support platform is 10μm~30μm.

[0009] Optionally, the first adhesive layer is an epoxy adhesive layer with an elastic modulus of 1 GPa to 20 GPa and a coefficient of thermal expansion of 10 ppm / ℃ to 50 ppm / ℃. The second adhesive layer is a silicone gel buffer layer with an elastic modulus of 0.001 MPa to 0.1 MPa and a coefficient of thermal expansion of 150 ppm / ℃ to 350 ppm / ℃. The third adhesive layer is a modified silicone adhesive layer with an elastic modulus of 0.1MPa to 20MPa and a coefficient of thermal expansion of 50ppm / ℃ to 150ppm / ℃.

[0010] Optionally, the metal sealing cover is a Kovar alloy integral molding structure; The outer surface of the metal sealing cover is equipped with an array of heat dissipation fins, and the inner surface is fixed with a non-evaporative getter.

[0011] Optionally, the upper surface of the central support platform is provided with an annular stress relief blind groove, and the bottom height of the annular stress relief blind groove is higher than the lower surface of the central support platform. The ceramic package has thermal isolation grooves at the base of its external pins, and the depth of the thermal isolation grooves on the multiple external pins increases linearly along the heat transfer direction.

[0012] Optionally, the redistribution layer is a titanium-platinum multilayer metal stacked structure, and the MEMS chip is bonded to the redistribution layer via gold alloy wires or aluminum-silicon alloy wires.

[0013] Optionally, the composite stress isolation base is integrally formed from semiconductor material, silicon-on-insulator material, or glass material.

[0014] In a second aspect, the present invention provides a MEMS accelerometer packaging process for fabricating the MEMS accelerometer packaging structure described in any one of the first aspects, comprising: A composite stress isolation base with flexible support beams, a central bearing platform, a rigid support frame and support bosses is formed by integrally molding the substrate through etching process, and a redistribution layer is prepared on the surface of the central bearing platform. The MEMS chip is bonded and fixed to the preset position of the central support platform through the first adhesive layer, and then cured. A chip-level flexible damping limiting protrusion is fabricated at a predetermined position on the central support platform, and the electrode pads of the MEMS chip are electrically connected to the redistribution layer through a bonding process. A third adhesive layer is coated in a preset area at the bottom of the inner cavity of the ceramic package shell. The composite stress isolation base is positioned in the inner cavity of the ceramic package shell through the support boss, so that the third adhesive layer fills the non-support gap area. After curing, a second adhesive layer is coated on the side wall of the MEMS chip and cured, so that the coating area of ​​the second adhesive layer avoids the deformation area of ​​the flexible support beam. A package-grade elastic buffer pillar is fixed on the inner surface of the metal sealing cover, and the redistribution layer is electrically connected to the external pins of the ceramic package via transition leads. In a vacuum or inert atmosphere, the metal sealing cover is welded to the ceramic encapsulation shell in parallel seams to complete the hermetically sealed packaging.

[0015] Optionally, when the substrate is silicon-on-insulator, a deep silicon etching process is used; when the substrate is borosilicate glass, a precision etching process is used. The chip-level flexible damping limiting boss is fabricated using a photolithography curing process.

[0016] Compared with existing technologies, the beneficial effects achieved by this invention are as follows: the rigid support frame of the composite stress isolation base forms a point-contact support with the ceramic package shell through point-shaped support bosses, which greatly reduces the contact area for the transmission of thermal stress and thermal deformation. Combined with the elastic deformation of the flexible support beam to absorb the thermal deformation of the shell, the modulus gradient bonding structure of the gradient thermal matching bonding system releases thermal stress step by step. Then, the chip-level flexible damping limiting boss of the multi-dimensional limiting and vibration-damping component and the package-level elastic buffer column form an omnidirectional limiting buffer in the plane and normal direction. Without interfering with the detection accuracy of MEMS chips, it simultaneously achieves efficient thermal stress isolation and high g-value impact protection. It perfectly adapts to the high sensitivity and stress interference characteristics of large mass MEMS chips, and solves the problem of high-temperature interface peeling and thermal stress drift caused by the mismatch of thermal expansion coefficients between silicon-based MEMS chips and ceramic package shells. Attached Figure Description

[0017] Figure 1 The figure shown is a longitudinal cross-sectional view of a low-stress packaging structure for a MEMS chip in one embodiment of the present invention.

[0018] Figure 2 For the present invention Figure 1 Enlarged diagram of point A in the diagram;

[0019] Figure 3 For the present invention Figure 1 Enlarged diagram of point B in the diagram;

[0020] Figure 4 For the present invention Figure 1 Enlarged diagram of point C in the image.

[0021] In the diagram: 1. Ceramic encapsulation shell; 2. MEMS chip; 3. Composite stress isolation base; 301. Central support platform; 302. Rigid support frame; 303. Flexible support beam; 304. Support boss; 4. Gradient thermal matching bonding system; 401. First bonding layer; 402. Second bonding layer; 403. Third bonding layer; 5. Multi-dimensional limiting and vibration-damping component; 501. Chip-level flexible damping limiting boss; 502. Encapsulation-level elastic buffer pillar; 503. Helical spring frame; 6. Metal sealing cover; 7. External pins; 8. Thermal isolation groove. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0023] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0024] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] Example 1

[0026] This embodiment provides a MEMS accelerometer packaging structure suitable for harsh operating conditions in the aerospace field, including a wide temperature range of -55℃ to 150℃, high vacuum, and strong impact. It is a core preferred embodiment and fully covers all the technical features of this invention. (Reference) Figure 1 The MEMS accelerometer packaging structure includes a ceramic package shell 1, a MEMS chip 2 disposed in the inner cavity of the ceramic package shell 1, a composite stress isolation base 3, a gradient thermal matching bonding system 4, a multi-dimensional limiting and vibration-damping component 5, and a metal sealing cover plate 6 covering the opening end of the ceramic package shell 1. The structure, operating principle, and synergistic effect of each component are as follows:

[0027] I. Working Principle of Two-Level Stress Isolation

[0028] like Figure 2As shown, the composite stress isolation base 3 serves as the core of chip-level stress decoupling. The rigid support frame 302 has a gap between its sidewall and the inner wall of the ceramic packaging shell 1. The rigid support frame 302 forms a point contact support with the bottom of the inner cavity of the ceramic packaging shell 1 only through the support boss 304. This significantly reduces the stress transmission and heat conduction contact area between the packaging shell and the base, thereby reducing the efficiency of heat deformation of the ceramic packaging shell 1 in transferring to the interior of the base from the source.

[0029] The central support platform 301 is connected to the internal area of ​​the rigid support frame 301 through a flexible support beam 303, and forms a gap between it and the bottom of the inner cavity of the ceramic packaging shell 1. The flexible support beam 303 is designed as an E-shaped composite flexible isolation beam with a preset resonant frequency. The beam completely absorbs the thermal expansion / contraction deformation of the ceramic packaging shell 1 caused by temperature cycling through its own elastic deformation, so that the amount of thermal deformation cannot be transmitted to the central support platform 301. This achieves stress decoupling between the MEMS chip 2 and the packaging shell, and fundamentally solves the problem of thermal stress zero-point drift caused by the mismatch of thermal expansion coefficients between silicon and ceramic.

[0030] like Figure 3 As shown, the gradient thermal matching adhesive system 4 serves as the core for stress relief at the encapsulation level. The three-layer adhesive structure with a gradient matching modulus and coefficient of thermal expansion along the direction of thermal stress transmission forms a synergistic effect of two-level stress isolation with the composite stress isolation base 3.

[0031] The first adhesive layer 401 is disposed between the MEMS chip 2 and the central support stage 301 to achieve rigid fixation between the MEMS chip 2 and the central support stage 301, ensuring accurate transmission of vibration signals of the chip's sensitive structure. At the same time, by using a thermal expansion coefficient close to that of the silicon substrate, it reduces the thermal stress at the chip bonding interface.

[0032] The second adhesive layer 402 covers the sidewall of the MEMS chip 2 and does not cover the deformation area of ​​the flexible support beam 303. With an extremely low elastic modulus, it absorbs the local micro-stress, impact vibration energy and residual stress generated during the chip operation process, as well as the deformation process of the flexible support beam 303, while avoiding hard contact between the chip sidewall and the surrounding structure.

[0033] The third adhesive layer 403 is filled between the lower surface of the rigid support frame 302 and the bottom of the inner cavity of the ceramic encapsulation shell 1, achieving a smooth transition of the thermal expansion coefficient from the base material to the ceramic shell, releasing the macroscopic thermal stress generated by the shell step by step. At the same time, its coating area strictly avoids the deformation area of ​​the flexible support beam 303, completely avoiding the risk of limiting beam deformation after the adhesive layer cures, which could lead to stress isolation failure, and ensuring the long-term stability of the stress isolation function.

[0034] II. Working principle of multi-dimensional vibration protection.

[0035] like Figure 4 As shown, the multi-dimensional limiting and vibration-damping component 5 addresses the pain point of large-size inertial mass blocks being prone to structural damage under high g-value impacts by forming omnidirectional limiting protection in the plane and normal direction, which includes chip-level flexible damping limiting protrusions 501 and package-level elastic buffer pillars 502.

[0036] The chip-level flexible damping limiting protrusion 501 is set at the displacement limit position of the MEMS chip 2. When the chip is subjected to a lateral impact in the plane, it provides flexible damping buffer when the chip is displaced to the preset limit distance. This not only limits the excessive displacement of the chip and avoids plastic deformation or fracture of the resonant sensitive structure, but also does not constrain the micro-displacement of the chip during normal operation, thus ensuring the detection accuracy of the sensor.

[0037] The encapsulated elastic buffer column 502 is positioned directly above the central support platform 301. When subjected to a high g-value impact in the normal direction, it provides elastic buffering when the central support platform 301 displaces to the preset limit distance, limiting its normal limit displacement. The embedded helical spring skeleton 503 significantly improves the fatigue resistance and elastic recovery capability of the buffer column, maintaining stable buffering performance under repeated impact conditions. At the same time, it forms a dual anti-vibration synergy in the normal and tangential directions with the flexible support beam 303. Combined with the damping characteristics of the gradient thermal matching adhesive system 4, it forms a wide-frequency domain anti-vibration buffer system that can withstand half-sine impacts of more than 20,000g without structural damage.

[0038] III. Working principle of synergistic operation of high temperature resistance, heat dissipation, and airtightness

[0039] The array of heat dissipation fins on the outer surface of the metal sealing cover plate 6, in conjunction with the non-evaporative getter on the inner surface, achieves synergistic optimization of heat dissipation and airtightness.

[0040] The heat generated by the MEMS chip 2 during operation is directly conducted to the metal sealing cover 6 through the solid body heat conduction path of the central support platform 301, rigid support frame 302, and ceramic packaging shell 1, and dissipated outward through the heat dissipation fins. The entire process has no channel structure that penetrates the hermetically sealed packaging cavity, which achieves efficient heat dissipation while completely ensuring the hermetically tightness of the packaging cavity. The non-evaporable getter can adsorb the trace amount of gas released inside the cavity throughout its entire life cycle, maintain the vacuum degree inside the cavity, avoid packaging failure caused by gas expansion inside the cavity at high temperatures, and at the same time reduce the impact of air damping on the performance of the resonant sensitive structure of the MEMS chip 2.

[0041] The thermal isolation groove 8 set at the root of the external pin 7 of the ceramic package 1 has a linearly increasing depth along the heat transfer direction, so that the thermal resistance of each pin is linearly increasing. This not only blocks the conduction path of high temperature from the external environment to the cavity through the pin, reducing the temperature rise inside the cavity, but also suppresses the creep failure of the connection position between the pin and the bonding wire at high temperature.

[0042] An annular stress-relieving blind groove (not shown in the figure) is provided on the upper surface of the central support platform 301. This groove can release the local stress generated by the shrinkage of the adhesive layer during the bonding and curing process of the MEMS chip 2, and avoid the performance drift caused by the transmission of local stress to the sensitive structure of the chip. The redistribution layer of the titanium-platinum high-temperature resistant multilayer metal stack structure, combined with the creep-resistant optimized gold alloy bonding wires, can maintain stable electrical connection performance under wide temperature range cycling conditions, avoid fatigue fracture of the wires under high temperature cycling, and ensure the long-term reliability of the electrical signal transmission path.

[0043] Example 2

[0044] Based on the packaging structure described in Example 1, this embodiment provides a MEMS accelerometer packaging structure suitable for automotive electronics applications operating in temperatures ranging from -40℃ to 125℃. Addressing the demands of vehicle vibration and shock, frequent high and low temperature cycling, and low-cost mass production, the core structure of the packaging structure described in Example 1 is adapted and optimized. Its operating principle and technical implementation are as follows:

[0045] In this embodiment, the composite stress isolation base 3 is integrally precision etched from borosilicate glass material, and the flexible support beam 303 adopts an H-shaped symmetrical cantilever beam structure. Compared with single-crystal silicon substrate, the thermal expansion coefficient of borosilicate glass material is closer to that of ceramic encapsulation shell 1, which further reduces the thermal stress between the base and the shell. At the same time, the precision etching process is more suitable for mass production needs and reduces manufacturing costs. The H-shaped cantilever beam structure has better deformation consistency in all directions in the plane through symmetrical design, which is suitable for multi-directional irregular vibration and impact under vehicle conditions. The first-order resonant frequency of the beam is matched and designed to work synergistically with the damping characteristics of the gradient thermal matching bonding system 4 to achieve effective isolation of vehicle full-frequency vibration.

[0046] In this embodiment, the gradient thermal matching bonding system 4 adopts a three-layer optimized bonding structure. The first bonding layer 401 is a modified epoxy bonding layer, which reduces the difficulty of the curing process while ensuring high temperature resistance, and is suitable for mass production line operation. The second bonding layer 402 is a low-viscosity silicone gel, which can be automatically coated by dispensing process to cover the sidewall of MEMS chip 2. Under the frequent vibration conditions in the vehicle, it continuously absorbs vibration energy and reduces the amplitude of the resonance peak. The third bonding layer 403 is a room temperature curing modified silicone, which does not require a high temperature curing process, avoids the thermal stress effect of secondary high temperature curing on the chip and bonding structure, and at the same time achieves stress isolation between the base and the shell.

[0047] In this embodiment, the chip-level flexible damping limiting boss 501 is made of epoxy photosensitive adhesive, which has a simpler curing process and lower cost compared to photosensitive polyimide, while still providing a stable flexible damping limiting effect, suitable for lateral impact protection under automotive conditions; the encapsulation-level elastic buffer post 502 adopts a one-piece molded structure of perfluorosilicone rubber, which does not require an embedded metal skeleton, simplifies the manufacturing process, reduces costs, and has excellent high and low temperature resistance, oil resistance and aging resistance, suitable for complex automotive environments. The distance between it and the central bearing platform 301 has been optimized for automotive-grade impact conditions, ensuring the limiting protection effect while avoiding frequent contact under normal automotive vibration, thus ensuring the sensor detection accuracy.

[0048] In the electrical connection structure of this embodiment, the bonding leads are made of aluminum-silicon alloy wire, which is suitable for low-cost mass production requirements. The bonding arc is optimized for anti-creep and can withstand more than 1,000 temperature cycles of automotive grade without fatigue fracture. The ceramic package shell 1 is made of low-cost alumina ceramic material, and the thermal isolation groove 8 of the external pin 7 adopts a graded depth design, which simplifies the shell manufacturing process and reduces mass production costs while ensuring thermal isolation effect.

[0049] This embodiment meets the automotive-grade requirements for high temperature resistance, vibration resistance, and high reliability, while significantly reducing the manufacturing cost of the packaging structure, making it suitable for the mass production needs of the automotive electronics field.

[0050] Example 3

[0051] Based on the packaging structure described in Example 1, this example provides a MEMS accelerometer packaging structure adapted to the ultra-high temperature continuous working conditions of 150℃~200℃ in the industrial measurement and control field. Addressing the requirements of continuous high temperature, strong heat radiation, and long-term stable operation in scenarios such as industrial furnaces and energy equipment, the core structure of the packaging structure described in Example 1 is optimized for ultra-high temperature adaptation. Its operating principle and technical implementation are as follows:

[0052] In this embodiment, the composite stress isolation base 3 is integrally formed by deep silicon etching of silicon-on-insulator (SOI) material. The top silicon and buried oxide layer structure of SOI material can effectively suppress leakage current at high temperature, avoid the degradation of electrical performance of the base under ultra-high temperature environment, and ensure the signal transmission stability of the redistribution layer. The flexible support beam 303 adopts multiple sets of symmetrically distributed double E-shaped composite flexible isolation beams. The double beam structure greatly improves the high temperature resistance and fatigue resistance of the beam. Under ultra-high temperature continuous working conditions, it can still maintain stable elastic deformation capability, avoid stress isolation failure caused by stress relaxation of the beam under high temperature. Its resonant frequency is designed with modulus change compensation under ultra-high temperature working conditions. At a high temperature of 200℃, it can still form a synergy with the damping characteristics of the gradient thermal matching bonding system 4 to ensure the stress isolation effect in a wide temperature range.

[0053] In this embodiment, the gradient thermal matching bonding system 4 adopts a four-layer gradient bonding structure adapted to ultra-high temperature. On the basis of the original three-layer structure, a high-temperature resistant interface bonding layer is added. The first bonding layer 401 adopts a gold-tin eutectic solder layer. The rigid connection between the MEMS chip 2 and the central support platform 301 is achieved through eutectic bonding process. The melting point of the gold-tin eutectic solder is higher than 280°C. It does not soften or creep under continuous working conditions at 200°C. The interface bonding strength is stable for a long time. At the same time, it has excellent thermal conductivity and can quickly conduct the heat of the chip to the base to avoid the chip junction temperature from being too high.

[0054] The second adhesive layer 402 is made of high-temperature resistant phenyl silicone gel, with a long-term operating temperature of up to 220℃. It can maintain an extremely low elastic modulus and stable damping characteristics even at ultra-high temperatures, continuously absorbing thermal deformation stress and vibration energy. The third adhesive layer 403 is made of high-temperature resistant ceramicized silicone, which can form a ceramicized protective layer in ultra-high temperature environments, preventing the adhesive layer from aging and cracking at high temperatures, while achieving a smooth transition of the coefficient of thermal expansion. The added high-temperature resistant interface adhesive layer is coated on the interface between the rigid support frame 302 and the support boss 304, improving the interface bonding strength under ultra-high temperatures and preventing interface peeling under high-temperature cycling.

[0055] In the multi-dimensional limiting and vibration-damping component 5 of this embodiment, the chip-level flexible damping limiting boss 501 is made of high-temperature resistant photosensitive polyimide material, with a long-term operating temperature of up to 250°C. It does not exhibit thermal deformation or thermal decomposition under ultra-high temperatures, and continuously provides stable limiting protection. The encapsulation-level elastic buffer post 502 is made of high-temperature resistant perfluoroether rubber material, with an internally embedded high-temperature resistant Inconel alloy helical spring skeleton 503. It can still maintain stable elastic buffering performance under continuous operating conditions of 200°C, without aging or hardening, ensuring the limiting protection effect under ultra-high temperature impact.

[0056] In this embodiment, the metal sealing cover 6 adopts a high-temperature alloy integral molding structure. The size of the array-type heat dissipation fins on the outer surface is optimized for ultra-high temperature conditions to improve the efficiency of natural convection heat dissipation. The high-temperature non-evaporative getter fixed on the inner surface can continuously draw in gas at 200°C to maintain the vacuum inside the cavity. The ceramic encapsulation shell 1 is made of high thermal conductivity aluminum nitride ceramic material to improve heat dissipation efficiency at high temperatures. The thermal isolation groove 8 of the external pins 7 adopts a full-circumferential depth increasing design to maximize the blocking of external heat radiation and heat conduction to the cavity. The redistribution layer adopts a titanium-tungsten-gold high-temperature resistant multilayer metal stacking structure, and the bonding wires are made of high-temperature gold alloy wires. Under continuous operation at 200°C, there is no electromigration or creep breakage, ensuring the long-term stability of electrical signal transmission.

[0057] This embodiment can operate stably for a long time in an ultra-high temperature environment of 200℃, while maintaining excellent vibration resistance and low stress performance, making it suitable for the use needs of extreme high temperature industrial measurement and control scenarios.

[0058] Example 4

[0059] Based on the packaging structure described in Example 1, this example provides a MEMS accelerometer packaging structure suitable for ultra-high impact and strong continuous vibration conditions in fields such as oil drilling and weaponry. To address the requirements of high-g impacts exceeding 20,000g, wide-band continuous strong vibration, and extreme mechanical environments, the core vibration-resistant structure of the packaging structure described in Example 1 is strengthened and optimized. Its operating principle and technical implementation are as follows:

[0060] In this embodiment, the composite stress isolation base 3 is integrally formed by deep silicon etching of single-crystal silicon material, and the flexible support beam 303 adopts eight sets of symmetrically distributed hollow E-shaped composite flexible isolation beams. The hollow beam structure reduces the equivalent stiffness of the beam while ensuring structural strength and increases the deformation buffer stroke. At the same time, the multi-set symmetrical distribution design realizes stress isolation and vibration buffering in all directions in the plane. The first, second and third resonant frequencies of the beam are optimized for broadband vibration resistance and form a full-band synergy with the damping characteristics of the gradient thermal matching bonding system 4 and the buffering characteristics of the multi-dimensional limiting vibration resistance component 5. It can effectively isolate continuous strong vibrations in the 10Hz~10kHz wide frequency range and avoid structural damage caused by resonance amplification. The lower surface of the rigid support frame 302 is provided with eight evenly distributed support protrusions 304. The multi-point support improves the structural stability of the base under ultra-high impact and avoids the base from overturning and misalignment under impact, while still maintaining the low stress transmission characteristics of point contact.

[0061] In this embodiment, the gradient thermal matching bonding system 4 adopts a high-damping gradient bonding structure. The first bonding layer 401 is a high-toughness epoxy bonding layer, which ensures high modulus rigid fixation while possessing excellent impact toughness, avoiding bonding layer brittleness and interface debonding under ultra-high impact. The second bonding layer 402 is a high-damping silicone gel with a damping coefficient ≥0.8, which can efficiently absorb broadband vibration energy and impact kinetic energy, significantly reducing the transmission rate of impact acceleration. At the same time, it covers all sidewalls of the MEMS chip 2, forming a fully enclosed buffer protection to avoid local stress concentration under impact. The third bonding layer 403 is a high tear-resistant modified silicone, which has excellent impact and tear resistance properties. It does not crack or debond under ultra-high impact, and at the same time achieves packaging-level stress isolation. Together with the composite stress isolation base 3, it forms a two-level anti-vibration buffer system, which greatly improves the overall structure's impact resistance.

[0062] The multi-dimensional limiting and vibration-damping component 5 in this embodiment adopts a redundant omnidirectional limiting design. Eight chip-level flexible damping limiting protrusions 501 are evenly distributed around the perimeter of the MEMS chip 2. Each protrusion employs a stepped flexible structure, providing low-damping buffering for small displacements and high-damping rigid limiting for large displacements. This ensures the detection accuracy of the sensor during normal operation and provides progressively enhanced limiting protection under ultra-high lateral impacts, preventing excessive chip displacement from causing breakage of the resonant sensitive structure. The package-level elastic buffer post 502 is... Three buffer columns are arranged in an equilateral triangle on the inner surface of the metal sealing cover plate 6, respectively facing the center and two sides of the central bearing platform 301, forming a multi-point normal limiting protection. Each buffer column adopts a fluorosilicone rubber structure with an embedded double helical spring skeleton 503. The double spring skeleton greatly improves the impact bearing capacity and fatigue resistance of the buffer column, and can still maintain a stable elastic recovery capacity under repeated ultra-high impacts. At the same time, it forms a multi-level normal buffer with the flexible support beam 303 to avoid plastic deformation and fracture of the beam under ultra-high normal impacts.

[0063] Meanwhile, the annular stress relief blind groove of the central bearing platform 301 adopts a multi-ring nested design, which can effectively release local stress concentration under ultra-high impact; the ceramic package shell 1 is made of high-strength alumina ceramic material, and the external pins 7 are made of thickened Kovar alloy pins to improve impact and vibration resistance; the bonding wires are made of large-diameter gold alloy wires, and the bonding arc is optimized for impact resistance to avoid wire swinging and breakage under ultra-high impact.

[0064] This embodiment can withstand half-sine impacts of over 30,000g and can operate stably under strong vibration conditions with a wide frequency range of 10Hz to 10kHz, fully meeting the usage requirements under extreme mechanical environments.

[0065] In summary, this MEMS accelerometer packaging structure, through the rigid support frame 302 of the composite stress isolation base 3 and the support boss 304 forming a point contact support with the ceramic packaging shell 1, significantly reduces the contact area for the transmission of thermal stress and thermal deformation. Combined with the elastic deformation of the flexible support beam 303 absorbing the thermal deformation of the shell, and the modulus gradient bonding structure of the gradient thermal matching bonding system 4 releasing thermal stress step by step, it solves the problem of high-temperature interface peeling and thermal stress drift caused by the mismatch of thermal expansion coefficients between the silicon-based MEMS chip 2 and the ceramic packaging shell 1.

[0066] Furthermore, this MEMS accelerometer packaging structure, through the chip-level flexible damping limiting protrusion 501 of the multi-dimensional limiting and anti-vibration component 5 and the packaging-level elastic buffer pillar 502, forms an omnidirectional limiting buffer in the plane and normal direction. Combined with the damping characteristics of the flexible support beam 303 of the composite stress isolation base 3 and the gradient thermal matching bonding system 4, it achieves efficient thermal stress isolation and high g-value impact protection without interfering with the detection accuracy of the MEMS chip 2. It perfectly adapts to the high sensitivity and susceptibility to stress interference of the large mass MEMS chip 2, and solves the problem that existing packaging solutions cannot solve the high temperature failure and thermal stress drift caused by the mismatch of thermal expansion coefficients between silicon-based chips and ceramic shells, nor can they simultaneously take into account thermal stress isolation and high impact protection.

[0067] Example 5

[0068] This embodiment provides a MEMS accelerometer packaging process for fabricating the MEMS accelerometer packaging structure described in any one of steps 1 / 2 / 3 / 4, including the following steps:

[0069] S1. Base fabrication: A composite stress isolation base 3 is formed by integrally molding the substrate through an etching process, consisting of a flexible support beam structure 303, a central bearing platform 301, a rigid support outer frame 302, and dot-shaped support bosses 304. A redistribution layer is then fabricated on the surface of the central bearing platform 301. When the substrate is silicon-on-insulator (SiO2), a deep silicon etching process is used; when the substrate is borosilicate glass, a precision etching process is used.

[0070] S2. Chip bonding: The MEMS chip 2 with a resonant sensitive structure and a sandwich capacitor triangular electrode array is bonded and fixed at a preset position on the central support platform 301 through the first bonding layer 401, and the curing is completed; when the first bonding layer 401 is a gold-tin eutectic solder layer, the eutectic bonding process is adopted.

[0071] S3. Chip-level positioning and bonding: A chip-level flexible damping positioning protrusion 501 is prepared at a preset position on the central support stage 301, and the electrode pads of the MEMS chip 2 are electrically connected to the redistribution layer through a bonding process; the chip-level flexible damping positioning protrusion 501 is prepared by photolithography curing process.

[0072] S4. Base encapsulation bonding: A third adhesive layer 403 is coated in a preset area at the bottom of the inner cavity of the ceramic encapsulation shell 1. The composite stress isolation base 3 is positioned in the inner cavity of the ceramic encapsulation shell 1 by point support protrusions 304, so that the third adhesive layer 403 fills the non-support gap area. After curing, a second adhesive layer 402 is coated on the side wall of the MEMS chip 2 and the surface of the flexible support beam 303. After curing, the upper surface of the adhesive layer does not contact the lower surface of the flexible support beam 303, ensuring the flexible deformation space of the flexible support beam 303.

[0073] S5. Packaging-level buffer and electrical connection: The packaging-level elastic buffer post 502 and getter are fixed on the inner surface of the metal sealing cover plate 6, and the redistribution layer is electrically connected to the external pin 7 of the ceramic package shell 1 through the transition lead.

[0074] S6. Hermetic sealing: Under vacuum or inert atmosphere, the metal sealing cover 6 and the ceramic encapsulation shell 1 are welded in parallel to complete the hermetic sealing.

[0075] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A MEMS accelerometer packaging structure, comprising a ceramic package shell, a MEMS chip disposed within the cavity of the ceramic package shell, and a metal sealing cover plate covering the opening end of the ceramic package shell, characterized in that, The inner cavity of the ceramic encapsulation tube shell is also provided with: The composite stress isolation base includes a central support platform, a rigid support frame, and a flexible support beam. The rigid support frame forms a point-contact support with the bottom of the inner cavity of the ceramic encapsulation shell through a support boss on its lower surface, and there is a gap between the rigid support frame and the side wall of the inner cavity of the ceramic encapsulation shell. The central support platform is connected to the internal area of ​​the rigid support frame through the flexible support beam, and forms a gap with the bottom of the inner cavity of the ceramic encapsulation shell. The gradient thermal matching bonding system includes at least three bonding structures arranged sequentially along the thermal stress transmission direction. The three bonding structures are configured as follows: the first bonding layer located between the MEMS chip and the central support stage provides rigid fixation for the MEMS chip; the second bonding layer covering the sidewall of the MEMS chip provides flexible buffering; and the third bonding layer filling the lower surface of the rigid support frame and the bottom of the inner cavity of the ceramic package provides thermal expansion coefficient transition matching. The multi-dimensional limiting and vibration-damping components include a chip-level flexible damping limiting protrusion set on the upper surface of the central support platform and located outside the MEMS chip, and a package-level elastic buffer column set on the lower surface of the metal sealing cover and facing the upper part of the central support platform. A redistribution layer is disposed on the upper surface of the central support platform, through which the external pins of the MEMS chip and the ceramic package are electrically connected.

2. The MEMS accelerometer packaging structure according to claim 1, characterized in that, The flexible support beam comprises multiple sets of symmetrically distributed cantilever beams, each set of cantilever beams arranged in an E-shape.

3. The MEMS accelerometer packaging structure according to claim 1, characterized in that, The chip-level flexible damping limiting protrusion is a photosensitive polyimide, and its height is higher than the upper surface of the MEMS chip; the distance between the inner wall of the chip-level flexible damping limiting protrusion and the outer wall of the MEMS chip is 5μm~20μm. The encapsulation-grade elastic buffer post is made of fluorosilicone rubber and has an embedded helical spring skeleton inside; the distance between the lower end face of the encapsulation-grade elastic buffer post and the upper surface of the central support platform is 10μm~30μm.

4. The MEMS accelerometer packaging structure according to claim 1, characterized in that, The first adhesive layer is an epoxy adhesive layer with an elastic modulus of 1 GPa to 20 GPa and a coefficient of thermal expansion of 10 ppm / ℃ to 50 ppm / ℃. The second adhesive layer is a silicone gel buffer layer with an elastic modulus of 0.001 MPa to 0.1 MPa and a coefficient of thermal expansion of 150 ppm / ℃ to 350 ppm / ℃. The third adhesive layer is a modified silicone adhesive layer with an elastic modulus of 0.1MPa to 20MPa and a coefficient of thermal expansion of 50ppm / ℃ to 150ppm / ℃.

5. The MEMS accelerometer packaging structure according to claim 1, characterized in that, The metal sealing cover is a Kovar alloy integral molding structure; The outer surface of the metal sealing cover is equipped with an array of heat dissipation fins, and the inner surface is fixed with a non-evaporative getter.

6. The MEMS accelerometer packaging structure according to claim 1, characterized in that, The upper surface of the central support platform is provided with an annular stress relief blind groove, and the bottom height of the annular stress relief blind groove is higher than the lower surface of the central support platform. The ceramic package has thermal isolation grooves at the base of its external pins, and the depth of the thermal isolation grooves on the multiple external pins increases linearly along the heat transfer direction.

7. The MEMS accelerometer packaging structure according to claim 1, characterized in that, The redistribution layer is a titanium-platinum multilayer metal stack structure; The MEMS chip and the redistribution layer are bonded together via aluminum-silicon alloy wires or gold alloy wires.

8. The MEMS accelerometer packaging structure according to claim 1, characterized in that, The composite stress isolation base is integrally formed from semiconductor material, silicon-on-insulator material, or glass material.

9. A MEMS accelerometer packaging process for fabricating the MEMS accelerometer packaging structure according to any one of claims 1-8, characterized in that, include: A composite stress isolation base with flexible support beams, a central bearing platform, a rigid support frame and support bosses is formed by integrally molding the substrate through etching process, and a redistribution layer is prepared on the surface of the central bearing platform. The MEMS chip is bonded and fixed to the preset position of the central support platform through the first adhesive layer, and then cured. A chip-level flexible damping limiting protrusion is fabricated at a predetermined position on the central support platform, and the electrode pads of the MEMS chip are electrically connected to the redistribution layer through a bonding process. A third adhesive layer is coated in a preset area at the bottom of the inner cavity of the ceramic package shell. The composite stress isolation base is positioned in the inner cavity of the ceramic package shell through the support boss, so that the third adhesive layer fills the non-support gap area. After curing, a second adhesive layer is coated on the side wall of the MEMS chip and cured, so that the coating area of ​​the second adhesive layer avoids the deformation area of ​​the flexible support beam. A package-grade elastic buffer pillar is fixed on the inner surface of the metal sealing cover, and the redistribution layer is electrically connected to the external pins of the ceramic package via transition leads. In a vacuum or inert atmosphere, the metal sealing cover is welded to the ceramic encapsulation shell in parallel seams to complete the hermetically sealed packaging.

10. The MEMS accelerometer packaging process according to claim 9, characterized in that, When the substrate is silicon-on-insulator (SOI), deep silicon etching is used; when the substrate is glass, precision etching is used. The chip-level flexible damping limiting boss is fabricated using a photolithography curing process.

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