MEMS device low-stress packaging method and structure

Abstract

According to the MEMS device low-stress packaging method and structure, a sensitive structure is mounted on a cover plate, an ASIC chip is arranged in a ceramic tube shell, and electrical connection between the sensitive structure and the ASIC chip and electrical connection between the sensitive structure and a device output port are achieved through electrical connection between the cover plate and the ceramic tube shell. The electrical connection between the cover plate and the ceramic tube shell is realized through eutectic solder eutectic. Therefore, the technical problem existing in packaging of the MEMS device in the prior art can be solved.

Description

Technical Field

[0001] This invention belongs to the field of MEMS device packaging technology, and relates to a low-stress packaging method and structure for MEMS devices. Background Technology

[0002] MEMS device packaging often has specific requirements. For example, inertial MEMS devices such as silicon gyroscopes and silicon accelerometers have high requirements for patch stress. Furthermore, silicon pressure sensors require pressure transmission interfaces, and photoelectric sensors require light transmission windows. Currently, various MEMS device packages use ceramic housings, metal housings, or complex packages combining ceramic housings, metal covers, and glass windows. These packaging methods are all developed based on the specific needs of the devices, and most of these methods suffer from the following problems:

[0003] (1) Surface mount stress: For MEMS devices, surface mount stress affects their operating characteristics, which in turn affects the accuracy and environmental adaptability of MEMS devices. Therefore, surface mount stress control is one of the key issues in their packaging process. Currently, the sensitive structure of the device is usually surface mount on a ceramic shell or on a metal shell, both of which result in large surface mount stress due to the mismatch of the thermal expansion coefficients of the materials.

[0004] (2) ASIC chip integration issues: Generally, there are three ways to integrate ASIC chips into MEMS devices: 1) Place the ASIC chip and the sensitive structure side by side in the same package cavity, which will increase the lateral size of the package and may also cause electrical connection problems and electromagnetic interference; 2) Use a ceramic tube with two cavities, and place the ASIC chip in another cavity, which will increase the thickness of the package; 3) Place the ASIC chip on top of the device's sensitive structure, which may cause problems such as some MEMS devices not being suitable for this design. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0006] Therefore, the present invention provides a low-stress packaging method and structure for MEMS devices.

[0007] The technical solution of the present invention is as follows:

[0008] According to one aspect, a low-stress packaging method for MEMS devices is provided, the method comprising:

[0009] Step 1: Attach the sensitive structure to the cover plate. The sensitive structure and the cover plate are made of the same material.

[0010] Step 2: Process two sets of metal pads and two sets of metal leads on the mounting surface of the cover plate where the sensitive structure is located. The two sets of metal pads are set on both sides of the sensitive structure, and the two sets of metal pads and the two sets of metal leads are set one-to-one. Each set of metal pads includes multiple metal pads, and each set of metal leads includes multiple metal leads. One end of any metal lead is connected to the corresponding metal pad, and the other end is connected to the sensitive structure. Design a sealing area on the side of the cover plate where the sensitive structure is located.

[0011] Step 3: Select a ceramic tube shell as the encapsulation shell. Process multiple gold-plated pads for external output on the upper surfaces of the two opposite side walls of the ceramic tube shell, which correspond one-to-one with the two sets of metal pads in Step 2. Design a sealing area on the upper surfaces of the other set of opposite side walls of the ceramic tube shell.

[0012] Step 4: Mount the ASIC chip inside the ceramic housing, and process two sets of metal pads and two sets of metal leads on both sides of the ASIC chip. The two sets of metal pads are set on both sides of the ASIC chip, and the two sets of metal pads and two sets of metal leads are set one-to-one. Each set of metal pads includes multiple metal pads, and each set of metal leads includes multiple metal leads. One end of any metal lead is connected to the corresponding metal pad, and the other end is connected to the ASIC chip. One set of metal pads is connected to multiple gold-plated pads on one side wall, and the other set of metal pads is connected to multiple gold-plated pads on the other side wall.

[0013] Step 5: Align the sealing areas of the cover plate and the ceramic shell one by one. Align the two sets of metal pads on the cover plate with the external output gold-plated pads on both sides of the ceramic shell one by one. Use eutectic bonding to achieve electrical connection between the cover plate and the ceramic shell, thereby achieving electrical connection between the sensitive structure and the ASIC chip.

[0014] Furthermore, in step two, the metal lead is gold wire, and the electrical connection between the sensitive structure and the cover plate is achieved by flip-chip bonding or gold wire ball bonding.

[0015] Furthermore, in step two, gold plating is performed on the sealing area of ​​the cover plate for eutectic sealing; in step three, gold plating is performed on the sealing area of ​​the ceramic tube shell to achieve eutectic sealing between the ceramic tube shell and the cover plate.

[0016] Furthermore, in step two, microgrooves are machined between the metal pads and the sealing area on the cover plate to store the molten eutectic solder that flows out, so as to avoid short circuits between the metal lead pads and the sealing area.

[0017] Furthermore, in step four, the metal lead is a gold wire, and the electrical connection between the ASIC chip and the ceramic housing is achieved by gold wire ball bonding.

[0018] Furthermore, in step five, eutectic sealing of the ceramic tube shell and cover plate is achieved by using laser local heating or conductive heating welding.

[0019] Furthermore, in step five, before eutectic sealing, a deep degassing process is performed by vacuuming.

[0020] According to another aspect, a low-stress packaging structure for MEMS devices is provided, which is obtained by the packaging method described above.

[0021] Furthermore, the packaging structure includes a cover plate assembly and a ceramic housing assembly. The cover plate assembly includes a cover plate, a sensitive structure, two sets of metal pads a, and two sets of metal leads b. The sensitive structure is mounted on the cover plate and is made of the same material as the cover plate. The two sets of metal pads a are disposed on the cover plate and located on both sides of the sensitive structure. The two sets of metal pads a and the two sets of metal leads b are arranged in a one-to-one correspondence. Each set of metal pads a includes multiple metal pads a, and each set of metal leads b includes multiple metal leads b. One end of any metal lead b is connected to the corresponding metal pad a, and the other end is connected to the sensitive structure. The side of the cover plate where the sensitive structure is disposed also has a sealing area.

[0022] The ceramic housing assembly includes a ceramic housing, an ASIC chip, two sets of external gold-plated pads, two sets of metal pads c, and two sets of metal leads d. The ceramic housing serves as the encapsulation housing. Two sets of external gold-plated pads are machined on the upper surfaces of the opposite side walls of the ceramic housing, corresponding one-to-one with the two sets of metal pads a in step two. Each set of external gold-plated pads includes multiple external gold-plated pads. A sealing area is designed on the upper surface of the other set of opposite side walls of the ceramic housing. The ASIC chip is mounted inside the cavity of the ceramic housing and on lead A. The SIC chip has two sets of metal pads c and two sets of metal leads d on both sides. The two sets of metal pads c are set on both sides of the ASIC chip. The two sets of metal pads c and the two sets of metal leads d are set one-to-one. Each set of metal pads c includes multiple metal pads c. Each set of metal leads d includes multiple metal leads d. One end of any metal lead d is connected to the corresponding metal pad c, and the other end is connected to the ASIC chip. One set of metal pads c is connected one-to-one to multiple gold-plated pads on one side wall. The other set of metal pads c is connected one-to-one to multiple gold-plated pads on the other side wall.

[0023] The sealing area of ​​the cover plate and the sealing area of ​​the ceramic tube shell are connected by eutectic bonding. The two sets of metal pads a of the cover plate are respectively connected to the two sets of external output gold-plated pads of the ceramic tube shell. The electrical connection between the sensitive structure and the ASIC chip and the device output port is achieved through the electrical connection between the cover plate and the ceramic tube shell. The electrical connection between the cover plate and the ceramic tube shell is achieved through eutectic bonding of eutectic solder.

[0024] The above technical solution provides a low-stress packaging method and structure for MEMS devices. By mounting a sensitive structure on a cover plate and placing an ASIC chip inside a ceramic housing, the electrical connection between the sensitive structure, the ASIC chip, and the device output port is achieved through an electrical connection between the cover plate and the ceramic housing, which is achieved through eutectic solder. This overcomes the technical problems existing in the packaging of MEMS devices in the prior art. Specifically, this invention changes the traditional method of mounting the sensitive structure on a cover plate, replacing the previous method of mounting it on the ceramic housing. This design allows for selection of the cover plate material based on the material properties of the sensitive structure, achieving matching of parameters such as the coefficient of thermal expansion of the sensitive structure and its carrier, reducing or eliminating the stress of the sensitive structure mounting, and solving the problem of thermal stress caused by the mismatch of the coefficients of thermal expansion between the sensitive structure and the ceramic housing. Simultaneously, the ASIC chip is mounted inside the cavity of the ceramic housing, and the electrical connection between the ASIC chip, the ceramic housing, and the sensitive structure is achieved through gold wire ball bonding. This avoids an increase in the lateral and thickness dimensions of the package housing, achieving integration of the device's sensitive structure and ASIC chip into a smaller package size. Attached Figure Description

[0025] The accompanying drawings, which form part of this specification, are provided to further illustrate embodiments of the invention and, together with the textual description, explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0026] Figure 1 This is a schematic diagram of the packaging structure;

[0027] Figure 2 Schematic diagram of sensitive structure and cover plate;

[0028] Figure 3 This is a schematic diagram of the ceramic tube shell's solder pads and sealing area. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0032] like Figures 1 to 3As shown, in one embodiment of the present invention, a low-stress packaging structure for MEMS devices is provided. The packaging structure includes a cover plate assembly and a ceramic housing assembly. The cover plate assembly includes a cover plate 1, a sensitive structure 2, two sets of metal pads a4, and two sets of metal leads b5. The sensitive structure 2 is mounted on the cover plate 1, and the sensitive structure 2 is made of the same material as the cover plate 1. The two sets of metal pads a4 are disposed on the cover plate 1 and located on both sides of the sensitive structure 2. The two sets of metal pads a4 and the two sets of metal leads b5 are arranged in a one-to-one correspondence. Each set of metal pads a4 includes multiple metal pads a4, and each set of metal leads b5 includes multiple metal leads b5. One end of any metal lead b5 is connected to the corresponding metal pad a4, and the other end is connected to the sensitive structure 2. The side of the cover plate 1 where the sensitive structure 2 is disposed is also designed with a sealing area.

[0033] The ceramic housing assembly includes a ceramic housing 3, an ASIC chip 6, two sets of external gold-plated pads 7, two sets of metal pads c, and two sets of metal leads d. The ceramic housing 3 serves as the packaging housing. Two sets of external gold-plated pads are machined on the upper surfaces of the oppositely arranged side walls of the ceramic housing 3, corresponding one-to-one with the two sets of metal pads a4 in step two. Each set of external gold-plated pads includes multiple external gold-plated pads 7. A sealing area 8 is designed on the upper surface of the other set of oppositely arranged side walls of the ceramic housing 3. The ASIC chip 6 is mounted in the cavity of the ceramic housing 3 and on A... The SIC chip 6 has two sets of metal pads c and two sets of metal leads d on both sides. The two sets of metal pads c are arranged on both sides of the ASIC chip 6. The two sets of metal pads c and the two sets of metal leads d are arranged one-to-one. Each set of metal pads c includes multiple metal pads c. Each set of metal leads d includes multiple metal leads d. One end of any metal lead d is connected to the corresponding metal pad c, and the other end is connected to the ASIC chip 6. One set of metal pads c is connected one-to-one to multiple external output gold-plated pads 7 on one side wall. The other set of metal pads c is connected one-to-one to multiple external output gold-plated pads 7 on the other side wall.

[0034] The sealing area of ​​the cover plate 1 and the sealing area 8 of the ceramic tube shell 3 are connected by eutectic sealing. The two sets of metal pads a4 of the cover plate 1 are respectively connected to the two sets of external output gold-plated pads 7 of the ceramic tube shell 3. The electrical connection between the sensitive structure 2 and the ASIC chip 6 and the device output port is achieved through the electrical connection between the cover plate 1 and the ceramic tube shell 3. The electrical connection between the cover plate 1 and the ceramic tube shell 3 is achieved through eutectic solder eutectic bonding.

[0035] As can be seen, this invention provides a low-stress packaging method and structure for MEMS devices. By mounting a sensitive structure on a cover plate and placing an ASIC chip inside a ceramic housing, the electrical connection between the sensitive structure, the ASIC chip, and the device output port is achieved through the electrical connection between the cover plate and the ceramic housing, which is achieved through eutectic solder. This overcomes the technical problems existing in the packaging of MEMS devices in the prior art. Specifically, this invention changes the traditional method of mounting the sensitive structure on a cover plate, replacing the previous method of mounting it on the ceramic housing. This design allows for selection of the cover plate material based on the material properties of the sensitive structure, achieving matching of parameters such as the coefficient of thermal expansion of the sensitive structure and its carrier, reducing or eliminating the stress of the sensitive structure mounting, and solving the problem of thermal stress caused by the mismatch of the coefficients of thermal expansion between the sensitive structure and the ceramic housing. Simultaneously, the ASIC chip is mounted inside the cavity of the ceramic housing, and the electrical connection between the ASIC chip, the ceramic housing, and the sensitive structure is achieved through gold wire ball bonding. This avoids increasing the lateral and thickness dimensions of the package housing, achieving integration of the device's sensitive structure and ASIC chip into a smaller package volume.

[0036] According to another embodiment, a low-stress packaging method for MEMS devices is provided, the method comprising:

[0037] Step 1: Attach the sensitive structure to the cover plate. The sensitive structure and the cover plate are made of the same material.

[0038] Step 2: Process two sets of metal pads and two sets of metal leads on the mounting surface of the cover plate where the sensitive structure is located. The two sets of metal pads are set on both sides of the sensitive structure, and the two sets of metal pads and the two sets of metal leads are set one-to-one. Each set of metal pads includes multiple metal pads, and each set of metal leads includes multiple metal leads. One end of any metal lead is connected to the corresponding metal pad, and the other end is connected to the sensitive structure. Design a sealing area on the side of the cover plate where the sensitive structure is located.

[0039] Step 3: Select a ceramic tube shell as the encapsulation shell. Process multiple gold-plated pads for external output on the upper surfaces of the two opposite side walls of the ceramic tube shell, which correspond one-to-one with the two sets of metal pads in Step 2. Design a sealing area on the upper surfaces of the other set of opposite side walls of the ceramic tube shell.

[0040] Step 4: Mount the ASIC chip inside the ceramic housing, and process two sets of metal pads and two sets of metal leads on both sides of the ASIC chip. The two sets of metal pads are set on both sides of the ASIC chip, and the two sets of metal pads and two sets of metal leads are set one-to-one. Each set of metal pads includes multiple metal pads, and each set of metal leads includes multiple metal leads. One end of any metal lead is connected to the corresponding metal pad, and the other end is connected to the ASIC chip. One set of metal pads is connected to multiple gold-plated pads on one side wall, and the other set of metal pads is connected to multiple gold-plated pads on the other side wall.

[0041] Step 5: Align the sealing areas of the cover plate and the ceramic shell one by one. Align the two sets of metal pads on the cover plate with the external output gold-plated pads on both sides of the ceramic shell one by one. Use eutectic bonding to achieve electrical connection between the cover plate and the ceramic shell, thereby achieving electrical connection between the sensitive structure and the ASIC chip.

[0042] In other words, the encapsulation method of this invention changes the traditional method of attaching sensitive structures to a cover plate, replacing the method of attaching them to the ceramic tube shell. This design allows for the selection of the cover plate material based on the material properties of the sensitive structure, achieving a match between the thermal expansion coefficients and other parameters of the sensitive structure and its carrier, reducing or eliminating the stress on the sensitive structure patch, and solving the problem of thermal stress caused by the mismatch between the thermal expansion coefficients of the sensitive structure and the ceramic tube shell.

[0043] For example, the material of the surface mount cover is selected based on the sensitive structure of the device. If the sensitive structure is made of quartz, then a quartz surface mount cover can be used; if the sensitive structure is made of Pyrex glass, then a Pyrex glass surface mount cover can be used; if the sensitive structure is made of silicon, then a silicon surface mount cover can be used. Mounting the sensitive structure onto a cover of the same material minimizes surface mount stress.

[0044] In this embodiment of the invention, in step two, the metal lead is gold wire, and the electrical connection between the sensitive structure and the cover plate is achieved by flip-chip bonding or gold wire ball bonding.

[0045] Specifically, metal pads and metal leads are fabricated on the sensitive structure mounting surface of the cover plate (silicon cover plates require insulation treatment before fabrication). Electrical connection between the sensitive structure and the cover plate is achieved through flip-chip bonding or gold ball bonding. Gold plating is applied to the sealing area of ​​the cover plate for eutectic bonding. Microgrooves can be fabricated between the metal lead pads and the sealing area to store the molten eutectic solder, preventing short circuits between the metal lead pads and the sealing area.

[0046] In this embodiment of the invention, a ceramic casing is selected as the packaging casing. Gold-plated pads corresponding to the sensitive structure mounting substrate, which serves as the packaging cover, are machined on the ceramic casing. Electrical connections between the sensitive structure, the ceramic casing's output pads, and the ASIC chip are achieved through vertical holes. Simultaneously, gold plating is applied to the sealing area of ​​the ceramic casing to achieve eutectic bonding between the ceramic casing and the cover plate.

[0047] Furthermore, in this embodiment of the invention, the ASIC chip is mounted inside the cavity of the ceramic housing, and the electrical connection between the ASIC chip, the ceramic housing, and the sensitive structure is achieved through gold wire ball bonding. This avoids an increase in the lateral and thickness dimensions of the package housing, enabling the integration of the device's sensitive structure and the ASIC chip into a smaller package size.

[0048] In this embodiment of the invention, gold-tin solder can be processed in the sealing area of ​​the ceramic tube shell by magnetron sputtering or electroplating for hermetic sealing of the ceramic tube shell and the cover plate. Gold-indium solder can be processed on the pads for electrical connection on the ceramic tube shell as needed to achieve better electrical connection of the device. The eutectic solder can be processed in layers; for example, gold-tin solder can be plated with a layer of gold and then a layer of tin, forming an Au80Sn20 eutectic solder in a specific ratio.

[0049] That is, the embodiments of the present invention use eutectic welding to achieve electrical connection between the cover plate and the ceramic tube shell, thereby achieving electrical connection between the sensitive structure chip and the ASIC chip. The welding process can be selected according to the cover plate material, such as laser local heating welding and conduction heating welding, to further reduce stress, or to achieve electrical connection and sealing at the same time.

[0050] Preferably, for packaging methods using transparent materials such as Pyrex glass or quartz as the cover plate, eutectic bonding between the ceramic shell and the cover plate (which serves as the mounting substrate for sensitive structures) is achieved using localized laser heating. Localized laser heating for eutectic bonding enables quasi-cold soldering of ceramic MEMS devices, further reducing packaging stress. Different eutectic solders can be used for the electrical connection and bonding of the ceramic shell and cover plate, and eutectic bonding can be performed separately. For packaging methods using opaque materials such as silicon as the cover plate, eutectic bonding is achieved using a heat transfer heating method. When using conductive heating for eutectic bonding, the same eutectic solder must be used for the electrical connection and bonding of the ceramic shell and cover plate.

[0051] Furthermore, specialized packaging equipment is used to encapsulate the device according to the technical requirements of its sensitive structure. This equipment must be capable of high vacuum to achieve deep degassing before soldering. For packaging methods using transparent material covers, the vacuum chamber of the packaging equipment must have a glass window to enable laser-heated eutectic soldering without disrupting the vacuum or atmosphere.

[0052] To provide a better understanding of the method of the present invention, a specific embodiment is described in detail below:

[0053] This invention relates to a low-stress, high-integration packaging method for MEMS devices. A schematic diagram of the packaging structure is shown below. Figure 1 As shown, 1 is the cover plate, 2 is the sensitive structure, and 3 is the ceramic tube shell; schematic diagrams of the sensitive structure and cover plate are shown below. Figure 2 As shown, 1 is the cover plate, 2 is the sensitive structure, 4 is the metal pad a, and 5 is the metal lead b; the schematic diagram of the ceramic tube shell pads and sealing area is as follows. Figure 3 As shown, 3 is the ceramic housing, 6 is the ASIC chip, 7 is the gold-plated output pad, and 8 is the solder seal area. The specific implementation steps are as follows:

[0054] (1) Cover plate 1 processing: According to the material, size and electrical lead-out port requirements of the sensitive structure of the device, the cover plate 1, which serves as the mounting substrate for the sensitive structure 2, is designed and processed, including: 1) Selection of cover plate 1 material, such as Pyrex glass; 2) Cover plate 1 size, the outer dimensions are generally 0.5mm smaller than the ceramic tube shell; 3) Electrical lead-out lines of the cover plate, the tail end of the electrical lead-out lines should be designed with pads specifically for eutectic bonding, and correspond one-to-one with the lead terminals of the ceramic tube shell. The electrical lead-out lines are generally processed by magnetron gold plating.

[0055] (2) Eutectic Solder Processing: The electrical connection between the sensitive structure 2 and the ASIC chip 6, as well as the device output port, is achieved through the electrical connection between the cover plate 1 and the ceramic shell 3. This electrical connection is achieved through eutectic soldering. Simultaneously, the cover plate 1 and the ceramic shell 3 need to achieve hermetic eutectic sealing. Therefore, eutectic soldering is required on the external gold-plated pads 7 (i.e., electrical connection pads) and the sealing area 8 of the custom-processed ceramic shell. For example, gold-tin solder can be processed using electroplating. The solder thickness is generally 5μm, and the processing pattern is the custom-processed pad pattern and sealing area pattern.

[0056] (3) Sensitive structure patch: The sensitive structure 2 is mounted on the cover plate 1 to achieve a mechanical connection between the sensitive structure 2 and the cover plate 1. Specific implementation methods include: adhesive patch (including conductive adhesive, etc.), eutectic patch, and gold ball hot-press patch. The choice of specific implementation method depends on the patch strength requirements of the sensitive structure and the gas release characteristics of the encapsulation material, etc. In this embodiment, a eutectic patch is selected.

[0057] (4) Sensitive structure gold wire bonding: The electrical connection between the sensitive structure and the cover plate electrical leads is achieved by gold wire bonding. During the bonding process, the arc height needs to be controlled to avoid short circuit problems with the ASIC and its leads due to excessive arc height.

[0058] (5) ASIC mounting: that is, mounting the ASIC chip 6 onto the mounting area of ​​the ceramic housing 3. The ASIC mounting can be done by adhesive bonding or eutectic bonding. In this embodiment, the eutectic bonding method is selected.

[0059] (6) ASIC chip gold ball bonding wire: The electrical connection between the ASIC chip 6 and the ceramic housing 3 is achieved by gold ball bonding wire. During the bonding process, the arc height of the wire needs to be controlled to avoid short circuits with sensitive structures and their leads due to excessive arc height.

[0060] (4) Loading into the vacuum chamber: Open the vacuum chamber with the light-transmitting window of the packaging equipment, and put the ceramic tube shell 3 and the cover plate 1 with the chip and key wire completed into the vacuum chamber in sequence, with the ceramic tube shell 3 at the bottom and the cover plate at the top. At the same time, the tooling ensures that the ceramic tube shell 3 and the cover plate 1 are precisely aligned.

[0061] (5) Apply pressure: Determine the applied pressure based on the dimensions of the ceramic tube shell 3. For example, for a 10mm*10mm ceramic tube shell, the applied pressure is 400g. The applied pressure should ensure that the eutectic region is uniformly stressed;

[0062] (6) Degassing: Close the vacuum chamber, evacuate the vacuum, and heat the device to degas it. For example, the vacuum level is better than 10-4 Pa and the heating temperature is 100℃.

[0063] (7) Eutectic Sealing: Eutectic sealing requires achieving a hermetic seal between the cover plate 1 and the ceramic tube shell 3. The eutectic method can be achieved by methods such as graphite plate conduction heating or laser heating. In this embodiment, laser heating is selected to achieve eutectic sealing between the cover plate 1 and the ceramic tube shell 3, and to achieve electrical connection between the metal pad a4 and the gold-plated pad 7 output by the ceramic tube shell. The eutectic solder used in this embodiment is gold-tin solder, and the eutectic temperature is 280℃. It is necessary to control parameters such as the laser beam diameter, focusing distance, and irradiation time to achieve the control accuracy and temperature uniformity of the heating temperature.

[0064] (8) Remove the device: Close the vacuum valve to stop vacuuming, open the gas filling valve to inject nitrogen gas at one atmosphere into the vacuum chamber, open the vacuum chamber, and remove the sealed device.

[0065] (9) Electrical connection test: According to the pin definition, use a dedicated test socket and test circuit to perform a power-on test on the device to check whether the device can start oscillating normally and to confirm whether the electrical connection is normal.

[0066] (10) Leakage test: There are two methods for leak rate testing: helium back pressure leak detection and optical interference leak detection. In this embodiment, helium back pressure leak detection is selected.

[0067] The features described and / or illustrated above with respect to one embodiment may be used in the same or similar manner in one or more other embodiments, and / or in combination with or in lieu of features in other embodiments.

[0068] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, whole, step, or component, but does not exclude the presence or addition of one or more other features, wholes, steps, components, or combinations thereof.

[0069] The methods described above in this invention can be implemented in hardware or in combination with software. This invention relates to computer-readable programs that, when executed by a logic component, enable the logic component to implement the aforementioned apparatus or constituent parts, or to implement the various methods or steps described above. This invention also relates to storage media for storing the above programs, such as hard disks, magnetic disks, optical disks, DVDs, flash memory, etc.

[0070] Many features and advantages of these embodiments are apparent from this detailed description, and therefore the appended claims are intended to cover all such features and advantages of these embodiments that fall within their true spirit and scope. Furthermore, since many modifications and alterations will readily occur to those skilled in the art, the embodiments of the invention are not intended to be limited to the precise structures and operations illustrated and described, but rather to encompass all suitable modifications and equivalents falling within their scope.

[0071] The parts of this invention not described in detail are techniques known to those skilled in the art.

Claims

1. A method for low-stress packaging of a MEMS device, comprising: The method includes: Step 1: Attach the sensitive structure to the cover plate. The sensitive structure and the cover plate are made of the same material. Step 2: Process two sets of metal pads and two sets of metal leads on the mounting surface of the cover plate where the sensitive structure is located. The two sets of metal pads are set on both sides of the sensitive structure, and the two sets of metal pads and the two sets of metal leads are set one-to-one. Each set of metal pads includes multiple metal pads, and each set of metal leads includes multiple metal leads. One end of any metal lead is connected to the corresponding metal pad, and the other end is connected to the sensitive structure. Design a sealing area on the side of the cover plate where the sensitive structure is located. Step 3: Select a ceramic tube shell as the encapsulation shell. Process multiple gold-plated pads for external output on the upper surfaces of the two opposite side walls of the ceramic tube shell, which correspond one-to-one with the two sets of metal pads in Step 2. Design a sealing area on the upper surfaces of the other set of opposite side walls of the ceramic tube shell. Step 4: Mount the ASIC chip inside the ceramic housing, and process two sets of metal pads and two sets of metal leads on both sides of the ASIC chip. The two sets of metal pads are set on both sides of the ASIC chip, and the two sets of metal pads and two sets of metal leads are set one-to-one. Each set of metal pads includes multiple metal pads, and each set of metal leads includes multiple metal leads. One end of any metal lead is connected to the corresponding metal pad, and the other end is connected to the ASIC chip. One set of metal pads is connected to multiple gold-plated pads on one side wall, and the other set of metal pads is connected to multiple gold-plated pads on the other side wall. Step 5: Align the sealing areas of the cover plate and the ceramic shell one by one. Align the two sets of metal pads on the cover plate with the external output gold-plated pads on both sides of the ceramic shell one by one. Use eutectic bonding to achieve electrical connection between the cover plate and the ceramic shell, thereby achieving electrical connection between the sensitive structure and the ASIC chip.

2. The low-stress packaging method for MEMS devices according to claim 1, characterized in that, In step two, the metal lead is gold wire, and the electrical connection between the sensitive structure and the cover plate is achieved by flip-chip soldering or gold wire ball soldering.

3. A low-stress packaging method for MEMS devices according to claim 1 or 2, characterized in that, In step two, gold plating is performed on the sealing area of ​​the cover plate for eutectic sealing; in step three, gold plating is performed on the sealing area of ​​the ceramic tube shell to achieve eutectic sealing between the ceramic tube shell and the cover plate.

4. A low-stress packaging method for MEMS devices according to any one of claims 1-3, characterized in that, In step two, microgrooves are machined between the metal pads and the sealing area on the cover plate to store the molten eutectic solder that flows out, so as to avoid short circuits between the metal lead pads and the sealing area.

5. The low-stress packaging method for MEMS devices according to claim 1, characterized in that, In step four, the metal leads are gold wires, and the electrical connection between the ASIC chip and the ceramic housing is achieved by gold wire ball bonding.

6. The low-stress packaging method for MEMS devices according to claim 1, characterized in that, In step five, eutectic sealing of the ceramic tube shell and cover plate is achieved by using laser local heating or conductive heating welding.

7. A low-stress packaging method for MEMS devices according to claim 1, characterized in that, In step five, before eutectic sealing, a deep degassing process is performed by vacuuming.

8. A low-stress packaging structure for MEMS devices, characterized in that, The encapsulation structure is obtained using the encapsulation method described in any one of claims 1-7.

9. A low-stress packaging structure for a MEMS device according to claim 8, characterized in that, The packaging structure includes a cover plate assembly and a ceramic housing assembly. The cover plate assembly includes a cover plate, a sensitive structure, two sets of metal pads a, and two sets of metal leads b. The sensitive structure is mounted on the cover plate and is made of the same material as the cover plate. The two sets of metal pads a are disposed on the cover plate and located on both sides of the sensitive structure. Two sets of metal pads a and two sets of metal leads b are set in a one-to-one correspondence. Each set of metal pads a includes multiple metal pads a, and each set of metal leads b includes multiple metal leads b. One end of any metal lead b is connected to the corresponding metal pad a, and the other end is connected to the sensitive structure. The side of the cover plate where the sensitive structure is set is also designed with a sealing area. The ceramic housing assembly includes a ceramic housing, an ASIC chip, two sets of external gold-plated pads, two sets of metal pads c, and two sets of metal leads d. The ceramic housing serves as the encapsulation housing. Two sets of external gold-plated pads are machined on the upper surfaces of the opposite side walls of the ceramic housing, corresponding one-to-one with the two sets of metal pads a in step two. Each set of external gold-plated pads includes multiple external gold-plated pads. A sealing area is designed on the upper surface of the other set of opposite side walls of the ceramic housing. The ASIC chip is mounted inside the cavity of the ceramic housing and on lead A. The SIC chip has two sets of metal pads c and two sets of metal leads d on both sides. The two sets of metal pads c are set on both sides of the ASIC chip. The two sets of metal pads c and the two sets of metal leads d are set one-to-one. Each set of metal pads c includes multiple metal pads c. Each set of metal leads d includes multiple metal leads d. One end of any metal lead d is connected to the corresponding metal pad c, and the other end is connected to the ASIC chip. One set of metal pads c is connected one-to-one to multiple gold-plated pads on one side wall. The other set of metal pads c is connected one-to-one to multiple gold-plated pads on the other side wall. The sealing area of ​​the cover plate and the sealing area of ​​the ceramic tube shell are connected by eutectic bonding. The two sets of metal pads a of the cover plate are respectively connected to the two sets of external output gold-plated pads of the ceramic tube shell. The electrical connection between the sensitive structure and the ASIC chip and the device output port is achieved through the electrical connection between the cover plate and the ceramic tube shell. The electrical connection between the cover plate and the ceramic tube shell is achieved through eutectic bonding of eutectic solder.

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