Surface-mounted IMU (Inertial Measurement Unit) and preparation method thereof

Abstract

The invention is applicable to the technical field of semiconductor devices, and provides a surface-mounted IMU (inertial measurement unit) and a preparation method thereof, and the surface-mounted IMU comprises a PCBA (printed circuit board assembly), a ceramic adapter plate, an MEMS (micro-electromechanical system) inertial chip and a Teflon cover plate; a groove is formed in the ceramic adapter plate; the size of the groove is suitable for the MEMS inertial chip; the bottom bonding pad of the ceramic adapter plate is connected with the top bonding pad of the ceramic adapter plate through a half hole; the MEMS inertial chip is arranged in the groove and is bonded with the ceramic adapter plate through an insulating gold wire; the ceramic adapter plate is welded on the assembly surface of the PCBA; the Teflon cover plate and the PCBA form a cavity, and the ceramic adapter plate and the MEMS inertial chip are placed in the cavity. The requirements of small size, high precision and low power consumption can be met at the same time, the burden of a vehicle-mounted power supply is relieved, and the requirement for the integration level of the whole vehicle is improved.

Description

Technical Field

[0001] The present application belongs to the field of MEMS technology, and in particular, relates to a surface mounted IMU and a preparation method thereof. Background Art

[0002] At present, the field of autonomous driving is booming. As one of its core components, the Inertial Measurement Unit (IMU) can collect the vehicle's motion data while the car is driving. The IMU consists of a gyroscope and an accelerometer. The gyroscope collects the vehicle's rotation data, and the accelerometer detects the vehicle's linear motion. The displacement, posture and speed of the vehicle are further calculated, making it easier for the autonomous driving system to plan the vehicle's path and behavior.

[0003] At present, common IMUs are usually composed of a micro-electro-mechanical system (MEMS) inertial chip, a PCB board and a shell. The MEMS inertial chip is welded on the PCB board, and the data is processed by the PCB's single-chip microcomputer, crystal oscillator and other components, and then installed in the shell. The IMU is subsequently installed in the inertial navigation system on the car through connecting cables. The IMU needs to meet the requirements of small size, high precision, and low power consumption, reduce the burden on the vehicle power supply, and improve the integration of the entire vehicle. However, the size of the IMU is generally large, and there is a risk of failure when connected through an interface. As the product ages, the IMU will fail. -The accuracy of the IMU mainly depends on the MEMS inertial chip. The MEMS inertial chip can measure angular velocity and acceleration, but the accuracy is low, and it needs to be calibrated by the MCU to obtain accurate data. However, the traditional welding process will cause mechanical stress and thermal stress on the chip, causing the IMU to have zero drift, abnormal noise, etc., resulting in the product accuracy failing to meet the needs of autonomous driving. The accuracy of IMU can be improved by increasing the number of MEMS inertial chips and optimizing the algorithm, but the increase in chips will increase power consumption and increase the burden on the vehicle power supply. When a large number of inertial chips are used, when a chip fails, it will also cause data anomalies and increase the risk of failure of the autonomous driving system.

[0004] Therefore, the current IMU cannot simultaneously meet the above requirements of small size, high precision, and low power consumption, reduce the burden on the vehicle power supply, and improve the requirements for vehicle integration. Summary of the invention

[0005] In order to overcome the problems existing in the related technology, the embodiment of the present application provides a surface mount IMU and a preparation method thereof, which can simultaneously meet the requirements of small size, high precision, and low power consumption, reduce the burden of the vehicle power supply, and improve the requirements for the integration of the entire vehicle.

[0006] This application is implemented through the following technical solutions:

[0007] In a first aspect, an embodiment of the present application provides a surface mount IMU, including a printed circuit board assembly (PCBA), a ceramic adapter board, a MEMS inertial chip, and a Teflon cover plate;

[0008] A groove is provided in the ceramic adapter plate; the size of the groove is suitable for the MEMS inertial chip; the bottom pad of the ceramic adapter plate is connected to the top pad of the ceramic adapter plate through a half hole;

[0009] The MEMS inertial chip is set in the groove and bonded to the ceramic adapter plate through insulating gold wire;

[0010] The ceramic adapter plate is welded on the assembly surface of the PCBA;

[0011] The Teflon cover plate and the PCBA form a cavity, in which the ceramic adapter plate and the MEMS inertial chip are placed.

[0012] In one embodiment, the surface mount IMU further includes a copper pillar;

[0013] The copper column is arranged below the groove and connected to the MEMS inertial chip through the ceramic adapter plate; the copper column is grounded.

[0014] In one embodiment, the MEMS inertial chip is bonded in the groove using epoxy adhesive.

[0015] In one embodiment, the ceramic adapter plate is made of alumina ceramic; the alumina ceramic and the MEMS inertial chip have a thermal expansion coefficient within the same preset range.

[0016] In one embodiment, the preset size of the insulating gold wire is 10 μm to 50 μm; the outer surface of the insulating gold wire is protected by high-temperature silicone rubber.

[0017] In one embodiment, the ceramic transfer board bonded with the MEMS inertial chip is soldered to the assembly surface of the PCBA by using lead-free solder paste with a preset melting point.

[0018] In one embodiment, the surface mount IMU further includes a chip cover;

[0019] The chip cover plate is arranged inside the cavity and above the ceramic adapter plate, and is used to seal the MEMS inertial chip in the groove of the ceramic adapter plate.

[0020] In a second aspect, the present application provides a method for preparing a surface mounted IMU, comprising:

[0021] A groove is set in the ceramic adapter plate; the size of the groove is suitable for the MEMS inertial chip; the bottom pad of the ceramic adapter plate is connected to the top pad of the ceramic adapter plate through a half hole;

[0022] The MEMS inertial chip is placed in the groove and bonded to the ceramic adapter plate through insulating gold wires;

[0023] Solder the ceramic adapter board to the assembly surface of the PCBA;

[0024] The Teflon cover plate and the PCBA are assembled together to form a cavity, and the ceramic adapter plate and the MEMS inertial chip are sealed in the cavity.

[0025] One embodiment, bonding with a ceramic transfer plate through an insulating gold wire, comprises:

[0026] Determine the maximum continuous current that the insulating gold wire can withstand when bonding the MEMS inertial chip to the ceramic adapter plate;

[0027] Based on the maximum continuous current, determine the initial size range of the insulating gold wire;

[0028] Based on the initial size range of the insulating gold wire, determining the maximum allowable current and the fusing current of the insulating gold wire of each size within the initial size range;

[0029] Based on the maximum allowable current and fusing current of insulating gold wires of various sizes, as well as the cost and ultimate stress, the insulating gold wire is simulated to determine the preset size of the insulating gold wire;

[0030] The MEMS inertial chip is bonded to the ceramic interposer using insulated gold wires with preset dimensions.

[0031] In one embodiment, the method for preparing the surface mount IMU further includes:

[0032] After the ceramic adapter board is welded to the assembly surface of the PCBA, zero bias calibration and cross-coupling calibration are performed in the full temperature range, and the calibration parameters are burned into the MCU.

[0033] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0034] In the embodiment of the present application, a groove is provided in the ceramic adapter plate, and the size of the groove is suitable for the MEMS inertial chip, so that the MEMS inertial chip can be compactly arranged in the groove, reducing the additional support structure, thereby reducing the overall volume. The Teflon cover plate and the PCBA form a cavity, and the ceramic adapter plate and the MEMS inertial chip are placed in the cavity, which not only protects the internal components, but also further optimizes the spatial layout, reduces the additional protective structure, and helps to further achieve the design goal of small volume. Components such as PCBA, ceramic adapter plate, MEMS inertial chip and Teflon cover plate can be independently designed and manufactured, and then assembled. This modular design not only improves production efficiency, but also facilitates integration with other vehicle systems. The small volume design of the surface mount IMU can be more easily integrated into various systems of the vehicle, such as the chassis system, power system, navigation system, etc., further improving the integration of the entire vehicle.

[0035] The MEMS inertial chip is bonded to the ceramic adapter plate through an insulating gold wire to ensure that when the gold wire is abnormal, it will not cause risks such as short circuits, thereby ensuring safety during autonomous driving. At the same time, the insulation layer of the gold wire reduces the interference of external electromagnetic fields on the gold wire transmission signal, ensures a stable connection between the MEMS inertial chip and the ceramic adapter plate, reduces the impact of vibration and noise on measurement accuracy, and further improves the accuracy of the IMU. Compared with traditional inertial measurement units, MEMS technology can significantly reduce power consumption, thereby reducing the burden on the vehicle power supply and extending the service life of the vehicle power supply. The ceramic adapter plate has good thermal conductivity and can effectively transfer the heat generated by the MEMS inertial chip to the PCBA, avoiding local overheating, reducing power consumption, and further achieving the goal of low power consumption. High-precision IMUs can provide more accurate vehicle motion data, help optimize the vehicle's control strategy and energy management, and improve the overall energy efficiency of the vehicle.

[0036] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0038] Figure 1 is an exploded view of a surface mount IMU provided in one embodiment of the present application;

[0039] Figure 2is an axonometric diagram of a surface mounted IMU provided in one embodiment of the present application;

[0040] Figure 3 1 is a diagram of various orientations of a surface mount IMU provided by an embodiment of the present application; Figure 3 (a) is a front view of a surface mounted IMU provided in one embodiment of the present application; Figure 3 (b) is a right side view of the surface mount IMU provided in one embodiment of the present application; Figure 3 (c) is a bottom view of a surface mounted IMU provided in one embodiment of the present application; Figure 3 (d) is a left view of the surface mount IMU provided in one embodiment of the present application;

[0041] Figure 4 It is a schematic diagram of the structure of the insulating gold wire provided in one embodiment of the present application;

[0042] Figure 5 is an exploded view of another surface mounted IMU provided in one embodiment of the present application. DETAILED DESCRIPTION

[0043] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0044] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0045] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0046] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0047] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0048] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0049] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] Figure 1 is an exploded view of a surface mount IMU provided in one embodiment of the present application; Figure 2 is an axonometric diagram of a surface mounted IMU provided in one embodiment of the present application; Figure 3 are various directional views of a surface mount IMU provided in one embodiment of the present application; wherein, Figure 3 (a) is a front view of a surface mounted IMU provided in one embodiment of the present application; Figure 3 (b) is a right side view of the surface mount IMU provided in one embodiment of the present application; Figure 3 (c) is a bottom view of a surface mounted IMU provided in one embodiment of the present application; Figure 3 (d) is a left view of the surface mount IMU provided by one embodiment of the present application; Figures 1 to 3 , mainly for the preparation of MEMS multi-layer wiring or small line width signal lines, the detailed description of the surface mount IMU is as follows:

[0051] An embodiment of the present application provides a surface mount IMU, including a PCBA 100 , a ceramic adapter board 200 , a MEMS inertial chip 300 , and a Teflon cover plate 400 .

[0052] A groove 201 is provided in the ceramic adapter plate 200; the size of the groove 201 is suitable for the MEMS inertial chip 300; the bottom pad of the ceramic adapter plate 200 is connected to the top pad of the ceramic adapter plate 200 through a half hole.

[0053] Exemplarily, the size of the groove 201 is just suitable for accommodating the MEMS inertial chip 300 , for example, the upper surface of the MEMS inertial chip 300 can be flush with the upper surface of the groove 201 , or the upper surface of the MEMS inertial chip 300 can be partially beyond the groove 201 .

[0054] Among them, considering that the car needs to have an extremely fast response time during high-speed driving, the use of half holes can reduce the volume of the ceramic adapter plate 200, increase signal transmission within the plate, and reduce noise signals. At the same time, the half hole can make the welding effect more firm and improve the welding quality. In the inspection process, the tin climbing height of the half hole can be seen to determine the welding quality.

[0055] The MEMS inertial chip 300 is disposed in the groove 201 and bonded to the ceramic transfer board 200 via an insulating gold wire 600 .

[0056] For example, the insulating gold wire 600 can ensure that when the gold wire is abnormal, it will not cause risks such as short circuit, thereby ensuring safety during the autonomous driving process. The insulating layer of the insulating gold wire 600 can reduce the interference of the external electromagnetic field on the gold wire transmission signal, making the signal transmission more stable and accurate, and reducing signal distortion and bit error rate. Because there are many types of car driving environments, the insulating layer can isolate the gold wire from the contact with corrosive substances such as water vapor, oxygen, acid and alkali in the external environment, slow down the oxidation and corrosion rate of the gold wire, and extend the service life of the gold wire. Considering that the surface packaged IMU needs to be reflowed through surface mount technology (SMT), the insulating gold wire 600 has good high temperature resistance. Even in a high temperature environment, the insulating layer can maintain good insulation performance and physical stability, ensuring that the gold wire can still work normally under high temperature conditions, ensuring that the gold wire will not fall off during the reflow process, and improving the reliability of the product.

[0057] The ceramic adapter board 200 is welded on the assembly surface of the PCBA 100 .

[0058] The Teflon cover plate 400 and the PCBA 100 form a cavity, and the ceramic adapter plate 200 and the MEMS inertial chip 300 are placed in the cavity.

[0059] For example, PCBA 100 is selected to use a material with low thermal conductivity to reduce the heat generated in welding during subsequent use and transferred to the ceramic adapter plate 200. Then, a high-temperature epoxy adhesive is used to bond the Teflon cover plate 400 to the PCBA 100. The use of the Teflon cover plate 400 can reduce the thermal shock of the temperature on the IMU during the SMT reflow process, minimizing the thermal shock to the MEMS inertial chip 300.

[0060] In this embodiment, a groove 201 is provided in the ceramic adapter plate 200, and the size of the groove 201 is suitable for the MEMS inertial chip 300, so that the MEMS inertial chip 300 can be compactly arranged in the groove 201, reducing the additional support structure, thereby reducing the overall volume. The Teflon cover plate 400 and the PCBA 100 form a cavity, and the ceramic adapter plate 200 and the MEMS inertial chip 300 are placed in the sealed cavity, which not only protects the internal components, but also further optimizes the spatial layout, reduces the additional protective structure, and helps to further achieve the design goal of small volume. Components such as PCBA 100, ceramic adapter plate 200, MEMS inertial chip 300 and Teflon cover plate 400 can be independently designed and manufactured, and then assembled. This modular design not only improves production efficiency, but also facilitates integration with other vehicle systems. The small volume design of the surface mount IMU can be more easily integrated into various systems of the vehicle, such as the chassis system, power system, navigation system, etc., further improving the integration of the whole vehicle.

[0061] The MEMS inertial chip 300 is bonded to the ceramic adapter plate 200 through the insulating gold wire 600 to ensure that when the gold wire is abnormal, it will not cause risks such as short circuit, thereby ensuring safety during the autonomous driving process. At the same time, the insulation layer of the gold wire reduces the interference of the external electromagnetic field on the gold wire transmission signal, ensures a stable connection between the MEMS inertial chip 300 and the ceramic adapter plate 200, reduces the impact of vibration and noise on the measurement accuracy, and further improves the accuracy of the IMU. Compared with traditional inertial measurement units, MEMS technology can significantly reduce power consumption, thereby reducing the burden on the vehicle power supply and extending the service life of the vehicle power supply. The ceramic adapter plate 200 has good thermal conductivity and can effectively conduct the heat generated by the MEMS inertial chip 300 to the PCBA 100 to avoid local overheating and further achieve the goal of low power consumption. High-precision IMU can provide more accurate vehicle motion data, help optimize the vehicle's control strategy and energy management, and improve the overall energy efficiency of the vehicle.

[0062] In one embodiment, the surface mount IMU further includes a copper pillar.

[0063] The copper column is disposed below the groove 201 and is connected to the MEMS inertial chip 300 through the ceramic adapter plate 200 ; the copper column is grounded.

[0064] Exemplarily, a copper pillar is fixed under the groove 201 and inserted into the adapter board to facilitate heat dissipation, and the copper pillar is grounded to make signal transmission more stable.

[0065] In one embodiment, the MEMS inertial chip 300 is bonded in the groove 201 using epoxy adhesive.

[0066] Exemplarily, the MEMS inertial chip 300 is bonded to the groove 201 using epoxy adhesive so that the chip is completely inside the groove 201, which greatly reduces the stress caused by the bonding process, plays a good stress isolation role, and avoids chip warping.

[0067] If the chip is offset, the angular velocity, acceleration and other data of the XYZ axis output by the chip will deviate from the actual data. Using high-temperature epoxy glue to fix the chip can make the MEMS inertial chip 300 more tightly connected to the circuit board during vibration, reduce the movement of the chip during vibration and impact, and reduce data deviation.

[0068] The groove 201 in the ceramic adapter plate 200 also has a buffering effect, allowing the chip to be directly connected to the circuit board to prevent the chip from sticking. Since the epoxy glue is liquid before curing, the shape of the epoxy glue can be better controlled by using the groove 201, reducing the generation of stress and making the product more consistent.

[0069] In one embodiment, the ceramic transfer plate 200 is made of alumina ceramic; the alumina ceramic and the MEMS inertial chip 300 have a thermal expansion coefficient within the same preset range.

[0070] Exemplarily, the main component of the ceramic adapter plate 200 is alumina ceramic, and the formed ceramic adapter plate 200 has the advantages of high thermal conductivity, heat shock resistance, good electrical conductivity, and low corrosion resistance. Alumina ceramic and the MEMS inertial chip 300 have thermal expansion coefficients in the same preset range, that is, alumina ceramic and the MEMS inertial chip 300 have similar thermal expansion coefficients, so that the ceramic adapter plate 200 and the MEMS inertial chip 300 have better fit, which can reduce the temperature shock during the SMT reflow process. When the temperature changes during the use of the IMU, the zero position of the IMU will also change. The smaller the temperature shock, the smaller the zero offset of the IMU, and the more stable the data.

[0071] In one embodiment, the preset size of the insulating gold wire 600 is 10 μm to 50 μm; the outer surface of the insulating gold wire 600 is protected by high-temperature silicone rubber.

[0072] For example, bonding the MEMS inertial chip 300 to the ceramic adapter plate 200 via the insulating gold wire 600 instead of welding the MEMS inertial chip 300 to the ceramic adapter plate 200 can further reduce welding stress and improve chip performance.

[0073] Preferably, the preset size of the insulating gold wire 600 is 30 μm.

[0074] For example, by performing vibration simulation on products with different bonding wire diameters, it is found that the gold wire has a scale effect, that is, the larger the diameter of the insulating gold wire 600 used for bonding, the greater the ultimate stress it can withstand. Considering the cost, maximum allowable current, larger fusing current, ultimate stress and other indicators, a 30μm insulating gold wire 600 is selected.

[0075] The use of 30μm insulated gold wire 600 has lower resistance and inductance, which can achieve more efficient signal transmission, reduce signal delay and distortion, and improve the operating speed and data processing capabilities of electronic devices. Compared with the small-sized insulated gold wire 600 used for bonding, the 30μm insulated gold wire 600 still has sufficient mechanical strength and flexibility, and can withstand a certain degree of stretching, bending and vibration, improving the dynamic performance of the chip. During the chip packaging process, the insulated gold wire 600 needs to be precisely bonded to the chip and lead frame. The 30μm bonding wire can better adapt to the various stresses in the bonding process, ensure the reliability and stability of the bonding, reduce bonding failures caused by external forces, and improve the product yield.

[0076] Exemplarily, the insulating gold wire 600 is in the form of two similar bonding wires, such as Figure 4 As shown, the fusing current value can be further increased.

[0077] During the research process, it was found that for MEMS inertial chips 300 in the range of 5mm×5mm to 10mm×10mm, the connection quality between the bonding wire and the chip and the package pins has a significant impact on the standing wave ratio. For example, for a 5mm×5mm MEMS inertial chip 300 and a 7mm×7mm ceramic adapter plate 200, if the bonding point is not firm, there is an oxide layer, or the bonding shape is irregular, the impedance at the bonding point will change, generating a reflected wave and increasing the standing wave ratio. Therefore, this embodiment designs the insulating layer and preset size of the insulating gold wire 600 to form a good bonding process, which can ensure good impedance matching between the bonding wire and the connection point, thereby reducing the standing wave ratio.

[0078] In one embodiment, the ceramic transfer board 200 bonded with the MEMS inertial chip 300 is soldered to the assembly surface of the PCBA 100 by using a lead-free solder paste with a preset melting point.

[0079] For example, through SMT technology, high-temperature lead-free solder paste is used to weld the ceramic adapter board 200 bonded with the MEMS inertial chip 300 to the PCBA100. Select a high-temperature lead-free solder paste with a melting point of 280°C and a reflow temperature of 310°C to 330°C. After the product is soldered, when the module is subsequently soldered, when a conventional lead-free solder paste is used for secondary reflow, the high melting point and high reflow temperature of the high-temperature lead-free solder paste can ensure that during the secondary reflow process, the solder paste between the ceramic adapter board 200 and the PCB will not enter a molten state, and the impact on the internal structure of the chip is minimized. When the stress on the IMU does not change, the performance of the product will remain stable, which can meet the lead-free requirements of automotive products.

[0080] For example, the pads on the assembly surface of PCBA100 and the pads on the bottom surface of PCBA100 may also be connected through half holes, such as Figure 3 As shown, after the metallization inside the half hole, the circuit is connected, which reduces the volume of PCBA100 and increases the overall integration of the IMU.

[0081] For an embodiment, see Figure 5 , the surface mount IMU also includes a chip cover 500 .

[0082] The chip cover plate 500 is disposed inside the cavity and above the ceramic adapter plate 200 , and is used to seal the MEMS inertial chip 300 in the groove 201 of the ceramic adapter plate 200 .

[0083] Exemplarily, after the chip cover plate 500 is set, the interior of the chip cover plate 500 is an airtight package, and the cavity between the chip cover plate 500 and the Teflon cover plate 400 is a non-airtight package. At this time, a ventilation hole can be opened on the Teflon cover plate 400 to allow ventilation during subsequent welding to reduce the impact of SMT reflow and temperature.

[0084] The use of high-temperature silicone rubber for the outer layer to protect the bonding wire is to reduce the impact of the outside world on the bonding wire. Silicone rubber is more stable under temperature changes, reduces data fluctuations, and can provide more accurate information. After using high-temperature silicone rubber to protect the bonding wire, a high-temperature resistant and corrosion-resistant chip cover plate 500 is glued to the PCBA circuit board to further reduce the impact of temperature on the MEMS inertial chip 300 during reflow, helping the chip to dissipate heat more evenly and avoid heat accumulation in the chip. The chip cover plate 500 can serve as an internal physical barrier to effectively block the direct effects of these external forces on the chip, reduce scratches and wear on the chip surface, and damage to the internal structure. There are a lot of dust, fibers and other tiny particles in the air. Once these particles fall on the chip surface or enter the inside of the chip, they may cause a short circuit in the chip circuit, interfere with signal transmission or affect the heat dissipation performance of the chip. The chip cover 500 can be combined with the Teflon cover 400 to prevent the entry of dust and particles, keep the internal environment of the chip clean, and ensure the normal operation of the chip. Even if the Teflon cover 400 is damaged due to some unexpected circumstances, the chip cover 500 can protect the MEMS inertial chip 300 to work normally.

[0085] In one embodiment, bumps are disposed on both sides of the Teflon cover plate 400 ; the bumps include a first bump 401 and a second bump 402 .

[0086] The first protrusion 401 is disposed on the left side of the Teflon cover plate 400. Figure 1 , Figure 3 and Figure 5 As shown, the second protrusion 402 is disposed on the right side of the Teflon cover plate 400. Figure 2 and Figure 3 The size of the first bump 401 is greater than the size of the second bump 402 .

[0087] Corresponding to the bump, notches are provided on both sides of PCBA100, and the notches include a first notch 101 and a second notch 102. The first notch 101 is provided on the left side of PCBA100. Figure 3 As shown, the second notch 102 is disposed on the right side of the PCBA 100. The first notch 101 cooperates with the first bump 401, and the second notch 102 cooperates with the second bump 402. The size of the first notch 101 is larger than the size of the second notch 102.

[0088] By providing bumps (first bump 401 and second bump 402) on both sides of the Teflon cover plate 400 and matching them with the notches (first notch 101 and second notch 102) on the PCBA 100 (printed circuit board assembly), precise positioning and firm fixation between the two can be ensured, which helps prevent displacement or loosening due to vibration or external force during use, thereby improving the stability and reliability of the overall structure.

[0089] The combination of bumps and recesses of different sizes can provide more accurate positioning for the assembly of the Teflon cover and the PCBA. During the assembly process, the larger first bump 401 and recess can be roughly positioned first to determine the approximate position of the two; then the smaller second bump 402 and recess can be used for fine adjustment to further improve the accuracy of positioning.

[0090] Considering the miniaturization of IMU products, the different sizes of bumps and recesses make it easier to judge their correspondence by observation and touch during installation, so as to quickly find the correct installation position. Especially when the size of the Teflon cover and PCBA is large or the installation space is small, this design can significantly improve the installation efficiency and reduce the possibility of installation errors and rework.

[0091] The surface mount IMU of the embodiment of the present application realizes a low-stress, miniaturized, high-precision surface mount IMU, which can enable the MEMS inertial chip 300 to maintain good performance after welding and reduce the impact of stress on it. In the subsequent full-temperature range calibration and compensation process, the IMU can maintain high precision during use. The reliability of the IMU is ensured by welding, and the level of autonomous driving of the car is further improved.

[0092] The present application also provides a method for preparing a surface mounted IMU, including:

[0093] Step S1, setting a groove in the ceramic adapter plate.

[0094] The size of the groove 201 is suitable for the MEMS inertial chip 300; the bottom pad of the ceramic adapter board 200 is connected to the top pad of the ceramic adapter board 200 through a half hole.

[0095] Step S2, placing the MEMS inertial chip in the groove 1, and bonding it to the ceramic adapter plate through insulating gold wires.

[0096] Step S3, welding the ceramic adapter plate to the assembly surface of the PCBA.

[0097] Exemplarily, step S3 may be performed first to weld the ceramic adapter plate to the assembly surface of the PCBA, and then step S2 may be performed to set the MEMS inertial chip in the groove 201 to avoid a significant impact of the welding temperature and stress of step S3 on the MEMS inertial chip.

[0098] Step S4, assembling the Teflon cover plate and the PCBA together to form a cavity, and sealing the ceramic adapter plate and the MEMS inertial chip in the cavity.

[0099] Exemplarily, a method for preparing a surface mount IMU further includes:

[0100] After step S2 and step S3 , the chip cover plate 500 is buckled onto the outer sides of the ceramic transfer plate 200 and the MEMS inertial chip 300 , and welded to the assembly surface of the PCBA 100 .

[0101] In one embodiment, in step S4, bonding the ceramic transfer plate together through the insulating gold wire 600 includes:

[0102] Step S41 , determining the maximum continuous current that the insulating gold wire 600 is subjected to when the MEMS inertial chip 300 is bonded to the ceramic adapter plate 200 .

[0103] During the design process, the lead wire is designed so that the maximum continuous current it can withstand under the maximum rated current is determined by formula (1). The maximum continuous current that the insulating gold wire 600 can withstand is expressed as:

[0104]

[0105] Wherein, I is the maximum allowable current, in A; d is the diameter of the insulating gold wire 600, in mm; and K is a constant. Wherein, when the length of the insulating gold wire 600 is ≤1.0 mm, K=234; when the length of the insulating gold wire 600 is >1 mm, K=160).

[0106] Step S42, determining the initial size range of the insulating gold wire 600 based on the maximum continuous current.

[0107] Step S43 , based on the initial size range of the insulating gold wire 600 , determining the maximum allowable current and the fusing current of the insulating gold wire 600 of each size within the initial size range.

[0108] The calculation method of the fusing current of the insulating gold wire 600 is:

[0109]

[0110] Wherein, D is the diameter of the insulating gold wire 600, in mm; L is the length of the insulating gold wire 600, in mm. When packaging the MEMS inertial chip 300, the length of the insulating gold wire 600 will be greater than 1 mm, and the length of the insulating gold wire 600 is bonded at 1.5 mm. At this time, the maximum allowable current and the fusing current of several common bonding wires are shown in Table 1.

[0111] Table 1 Maximum allowable current and fuse current of several common bonding wires

[0112] Insulated gold wire 600 diameter (μm) Maximum allowable current (A) Fusing current(A) 15 0.2939 0.4724 20 0.4525 0.8399 25 0.6325 1.3123 30 0.8314 1.8898 50 1.7889 5.2494

[0113] Step S44 , based on the maximum allowable current and the fusing current of the insulating gold wire 600 of various sizes, as well as the cost and the ultimate stress, the insulating gold wire 600 is simulated to determine the preset size of the insulating gold wire 600 .

[0114] Combined with the above calculation results, the larger the diameter of the bonding wire, the larger the maximum allowable current and the fuse current. When the IMU is in use, in order to prevent a single bonding wire from fusing or disconnecting, combined with the size of the bonding pad, in this embodiment, two wires can be selected to further increase the fuse current value, such as Figure 4 shown.

[0115] Vibration simulations were performed on products with different bonding wire diameters. Gold wire has a scale effect, that is, the larger the diameter of the bonding wire, the greater the ultimate stress it can withstand. Considering the comprehensive cost, maximum allowable current, fusing current, and ultimate stress, 30μm insulating gold wire 600 was selected.

[0116] The 30μm insulated gold wire 600 has lower resistance and inductance, which can achieve more efficient signal transmission, reduce signal delay and distortion, and improve the operating speed and data processing capabilities of electronic devices. Compared with small-sized bonding wires, the 30μm insulated gold wire 600 still has sufficient mechanical strength and flexibility, and can withstand a certain degree of stretching, bending and vibration, improving the dynamic performance of the chip. In the chip packaging process, the bonding wire needs to be precisely bonded to the chip and lead frame. The 30μm insulated gold wire 600 can better adapt to various stresses in the bonding process, ensure the reliability and stability of the bonding, reduce bonding failures caused by external forces, and improve the product yield. .

[0117] Step S45 , using an insulating gold wire 600 with a preset size, the MEMS inertial chip 300 is bonded to the ceramic transfer plate 200 .

[0118] The connection quality of the 30μm insulated gold wire 600 to the chip and package pins has a significant impact on the standing wave ratio. If the bonding point is not firm, has an oxide layer or the bonding shape is irregular, the impedance of the bonding point will change, generating reflected waves and increasing the standing wave ratio. A good bonding process can ensure good impedance matching between the bonding wire and the connection point, thereby reducing the standing wave ratio.

[0119] In one embodiment, the method for preparing the surface mount IMU further includes:

[0120] After the ceramic adapter board 200 is welded to the assembly surface of the PCBA 100, zero bias calibration and cross-coupling calibration are performed in the full temperature range, and the calibration parameters are burned into the MCU.

[0121] The purpose of PCBA100 welding the ceramic adapter board 200 first is to make the MEMS inertial chip 300 have welding stress before calibration. After the Teflon cover plate 400 is assembled, zero bias calibration and cross-coupling calibration in the full temperature range are performed, and the calibration parameters are burned into the MCU. When the final surface-mounted IMU is welded to the inertial navigation system, the welding stress change of the MEMS inertial chip 300 is minimal. At this time, the original parameters can fit the new use environment, so that the surface-mounted IMU maintains low stress and high precision.

[0122] For the beneficial effects of the embodiments of the present application, refer to the beneficial effects of the surface mounted IMU.

[0123] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0124] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A surface mount IMU, characterized in that: Including PCBA, ceramic adapter board, MEMS inertial chip and Teflon cover; A groove is provided in the ceramic adapter plate; the size of the groove is suitable for the MEMS inertial chip; the bottom pad of the ceramic adapter plate is connected to the top pad of the ceramic adapter plate through a half hole; The MEMS inertial chip is arranged in the groove and bonded to the ceramic adapter plate through insulating gold wires; The ceramic adapter plate is welded on the assembly surface of the PCBA; The Teflon cover plate and the PCBA form a cavity, and the ceramic adapter plate and the MEMS inertial chip are placed in the cavity.

2. The surface mount IMU according to claim 1, characterized in that It also includes copper pillars; The copper column is arranged below the groove, passes through the ceramic adapter plate and is connected to the MEMS inertial chip; the copper column is grounded.

3. The surface mount IMU according to claim 1, characterized in that The MEMS inertial chip is bonded in the groove by epoxy adhesive.

4. The surface mount IMU according to claim 1, characterized in that The ceramic adapter plate is made of alumina ceramic; the alumina ceramic and the MEMS inertial chip have a thermal expansion coefficient within the same preset range.

5. The surface mount IMU according to claim 1, wherein: The preset size of the insulating gold wire is 10 μm to 50 μm; the outer surface of the insulating gold wire is protected by high-temperature silicone rubber.

6. The surface mount IMU of claim 1, wherein: The ceramic adapter plate bonded with the MEMS inertial chip is welded to the assembly surface of the PCBA by using lead-free solder paste with a preset melting point.

7. The surface mount IMU according to any one of claims 1 to 6, characterized in that: Also included is a chip cover plate; The chip cover plate is arranged inside the cavity and above the ceramic adapter plate, and is used to seal the MEMS inertial chip in the groove of the ceramic adapter plate.

8. A method for preparing a surface mounted IMU, characterized in that: include: A groove is provided in the ceramic adapter plate; the size of the groove is suitable for the MEMS inertial chip; the bottom pad of the ceramic adapter plate is connected to the top pad of the ceramic adapter plate through a half hole; The MEMS inertial chip is arranged in the groove and bonded to the ceramic adapter plate through insulating gold wires; Welding the ceramic adapter plate to the assembly surface of the PCBA; The Teflon cover plate and the PCBA are assembled together to form a cavity, and the ceramic adapter plate and the MEMS inertial chip are sealed in the cavity.

9. The method for preparing a surface mounted IMU as claimed in claim 8, characterized in that: The method of bonding the ceramic adapter plate with the insulating gold wire comprises: Determining the maximum continuous current that the insulating gold wire is subjected to when the MEMS inertial chip is bonded to the ceramic adapter plate; Based on the maximum continuous current, determining an initial size range of the insulating gold wire; Based on the initial size range of the insulating gold wire, determining the maximum allowable current and the fusing current of the insulating gold wire of each size within the initial size range; Based on the maximum allowable current and the fusing current of the insulating gold wires of various sizes, as well as the cost and the ultimate stress, the insulating gold wires are simulated to determine the preset size of the insulating gold wires; The MEMS inertial chip is bonded to the ceramic adapter plate by using an insulating gold wire having the preset size.

10. The method for preparing a surface mounted IMU according to claim 9, wherein: Also includes: After the ceramic adapter board is welded to the assembly surface of the PCBA, zero bias calibration and cross-coupling calibration are performed in the full temperature range, and the calibration parameters are burned into the MCU.

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