A patch type inertial measurement unit (IMU) module and a preparation method thereof

Abstract

This invention relates to the field of inertial measurement unit (IMU) technology and discloses a surface-mount IMU module and its fabrication method. The module includes a substrate with at least one IMU chip and a control chip mounted on it. The bottom of the substrate has external pads for surface mounting. After packaging and before mounting to an external motherboard, the IMU module has its inertial parameters calibrated and stored in the internal storage unit of the control chip. The substrate is a ceramic substrate with a sealing dam around its perimeter. A top cover is fixedly connected to the top of the sealing dam, forming an airtight or near-airtight packaging structure. This compact surface-mount IMU module and its fabrication method offer advantages such as avoiding the effects of welding stress, stable performance, low cost, small size, and ease of automated production. It solves the problems of poor performance stability, high cost, high production complexity, and large size of existing IMU modules.

Description

Technical Field

[0001] This invention relates to the field of inertial unit technology, specifically to a compact patch IMU module and its fabrication method. Background Technology

[0002] An inertial measurement unit (IMU) is a device that measures an object's three-axis attitude angles (or angular rates) and acceleration. Currently, most IMU modules on the market are encapsulated in a separate metal casing, containing the IMU chip, PCB board, and related circuitry. This metal-encased module is electrically connected to the main control board and transmits signals via connectors and wiring harnesses.

[0003] This traditional structure has the following significant drawbacks:

[0004] 1. Poor performance stability: IMU modules require high-precision calibration before leaving the factory (such as zero bias, scaling factor, installation error, etc.). However, during the subsequent soldering or assembly of the entire metal package module onto the user's motherboard, mechanical stress (such as welding thermal stress, structural locking stress) and assembly errors can cause slight deformation or positional changes in the micromechanical structure inside the IMU chip, rendering the factory calibration parameters invalid and ultimately resulting in a significant decrease in product performance.

[0005] 2. High cost: It requires an independent metal structure shell, internal support PCB, connectors and wiring harnesses, resulting in high material costs.

[0006] 3. High production complexity: The assembly process is cumbersome. It requires the internal packaging of the IMU module to be completed first, and then secondary assembly with the motherboard through wire harnesses and connectors. This increases the production process and difficulty, which is not conducive to automated production and also reduces the reliability of the product.

[0007] 4. Large size: The metal casing, connectors and other components make it difficult to reduce the overall size of the module, which cannot meet the growing demand for compactness and thinness in modern electronic devices.

[0008] Therefore, there is an urgent need in this field for a new IMU module structure that can solve the above problems. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a compact patch IMU module and its fabrication method, which has advantages such as avoiding the influence of welding stress, stable performance, low cost, small size and easy automated production. It solves the problems of poor performance stability, high cost, high production complexity and large size of existing IMU modules.

[0010] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A surface-mount inertial measurement unit (IMU) module includes a substrate, on which at least one IMU chip and a control chip are disposed. The bottom of the substrate is provided with external pads for surface mounting. After the IMU module is packaged and before being mounted to an external motherboard, the inertial parameters have been calibrated and the calibration parameters are stored in the internal storage unit of the control chip. The substrate is a ceramic substrate with a sealing dam around its perimeter. A top cover is fixedly connected to the top of the sealing dam to form an airtight or near-airtight packaging structure. The IMU chip includes a first IMU chip and a second IMU chip, which are arranged on the substrate at a 90° angle, and the control chip is located between the two.

[0011] The beneficial effects of this invention are:

[0012] 1) This surface-mount IMU module and its manufacturing method, by completing the inertial parameter calibration after packaging and before mounting to the external motherboard, and storing the calibration parameters in the internal storage unit of the control chip, fundamentally avoids the problem of "deformation of the micromechanical structure of the IMU chip and failure of calibration parameters due to welding thermal stress, structural locking stress and assembly errors during the mounting process after the traditional module is calibrated at the factory, ensuring that the accuracy of inertial measurement data (attitude angle, angular rate, acceleration) is not affected by the mounting process, significantly improving the performance stability of the module, and solving the core pain point of poor performance stability of IMU modules in the prior art.

[0013] 2) This surface-mount IMU module manufacturing method uses a ceramic substrate to replace the traditional module's "internal support PCB + independent metal shell", and forms an airtight or near-airtight packaging structure with the sealed dam and top cover, eliminating redundant components such as connectors and wire harnesses required by traditional modules. On the one hand, it reduces the types of materials and procurement costs, solving the problem of high cost of traditional modules; on the other hand, it removes the volume redundancy caused by the metal shell and connectors, making the overall module structure more compact, meeting the needs of modern electronic devices for compactness and thinness, and solving the problem of the large size of traditional modules.

[0014] 3) The angled arrangement of the dual IMU chips can cover a more comprehensive range of inertial measurement dimensions, reduce the blind spots of single-chip measurement (such as the problem that some attitude angles cannot be accurately acquired), and improve the integrity and accuracy of inertial data acquisition. Compared with traditional single-chip modules or unreasonable multi-chip modules, this design can further optimize measurement performance and help solve the problem of "poor performance stability" of traditional modules.

[0015] 4) By setting the 90° angle between the two IMU chips as the orthogonal dimension of inertial measurement (such as the X-axis and Y-axis), optimal coverage is provided, which can minimize the impact of non-orthogonal errors on the measurement results, directly improve data accuracy, and enhance performance stability. Furthermore, by setting the control chip to be centrally located, the signal transmission path between the two IMU chips can be shortened, reducing signal delay and interference, ensuring data processing efficiency, while making the internal layout of the module more compact, avoiding structural redundancy, further reducing the size, and solving the problems of poor performance stability and large size of traditional modules.

[0016] Based on the above technical solution, the present invention can be further improved as follows.

[0017] Furthermore, a crystal oscillator is provided on the top of the substrate, and the IMU chip and the control chip are electrically connected to the internal pads on the substrate by wire bonding. The internal pads are electrically connected to the external pads at the bottom through conductive paths within the substrate.

[0018] The beneficial effects of adopting the above-mentioned further solutions are that the crystal oscillator can provide a stable clock signal for the IMU chip and the control chip, ensuring the synchronization of their data acquisition and processing, avoiding measurement errors caused by clock deviation, and further enhancing performance stability; and the design of wire bonding + internal conductive path of the substrate replaces the wire harness and connector of the traditional module, which not only simplifies the electrical connection structure and reduces the risk of contact failure, but also eliminates the connector assembly process, reduces production complexity, and avoids the extra space occupied by the wire harness, further reducing the module size, and solving the problems of high production complexity, large size and poor performance stability of traditional modules.

[0019] Furthermore, the substrate is an alumina ceramic substrate or an aluminum nitride ceramic substrate, and its surface roughness Ra is less than 0.2 μm.

[0020] The beneficial effects of adopting the above-mentioned further solutions are that the ceramic substrate has excellent thermal conductivity and thermal stability, which can quickly conduct the heat generated by the IMU chip during operation, reduce the impact of temperature fluctuations on the chip's micromechanical structure, avoid measurement errors caused by temperature changes, and improve performance stability. In addition, the high strength of the ceramic substrate eliminates the need for additional support structures, further simplifying module design and reducing volume, thus solving the problems of poor performance stability and large size of traditional modules.

[0021] Furthermore, the external pad is an electroplated pad, with its surface plated with one or more combinations of tin, gold, or silver.

[0022] The beneficial effects of adopting the above-mentioned further solution are that the electroplated pads are compatible with surface mount technology, replacing the connectors of traditional modules, eliminating the need for subsequent wire harness assembly processes, simplifying the production process, reducing production complexity, facilitating automated mass production, and solving the problem of high production complexity of traditional modules; at the same time, the electroplated pads are directly integrated into the bottom of the substrate without additional protruding structures, further reducing the module thickness and solving the problem of the large size of traditional modules.

[0023] Furthermore, the sealing dam is a glass sintered layer or a metal ring, and the top cover is fixedly connected to the sealing dam by one or more of the following methods: laser welding, resistance welding, eutectic bonding, and glass sealing.

[0024] The beneficial effects of adopting the above-mentioned further solutions are that the connection between the glass sintering layer or the metal ring and the top cover can form a reliable airtight or near-airtight package, effectively isolating external humidity, dust, corrosive gases and other interference, protecting the internal IMU chip and control chip from the influence of harsh environments, avoiding the chip performance degradation problem caused by insufficient sealing performance of traditional metal shells, and improving performance stability and service life; moreover, this packaging structure does not require the complex processing technology of traditional metal shells (such as shell cutting and drilling), reducing material and processing costs, while making the overall structure lighter and thinner.

[0025] The present invention also provides a method for fabricating a compact patch IMU module, comprising the following steps:

[0026] S1: Provides a ceramic substrate on which internal pads, external pads, conductive paths, and metal interconnect layers are fabricated;

[0027] S2: The IMU chip, control chip and crystal oscillator are mounted on the substrate and fixed with adhesive.

[0028] S3: Heat-cur the adhesive;

[0029] S4: Electrically connect the IMU chip, control chip, and crystal oscillator to the internal pads via wire bonding;

[0030] S5: Form a sealed dam around the substrate and install the top cover to complete the encapsulation;

[0031] S6: Perform temperature cycling treatment on the packaged IMU module to release internal stress;

[0032] S7: Before mounting the module onto the external motherboard, perform multi-temperature point calibration on the module and write the calibration parameters into the internal storage unit of the control chip.

[0033] The beneficial effects of adopting the above-mentioned further solutions are that the surface-mount IMU module manufacturing method provided by the present invention integrates the cumbersome process of "internal packaging + secondary assembly (wire harness / connector connection)" of traditional modules into a single production link through a continuous process of "substrate fabrication → chip mounting and curing → wire bonding → packaging → stress release → multi-temperature point calibration". This eliminates the need for subsequent secondary assembly with the motherboard, greatly simplifies the production process, reduces production complexity, and improves the adaptability to automated production, thus solving the problem of high production complexity of traditional modules. At the same time, the process does not involve the assembly steps of components such as metal shells and connectors required by traditional modules, further reducing production time and material costs, thereby solving the problem of high cost of traditional modules.

[0034] Furthermore, the temperature cycling range in step S6 is -40℃ to +125℃, and the number of cycles is 3 to 10.

[0035] The beneficial effects of adopting the above-mentioned further solution are that the temperature range can simulate the extreme high and low temperature environment in actual use of the module. Through 3 to 10 cycles, the thermal and mechanical stress generated during the packaging process (such as adhesive curing and top cover welding) can be fully released, avoiding long-term stress residue that could cause deformation of the micromechanical structure of the IMU chip, thereby preventing calibration parameter deviation and solving the problem of poor performance stability caused by stress residue in traditional modules. At the same time, releasing stress in advance can improve the reliability of the module in extreme temperature environments and extend its service life.

[0036] Furthermore, the multi-temperature point calibration in step S7 includes:

[0037] The IMU module is placed in a temperature-controlled environment with multiple temperature points set at intervals of 5℃ to 20℃. Each temperature point is kept at a temperature of 5 to 15 minutes. Inertial data is collected and zero bias, scaling factor, and non-orthogonal error are calculated to generate calibration parameters.

[0038] The beneficial effect of adopting the above-mentioned further solution is that by collecting inertial data at multiple temperature points and calculating core error parameters, the generated calibration parameters can cover the entire operating temperature range of the module and can compensate for measurement errors at different temperatures in real time. Compared with the traditional module's single calibration at room temperature, this method completely solves the problem of calibration parameter failure and performance degradation caused by temperature changes, ensuring that the module maintains stable accuracy under complex working conditions such as high and low temperatures, and significantly improving performance stability. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of the present invention;

[0040] Figure 2 This is a schematic diagram of the bottom pads of the module of the present invention;

[0041] Figure 3This is an assembly diagram of the module and motherboard of the present invention;

[0042] Figure 4 This is a front sectional view of the present invention;

[0043] Figure 5 This is a top view of the module structure of the present invention.

[0044] In the figure: 10, substrate; 20, sealing dam; 30, top cover; 40, first IMU chip; 50, second IMU chip; 60, control chip; 70, crystal oscillator; 80, internal pad; 90, lead wire; 100, external pad; 110, metal interconnect layer. Detailed Implementation

[0045] 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 some embodiments of the present invention, and not all embodiments. 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.

[0046] Example 1, by Figure 1-4This invention discloses a surface-mount inertial measurement unit (IMU) module and its fabrication method. The module includes a substrate 10, which is an alumina ceramic substrate or an aluminum nitride ceramic substrate with a surface roughness Ra of less than 0.2 μm. At least one IMU chip and a control chip 60 are mounted on the substrate 10. The control chip 60 is a microcontroller (MCU), a field-programmable gate array (FPGA), or a system-on-a-chip (SoC). The IMU chip includes a first IMU chip 40 and a second IMU chip 50, arranged at an angle of 60° to 120° on the substrate 10 to achieve optimized coverage for multi-axis inertial measurement. External pads 100 for surface mounting are provided at the bottom of the substrate 10. The external pads 100 are distributed in a rectangular or L-shaped array at the bottom of the substrate 10, adapting to standard surface mount technology (SMT). The external pads 100 are electroplated pads, with their surfaces plated with one or more combinations of tin, gold, or silver to adapt to reflow soldering processes. A crystal oscillator 70 is also provided on the top of the substrate 10. The IMU chip and the control chip 60 are electrically connected to the internal pads 80 on the substrate 10 by wire bonding 90. The internal pads 80 are electrically connected to the external pads 100 at the bottom through conductive paths within the substrate. In the fabrication process of the IMU module, step S1 is first performed: providing a ceramic substrate and fabricating internal pads 80, external pads 100, conductive paths, and a metal interconnect layer 110 on its surface; and step S2: mounting the IMU chip, the control chip 60, and the crystal oscillator 70 on the substrate and fixing them with adhesive; after the chips and the crystal oscillator 70 are bonded, step S3 is performed: the adhesive is heat-cured; the heat-curing temperature in step S3 is 150℃~200℃, and the time is 1~3 hours. After the adhesive is cured, step S4 is performed: the IMU chip, the control chip 60, and the crystal oscillator 70 are electrically connected to the internal pads 80 by wire bonding.

[0047] The substrate 10 is a ceramic substrate with a sealing dam 20 around its perimeter. A top cover 30 is fixedly connected to the top of the sealing dam 20, forming an airtight or near-airtight packaging structure. The sealing dam 20 is a glass sintered layer or a metal ring. The top cover 30 is fixedly connected to the sealing dam 20 by one or more combinations of laser welding, resistance welding, eutectic bonding, and glass sealing. After connecting the chip, crystal oscillator 70, and internal pads 80, step S5 is performed: the sealing dam 20 is formed around the substrate 10, and the top cover 30 is installed to complete the packaging.

[0048] After the IMU module is packaged, step S6 is performed: the packaged IMU module undergoes temperature cycling to release internal stress; the temperature cycling range in step S6 is -40℃ to +125℃, and the number of cycles is 3 to 10. After the internal stress of the IMU module is released, step S7 is performed: before mounting the module to the external motherboard, the module is calibrated at multiple temperature points, and the calibration parameters are written into the internal storage unit of the control chip 60. The multi-temperature point calibration in step S7 includes:

[0049] The IMU module is placed in a temperature-controlled environment with multiple temperature points set at intervals of 5℃ to 20℃. Each temperature point is kept at a temperature of 5 to 15 minutes. Inertial data is collected and zero bias, scaling factor, and non-orthogonal error are calculated to generate calibration parameters.

[0050] After the IMU module is packaged and before it is mounted onto the external motherboard, the inertial parameters have been calibrated and the calibration parameters are stored in the internal storage unit of the control chip.

[0051] Example 2: Based on Example 1, after the IMU module has been calibrated, step S8 is performed: the IMU module is placed on a vibration-isolated stationary platform for full performance testing; test records can be automatically generated by the performance test data software; the vibration-isolated stationary platform test environment can eliminate external vibration interference, ensure the accuracy of performance data, and provide a reliable basis for subsequent sorting.

[0052] After the IMU module passes the performance test, step S9 is implemented: EOL (End of Line) offline test is carried out; passing the EOL offline test can screen out unqualified products before the module leaves the factory, ensuring that all qualified modules meet the performance indicators, controlling product consistency from the source, and solving the problem of unstable performance of traditional modules after leaving the factory. After the IMU module passes the performance test, the final step S10 is implemented: sorting according to the test results and weaving qualified modules into tape packaging.

[0053] Example 3, see Figure 5 Based on Embodiment 1, the first IMU chip 40 and the second IMU chip 50 are arranged at a 90° angle, with the control chip 60 located between them. By setting the 90° angle between the two IMU chips, optimal coverage is provided for the orthogonal dimensions of inertial measurement, such as the X and Y axes. This minimizes the impact of non-orthogonal errors on the measurement results, directly improving data accuracy and enhancing performance stability. Furthermore, by centrally arranging the control chip, the signal transmission path between the two IMU chips is shortened, reducing signal delay and interference, ensuring data processing efficiency, and making the internal layout of the module more compact, avoiding structural redundancy, further reducing the size, and solving the problems of poor performance stability and large size of traditional modules.

[0054] The heating and curing process in step S3 is carried out at a temperature of 180°C for 2 hours. The combination of high temperature of 180°C and two hours ensures that the adhesive is fully cured and forms a stable bonding structure, which avoids chip detachment during subsequent module assembly such as gold wire bonding, top cover welding or use, and improves the mechanical stability of the module.

[0055] In step S5, when installing the top cover 30, a sealing dam 20 is first formed around the perimeter using the DPC process. Then, the top cover 30 is placed inside the sealing dam 20, so that the four edges of the top cover 30 are in the middle of the sealing dam 20. Then, the edges of the top cover 30 are fixed to the sealing dam 20 to complete the encapsulation.

[0056] The temperature cycling range in step S6 is -40℃ to +105℃, and the number of cycles is 6. The wide temperature range of -40℃ to +105℃ covers most application scenarios, and the 6 cycles can fully release the internal stress generated in the module during the gold wire bonding and top cover welding process, such as the stress caused by the difference in thermal expansion coefficients between the substrate and the chip. This avoids chip displacement or gold wire breakage caused by stress release during subsequent use, fundamentally solving the problem of "stress-induced calibration failure" in traditional modules. At the same time, the wide temperature cycling can expose potential defects such as poor soldering and weak adhesion in advance, improving the reliability of the module at the factory.

[0057] Step S7, multi-temperature point calibration, involves placing the IMU module in a temperature-controlled environment, setting multiple temperature points at 10°C intervals, holding each temperature point for 10 minutes, collecting data for 5 minutes, collecting inertial data, and calculating zero bias, scaling factor, and non-orthogonal error to generate calibration parameters. By performing this process of 10°C intervals, holding for 10 minutes, and then collecting data for 5 minutes, the module can achieve sufficient thermal equilibrium at each temperature point, resulting in more accurate calibration parameters such as zero bias and scaling factor, ensuring calibration precision, and solving the problem of poor temperature adaptability in traditional modules.

[0058] In summary, this compact surface-mount IMU module and its fabrication method significantly simplify the structure by eliminating the traditional metal casing, internal PCB, connectors, and wiring harnesses, resulting in a substantial reduction in material and assembly costs. Furthermore, the module can be directly used as a standard SMT component, allowing for one-time assembly with the motherboard using a fully automated placement machine. This not only greatly reduces production difficulty and time but also avoids potential failure points such as poor contact caused by connectors and wiring harnesses, improving product consistency and reliability. Moreover, the surface-mount packaging significantly reduces size and weight compared to traditional metal-packaged IMUs, making it highly suitable for space-constrained applications such as embody intelligence. This achieves the goals of avoiding the effects of welding stress, stable performance, low cost, small size, and ease of automated production, solving the problems of poor performance stability, high cost, high production complexity, and large size of existing IMU modules.

[0059] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A surface-mount inertial measurement unit (IMU) module, comprising a substrate (10), wherein at least one IMU chip and a control chip (60) are disposed on the substrate (10), and the bottom of the substrate (10) is provided with external pads (100) for surface mounting, characterized in that... The inertial parameters of the IMU module have been calibrated after packaging and before being mounted on the external motherboard, and the calibration parameters are stored in the internal storage unit of the control chip. The substrate (10) is a ceramic substrate with a sealing dam (20) around it. The top of the sealing dam (20) is fixedly connected to a top cover (30) to form an airtight or near-airtight packaging structure. The IMU chip includes a first IMU chip (40) and a second IMU chip (50). The first IMU chip (40) and the second IMU chip (50) are arranged at a 90° angle on the substrate (10), and the control chip (60) is located between the two.

2. The surface-mount IMU module according to claim 1, characterized in that: The substrate (10) is also provided with a crystal oscillator (70) on the top. The IMU chip and the control chip (60) are electrically connected to the internal pad (80) on the substrate (10) by means of lead wire (90) bonding. The internal pad (80) is electrically connected to the external pad (100) at the bottom through the conductive path in the substrate.

3. The surface-mount IMU module according to claim 2, characterized in that: The substrate (10) is an alumina ceramic substrate or an aluminum nitride ceramic substrate, and its surface roughness Ra is less than 0.2 μm.

4. The surface-mount IMU module according to claim 3, characterized in that: The external pad (100) is an electroplated pad, with its surface plated with one or more combinations of tin, gold, or silver.

5. The surface-mount IMU module according to claim 4, characterized in that: The sealing dam (20) is a glass slurry sintered layer or a metal ring, and the top cover (30) is fixedly connected to the sealing dam (20) by one or more of the following methods: laser welding, resistance welding, eutectic bonding, and glass sealing.

6. A method for manufacturing a patch-type IMU module as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Provide a ceramic substrate on which internal pads (80), external pads (100), conductive paths and metal interconnect layers (110) are formed. S2: Mount the IMU chip, control chip (60) and crystal oscillator (70) on the substrate and fix them with adhesive; S3: Heat-cur the adhesive; S4: The IMU chip, control chip (60) and crystal oscillator (70) are electrically connected to the internal pads (80) by wire bonding; S5: A sealing dam (20) is formed around the substrate (10), and the top cover (30) is installed to complete the encapsulation; S6: Perform temperature cycling treatment on the packaged IMU module; S7: Before mounting the module onto the external motherboard, perform multi-temperature point calibration on the module and write the calibration parameters into the internal storage unit of the control chip (60).

7. The preparation method according to claim 6, characterized in that: The temperature cycling range in step S6 is -40℃ to +125℃, and the number of cycles is 3 to 10.

8. The preparation method according to claim 6, characterized in that: The multi-temperature point calibration in step S7 includes: The IMU module is placed in a temperature-controlled environment with multiple temperature points set at intervals of 5℃ to 20℃. Each temperature point is kept at a temperature for 5 to 15 minutes. Inertial data is collected and zero bias, scaling factor, and non-orthogonal error are calculated to generate calibration parameters.

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