Anti-electromagnetic interference filter for motor control and manufacturing method thereof

Abstract

The invention discloses an anti-electromagnetic interference filter for motor control and a manufacturing method thereof, and belongs to the technical field of anti-electromagnetic interference filters for motor control, the specific structure comprises a metal shell, a circuit board and a metal cover plate, the metal shell is provided with a containing cavity, the circuit board is installed in the containing cavity, and five guide pins are arranged at the bottom of the circuit board; wherein the four guide pins extend out of the bottom of the metal shell and are isolated from the bottom of the metal shell by adopting glass insulators, the four guide pins are respectively an input positive end, an input negative end, an output positive end and an output negative end, and the fifth guide pin is a grounding end and is fixedly connected to the bottom of the metal shell; the containing cavity is filled with pouring sealant after the circuit board is installed, and the bottom of the metal shell is connected to a grounding bonding pad on the circuit board. According to the filter, a multi-stage LC filter circuit is formed in a small enough space, high suppression capability is provided, and meanwhile, the filter is manufactured by metal packaging and can resist interference.

Description

Technical Field

[0001] The invention relates to a filter for motor control and anti-electromagnetic interference and a manufacturing method thereof, belonging to the technical field of filters. Background Art

[0002] When a brushless motor starts working, the voltage will overshoot at the moment of power-on, and the magnetic field will change instantly, generating very strong current and electromagnetic field, which can easily cause sparks; in addition, due to the insufficient precision between the rotor and stator of the brushless motor, during operation, due to the effect of rotational inertia and repeated switching of the magnetic field, weak contact or friction is often generated, which can also generate sparks; these sparks will be transmitted to the motor control system along the brushless motor power circuit when the motor rotates at high speed, and will be coupled with the interference caused by the conduction switching of the MOS tubes and diodes in the motor control system, and will be transmitted through the power interface of the motor control system, thereby interfering with the normal operation of other equipment.

[0003] Considering the operating characteristics of brushless motors and the conduction path of interference, it is necessary to install a filter with high suppression capability in front of the power interface of the motor control system to suppress the electromagnetic interference of the brushless motor's rotation speed of up to 20kHz-75kHz and its frequency multiplication. This ensures that it does not affect the normal operation of other equipment and completely solves the problem in the conduction path by using the filter.

[0004] Typically, the space in motor control system modules is limited, and the space for installing filters is very limited. Only filters with a size of 51mmx31mm or smaller can be installed. However, smaller filters often need to consider space utilization and circuit layout, and the suppression capabilities they can provide are poor. A single filter cannot solve the problem, and usually two or even three filters of similar size need to be connected in series, which far exceeds the space required by the motor control system and is therefore impossible to implement. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a filter for motor control to resist electromagnetic interference and a manufacturing method thereof, which provides high suppression capability. At the same time, the filter is made of metal packaging and can also resist interference itself.

[0006] The technical solution adopted by the present invention is: a filter for motor control anti-electromagnetic interference, including a metal shell, a circuit board and a metal cover plate, the metal shell is provided with a accommodating cavity with an upper end opening, the circuit board is installed in the accommodating cavity, the circuit board is installed on the circuit board, and five guide pins are provided at the bottom of the circuit board, among which four guide pins extend out of the bottom of the metal shell and are isolated from the bottom of the metal shell by glass insulators, the four guide pins are respectively the input positive terminal, the input negative terminal, the output positive terminal and the output negative terminal, the fifth guide pin is the grounding terminal, which is fixedly connected to the bottom of the metal shell, the metal cover plate covers the opening of the metal shell, and the accommodating cavity is filled with potting glue after the circuit board is installed, and the bottom of the metal shell is connected to the grounding pad on the circuit board through the internal grounding guide pin.

[0007] Furthermore, a groove is provided at the bottom of the above-mentioned accommodating cavity, four guide pin fixing seats are provided at the four corners of the groove, a resin plate is provided at the bottom of the groove, a circuit board support step is provided around the bottom of the accommodating cavity, the circuit board support step is higher than the guide pin fixing seat, the bottom surface of the circuit board contacts the circuit board support step, and the four guide pins are located on the guide pin fixing seat.

[0008] Furthermore, both ends of the metal shell bottom plate extend outward to form an extension portion, a mounting hole is provided in the middle of the extension portion, and an inwardly convex arc structure is provided on the side wall of the metal shell opposite to the mounting hole, and the arc structure is coaxial with the mounting hole.

[0009] Furthermore, a sunken step is provided on the top of the metal shell, the metal cover is embedded in the step for sealing and the top surface is kept flush with the top surface of the metal shell, a boss is provided at the bottom of the metal cover, the boss is embedded in the side wall of the metal shell, and an insulating film layer is provided at the bottom of the boss.

[0010] Furthermore, the top surface and surrounding side surfaces of the metal cover plate are subjected to copper-nickel plating surface treatment.

[0011] Furthermore, the circuit structure of the above filter includes a differential mode inductor L1, a differential mode inductor L2, a common mode inductor L3 and a common mode inductor L4, wherein the input ends of the differential mode inductor L1 and the differential mode inductor L2 are respectively connected to the input positive terminal P and the input negative terminal N, the other end of the differential mode inductor L1 is connected to the input end of the common mode inductor L3 and one end of the capacitor C1, the other end of the differential mode inductor L2 is respectively connected to the other input end of the common mode inductor L3 and the other end of the capacitor C1, and the output end of the common mode inductor L3 is connected to the capacitor C2. , capacitor C3, one end of capacitor C5 and one end of the input of the common-mode inductor L4, the other end of the output of the common-mode inductor L3 is connected to the other end of capacitor C2, the other end of capacitor C3, one end of capacitor C6 and the other end of the input of the common-mode inductor L4, the other end of capacitor C5 and the other end of capacitor C6 are connected to the ground terminal, one end of the output of the common-mode inductor L4 is connected to one end of capacitor C4 and the positive output terminal P', and the other end of the output of the common-mode inductor L4 is connected to the other end of capacitor C4 and the positive output terminal N'.

[0012] Furthermore, the common-mode inductor L3 and the common-mode inductor L4 are symmetrically arranged on the input side and the output side of the circuit board.

[0013] A method for manufacturing a filter for motor control against electromagnetic interference, the method comprising the following steps: 1) The metal shell and metal cover are made of 4J29 alloy material and processed into cavity-shaped structural parts and plate-shaped structural parts respectively. Then the metal shell and glass are co-fired at a high temperature of 1400℃ to obtain a sealed and fixed connection between the glass insulator and the metal shell, thus achieving a sealed connection between the metal shell and the glass insulator; 2) The metal shell is first sandblasted on the bottom, then pre-treated with degreasing and rust removal. The surface of the metal shell is cleaned and electroplated with 2μm thick copper on the inner and outer surfaces, followed by 10-15μm thick nickel. The double layer of metal improves the conductivity, oxidation resistance and adhesion of the metal shell. 3) The bottom surface of the metal cover is first sprayed with fine sand, and then pre-treated with degreasing and rust removal. The surface of the metal cover is cleaned and electroplated with 2μm thick copper on the inner and outer surfaces, followed by 10-15μm thick nickel. Finally, the convex surface of the metal cover is polished to remove the plating layer, and then anodized to form an insulating film layer on the convex surface with a thickness of 0.3-0.8μm. 4) Select 1210 size ceramic capacitors C1-C6, where C1-C4 are used as Cx capacitors and C5-C6 are used as Cy capacitors. 5) Use alcohol to clean the steel mesh and carrier. Make sure the steel mesh and carrier are clean before use, and the window holes are free of impurities; 6) Use Sn-5Sb solder paste for soldering between the PAD (solder pad) of the circuit board and the capacitor. Before use, take the solder paste out of the freezer and place it at room temperature for 30 minutes to 60 minutes to thaw. Then use a stirring rod to stir the solder paste repeatedly in a clockwise and counterclockwise rotation for 30 seconds to 60 seconds until the solder paste is in a wire-drawn state; 7) Fix the PCB on the carrier and adjust the PCB PAD to be consistent with the stencil opening. Close the stencil to ensure that the stencil and the PCB on the carrier are flat. 8) Pour a set amount of solder paste onto the steel mesh surface and use a scraper to evenly scrape the solder paste into the window holes so that the solder paste covers the C1-C6 pads of the circuit board; 9) Use a 12-zone reflow oven to solder the circuit board and capacitors C1-C6; 10) After the capacitors C1-C6 are reflowed and cooled naturally, the common-mode inductors L3-L4 and differential-mode inductors L1-L2 are soldered with a soldering iron. 11) To achieve a greater suppression effect at 20kHz~75kHz, the inductance of the common-mode inductor should be no less than 10mH, and the inductance of the differential-mode inductor should be no less than 100uH. Common-mode inductors are made of 1K107F nanocrystalline amorphous tape with a magnetic permeability greater than 80,000. Differential-mode inductors are made of microcrystalline iron-based amorphous tape with a magnetic permeability not exceeding 1200. To reduce the height of the product, high-temperature enameled round copper wire is used to pass through the common-mode inductor or differential-mode inductor magnetic ring to form a coil. The free end of the high-temperature enameled round copper wire after de-enamelling is used as the lead-out terminal of the common-mode inductor or differential-mode inductor. The lead-out terminal of the common-mode inductor or differential-mode inductor is soldered to the through-hole of the circuit board using Sn-5Sb tin wire, and the excess tail wire is cut off. The soldering temperature setting condition of the soldering iron is 400℃±30℃. 12) After soldering in steps 10) and 11), clean the circuit board using JD-086 board cleaning water. Soak the circuit board in the water for 5-10 minutes. Then, use a dense, soft, fine-bristled toothbrush to scrub the solder joints, circuit board, and components on the circuit board back and forth, repeating the scrubbing cycle at least 10 times. After the first cleaning, replace the board with clean cleaning water and soak and clean again. 13) After the cleaned circuit board is dried naturally, continue to solder the lead terminals and ground terminals on the circuit board. The lead terminals include the positive input terminal, negative input terminal, positive output terminal and negative output terminal. 14) Place the resin board into the groove in the accommodating cavity of the metal shell, then align the lead-out holes of the circuit board with the lead-out ends of the inner cavity of the metal shell, pass the lead-out ends through the through holes, and install the circuit board; 15) First, adjust the temperature of the heating plate (the purpose of heating the heating plate is to preheat, reduce the temperature difference between the welding lead and the ground end, and improve the welding quality) to 100℃. After waiting for the heating plate temperature to reach the required level, place the metal housing with the installed circuit board and the fixed carrier (the fixed carrier is a fixed tool for the metal housing to be welded to prevent the housing from being loose during welding and preventing the metal housing from moving during welding, which is not conducive to welding) on the heating plate. After heating for 1-2 minutes, use a soldering iron and Sn-5Sb tin wire to solder the lead-out holes of the circuit board, ensuring that the input, output and ground terminals are well soldered. The soldering temperature of the soldering iron is set to 400℃±30℃; 16) Soak the soldered product from step 15 in the cleaning water for 5 minutes. After leaving it at room temperature for 30 minutes, bake it in a drying oven to ensure it is dry. The baking temperature and time should be set at 130°C ± 10°C and 60 minutes ± 5 minutes. 17) Use two-component silicone sealant to pot the metal housing cavity. The potting height is controlled to just cover the highest common-mode inductor L3-L4 and differential-mode inductor L1-L2 surface; 18) Cover the metal cover plate and use laser sealing process to remelt the gap between the metal cover plate and the metal shell to form a sealing pattern; 19) Finally, the product logo is etched on the middle of the metal cover by laser marking process. The logo may include but is not limited to model, name, manufacturer, terminal symbol, batch number, etc.

[0014] 20) By testing the insertion loss of the filter, the maximum suppression capability of the differential mode insertion loss in 10kHz~30MHz can reach 100dB, and the maximum suppression capability of the common mode insertion loss in 10kHz~30MHz can reach 90dB.

[0015] Furthermore, the upper and lower temperature settings for the 12 temperature zones in step 9) above are: 146°C, 155°C, 160°C, 170°C, 185°C, 200°C, 220°C, 240°C, 270°C, 270°C, 240°C, and 200°C. The temperature tolerance for each zone is ±5°C, depending on the number of reflow cycles. The reflow chain speed is 0.70 m / min. Beneficial effects of the present invention: Compared with the prior art, the filter of the present invention realizes the formation of a multi-stage LC filter circuit in a sufficiently small space, providing high suppression capability. At the same time, the filter is made of metal packaging and can also resist interference itself. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the three-dimensional structure of the filter used for motor control to resist electromagnetic interference; Figure 2 This is a schematic diagram of the front view structure of the filter used for motor control to resist electromagnetic interference; Figure 3 yes Figure 2 Schematic diagram of the AA section structure; Figure 4 This is a schematic diagram of the top view of the filter structure used for motor control anti-electromagnetic interference (without the metal cover); Figure 5 yes Figure 4 Schematic diagram of the BB structure; Figure 6 It is a schematic diagram of the three-dimensional structure of the metal shell; Figure 7 This is a schematic diagram of the three-dimensional structure of the metal shell from another perspective; Figure 8 This is a schematic diagram of the filter circuit structure used for motor control to resist electromagnetic interference; Figure 9 It is a schematic diagram of the structure of electrical components; Figure 10 It is a schematic diagram of the existing filter circuit structure; Figure 11 is the common mode insertion loss curve; Figure 12 is the differential mode insertion loss curve; Figure 13 It is the test qualification curve of electromagnetic compatibility of the filter used for motor control anti-electromagnetic interference; Figure 14 It is a test failure curve of the existing filter's electromagnetic compatibility. DETAILED DESCRIPTION

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0018] Example 1: Figure 1-9 As shown, a filter for motor control against electromagnetic interference includes a metal housing 1, a resin board 2, a circuit board 3, and a metal cover 4. The metal housing, the metal cover, the circuit board, the resin board, two common-mode inductors, two differential-mode inductors, and six capacitors C1-C6, of which four are Cx capacitors and two are Cy capacitors. The metal shell 1 is provided with a accommodating cavity 5 with an upper opening, a groove 6 is provided at the bottom of the accommodating cavity 5, four guide pin fixing seats 7 are provided at the four corners of the groove 6, and a 0.1mm resin board 2 is provided at the bottom of the groove 6. The resin board ensures that the electrical conductive solder joints on the circuit board are completely electrically isolated from the bottom groove in the metal shell cavity to prevent short circuit. A circuit board support step 8 is provided around the bottom of the accommodating cavity 5. The circuit board support step 8 is higher than the guide pin fixing seat 7. The bottom surface of the circuit board 3 contacts the circuit board support step 8, and the four guide pins are located on the guide pin fixing seat 7.

[0019] A circuit board 3 is installed in the accommodating cavity 5. The circuit components of the filter are installed on the circuit board 3. The circuit components include capacitors C1-C6, common-mode inductors L3-L4 and differential-mode inductors L1-L2. Five guide pins are set at the bottom of the circuit board, of which four guide pins extend out of the bottom of the metal shell 1 and are isolated from the bottom of the metal shell 1 by a glass insulator 9. The glass insulator realizes electrical isolation. The four guide pins are respectively the input positive terminal 10, the input negative terminal 11, the output positive terminal 12 and the output negative terminal 13. The input positive terminal 10, the input negative terminal 11, the output positive terminal 12 and the output negative terminal 1 3 are respectively connected to the input positive terminal IN+, input negative terminal IN-, output positive terminal OUT+ and output negative terminal OUT- of the circuit board. The fifth guide pin is the ground terminal 14, which is fixedly connected to the bottom of the metal shell 1. The metal cover 4 covers the opening of the metal shell 1. After the circuit board 3 is installed in the accommodating cavity 5, it is filled with potting glue. The main purpose of potting glue is to protect the components, increase the vibration resistance, heat dissipation and moisture resistance of the internal components, and improve product reliability. The bottom of the metal shell 1 is connected to the ground pad (i.e., ground terminal G) on the circuit board through the internal ground guide pin 15.

[0020] In order to facilitate the installation of the metal shell, the two ends of the bottom plate of the metal shell 1 extend outward to form an extension part 16, and a mounting through hole 17 is provided in the middle of the extension part 16. The metal shell is fixed to the circuit board of the device to be installed by screws passing through the mounting through hole 17. In order to make full use of the space, the projection surface of the cavity is an anisotropic structure. The side wall of the metal shell 1 opposite to the mounting through hole 17 is provided with an inwardly convex arc structure 18. The arc structure 18 is coaxial with the mounting through hole 17, and the space at the four corners of the cavity is fully utilized for circuit layout, so as to achieve the purpose of making full use of the space.

[0021] Furthermore, the top of the metal housing 1 is provided with an inwardly sunken step 19, into which the metal cover 4 is embedded and sealed, with its top surface flush with the top surface of the metal housing 1. A boss 20 is provided at the bottom of the metal cover 4, which is embedded within the side wall of the metal housing. An insulating film layer 21 is provided at the bottom of the boss 20. The step structure ensures that the boss structure of the metal cover and the metal housing are aligned horizontally after assembly. The top surface and surrounding side surfaces of the metal cover are copper-nickel plated to ensure that the outer surface of the metal cover is conductive, forming a Faraday cage with the metal housing, thereby ensuring that the filter has good anti-interference capabilities. The boss surface of the metal cover is anodized to form an insulating film to prevent arcing between internal components and the metal housing.

[0022] The metal shell and lead-out terminals are both copper-nickel plated to ensure that the metal shell is conductive and forms a Faraday cage with the metal cover, which can ensure that the filter has good anti-interference ability.

[0023] Furthermore, the top surface and surrounding side surfaces of the metal cover plate are subjected to a copper-nickel plating surface treatment to form a copper-nickel plating layer.

[0024] Existing filter circuit structures, such as Figure 10 As shown, the first-stage circuit is an L-type topology structure, and the second-stage circuit is a π-type topology structure, which cannot pass the electromagnetic compatibility test. This circuit structure is difficult to meet the suppression effect.

[0025] The schematic diagram of the filter circuit structure is as follows Figure 8 As shown and the specific layout is as Figure 9As shown, the specific structure includes differential mode inductor L1, differential mode inductor L2, common mode inductor L3 and common mode inductor L4. The input ends of differential mode inductor L1 and differential mode inductor L2 are connected to the input positive terminal P and the input negative terminal N respectively. The other end of differential mode inductor L1 is connected to the input end of common mode inductor L3 and one end of capacitor C1. The other end of differential mode inductor L2 is connected to the other input end of common mode inductor L3 and the other end of capacitor C1 respectively. The output end of common mode inductor L3 is connected to capacitor C2, capacitor C3, one end of capacitor C5 and the input end of common mode inductor L4. Common mode inductor L3 The other end of the output is connected to the other end of capacitor C2, the other end of capacitor C3, one end of capacitor C6 and the other end of the input of common-mode inductor L4, the other end of capacitor C5 and the other end of capacitor C6 are connected to the ground end, one end of the output of common-mode inductor L4 is connected to one end of capacitor C4 and the positive output terminal P', and the other end of the output of common-mode inductor L4 is connected to the other end of capacitor C4 and the positive output terminal N'; common-mode inductor L3 and common-mode inductor L4 are symmetrically arranged on the input side and output side of the circuit board, and differential-mode inductor L1 and differential-mode inductor L2 are symmetrically arranged on the front and back sides of the circuit board.

[0026] The filter utilizes a three-stage LC circuit design, with the circuit board layout establishing the logical connections between the common-mode inductors (L3, L4), differential-mode inductors (L1, L2), and capacitors (C1, C2, C3, C4, C5, and C6). The series connection of common-mode inductors L3 and L4 with C5 and C6 forms a ground loop, leveraging the high-resistance characteristics of the common-mode inductors and the high-pass characteristics of the capacitors to achieve common-mode suppression. L1 (L2) and C1 form an LC topology, providing primary filtering for differential-mode interference. The leakage inductance of common-mode inductor L3, along with C1 and C2, forms a π-shaped topology, providing secondary filtering for differential-mode interference. The leakage inductance of common-mode inductor L4, along with C3 and C4, forms a π-shaped topology, providing tertiary filtering for differential-mode interference. The entire circuit suppresses both common-mode and differential-mode interference on both the positive and negative lines.

[0027] Embodiment 2: A method for manufacturing a filter for motor control against electromagnetic interference, the method comprising the following steps: 1) The metal shell and metal cover are made of 4J29 alloy material and processed into cavity-shaped structural parts and plate-shaped structural parts respectively. Then the metal shell and glass are co-fired at a high temperature of 1400℃ to obtain a sealed and fixed connection between the glass insulator and the metal shell, thus achieving a sealed connection between the metal shell and the glass insulator; 2) The metal shell is first sandblasted on the bottom, then pre-treated with degreasing and rust removal. The surface of the metal shell is cleaned and electroplated with 2μm thick copper on the inner and outer surfaces, followed by 10-15μm thick nickel. The purpose of the double metal layer is to improve the conductivity, oxidation resistance and adhesion of the metal shell. 3) The bottom surface of the metal cover is first sprayed with fine sand, and then pre-treated with degreasing and rust removal. The surface of the metal cover is cleaned and electroplated with 2μm thick copper on the inner and outer surfaces, followed by 10-15μm thick nickel. Finally, the convex surface of the metal cover is polished to remove the plating layer, and then anodized to form an insulating film layer on the convex surface with a thickness of 0.3-0.8μm. 4) Select 1210 size ceramic capacitors C1-C6, where C1-C4 are used as Cx capacitors and C5-C6 are used as Cy capacitors. 5) Use alcohol to clean the steel mesh and carrier. Make sure the steel mesh and carrier are clean before use, and the window holes are free of impurities; 6) Use Sn-5Sb solder paste for soldering between the PAD (solder pad) of the circuit board and the capacitor. Before use, take the solder paste out of the freezer and place it at room temperature for 30 minutes to 60 minutes to thaw. Then use a stirring rod to stir the solder paste repeatedly in a clockwise and counterclockwise rotation for 30 seconds to 60 seconds until the solder paste is in a wire-drawn state; 7) Fix the PCB on the carrier and adjust the PCB PAD to be consistent with the stencil opening. Close the stencil to ensure that the stencil and the PCB on the carrier are flat. 8) Pour a set amount of solder paste onto the steel mesh surface and use a scraper to evenly scrape the solder paste into the window holes so that the solder paste covers the C1-C6 pads of the circuit board; 9) Use a 12-zone reflow oven to solder the circuit board and capacitors C1-C6; The upper and lower temperature settings for the 12 temperature zones are: 146°C, 155°C, 160°C, 170°C, 185°C, 200°C, 220°C, 240°C, 270°C, 270°C, 240°C, and 200°C. The temperature tolerance for each zone is ±5°C, depending on the number of reflow operations. The reflow chain speed is 0.70m / min. 10) After the capacitors C1-C6 are reflowed and cooled naturally, the common-mode inductors L3-L4 and differential-mode inductors L1-L2 are soldered with a soldering iron. 11) To achieve a greater suppression effect at 20kHz~75kHz, the inductance of the common-mode inductor should be no less than 10mH, and the inductance of the differential-mode inductor should be no less than 100uH. Common-mode inductors are made of 1K107F nanocrystalline amorphous tape with a magnetic permeability greater than 80,000. Differential-mode inductors are made of microcrystalline iron-based amorphous tape with a magnetic permeability not exceeding 1200. To reduce the height of the product, high-temperature enameled round copper wire is used to pass through the common-mode inductor or differential-mode inductor magnetic ring to form a coil. The free end of the high-temperature enameled round copper wire after de-enamelling is used as the lead-out terminal of the common-mode inductor or differential-mode inductor. The lead-out terminal of the common-mode inductor or differential-mode inductor is soldered to the through-hole of the circuit board using Sn-5Sb tin wire, and the excess tail wire is cut off. The soldering temperature setting condition of the soldering iron is 400℃±30℃. 12) After soldering in steps 10) and 11), clean the circuit board using JD-086 board cleaning water. Soak the circuit board in the water for 5-10 minutes. Then, use a dense, soft, fine-bristled toothbrush to scrub the solder joints, circuit board, and components on the circuit board back and forth, repeating the scrubbing cycle at least 10 times. After the first cleaning, replace the board with clean cleaning water and soak and clean again. 13) After the cleaned circuit board is dried naturally, continue to solder the lead terminals and ground terminals on the circuit board. The lead terminals include the positive input terminal, negative input terminal, positive output terminal and negative output terminal. 14) Place the resin board into the groove in the housing cavity of the metal shell, then align the lead-out hole of the circuit board with the lead-out hole in the metal shell cavity, and install the circuit board (step 6 is to solder the pads of the capacitor to the corresponding pad positions on the circuit board, step 11 is to solder the solder points of the common mode inductor and the differential mode inductor, and step 14 is to solder the lead-out terminals in the metal shell cavity ( Figure 6 10, 11, 12, 13) and ground terminal ( Figure 6 15)); 15) First, adjust the temperature of the heating plate (the purpose of heating the heating plate is to preheat, reduce the temperature difference between the welding lead and the ground end, and improve the welding quality) to 100℃. After waiting for the heating plate temperature to reach the required level, place the metal housing with the installed circuit board and the fixed carrier (the fixed carrier is a fixed tool for the metal housing to be welded to prevent the housing from being loose during welding and preventing the metal housing from moving during welding, which is not conducive to welding) on the heating plate. After heating for 1-2 minutes, use a soldering iron and Sn-5Sb tin wire to solder the lead-out holes of the circuit board, ensuring that the input, output and ground terminals are well soldered. The soldering temperature of the soldering iron is set to 400℃±30℃; 16) Soak the soldered product from step 15 in the cleaning water for 5 minutes. After leaving it at room temperature for 30 minutes, bake it in a drying oven to ensure it is dry. The baking temperature and time should be set at 130°C ± 10°C and 60 minutes ± 5 minutes. 17) Use two-component silicone sealant to pot the metal housing cavity. The potting height is controlled to just cover the highest common-mode inductor L3-L4 and differential-mode inductor L1-L2 surface; 18) Cover the metal cover plate and use laser sealing process to remelt the gap between the metal cover plate and the metal shell to form a sealing pattern; 19) Finally, the product logo is etched on the middle of the metal cover by laser marking process. The logo may include but is not limited to model, name, manufacturer, terminal symbol, batch number, etc.; 20) By testing the insertion loss of the filter, the maximum suppression capability of the differential mode insertion loss in 10kHz~30MHz can reach 100dB, and the maximum suppression capability of the common mode insertion loss in 10kHz~30MHz can reach 90dB. Figure 11-12 shown.

[0028] The filter of the present invention is undergoing electromagnetic capacitance test and the effect is obvious. Figure 14 As shown in the figure, when conducting the R102 conduction test, the interference at 10kHz~10MHz by using the existing filter obviously exceeds the standard by nearly 50dB, and the test fails. After the rectification is made according to the present invention, Figure 13 As shown, the frequency range from 10kHz to 10MHz does not exceed the standard at all, and the margin is at least 10dB, so the test passed.

[0029] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A filter for motor control against electromagnetic interference, characterized in that: It includes a metal shell, a circuit board and a metal cover. The metal shell is provided with a accommodating cavity with an upper opening. The circuit board is installed in the accommodating cavity. The circuit board is installed on the circuit board. Five guide pins are provided at the bottom of the circuit board, among which four guide pins extend out of the bottom of the metal shell and are isolated from the bottom of the metal shell by glass insulators. The four guide pins are the input positive terminal, the input negative terminal, the output positive terminal and the output negative terminal respectively. The fifth guide pin is the grounding terminal, which is fixedly connected to the bottom of the metal shell. The metal cover is closed at the opening of the metal shell. After the circuit board is installed in the accommodating cavity, it is filled with potting glue. The bottom of the metal shell is connected to the grounding pad on the circuit board through the internal grounding guide pin.

2. The filter for motor control against electromagnetic interference according to claim 1, characterized in that: A groove is provided at the bottom of the accommodating cavity, four guide pin fixing seats are provided at the four corners of the groove, a resin plate is provided at the bottom of the groove, a circuit board support step is provided around the bottom of the accommodating cavity, the circuit board support step is higher than the guide pin fixing seat, the bottom surface of the circuit board contacts the circuit board support step, and the four guide pins are located on the guide pin fixing seat.

3. The filter for motor control against electromagnetic interference according to claim 1, characterized in that: The two ends of the metal shell bottom plate extend outward to form an extension part, a mounting hole is set in the middle of the extension part, and the side wall of the metal shell opposite to the mounting hole is provided with an inward convex arc structure, which is coaxial with the mounting hole.

4. The filter for motor control against electromagnetic interference according to claim 1, characterized in that: A sunken step is set on the top of the metal shell, the metal cover is embedded in the step for sealing and the top surface is kept flush with the top surface of the metal shell, a boss is set at the bottom of the metal cover, the boss is embedded in the side wall of the metal shell, and an insulating film layer is set at the bottom of the boss.

5. The filter for motor control against electromagnetic interference according to claim 4, characterized in that: The top surface and surrounding sides of the metal cover are copper-nickel plated.

6. The filter for motor control against electromagnetic interference according to claim 2, characterized in that: The circuit structure of the filter includes a differential mode inductor L1, a differential mode inductor L2, a common mode inductor L3 and a common mode inductor L4. The input ends of the differential mode inductor L1 and the differential mode inductor L2 are respectively connected to the input positive terminal P and the input negative terminal N, the other end of the differential mode inductor L1 is connected to the input end of the common mode inductor L3 and one end of the capacitor C1, the other end of the differential mode inductor L2 is respectively connected to the other input end of the common mode inductor L3 and the other end of the capacitor C1, the output end of the common mode inductor L3 is connected to the capacitor C2, the capacitor C3, one end of the capacitor C5 and the input end of the common mode inductor L4, the other output end of the common mode inductor L3 is connected to the other end of the capacitor C2, the other end of the capacitor C3, one end of the capacitor C6 and the other input end of the common mode inductor L4, the other end of the capacitor C5 and the other end of the capacitor C6 are connected to the ground terminal, the output end of the common mode inductor L4 is connected to one end of the capacitor C4 and the output positive terminal P', and the other output end of the common mode inductor L4 is connected to the other end of the capacitor C4 and the output positive terminal N'.

7. The filter for motor control against electromagnetic interference according to claim 6, characterized in that: The common-mode inductor L3 and the common-mode inductor L4 are symmetrically arranged on the input side and the output side of the circuit board.

8. The method for manufacturing a filter for motor control against electromagnetic interference according to claim 1, characterized in that: The method comprises the following steps: 1) The metal shell and metal cover are made of 4J29 alloy material and processed into cavity-shaped structural parts and plate-shaped structural parts respectively. Then the metal shell and glass are co-fired at a high temperature of 1400℃ to obtain a sealed and fixed connection between the glass insulator and the metal shell; 2) The bottom of the metal shell is first sprayed with fine sand, and then pre-treated with degreasing and rust removal. The surface of the metal shell is cleaned and electroplated with 2μm thick copper on the inner and outer surfaces, and then 10-15μm thick nickel. 3) The bottom surface of the metal cover is first sprayed with fine sand, and then pre-treated with degreasing and rust removal. The surface of the metal cover is cleaned and electroplated with 2μm thick copper on the inner and outer surfaces, followed by 10-15μm thick nickel. Finally, the convex surface of the metal cover is polished to remove the plating layer, and then anodized to form an insulating film layer on the convex surface with a thickness of 0.3-0.8μm. 4) Select chip ceramic capacitors C1-C6, where C1-C4 are used as Cx capacitors and C5-C6 are used as Cy capacitors; 5) Use alcohol to clean the steel mesh and carrier. Make sure the steel mesh and carrier are clean and the window holes are free of impurities before use; 6) Use Sn-5Sb solder paste for soldering between the PAD and capacitor on the circuit board. Before use, take the solder paste out of the freezer and place it at room temperature for 30-60 minutes to thaw. Then use a stirring rod to repeatedly stir the solder paste in a clockwise and counterclockwise rotation for 30-60 seconds until the solder paste becomes a wire-drawing state. 7) Fix the PCB on the carrier and adjust the PCB PAD to be consistent with the stencil opening. Close the stencil to ensure that the stencil and the PCB on the carrier are flat. 8) Pour a set amount of solder paste onto the steel mesh surface and use a scraper to evenly scrape the solder paste into the window holes so that the solder paste covers the C1-C6 pads of the circuit board; 9) Use a 12-zone reflow oven to solder the circuit board and capacitors C1-C6; 10) After the capacitors C1-C6 are reflowed and allowed to cool naturally, solder the common-mode inductors L3-L4 and differential-mode inductors L1-L2 with a soldering iron. 11) Common-mode inductors are made of 1K107F nanocrystalline amorphous tape with a magnetic permeability greater than 80,000. Differential-mode inductors are made of microcrystalline iron-based amorphous tape with a magnetic permeability not exceeding 1,200. High-temperature enameled round copper wire is used to form a coil on the common-mode inductor or differential-mode inductor. The free end of the high-temperature enameled round copper wire after de-enamelling is used as the lead-out terminal of the common-mode inductor or differential-mode inductor. The lead-out terminals of the common-mode inductor or differential-mode inductor are soldered to the through-holes of the circuit board using Sn-5Sb tin wire, and the excess tail wire is cut off. The soldering temperature setting condition of the soldering iron is 400°C ± 30°C. 12) After soldering in steps 10) and 11), clean the circuit board using JD-086 board cleaning water. Soak the circuit board in the water for 5-10 minutes. Then, use a fine-bristled toothbrush to scrub the solder joints, circuit board, and components on the circuit board back and forth, repeating the scrubbing cycle at least 10 times. After the first cleaning, replace the circuit board with clean water and soak and clean it again. 13) After the cleaned circuit board is dried naturally, continue to solder the lead terminals and ground terminals on the circuit board. The lead terminals include the positive input terminal, negative input terminal, positive output terminal and negative output terminal. 14) Place the resin board into the groove in the accommodating cavity of the metal shell, then align the lead-out holes of the circuit board with the lead-out ends of the inner cavity of the metal shell, pass the lead-out ends through the through holes, and install the circuit board; 15) First, adjust the heating plate temperature to 100℃ and wait until the heating plate temperature reaches the required level. Place the metal housing with the installed circuit board and the fixed carrier on the heating plate and heat it for 1-2 minutes. Then, use a soldering iron and Sn-5Sb tin wire to solder the lead-out holes of the circuit board. The soldering temperature of the soldering iron should be set at 400℃±30℃. 16) Soak the soldered product from step 15 in the cleaning water for 5 minutes. After leaving it at room temperature for 30 minutes, bake it in a drying oven to ensure it is dry. The baking temperature and time should be set at 130°C ± 10°C and 60 minutes ± 5 minutes. 17) Use two-component silicone sealant to pot the metal housing cavity. The potting height is controlled to just cover the highest common-mode inductor L3-L4 and differential-mode inductor L1-L2 surface; 18) Put on the metal cover and use laser sealing technology to remelt the gap between the metal cover and the metal shell to form a sealing pattern.

9. The method for manufacturing a filter for motor control against electromagnetic interference according to claim 8, characterized in that: In step 9), the upper and lower temperature setting parameters of the 12 temperature zones are: 146℃, 155℃, 160℃, 170℃, 185℃, 200℃, 220℃, 240℃, 270℃, 270℃, 240℃, 200℃; based on the number of reflow soldering times, the temperature tolerance allowed for each temperature zone is ±5℃; the reflow soldering chain speed is 0.70m / min.

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