Manufacturing method of direct-current high-voltage bus filter

Abstract

The invention belongs to the technical field of integrated circuit manufacturing processes, and discloses a manufacturing method of a direct-current high-voltage bus filter, which comprises the following steps of: riveting a first group of embedded nuts on a connecting copper bar; acquiring a first image of the riveting connection copper bar, and judging whether the riveting connection copper bar is qualified or not; performing injection molding on the second group of embedded nuts and the qualified riveting connection copper bar to obtain a connection copper bar injection molding piece; collecting a second image of the connecting copper bar injection molding part, and judging whether the connecting copper bar injection molding part is qualified or not; the capacitor X and the capacitor X2 are installed in the installation grooves of the qualified connecting copper bar injection molding part; welding a Y capacitor and a Y2 capacitor with a grounding copper bar, and then loading the Y capacitor and the Y2 capacitor into a mounting groove of a connecting copper bar injection molding piece; mounting a magnetic ring in a magnetic ring fixing groove connected with the copper bar injection molding part; and welding each capacitor with the positive and negative copper bars to obtain the direct-current high-voltage bus filter. According to the invention, on-line quality inspection of the direct-current high-voltage bus filter can be realized, and the yield and the production efficiency are improved.

Description

Technical Field

[0001] The present application relates to the technical field of integrated circuit manufacturing processes, and in particular to a method for manufacturing a DC high-voltage bus filter. Background Art

[0002] In the context of the rapid development of new energy vehicles, the operation of high-power vehicle electricity poses a huge design challenge to the electrical connection of the filter in the motor controller system. In the electric drive system, the filter is a key component for filtering, removing low-frequency noise, and optimizing EMC electromagnetic parameters. Due to the compact space of the electric drive controller and the structure of the filter itself, multiple functional components such as capacitors, magnetic rings, positive and negative high-voltage rows need to be connected, which increases the complexity of the filter.

[0003] However, in the existing filter production system, it is impossible to realize online detection of product production status during the manufacturing process, resulting in a high rate of defective filters, low production efficiency, and a large amount of raw material waste. Summary of the invention

[0004] The present application provides a method for manufacturing a DC high-voltage bus filter, which can realize online quality inspection of the DC high-voltage bus filter and improve the yield rate and production efficiency of the DC high-voltage bus filter.

[0005] The present application provides a method for manufacturing a DC high voltage bus filter, comprising:

[0006] Riveting the first set of embedded nuts onto the nut through holes of the connecting copper busbar to form a riveted connecting copper busbar;

[0007] Acquire a first image of the riveted copper busbar;

[0008] Judging whether the riveted copper busbar is qualified according to the first image;

[0009] The second set of inlaid nuts and the qualified riveted connection copper bar are injection molded to obtain a connection copper bar injection molded part;

[0010] Acquire a second image of the injection molded part connected to the copper busbar;

[0011] Judging whether the injection-molded connecting copper bar is qualified according to the second image;

[0012] Install the X capacitor and X2 capacitor into the mounting groove of the qualified copper busbar injection molding;

[0013] After welding the Y capacitor and Y2 capacitor to the grounding copper bar, install them into the installation groove of the injection molded part of the copper bar;

[0014] Install the magnetic ring into the magnetic ring fixing groove of the injection molded part connected to the copper busbar;

[0015] The X capacitor, the X2 capacitor, the Y capacitor and the Y2 capacitor are welded to the positive and negative copper bars to obtain a DC high-voltage bus filter.

[0016] Furthermore, the first group of inlay nuts includes M6 inlay nuts and M5 inlay nuts.

[0017] Furthermore, the second set of inlay nuts includes 2 M8 inlay nuts, 1 M6 inlay nut and 3 M5 inlay nuts.

[0018] Furthermore, judging whether the riveted copper busbar is qualified according to the first image includes:

[0019] The first image is input into the image recognition model to obtain the first gap between the first group of embedded nuts and the riveted copper busbar and the scratch depth of the riveted copper busbar; determine whether the first gap is greater than a preset gap threshold, or whether the scratch depth is greater than a preset depth threshold; if so, the riveted copper busbar is unqualified.

[0020] Furthermore, judging whether the injection molded copper bar connection part is qualified according to the second image includes:

[0021] The second image is input into the image recognition model to obtain the center offset distance of the second group of embedded nuts and the cracks, missing material positions and missing material areas on the injection molded connecting copper bar;

[0022] Determine whether there are cracks in the copper bar injection molded part, or whether the missing material position is within the preset range of the second set of embedded nuts; if so, the copper bar injection molded part is unqualified;

[0023] If not, it is determined whether the center offset distance is greater than the preset offset threshold, or whether the missing material area is greater than the preset missing material threshold; if so, the copper bar injection molded part is unqualified.

[0024] Furthermore, after the Y capacitor and the Y2 capacitor are welded to the grounding copper bar, they are installed in the installation groove of the injection molded part connecting the copper bar, including:

[0025] Bend one pin of the Y capacitor and the Y2 capacitor;

[0026] Solder the bent pins of the Y capacitor and the Y2 capacitor to the grounding copper busbar;

[0027] Place the grounding copper bar into the positioning groove of the connecting copper bar injection molding;

[0028] Install the Y capacitor and Y2 capacitor into the mounting groove of the injection molded copper busbar.

[0029] Furthermore, the method further comprises: after the Y capacitor and the Y2 capacitor are installed into the installation groove of the copper bar injection molding, the installation grooves of the X capacitor and the X2 capacitor, and the installation grooves of the Y capacitor and the Y2 capacitor are filled with glue and dried.

[0030] Furthermore, the above-mentioned welding of the X capacitor, the X2 capacitor, the Y capacitor and the Y2 capacitor with the positive and negative copper bars to obtain a DC high-voltage bus filter includes: connecting the positive and negative copper bars with the connecting copper bar injection molding using screws; welding the pins of the X capacitor and the X2 capacitor and the unbent pins of the Y capacitor and the Y2 capacitor with the positive and negative copper bars to obtain a DC high-voltage bus filter.

[0031] Furthermore, the preset gap threshold is 1 mm, and the preset depth threshold is 3 μm.

[0032] Furthermore, the preset offset threshold is 0.2 mm, and the preset material shortage threshold is 0.2 square millimeters.

[0033] In summary, compared with the prior art, the technical solution provided in the embodiment of the present application has at least the following beneficial effects:

[0034] A manufacturing method for a DC high-voltage bus filter provided in an embodiment of the present application performs quality inspection on semi-finished products in the manufacturing process through image acquisition and recognition during the manufacturing process of the filter. Not only is the quality inspection speed fast and does not affect the operation efficiency of the assembly line, but unqualified semi-finished products can also be screened out in time to avoid unqualified products wasting materials in subsequent process flows, thereby achieving efficient production of the DC high-voltage bus filter and improving the yield rate and production efficiency of the DC high-voltage bus filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flowchart of a method for manufacturing a DC high-voltage bus filter is provided as an exemplary embodiment of the present application.

[0036] Figure 2 A flowchart of the steps for installing a Y capacitor and a Y2 capacitor is provided for an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0038] Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of this application.

[0039] See also Figure 1 The present application embodiment provides a method for manufacturing a DC high voltage bus filter, comprising:

[0040] Step S1, riveting a first set of embedded nuts onto the nut through holes of the connecting copper busbar to form a riveted connecting copper busbar.

[0041] Among them, the first group of inlay nuts includes M6 inlay nuts and M5 inlay nuts.

[0042] Specifically, the connecting copper busbar is loaded onto the connecting copper busbar jig, and transferred to the riveting station by the first conveyor line. The nut loading robot clamps the M6 ​​inlaid nuts and M5 inlaid nuts to the nut through holes of the connecting copper busbar. The connecting copper busbar jig is driven by the first conveyor line to continue moving to the nut riveting station, and the riveting cylinder feeds to complete the riveting of the M6 ​​inlaid nuts and M5 inlaid nuts. The connecting copper busbar is red copper T2, with a nickel base and matte tin on the surface.

[0043] Step S2, collecting a first image of the riveted copper busbar; and judging whether the riveted copper busbar is qualified according to the first image.

[0044] If the test fails, the riveted copper busbar will be directly sent to the recycling box without executing the subsequent process.

[0045] Step S3, injection molding the second set of embedded nuts and the qualified riveted copper busbar to obtain a connected copper busbar injection molded part.

[0046] Among them, the second group of inlay nuts includes 2 M8 inlay nuts, 1 M6 inlay nut and 3 M5 inlay nuts.

[0047] Specifically, the injection molding feeding robot clamps the qualified riveted copper bar into the injection mold, and the injection molding feeding robot clamps 2 M8 inlay nuts, 1 M6 inlay nut, and 3 M5 inlay nuts into the injection mold, and injection molds each inlay nut together with the riveted copper bar; the injection molding process includes: installing the injection mold into the corresponding position in the middle of the injection molding machine, locking the mold screws, connecting the mold water supply; setting the injection molding parameters, confirming that there are no missing parts, and starting the injection molding. The injection molding parameters can be seen in the following table:

[0048]

[0049]

[0050] Step S4, collecting a second image of the injection-molded copper busbar connection; and judging whether the injection-molded copper busbar connection is qualified according to the second image.

[0051] Similarly, if the test fails, the riveted copper busbar will be directly sent to the recycling box without executing the subsequent process.

[0052] Step S5, installing the X capacitor and the X2 capacitor into the installation groove of the qualified connection copper bar injection molded part.

[0053] Step S6, after welding the Y capacitor and the Y2 capacitor to the grounding copper bar, install them into the installation groove of the injection molded part connecting the copper bar.

[0054] The mounting grooves where the X capacitor and the X2 capacitor are located are not the same as the mounting grooves where the Y capacitor and the Y2 capacitor are located.

[0055] Step S7, installing the magnetic ring into the magnetic ring fixing groove of the injection molded part connected to the copper busbar.

[0056] Specifically, the first conveyor line transports the connecting copper busbar injection molded parts to the magnetic ring assembly station, and the automatic glue injection machine injects 2-3mm high fixing glue at the bottom of the magnetic ring fixing groove of the connecting copper busbar injection molded parts. The magnetic ring loading robot places the cleaned magnetic ring in the magnetic ring fixing groove and presses the bottom of the magnetic ring groove to make it tightly integrated with the fixing glue; the first conveyor line continues to transport the connecting copper busbar injection molded parts to the magnetic ring glue pouring station, and the automatic glue pouring machine injects glue at multiple points along the gap between the magnetic ring and the fixing groove until the glue and the top surface of the magnetic ring are basically level.

[0057] Step S8, welding the X capacitor, X2 capacitor, Y capacitor and Y2 capacitor to the positive and negative copper bars to obtain a DC high voltage bus filter. Specifically, the welding process parameters are shown in the following table:

[0058]

[0059] After obtaining the finished DC high-voltage bus filter, it is also necessary to transport the DC high-voltage bus filter to the cold insulation resistance test station, the withstand voltage test station, the inter-pole capacitance station, the pole capacitance station, and the inductance test station for various electrical performance tests.

[0060] Among them, measuring inductance includes selecting LS-Q test items on the digital bridge instrument, test condition ①: 10KHZ 0.3V result ≥13μH; test condition ②: 100KHZ 0.3V result ≥5μH, a total of 2 times.

[0061] The test capacitor includes selecting the CS-Q test item on the digital bridge instrument, and the test conditions are: test voltage 1V, frequency 1KHZ, and a total of 3 tests; ① measuring the positive copper busbar and the negative copper busbar, the test result is 1170μH±10%; ② measuring the positive copper busbar and the grounding copper busbar, the test result is 563μH±20%; ③ measuring the negative copper busbar and the grounding copper busbar, the test result must be 563μH±20%.

[0062] Torque test includes: 1) M5 inserts should be able to withstand torque ≥ 7.5Nm; 2) M6 inserts should be able to withstand torque ≥ 10N.m; 3. M8 inserts should be able to withstand torque ≥ 25N.m installation torque. Finally, qualified products will be packaged and stored.

[0063] The above embodiment provides a method for manufacturing a DC high-voltage bus filter. During the manufacturing process of the filter, quality inspection of semi-finished products in the manufacturing process is performed through image acquisition and recognition. Not only is the quality inspection speed fast and does not affect the efficiency of the assembly line operation, but unqualified semi-finished products can also be screened out in time to avoid unqualified products wasting materials in subsequent process flows, thereby achieving efficient production of the DC high-voltage bus filter and improving the yield and production efficiency of the DC high-voltage bus filter.

[0064] In some embodiments, judging whether the riveted copper busbar is qualified according to the first image includes:

[0065] The first image is input into the image recognition model to obtain the first gap between the first group of embedded nuts and the riveted copper busbar and the scratch depth of the riveted copper busbar; determine whether the first gap is greater than a preset gap threshold, or whether the scratch depth is greater than a preset depth threshold; if so, the riveted copper busbar is unqualified.

[0066] Among them, the image recognition model is a machine learning model trained using images of riveted copper busbars with the first gap and scratch depth marked. The preset gap threshold can be 1 mm, and the preset depth threshold can be 3 microns.

[0067] Specifically, there should be no gap of more than 1mm between the embedded nut and the connecting copper busbar after riveting. The allowable deformation of the copper busbar is that the deformation of the relevant hole line is within the range of 0.1mm. As for scratches, the main thing is not to scrape off the tin plating on the surface of the copper busbar. The standard tin plating thickness at the connection of the copper busbar is generally 3-10 microns. Therefore, the scratch depth cannot exceed 3 microns.

[0068] The above-mentioned embodiment can quickly identify and obtain various parameters on the riveted copper busbar through image recognition, and can realize rapid quality inspection of semi-finished products without affecting the operating efficiency of the production line.

[0069] In some embodiments, judging whether the connected copper bar injection molded part is qualified according to the second image includes:

[0070] The second image is input into the image recognition model to obtain the center offset distance of the second group of inlaid nuts and the cracks, missing material positions and missing material areas on the connecting copper bar injection molded part; determine whether there are cracks on the connecting copper bar injection molded part, or whether the missing material positions are within the preset range of the second group of inlaid nuts; if so, the connecting copper bar injection molded part is unqualified; if not, determine whether the center offset distance is greater than the preset offset threshold, or whether the missing material area is greater than the preset missing material threshold; if so, the connecting copper bar injection molded part is unqualified.

[0071] Among them, the image recognition model is a machine learning model trained with images of copper busbar injection molded parts that have been marked with scratches, missing material area and corresponding positions, as well as the center offset distance. The preset offset threshold can be 0.2 mm, and the preset missing material threshold can be 0.2 square millimeters. Specifically, there cannot be any scratches on the copper busbar injection molded parts, and there cannot be missing material within the preset range of each nut. This is a necessary condition for qualification; secondly, after meeting the above conditions, it is necessary to ensure that the center position offset distance of each embedded nut is within 0.2mm. If any nut does not meet the requirements, it will be judged as unqualified; finally, if the missing material area outside the preset range of each nut is greater than 0.2 square millimeters, it will also be judged as unqualified.

[0072] The above-mentioned embodiment can quickly identify and obtain various parameters on the injection-molded connecting copper bar through image recognition, and can realize rapid quality inspection of semi-finished products without affecting the operating efficiency of the production line.

[0073] See also Figure 2 In some embodiments, after the Y capacitor and the Y2 capacitor are welded to the grounding copper bar, they are installed in the installation groove of the injection molded part connecting the copper bar, including:

[0074] Step S61, bending one pin of the Y capacitor and the Y2 capacitor.

[0075] Step S62, welding the bent pins of the Y capacitor and the Y2 capacitor to the grounding copper busbar.

[0076] Step S63, inserting the grounding copper bar into the positioning groove of the connecting copper bar injection molding.

[0077] Step S64, installing the Y capacitor and the Y2 capacitor into the installation groove of the injection molded part of the connecting copper busbar.

[0078] Specifically, the first conveyor line conveys the connecting copper busbar injection molded parts to the grounding copper busbar assembly station; the Y capacitor loader and the Y2 capacitor loader load the Y capacitor and the Y2 capacitor respectively, and the Y capacitor and the Y2 capacitor are placed on the capacitor fixture and conveyed and loaded by the conveyor line. During the loading process, they pass through the capacitor pin bending guide part, and one of the capacitor pins of the Y capacitor and the Y2 capacitor is bent by the guide angle of the capacitor pin bending guide part, and the bending height is adapted to the height of the corresponding positioning groove of the grounding copper busbar.

[0079] The second conveyor line automatically conveys and loads the grounding copper bar to the first welding station of the grounding copper bar. The Y capacitor loading robot clamps the two bent Y capacitors to the first welding station of the grounding copper bar, and one pin of each Y capacitor contacts the grounding copper bar for welding; the second conveyor line continues to convey the welded grounding copper bar to the second welding station of the grounding copper bar, and the Y2 capacitor loading robot clamps the two bent Y2 capacitors to the second welding station of the grounding copper bar, and one pin of each Y2 capacitor contacts the grounding copper bar for welding; the grounding copper bar loading robot clamps the grounding copper bar with the welded capacitor on the second conveyor line to the grounding copper bar assembly station, places the grounding copper bar into the positioning groove of the connecting copper bar injection molding, and installs the Y capacitor and Y2 capacitor into the installation groove of the connecting copper bar injection molding.

[0080] In some embodiments, the method further comprises: after installing the Y capacitor and the Y2 capacitor into the installation groove of the copper busbar injection molding, filling the installation grooves of the X capacitor and the X2 capacitor, and the installation grooves of the Y capacitor and the Y2 capacitor with glue and drying.

[0081] Specifically, the first conveyor line continues to convey the connecting copper busbar injection molding to the capacitor glue pouring station, and the automatic glue pouring machine pours insulating glue into the gap between the X capacitor, X2 capacitor, Y2 capacitor and Y2 capacitor and the connecting copper busbar injection molding installation groove, so that the capacitor is fixed in the installation groove; the connecting copper busbar injection molding is conveyed to the drying station, and the automatic dryer dries the capacitor fixing glue.

[0082] In the above embodiment, the capacitors on the filter are fixed by glue filling, which ensures the stability of the capacitors and indirectly increases the life of the filter.

[0083] In some embodiments, the above-mentioned welding of the X capacitor, the X2 capacitor, the Y capacitor and the Y2 capacitor with the positive and negative copper bars to obtain a DC high-voltage bus filter includes: connecting the positive and negative copper bars with the connecting copper bar injection molding using screws; welding the pins of the X capacitor and the X2 capacitor and the unbent pins of the Y capacitor and the Y2 capacitor to the positive and negative copper bars to obtain a DC high-voltage bus filter.

[0084] Specifically, the first conveyor line continues to convey the connecting copper bar injection molding to the positive and negative copper bar assembly stations, the positive and negative copper bar robots clamp the positive and negative copper bar, and place the positive and negative copper bar on the connecting copper bar injection molding respectively, the positive and negative copper bar robots lock the M6 ​​screws and M8 screws on the positive copper bar, the positive copper bar is fastened to the connecting copper bar through the M6 ​​screws, and the positive and negative copper bar robots lock the M5 and M8 screws on the negative copper bar.

[0085] Furthermore, before conveying the DC high-voltage bus filter to the cold insulation resistance detection station, the first conveyor line can first convey the DC high-voltage bus filter to the bolt removal station, and use the bolt removal robot to remove the two M8 bolts that fix the positive and negative copper busbars for auxiliary welding; thereby eliminating the step of manual bolt removal and improving automation capabilities.

[0086] In the above embodiment, the capacitor is welded after the positive and negative copper bars are fixed by screws, which ensures the welding accuracy, reduces the situation where errors in the capacitor welding process lead to unqualified products, and indirectly improves the yield rate.

[0087] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for manufacturing a DC high voltage bus filter, characterized in that: include: Riveting the first set of embedded nuts onto the nut through holes of the connecting copper busbar to form a riveted connecting copper busbar; Acquiring a first image of the riveted copper busbar; judging whether the riveted copper busbar is qualified according to the first image; Injection molding the second set of embedded nuts and the qualified riveted copper bar to obtain an injection-molded copper bar connection part; Acquire a second image of the injection-molded connecting copper bar; judging whether the connecting copper bar injection molding is qualified according to the second image; Install the X capacitor and the X2 capacitor into the installation groove of the qualified connection copper bar injection molding; After welding the Y capacitor and the Y2 capacitor to the grounding copper bar, install them into the installation groove of the injection molded part of the connecting copper bar; Installing the magnetic ring into the magnetic ring fixing groove of the injection molded part connecting the copper bar; The X capacitor, the X2 capacitor, the Y capacitor and the Y2 capacitor are welded to the positive and negative copper bars to obtain a DC high-voltage bus filter.

2. The method for manufacturing a DC high voltage bus filter according to claim 1, characterized in that: The first group of inlay nuts includes M6 inlay nuts and M5 inlay nuts.

3. The method for manufacturing a DC high voltage bus filter according to claim 1, characterized in that: The second set of inlay nuts includes 2 M8 inlay nuts, 1 M6 inlay nut and 3 M5 inlay nuts.

4. The method for manufacturing a DC high voltage bus filter according to claim 1, characterized in that: The step of judging whether the riveted copper busbar is qualified according to the first image includes: Inputting the first image into an image recognition model to obtain a first gap between the first group of embedded nuts and the riveted copper bar and a scratch depth of the riveted copper bar; It is determined whether the first gap is greater than a preset gap threshold, or whether the scratch depth is greater than a preset depth threshold; if so, the riveted copper busbar is unqualified.

5. The method for manufacturing a DC high voltage bus filter according to claim 1, characterized in that: The step of judging whether the connection copper bar injection molded part is qualified according to the second image includes: Inputting the second image into an image recognition model to obtain the center offset distance of the second group of embedded nuts and the cracks, missing material positions and missing material areas on the connecting copper bar injection molded part; Determine whether the injection-molded connecting copper bar has cracks, or whether the missing material position is within a preset range of the second set of embedded nuts; if so, the injection-molded connecting copper bar is unqualified; If not, it is determined whether the circle center offset distance is greater than a preset offset threshold, or whether the material shortage area is greater than a preset material shortage threshold; if so, the connecting copper bar injection molding is unqualified.

6. The method for manufacturing a DC high voltage bus filter according to claim 1, characterized in that: After welding the Y capacitor and the Y2 capacitor to the grounding copper bar, they are installed in the installation groove of the injection molded part of the connecting copper bar, including: Bend one pin of the Y capacitor and the Y2 capacitor; Welding the bent pins of the Y capacitor and the Y2 capacitor to the grounding copper busbar; Insert the grounding copper bar into the positioning groove of the connecting copper bar injection molding; Install the Y capacitor and the Y2 capacitor into the mounting groove of the connecting copper bar injection molding.

7. The method for manufacturing a DC high voltage bus filter according to claim 6, characterized in that: Also includes: After the Y capacitor and the Y2 capacitor are installed in the installation groove of the connecting copper bar injection molding, the installation grooves of the X capacitor and the X2 capacitor, and the installation grooves of the Y capacitor and the Y2 capacitor are filled with glue and dried.

8. The method for manufacturing a DC high voltage bus filter according to claim 6, characterized in that: The method of welding the X capacitor, the X2 capacitor, the Y capacitor and the Y2 capacitor to the positive and negative copper bars to obtain a DC high voltage bus filter comprises: Connecting the positive and negative copper bars to the connecting copper bar injection molded part using screws; The pins of the X capacitor and the X2 capacitor and the unbent pins of the Y capacitor and the Y2 capacitor are welded to the positive and negative copper bars to obtain the DC high-voltage bus filter.

9. The method for manufacturing a DC high voltage bus filter according to claim 4, characterized in that: The preset gap threshold is 1 mm, and the preset depth threshold is 3 μm.

10. The method for manufacturing a DC high voltage bus filter according to claim 5, characterized in that: The preset offset threshold is 0.2 mm, and the preset material shortage threshold is 0.2 square millimeters.

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