Failure mode identification and disassembly method for power filter failure analysis

Abstract

The present invention discloses a failure mode confirmation and disassembly method for failure analysis of a power filter, comprising the following steps: failure mode confirmation; power filter disassembly, specifically comprising the following steps: opening the cover; removing the outer shell; preheating; uniform heating; taking out the heat preservation; local spot blowing; removing the epoxy resin at the spot blowing part; repeating the local spot blowing and removing the epoxy resin at the spot blowing part until all the epoxy resin is removed to obtain a circuit component. The present invention softens the epoxy resin of the potting component by preheating, uniform segmented heating, heat preservation, and local spot blowing heating, and then partially removes the epoxy resin by a glue removal tool after softening, and can complete the dissection of the epoxy resin without damaging the circuit component at all, and finally realizes the smooth disassembly of the power filter potted with epoxy resin, and the obtained circuit component is complete without secondary damage, and the epoxy resin is completely removed, which is significantly beneficial to improve the accuracy of the later failure analysis.

Description

Technical Field

[0001] The present invention relates to a method for power filter failure analysis, and in particular to a failure mode confirmation and disassembly method for power filter failure analysis, belonging to the technical field of power filter production and application. Background Art

[0002] During testing, experimentation and use, power filters often fail due to abnormal electrical performance due to internal component failures, poor welding quality, loose fasteners, broken leads and other problems. Therefore, it is necessary to conduct failure analysis and make improvements based on the results of the failure analysis to improve product quality.

[0003] In the failure analysis of power filter, failure mode confirmation and disassembly of failed products (often also called dissection) are the key to ensure the accuracy of failure analysis results. The traditional disassembly method and failure mode confirmation method and their defects are as follows:

[0004] Traditional disassembly methods include direct glue removal, slicing and grinding, and immersion decomposition. Among them, direct glue removal is to directly use special glue removal tools to remove the potting glue to obtain the internal circuit components. This method is more suitable for power filters with thermal conductive silicone rubber potting materials. Since thermal conductive silicone rubber potting materials are elastic and have low hardness after curing, they can be directly taken out with tools. However, it is not applicable to power filters with epoxy resin potting materials, because the epoxy resin potting materials have high hardness after curing and it is basically impossible to take them out directly; slicing and grinding is to directly slice and grind the failed power filter as a whole, and then observe the local cross-section of the product for further analysis. This method also has many defects for power filters with epoxy resin potting materials: due to the high hardness of epoxy resin potting materials, the grinding efficiency is low, and it is impossible to fully check the internal situation of the failed power filter. It is very easy to miss the fault point during grinding. If the filter is large or the internal devices include non-chip multilayer ceramic capacitors, this method is even less suitable. Immersion decomposition is to remove the epoxy resin potting material by immersion in a solution. This method has the following defects: the decomposition rate of the epoxy resin potting material in the solution is very slow, and the failure analyst needs to take out the immersed power filter from the solution several times, peel off a part of the potting material, and then continue to immerse and peel off another part of the potting material until the epoxy resin potting material is completely removed. This process is extremely time-consuming, resulting in lower efficiency of failure analysis, and the solvent that can remove the epoxy resin potting material will also cause decomposition and damage to other organic materials or plastic-sealed devices inside the power filter, which will also affect subsequent analysis. At the same time, the immersion solvent is volatile, which not only pollutes the environment but also threatens human health.

[0005] The traditional method of confirming failure modes is to determine the failure mode through electrical performance testing. During the electrical performance test, the withstand voltage and insulation resistance of the power filter are directly tested. This method is likely to cause secondary damage to the circuit or even destroy the fault point, reducing the accuracy of failure analysis. Summary of the invention

[0006] The purpose of the present invention is to provide a safe and efficient failure mode confirmation and disassembly method for power filter failure analysis in order to solve the above problems.

[0007] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0008] A failure mode confirmation and disassembly method for power filter failure analysis, characterized in that it includes the following steps:

[0009] Step 1: Failure mode confirmation;

[0010] Step 2: Dismantle the power filter, including the following steps:

[0011] Step 2.1, open the cover: For the power filter with screw cover, directly use a screwdriver to unscrew the screws and remove the cover; for other cover structures, first fix the power filter on the milling machine, and then use a milling cutter to mill around the cover to remove the cover;

[0012] Step 2.2, removing the outer shell: peeling off the outer shell of the power filter after removing the cover plate from the epoxy resin, removing the outer shell, and obtaining a potting component, wherein the potting component includes the epoxy resin and a circuit component placed in the epoxy resin;

[0013] Step 2.3, preheating: placing the potting component in an oven for preheating;

[0014] Step 2.4, uniform heating: set the oven to gradually heat up the preheated potting components and keep them warm, so that each temperature section in the oven is maintained for a certain period of time;

[0015] Step 2.5, take out and keep warm: take out the potting component from the oven and place it on a heating table to keep warm;

[0016] Step 2.6, local spot blowing: turn on the spot blowing device, and aim the air outlet of the spot blowing device at the potting component on the heating table for local heating; the spot blowing device here is a device that can send hot air to a small area, and the simplest spot blowing device is a hair dryer;

[0017] Step 2.7, remove the epoxy resin at the spot blowing part: after locally heating the epoxy resin at the spot blowing part, immediately use the special glue removal tool prepared in advance to pick out the epoxy resin at that part;

[0018] Step 2.8, repeat steps 2.6 and 2.7 to spot-blow other parts of the potting component and remove the epoxy resin in the spot-blow parts until all the epoxy resin is removed to obtain a circuit component.

[0019] Preferably, in order to remove the shell more quickly and avoid secondary damage to the power filter caused by violent shell removal, in step 2.2, the edges and corners of the shell are first ground off by a grinder, and then each surface of the shell is peeled off from the epoxy resin respectively.

[0020] Preferably, in order to prevent the epoxy resin from expanding too quickly due to overheating and causing damage to the circuit components, in step 2.3, the preheating temperature is 60° C. and the preheating time is 30 min-40 min.

[0021] Preferably, in order to slowly release the internal stress of the epoxy resin due to thermal expansion during the entire heating process and effectively avoid damage to the circuit components, in step 2.4, the oven is set to the following three temperature sections: 85°C, 110°C, and 135°C, and the temperature is uniformly increased at a heating rate of 5°C / min, and maintained in each temperature section for 10 minutes.

[0022] Preferably, in order to avoid a significant drop in temperature of the potting components taken out of the oven that affects the work efficiency and to avoid a sharp change in the internal stress of the epoxy resin during spot-blowing heating due to a large temperature difference caused by the temperature drop, which may damage the circuit components, in step 2.5, the temperature of the heating table is set to 135°C and kept warm continuously.

[0023] Preferably, in order to achieve the purpose of quickly taking out the epoxy resin, in step 2.6, the temperature of the spot blowing device is set to 160°C-200°C, and the local heating time of the air outlet of the spot blowing device is 10s-20s. 160°C has reached the glass transition temperature of the epoxy resin, which promotes the transition of the epoxy resin from the glass state to the highly elastic state, showing high elasticity. After heating for 10s-20s, the molecular structure of the heated part begins to relax, which is convenient for the glue removal tool to easily and effectively remove it.

[0024] Preferably, in order to avoid secondary damage to the power filter that may have been damaged, especially the power filter that has been electrically broken down, by the voltage during the withstand voltage and insulation resistance test, in the step 1, the line-to-line continuity and the line-to-shell continuity of the power filter are first measured, and then the line-to-line capacitance and its loss tangent value, and the line-to-ground capacitance and its loss tangent value are tested, so as to preliminarily judge whether the function of the power filter is normal or abnormal; after determining that there is no line-to-line or line-to-shell short circuit or capacitor breakdown inside the power filter, the withstand voltage and insulation resistance test are performed on it; if it is determined that there is a line-to-line or line-to-shell short circuit or capacitor breakdown inside the power filter, the withstand voltage and insulation resistance test is not performed on the power filter, and a DC resistance tester is used to determine the fault condition of the power filter by testing the line-to-line resistance value and the line-to-ground resistance value of the power filter, otherwise the fault point of the power filter will be destroyed or enlarged, making it difficult to obtain accurate failure analysis results.

[0025] The beneficial effects of the present invention are:

[0026] The present invention softens the epoxy resin of the potting component by preheating, uniform speed segmented heating, heat preservation, and local spot blowing heating. After softening, the epoxy resin is partially taken out by a glue removal tool. Multiple local glue removals can complete the dissection of the epoxy resin without damaging the circuit components at all, and finally achieve smooth disassembly of the power filter potted with epoxy resin. The obtained circuit components are complete without secondary damage, and the epoxy resin is completely removed, which is significantly beneficial to improve the accuracy of subsequent failure analysis. Compared with traditional methods, it is faster and more efficient and will not cause environmental pollution or harm the health of operators. By first judging whether there is a line-to-line or line-to-shell short circuit or a capacitor breakdown in the power filter, it is determined whether to perform a withstand voltage and insulation resistance test to ensure the accuracy of the failure mode confirmation, effectively avoiding the voltage during the direct withstand voltage and insulation resistance test from causing secondary damage to the power filter that may have been damaged inside, especially the power filter that has been electrically broken down, thereby improving the accuracy of the failure analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a three-dimensional diagram of the power supply filter of the present invention;

[0028] Figure 2 It is a three-dimensional diagram of the power filter of the present invention after the edges of three sides of the cover plate are milled off;

[0029] Figure 3 is a three-dimensional diagram of the power filter of the present invention with the cover plate removed;

[0030] Figure 4 It is a three-dimensional diagram of the power filter of the present invention after the cover plate is removed and the edges and corners of the side of the shell are ground off;

[0031] Figure 5 It is a stereoscopic diagram of the potting assembly of the power filter of the present invention after the cover plate and the shell are removed;

[0032] Figure 6 It is a stereoscopic diagram of the circuit assembly of the power filter of the present invention after the cover plate and the housing are removed and the epoxy resin is removed.

[0033] In the figure, 1-cover, 2-lead, 3-housing, 4-potting component, 5-circuit component. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0035] like Figure 1-Figure 6 As shown, the power supply filter of the present invention includes a housing 3, a potting component 4, a cover plate 1 and a lead 2, the potting component 4 is placed in the housing 3, the cover plate 1 is connected to the housing 3, the potting component 4 includes epoxy resin and a circuit component 5 placed in the epoxy resin, and the lead 2 is connected to the circuit component 5 and passes through the corresponding through hole on the housing 3.

[0036] Example:

[0037] Combination Figure 1-Figure 6 , a failure mode confirmation and disassembly method for power filter failure analysis, comprising the following steps:

[0038] Step 1, failure mode confirmation, the specific method is: first measure the continuity between the lines and the continuity between the lines and the shell of the power filter, and then test the line capacitance and its loss tangent value, the line-to-ground capacitance and its loss tangent value, so as to preliminarily judge whether the function of the power filter is normal or abnormal; after determining that there is no line-to-line, line-to-shell short circuit or capacitor breakdown inside the power filter, perform withstand voltage and insulation resistance tests on it; if it is determined that there is a line-to-line, line-to-shell short circuit or capacitor breakdown inside the power filter, the withstand voltage and insulation resistance tests are not performed on the power filter, but a DC resistance tester is used to test the line resistance value and line-to-ground resistance value of the power filter to determine the fault condition of the power filter, and finally complete the failure mode confirmation;

[0039] Step 2: Dismantle the power filter, including the following steps:

[0040] Step 2.1, open the cover: For the power filter with screw cover, directly use a screwdriver to unscrew the screws and remove the cover 1; for other cover structures, first fix the power filter on the milling machine, then use a milling cutter to mill around the cover 1 to remove the cover 1, such as Figure 2 and Figure 3 As shown;

[0041] Step 2.2, removing the outer shell 3: firstly grind the edges and corners of the outer shell 3 of the power filter after removing the cover plate 1 by a grinder (not shown in the figure), then peel off the epoxy resin from each surface of the outer shell 3, remove the outer shell 3, and obtain a potting component 4, wherein the potting component 4 includes the epoxy resin and the circuit component 5 placed in the epoxy resin;

[0042] Step 2.3, preheating: placing the potting component 4 in an oven (not shown in the figure) for preheating, the preheating temperature is 60° C., and the preheating time is 30 min-40 min;

[0043] Step 2.4, uniform heating: the oven is set to gradually heat up the preheated potting component 4 from low to high temperature sections and keep it warm, so that each temperature section in the oven is kept for a certain time. The oven is set to the following three temperature sections: 85°C, 110°C, 135°C, and the temperature is uniformly increased at a heating rate of 5°C / min, and each temperature section is kept for 10 minutes;

[0044] Step 2.5, take out and keep warm: take out the potting component 4 from the oven and place it on a heating table (not shown in the figure) for keeping warm. The temperature of the heating table is set to 135° C. and the temperature is kept continuously;

[0045] Step 2.6, local spot blowing: turn on the spot blowing device (not shown in the figure), and align the air outlet of the spot blowing device with the potting component 4 on the heating table for local heating;

[0046] Step 2.7, remove the epoxy resin in the spot blowing area: locally heat the epoxy resin in the spot blowing area, set the temperature of the spot blowing equipment to 160℃-200℃, and the air outlet of the spot blowing equipment heats the area for 10s-20s. After local heating, immediately use the special glue removal tool prepared in advance to pick out the epoxy resin in the area;

[0047] Step 2.8, repeating steps 2.6 and 2.7, spot-blowing other parts of the potting component 4 and removing the epoxy resin in the spot-blown parts until all the epoxy resin is removed, thereby obtaining the circuit component 5.

[0048] The circuit assembly 5 obtained by the above method is very complete without secondary damage, and the epoxy resin is completely removed, which is significantly beneficial to improving the accuracy of subsequent failure analysis. Compared with traditional methods, it is faster and more efficient and will not cause environmental pollution or harm the health of operators.

[0049] The above embodiments are only preferred embodiments of the present invention and are not limitations of the technical solutions of the present invention. Any technical solution that can be implemented on the basis of the above embodiments without creative work should be deemed to fall within the scope of protection of the patent of the present invention.

Claims

1. A failure mode confirmation and disassembly method for power filter failure analysis, characterized in that: The following steps are involved: Step 1, failure mode confirmation, the specific method is: first measure the continuity between the lines and the continuity between the lines and the shell of the power filter, and then test the line capacitance and its loss tangent value, the line-to-ground capacitance and its loss tangent value, so as to preliminarily judge whether the function of the power filter is normal or abnormal; after determining that there is no line-to-line short circuit, line-to-shell short circuit or capacitor breakdown inside the power filter, perform withstand voltage and insulation resistance tests on it; if it is determined that there is a line-to-line short circuit, line-to-shell short circuit or capacitor breakdown inside the power filter, the withstand voltage and insulation resistance tests are not performed on the power filter, but a DC resistance tester is used to test the line resistance value and line-to-ground resistance value of the power filter to determine the fault condition of the power filter, and finally complete the failure mode confirmation; Step 2: Dismantle the power filter, including the following steps: Step 2.1, open the cover: For the power filter with screw cover, directly use a screwdriver to unscrew the screws and remove the cover; for other cover structures, first fix the power filter on the milling machine, and then use a milling cutter to mill around the cover to remove the cover; Step 2.2, removing the outer shell: peeling off the outer shell of the power filter after removing the cover plate from the epoxy resin, removing the outer shell, and obtaining a potting component, wherein the potting component includes the epoxy resin and a circuit component placed in the epoxy resin; Step 2.3, preheating: placing the potting component in an oven for preheating; Step 2.4, uniform heating: set the oven to gradually heat up the preheated potting components and keep them warm, so that each temperature section in the oven is maintained for a certain period of time; Step 2.5, take out and keep warm: take out the potting component from the oven and place it on a heating table to keep warm; Step 2.6, local spot blowing: turn on the spot blowing device, and align the air outlet of the spot blowing device with the potting component on the heating table for local heating; Step 2.7, remove the epoxy resin at the spot blowing part: after locally heating the epoxy resin at the spot blowing part, immediately use the special glue removal tool prepared in advance to pick out the epoxy resin at that part; Step 2.8, repeat steps 2.6 and 2.7 to spot-blow other parts of the potting component and remove the epoxy resin in the spot-blow parts until all the epoxy resin is removed to obtain a circuit component.

2. The failure mode confirmation and disassembly method for power filter failure analysis according to claim 1 is characterized in that: In the step 2.2, the edges and corners of the shell are first ground off by a grinder, and then the epoxy resin is peeled off from each surface of the shell.

3. The failure mode confirmation and disassembly method for power filter failure analysis according to claim 1 is characterized in that: In the step 2.3, the preheating temperature is 60° C. and the preheating time is 30 min-40 min.

4. The failure mode confirmation and disassembly method for power filter failure analysis according to claim 1 is characterized in that: In step 2.4, the oven is set to the following three temperature sections: 85° C., 110° C., and 135° C., and the temperature is raised at a uniform rate of 5° C. / min, and each temperature section is maintained for 10 minutes.

5. The failure mode confirmation and disassembly method for power filter failure analysis according to claim 1, characterized in that: In step 2.5, the temperature of the heating stage is set to 135° C. and kept warm.

6. The failure mode confirmation and disassembly method for power filter failure analysis according to claim 1 is characterized in that: In the step 2.6, the temperature of the spot blowing device is set to 160° C.-200° C., and the local heating time of the air outlet of the spot blowing device is 10s-20s.

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