A method for evaluating the anti-sulfidation corrosion performance of conformal coating materials

Abstract

The present invention discloses a method for evaluating the anti-sulfidation corrosion performance of conformal coating materials, which belongs to the field of test and evaluation technology. The evaluation method includes the following steps: covering the first metal foil and the second metal foil on the same side surface of the test substrate under the same conditions, the first metal foil and the second metal foil are equal and spaced apart from each other; coating the surface of the first metal foil with conformal coating, and not coating the surface of the second metal foil with conformal coating; then, performing a sulfidation corrosion test on the sample substrate according to the preset sulfidation corrosion test method and test conditions; after the test is completed, evaluating the anti-sulfidation corrosion performance of the conformal coating material based on the blackened area of ​​the first metal foil and the second metal foil; the evaluation standard is: if the blackened area of ​​the first metal foil is smaller than the blackened area of ​​the second metal foil, it indicates that the conformal coating has an anti-sulfidation corrosion effect. This method can effectively qualitatively and quantitatively evaluate the anti-sulfidation corrosion performance of the conformal coating.

Description

Technical Field

[0001] The present invention relates to the field of testing and evaluation technology, and in particular to a method for evaluating the anti-sulfidation corrosion performance of a conformal coating material. Background Art

[0002] With the advancement of industrialization, environmental pollution has become increasingly serious. The burning of fossil fuels, ore smelting, and industrial waste gas emissions have led to a year-on-year increase in sulfur content in the air. Representative gases include hydrogen sulfide, sulfur dioxide, sulfur trioxide, carbon disulfide, and various sulfates. In combination with water and oxygen, sulfur-containing gases have a strong corrosive effect on active metals such as silver, copper, aluminum, iron, and zinc.

[0003] Printed circuit board assemblies are core components of electronic products and play an important role in aerospace, rail transportation, electric power, automotive electronics, industrial control, home appliances and other fields. As the service environment of electronic products becomes more complex and harsher, the probability of sulfide corrosion failure of printed circuit board assemblies has increased year by year, posing a serious threat to the service reliability of various electronic products. The accidents and losses caused by this are no longer uncommon.

[0004] Conformal coatings are used to coat printed circuit boards. After curing, they form a transparent polymer protective film on the surface of the PCB assembly, improving its resistance to moisture, salt spray, mold, and corrosive gases, thereby extending the service life of the PCB assembly. However, conformal coatings with different compositions, modification methods, and production processes vary significantly in their anti-sulfidation corrosion performance. Some conformal coatings may even accelerate corrosion of PCB assemblies by adsorbing sulfur-containing gases.

[0005] Therefore, it is necessary to evaluate the anti-sulfidation corrosion performance of conformal coatings to ensure the effectiveness of conformal coating applications, reduce the application risks of conformal coatings, and thus improve the service reliability of electronic products.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for evaluating the anti-sulfidation corrosion performance of conformal coating materials to solve the above technical problems.

[0008] This application can be implemented as follows:

[0009] The present application provides a method for evaluating the anti-sulfidation corrosion performance of a conformal coating material, comprising the following steps:

[0010] Covering the same side surface of the test substrate with a first metal foil and a second metal foil under the same conditions, wherein the first metal foil and the second metal foil are equal in size and spaced apart from each other;

[0011] A conformal coating is applied to a surface of the first metal foil, and no conformal coating is applied to a surface of the second metal foil;

[0012] Subsequently, a sulfidation corrosion test is conducted on the sample substrate according to the preset sulfidation corrosion test method and test conditions. After the test is completed, the anti-sulfidation corrosion performance of the conformal coating material is evaluated based on the blackened area of ​​the first metal foil and the second metal foil.

[0013] The evaluation criteria are: if the blackened area of ​​the first metal foil is smaller than the blackened area within the second metal foil, it indicates that the conformal coating has anti-sulfidation corrosion effect; if the blackened area of ​​the first metal foil is equal to the blackened area within the second metal foil, it indicates that the conformal coating does not have anti-sulfidation corrosion effect; and if the blackened area of ​​the first metal foil is larger than the blackened area within the second metal foil, it indicates that the conformal coating will accelerate sulfidation corrosion.

[0014] In an optional embodiment, the material of the test substrate is the same as that of the printed circuit board; and / or the material of the first metal foil and the second metal foil is a material that is easily corroded by sulfidation.

[0015] In an optional embodiment, the test substrate is made of glass fiber cloth reinforced epoxy resin; and / or the first metal foil and the second metal foil are made of silver or copper.

[0016] In an optional embodiment, a height difference between the first metal foil and the test substrate is less than 30 μm.

[0017] In an optional embodiment, the first metal foil is in a square, circular or rectangular shape.

[0018] In an optional embodiment, when the first metal foil is square, the side length of the first metal foil is 25-50 mm; when the first metal foil is circular, the diameter of the first metal foil is 25-50 mm.

[0019] In an optional embodiment, the edge of the first metal foil is 20-30 mm away from the edge of the test substrate.

[0020] In an optional embodiment, the distance between the first metal foil and the second metal foil is 20-30 mm.

[0021] In an alternative embodiment, the conformal coating completely covers the first metal foil and extends along the edge of the first metal foil to the surface of the test substrate.

[0022] In an alternative embodiment, the conformal coating extends a distance of 10-15 mm and the edge of the conformal coating on the test substrate after extension is spaced 5-10 mm from the edge of the test substrate.

[0023] In an optional embodiment, the thickness of the conformal coating after curing is 25-200 μm.

[0024] In an optional embodiment, the sulfidation corrosion test method includes:

[0025] When the product is in service under normal conditions, a sulfide corrosion test is conducted according to Method 1 of GB / T 2423.51 "Environmental testing for electrical and electronic components - Part 2: Test method Ke: Flowing mixed gas corrosion test" for a test duration of 96-336 hours.

[0026] When the product is in a harsh service environment, according to ASTM B809 "Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor ("Flowers-of-Sulfur")"

[0027] Sulfidation corrosion test is carried out at a test temperature of 50-85°C and a test time of 96-336h.

[0028] In an optional embodiment, the test substrate after the sulfide corrosion test is first conditioned at 21-25° C. for 4-8 hours, and then the anti-sulfide corrosion performance of the conformal coating material is evaluated based on the blackened area.

[0029] In an optional embodiment, the method for calculating the blackened area includes a grid method or a software method.

[0030] In an alternative embodiment, the software method includes Image-ProPlus or Photoshop.

[0031] The beneficial effects of this application include:

[0032] This application covers the first and second metal foils set at intervals on the same side surface of the test substrate under the same conditions, and coats the surface of the first metal foil with a conformal coating, while the surface of the second metal foil is not coated with a conformal coating; then, a sulfide corrosion test is performed on the sample substrate according to a preset sulfide corrosion test method and test conditions; and the anti-sulfide corrosion performance of the conformal coating material is evaluated based on the blackened area of ​​the two metal foils.

[0033] This method is simple and easy to operate, and can effectively qualitatively and quantitatively evaluate the anti-sulfidation corrosion performance of conformal coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 Schematic diagram of the coating effect when the height difference between the metal foil and the resin substrate is too large;

[0036] Figure 2 Schematic diagram of the coating effect corresponding to a moderate height difference between the metal foil and the resin substrate;

[0037] Figure 3 This is a schematic diagram of the penetration path of sulfide corrosive gas on the printed circuit board;

[0038] Figure 4 For test products Figure 3 The middle penetration path ① is the corrosion morphology corresponding to the penetration path;

[0039] Figure 5 For test products Figure 3 The middle penetration path ② is the corrosion morphology corresponding to the penetration path;

[0040] Figure 6 For the test product Figure 3 The penetration paths ① and ② in the middle are the corrosion morphologies corresponding to the penetration paths;

[0041] Figure 7 This is a schematic diagram of the appearance of a test substrate with a metal foil coated on its surface in an embodiment of the present application;

[0042] Figure 8 This is a schematic diagram of the appearance of a test substrate after being coated with a conformal coating in an embodiment of the present application;

[0043] Figure 9 This is a schematic diagram of the sulfidation corrosion area calculation process in the embodiment of this application;

[0044] Figure 10 This is a diagram showing the blackening results of each copper foil after sulfidation corrosion in the examples of this application;

[0045] Figure 11 This is the coating result diagram corresponding to the printed circuit board in Test Example 1 of this application;

[0046] Figure 12 This is the coating result diagram corresponding to the non-printed circuit board in Test Example 1 of this application;

[0047] Figure 13This is the sulfidation corrosion result diagram corresponding to the tinned pad in Test Example 2 of this application;

[0048] Figure 14 This is the sulfidation corrosion result diagram corresponding to the silver-plated pad in Test Example 2 of this application;

[0049] Figure 15 This is the sulfidation corrosion result diagram corresponding to the gold finger in Test Example 2 of this application;

[0050] Figure 16 This is the sulfidation corrosion result diagram corresponding to the copper pad in Test Example 2 of this application;

[0051] Figure 17 This is the sulfidation corrosion result diagram corresponding to the thickness difference between the metal foil and the test substrate of Test Example 3 of this application being 30 μm;

[0052] Figure 18 This is a graph showing the sulfidation corrosion results corresponding to a thickness difference of 35 μm between the metal foil and the test substrate in Test Example 3 of this application.

[0053] Icons: 11 - first metal foil; 12 - second metal foil; 2 - test substrate; 3 - conformal coating. DETAILED DESCRIPTION

[0054] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0055] The following is a detailed description of the evaluation method for the anti-sulfidation corrosion performance of the conformal coating material provided in this application.

[0056] This application proposes a method for evaluating the anti-sulfidation corrosion performance of conformal coating materials, comprising the following steps:

[0057] The first metal foil and the second metal foil are covered on the same side surface of the test substrate under the same conditions. The first metal foil and the second metal foil are equal and spaced apart from each other.

[0058] A conformal coating is applied to a surface of the first metal foil, and no conformal coating is applied to a surface of the second metal foil;

[0059] Subsequently, a sulfidation corrosion test is conducted on the sample substrate according to the preset sulfidation corrosion test method and test conditions. After the test is completed, the anti-sulfidation corrosion performance of the conformal coating material is evaluated based on the blackened area of ​​the first metal foil and the second metal foil.

[0060] The evaluation criteria are: if the blackened area of ​​the first metal foil is smaller than the blackened area within the second metal foil, it indicates that the conformal coating has anti-sulfidation corrosion effect; if the blackened area of ​​the first metal foil is equal to the blackened area within the second metal foil, it indicates that the conformal coating does not have anti-sulfidation corrosion effect; and if the blackened area of ​​the first metal foil is larger than the blackened area within the second metal foil, it indicates that the conformal coating will accelerate sulfidation corrosion.

[0061] For reference, the material of the test substrate is the same as that of the printed circuit board, specifically, glass fiber cloth reinforced epoxy resin.

[0062] Glass fiber cloth reinforced epoxy resin is a commonly used material for printed circuit boards. Conformal coating materials on the market are basically developed specifically for this material and have high adhesion and low thermal expansion coefficient for this material. Using other materials as substrates will affect the adhesion of the coating. Under test conditions, the coating may delaminate, bubble, or fall off, resulting in inaccurate test results.

[0063] The material of the first metal foil (the second metal foil) is a material that is easily corroded by sulfidation, and can be copper, gold, silver or tin by way of example but not limitation, preferably silver or copper.

[0064] Among the materials susceptible to sulfidation corrosion, copper and silver are particularly sensitive to sulfur. PCB assembly failures often occur due to corrosion of copper pads, copper pins, silver pads, and silver electrodes, generating copper and silver sulfides. Gold and tin, on the other hand, are less susceptible to sulfur corrosion. Using copper and silver foil as the test metals offers greater specificity and effectiveness.

[0065] It should be noted that the second metal foil is the same as the first metal foil in terms of material, shape, size and covering thickness. It can be understood that the second metal foil is mainly provided for comparison with the first metal foil.

[0066] The main reason for the need for a control is that some conformal coatings adsorb sulfur-containing gases, and applying these coatings can actually accelerate sulfidation corrosion of printed circuit board components. Without a control, it's impossible to determine after the test whether the coating is effective or harmful—in other words, it's impossible to determine if the conformal coating material has a negative effect.

[0067] Preferably, the first metal foil (the second metal foil) has a regular shape, such as a square, a circle or a rectangle.

[0068] In the present application, the height difference between the first metal foil and the test substrate is less than 30 μm, such as 30 μm, 25 μm, 20 μm, 15 μm, 10 μm, or 5 μm. Accordingly, the thickness of the conformal coating after curing is 25-200 μm, such as 25 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, or 200 μm.

[0069] It should be noted that if the height difference between the metal foil and the resin substrate is too large, the side of the metal foil will be missing or the coating thickness will be insufficient during the coating process (e.g. Figure 1 As shown), at the same time, due to the stress concentration at the edge of the metal foil, the thin coating is prone to cracking during the curing shrinkage process, thereby affecting the test results. Coating according to the height difference of this application can obtain a good and uniform coating effect. (As shown Figure 2 shown).

[0070] For reference, when the first metal foil (second metal foil) is square, the side length of the first metal foil (second metal foil) can be 25-50mm, such as 25mm, 30mm, 35mm, 40mm, 45mm or 50mm, etc.; when the first metal foil (second metal foil) is round, the diameter of the first metal foil (second metal foil) is 25-50mm, such as 25mm, 30mm, 35mm, 40mm, 45mm or 50mm, etc.

[0071] The edge of the first metal foil (the second metal foil) is 20-30 mm away from the edge of the test substrate, such as 20 mm, 22 mm, 25 mm, 28 mm or 30 mm.

[0072] The distance between the first metal foil and the second metal foil may be 20-30 mm, such as 20 mm, 22 mm, 25 mm, 28 mm or 30 mm.

[0073] In the present application, the conformal coating completely covers the first metal foil and extends along the edge of the first metal foil to the surface of the test substrate.

[0074] Exemplarily, the conformal coating extends a distance of 10-15 mm (e.g., 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, or 15 mm, etc.) and after extension, the edge of the conformal coating on the test substrate is spaced 5-10 mm (e.g., 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm, etc.) from the edge of the test substrate.

[0075] That is, the conformal coating completely covers the first metal foil and extends 10-15 mm beyond each edge of the metal foil, and a gap of 5-10 mm is left between the edge of the coating and the edge of the test substrate.

[0076] It should be noted that the reasons why the coating is completely covered and extends 10-15 mm beyond the edge of the metal foil in this application include: sulfide corrosive gas has the following two main penetration pathways on the printed circuit board (such as Figure 3 (as shown): ① directly through the coating, ② through the interface between the coating and the substrate.

[0077] Different penetration paths correspond to different corrosion morphologies. Taking the same test product as an example, the corrosion morphology based on penetration path ① is as follows: Figure 4 As shown in Figure 2, the corrosion morphology mainly based on the penetration path ② is as follows: Figure 5 As shown in the figure, the corrosion morphology of the coexistence of permeation path ① and permeation path ② is as follows Figure 6 shown.

[0078] It can be seen from this that both the individual permeation path ① and the permeation path ② will lead to inaccurate results. Only by following the coverage method provided in this application so that the permeation path includes both the permeation path ① and the permeation path ② can the results be accurate.

[0079] The coating method provided in this application can better examine the influence of the above two penetration paths, which has guiding significance for the coating process design of the product. For example, the penetration path ① can be improved by increasing the coating thickness, and the penetration path ② can be improved by increasing the continuity of the spraying.

[0080] After applying the conformal coating, the coating quality is inspected.

[0081] For example, the coating quality of the test substrate surface can be observed macroscopically and microscopically to ensure that the coating completely and evenly covers the test substrate surface without bubbles, pinholes, delamination, coating defects, etc. For materials with added fluorescent indicators, observation can be performed under fluorescent light.

[0082] Furthermore, a sulfidation corrosion test was performed.

[0083] For reference, the sulfide corrosion test method may include:

[0084] When the product is in service under normal conditions, the sulfide corrosion test is carried out according to Method 1 of GB / T 2423.51 "Environmental testing for electrical and electronic components - Part 2: Test method Ke: Flowing mixed gas corrosion test", and the test duration can be 96-336 hours.

[0085] When the product is in service in harsh conditions, a sulfide corrosion test is performed according to ASTM B809 "Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor ("Flowers-of-Sulfur")". The test temperature can be 50-85°C and the test time can be 96-336 hours.

[0086] It should be noted that the test temperature specified in ASTM B809 is 50°C. However, actual measurements show that increasing temperature and humidity during testing increase the concentration of sulfides and the corrosion intensity. At high temperatures, thermal expansion increases the gap between the coating and the substrate, making it easier for the sulfur-containing atmosphere to corrode the metal foil through the interface between the coating and the substrate, which is inconsistent with the corrosion conditions under actual application conditions. 85°C is the maximum temperature for the damp heat test, which meets the requirements of accelerating the test process while not changing the corrosion mechanism. In this application, the test temperature corresponding to the harsh service environment of the product is set to 50-85°C to ensure accurate results.

[0087] In this application, the blackened area of ​​the test substrate after the sulfide corrosion test is completed can be directly calculated, or it can be conditioned at 21-25°C for 4-8 hours and then the anti-sulfide corrosion performance of the conformal coating material can be evaluated based on the blackened area.

[0088] It should be noted that after the high temperature test, the shape and size of the coating will change. By adjusting it at 21-25℃ for 4-8 hours, the shape and size of the corresponding coating can be restored.

[0089] Specifically, after the test is completed, the test substrate is placed at 21-25℃ for 4-8 hours, and then the metal foil is photographed. The proportion of the blackened area of ​​the copper foil photo is calculated. The calculation method can use the grid method or software method (the grid method is to divide the metal foil area on the picture into sufficiently small square grids, and the blackened area of ​​the metal foil is obtained by calculating the proportion of the blackened grids to the total grids. The software method is to use software such as Image-ProPlus or Photoshop to distinguish the colors of the blackened position and the non-blackened position to intelligently calculate the blackening proportion of the metal foil).

[0090] In this application, the evaluation of test results is divided into the following situations:

[0091] ① The blackened area of ​​the first metal foil coated with the conformal coating is less than the blackened area of ​​the second metal foil not coated with the conformal coating, indicating that the conformal coating has an anti-sulfidation corrosion effect.

[0092] The acceptability of the blackened area of ​​the first metal foil coated with the conformal coating is determined by the specific test method, test duration, and material application requirements. Generally speaking, if the blackened area of ​​the first metal foil coated with the conformal coating is less than 5% of the area of ​​the first metal foil, the conformal coating is considered to have excellent anti-sulfidation corrosion performance. If the blackened area of ​​the first metal foil is between 5% (inclusive) and 10%, the conformal coating is considered to have good anti-sulfidation corrosion performance; if the blackened area of ​​the first metal foil is between 10% (inclusive) and 20%, the conformal coating is considered to have average anti-sulfidation corrosion performance; if the blackened area of ​​the first metal foil is greater than 20%, the conformal coating is considered to have poor anti-sulfidation corrosion performance.

[0093] ② The blackened area of ​​the first metal foil coated with conformal coating = the blackened area of ​​the second metal foil not coated with conformal coating (it can also be understood that the blackened areas of the two are equivalent), indicating that the conformal coating does not have anti-sulfidation corrosion performance, that is, there is no practical significance in using this conformal coating material for anti-sulfidation corrosion protection.

[0094] ③ The blackened area of ​​the first metal foil coated with conformal coating is greater than the blackened area of ​​the second metal foil not coated with conformal coating, indicating that the conformal coating has an adsorption effect on sulfur-containing gas, and coating with this material will accelerate sulfidation corrosion.

[0095] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0096] Example

[0097] A company's key printed circuit board components experienced sulfidation corrosion during field service, leading to product failure. To improve product reliability, they decided to replace the product with a conformal coating with improved sulfidation corrosion resistance. They selected three domestically produced conformal coatings. The selection process for each conformal coating was the same, as follows:

[0098] (1) Preparation of test substrate 2. A glass fiber cloth reinforced epoxy resin substrate was used, and two square copper foils (first metal foil 11 and second metal foil 12) were covered on the surface. The height difference between each copper foil and the resin substrate was 10 μm, the edge of each copper foil was 20 mm from the edge of the substrate, and the distance between the two copper foils was 20 mm. The appearance diagram is shown in the figure below. Figure 7 shown.

[0099] Where a is the distance between the edge of the copper foil and the edge of the substrate, and b is the distance between the two pieces of copper foil.

[0100] (2) Coating and curing. The conformal coating 3 is applied to the left copper foil of the test substrate 2. The coating completely covers the copper foil and exceeds the edges of the metal foil by 10 mm. A distance of 10 mm is left between the edge of the coating coverage area and the edge of the test substrate 2. The right copper foil is not coated. The coating thickness is 100 μm. Then, the conformal coating 3 on the test substrate 2 is cured according to the curing conditions provided by the manufacturer. The appearance diagram is shown in FIG. Figure 8 shown.

[0101] Wherein, c is the distance that the conformal coating 3 exceeds the edge of the metal foil, and d is the distance between the edge of the coating coverage area and the edge of the test substrate.

[0102] (3) Coating quality inspection: Check the coating quality under a microscope to ensure that the coating completely and evenly covers the surface of the test substrate 2 without any bubbles, pinholes, delamination, coating defects, etc.

[0103] (4) Sulfidation corrosion test. Since conformal coating 3 is used in key components of the product with high reliability requirements and a harsh service environment, the sulfidation corrosion test was conducted using ASTM B809 "Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor ("Flowers-of-Sulfur")" with a test temperature of 85°C and a test duration of 168 hours.

[0104] (5) Calculation of sulfidation corrosion area. After the test is completed, the test substrate 2 is placed at 23±2℃ for 6 hours, and then the copper foil is photographed. The blackened area on the copper foil photograph is calculated using Image-ProPlus software.

[0105] Calculation example: Figure 9 As shown, Figure 9 The left picture is the original picture, the middle picture is the black area filling situation, and the right picture is the black area calculation form.

[0106] The calculation results are as follows Figure 10 As shown. Among them, Figure 10 The upper left corner corresponds to the blackening of the copper foil coated with conformal coating A, and the specific blackening area is 0%; Figure 10 The upper right corner corresponds to the blackening of the copper foil coated with conformal coating B, with a specific blackening area of ​​85%; Figure 10 The lower left corner corresponds to the blackening of the copper foil coated with conformal coating C, with a specific blackening area of ​​11%; Figure 10 The lower right corner corresponds to the blackening of the copper foil without any conformal coating, and the specific blackening area is 100%.

[0107] (6) Evaluation of anti-sulfurization corrosion performance.

[0108] The blackened area of ​​the copper foil coated with conformal coating A is 0%, indicating that conformal coating A can effectively block sulfide corrosion gas and has good anti-sulfide corrosion performance; the blackened area of ​​the copper foil coated with conformal coating B exceeds 20%, indicating that conformal coating B cannot effectively block sulfide corrosion gas and has poor anti-sulfide corrosion performance; the blackened area of ​​the copper foil coated with conformal coating C is between 10-20%, indicating that the anti-sulfide corrosion performance of conformal coating C is average.

[0109] As above, conformal coating A is used to replace the original coating.

[0110] After actual testing, after the original coating was replaced with conformal coating A, the above-mentioned key printed circuit board components did not suffer from sulfide corrosion under field service conditions, indicating that the method provided in this application is effective and feasible.

[0111] Test Example 1

[0112] The purpose of this test example is to demonstrate the effect of different test substrate materials on the coating after sulfidation corrosion testing.

[0113] The test was conducted on printed circuit boards and non-printed circuit boards. Each circuit board was coated with the same coating under the same conditions. After the same sulfide corrosion test, the test conditions were referred to the examples. The coating conditions were as follows: Figure 11 and Figure 12 shown.

[0114] Figure 11 Shows: The coating applied on the printed circuit board is in good condition after the sulfidation corrosion test; Figure 12 Shows: The coating applied on a non-printed circuit board delaminated and fell off after the sulfidation corrosion test.

[0115] This proves that the material of the test substrate is different from that of the printed circuit board, which will lead to inaccurate results.

[0116] Test Example 2

[0117] The purpose of this test example is to demonstrate the effect of different metal foil materials on the coating after sulfidation corrosion testing.

[0118] Taking tinned pads, silver-plated pads, gold fingers and copper pads as examples, after the same sulfide corrosion test, their appearance photos are as follows: Figures 13 to 16 shown.

[0119] Figure 13 Display: There is no obvious change in the solder pad after the sulfidation corrosion test of the tinned solder pad; Figure 14 Display: The silver-plated pad turns black after the sulfide corrosion test; Figure 15 Display: There is no obvious change after the gold finger sulfide corrosion test; Figure 16Display: Copper pad resistor turns black after sulfidation corrosion test.

[0120] This proves that among the materials of metal foil, gold, tin, etc. are not sensitive to sulfur and are not easily corroded; using copper and silver foil as the tested metals is targeted and effective.

[0121] Test Example 3

[0122] The purpose of this test example is to demonstrate the effect of the thickness difference between the metal foil and the test substrate on the coating after the sulfidation corrosion test.

[0123] Taking the thickness difference of 30μm and 35μm as an example, the metal foil was coated with polyurethane conformal coating with a spray thickness of 25μm (the lower limit of spray thickness in the industry), and then the sulfide corrosion test was carried out according to ASTM B809, the test temperature was 85℃, and the test time was 168h. After the sulfide corrosion test, the appearance photos are as follows Figures 17 and 18 shown.

[0124] Figure 17 Display: The copper foil with a height difference of 30μm has no corrosion or blackening phenomenon; Figure 18 Display: The copper foil with a height difference of 35μm appears black at the edge.

[0125] This proves that when the height difference is 35μm, there are defects in the coating quality at the edge position, which leads to abnormal test results.

[0126] In summary, the method provided in this application can effectively qualitatively and quantitatively evaluate the anti-sulfidation corrosion performance of conformal coatings.

[0127] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for evaluating the anti-sulfidation corrosion performance of conformal coating materials, characterized in that: The following steps are involved: Covering the same side surface of the test substrate with a first metal foil and a second metal foil under the same conditions, wherein the first metal foil and the second metal foil are equal in size and spaced apart from each other; Coating a conformal coating on a surface of the first metal foil, while not coating a conformal coating on a surface of the second metal foil; Subsequently, a sulfide corrosion test is performed on the sample substrate according to the preset sulfide corrosion test method and test conditions; After the test is completed, the anti-sulfidation corrosion performance of the conformal coating material is evaluated based on the blackened areas of the first metal foil and the second metal foil; The evaluation criteria are: if the blackened area of ​​the first metal foil is smaller than the blackened area within the second metal foil, it indicates that the conformal coating has an anti-sulfidation corrosion effect; if the blackened area of ​​the first metal foil is equal to the blackened area within the second metal foil, it indicates that the conformal coating does not have an anti-sulfidation corrosion effect; and if the blackened area of ​​the first metal foil is larger than the blackened area within the second metal foil, it indicates that the conformal coating will accelerate sulfidation corrosion. The material of the test substrate is glass fiber cloth reinforced epoxy resin; the material of the first metal foil and the second metal foil is silver or copper; The height difference between the first metal foil and the test substrate is less than 30 μm; The conformal coating completely covers the first metal foil and extends along the edge of the first metal foil to the surface of the test substrate; the conformal coating extends a distance of 10-15 mm, and after extension, the edge of the conformal coating on the test substrate is spaced 5-10 mm from the edge of the test substrate; Sulfidation corrosion test methods include: When the product is in service under normal conditions, a sulfide corrosion test is conducted according to Method 1 of GB / T 2423.51 "Environmental testing for electrical and electronic components - Part 2: Test method Ke: Flowing mixed gas corrosion test" for a test duration of 96-336 hours. When the product is in service in harsh conditions, the sulfide corrosion test is carried out according to ASTM B809 "Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor ("Flowers-of-Sulfur")", with a test temperature of 50-85°C and a test time of 96-336 hours.

2. The evaluation method according to claim 1, wherein The shape of the first metal foil is square, circular or rectangular.

3. The evaluation method according to claim 2, wherein: When the first metal foil is square, the side length of the first metal foil is 25-50 mm; when the first metal foil is circular, the diameter of the first metal foil is 25-50 mm.

4. The evaluation method according to claim 1, wherein: The edge of the first metal foil is 20-30 mm away from the edge of the test substrate.

5. The evaluation method according to claim 1, wherein: The distance between the first metal foil and the second metal foil is 20-30 mm.

6. The evaluation method according to claim 1, wherein: The thickness of the conformal coating after curing is 25-200 μm.

7. The evaluation method according to claim 1, wherein: After the sulfide corrosion test, the test substrate is first placed at 21-25°C for 4-8 hours, and then the anti-sulfide corrosion performance of the conformal coating material is evaluated based on the blackened area.

8. The evaluation method according to claim 7, wherein: Methods for calculating the blackened area include a grid method or a software method.

9. The evaluation method according to claim 8, characterized in that The software method includes Image-ProPlus or Photoshop.

Images