CN111103017A - Method for rapidly verifying three-proofing coating performance of circuit board assembly - Google Patents
Method for rapidly verifying three-proofing coating performance of circuit board assembly Download PDFInfo
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Abstract
The invention discloses a method for rapidly verifying three-proofing coating performance of a printed circuit board assembly, and aims to solve the problems of multiple sample pieces, high cost, long verification period and the like in the performance verification of a three-proofing coating of a printed circuit board. The invention is realized by the following technical scheme: manufacturing an integrated verification printed circuit board for coating three-proofing paint and a low-noise amplifier circuit component for evaluating the influence degree of the three-proofing paint on a circuit; then verifying the three-proofing capability of the integrated spraying process, the coating thickness test, the coating adhesion test, the insulation resistance test, the medium voltage withstanding test, the test gain, the standing wave and the welding spot; evaluating the quality of the performance of the coating by using the test result; after carrying out damp-heat, salt spray and mould test tests, detecting the appearance state, verifying the protection capability of the coating, testing the insulation resistance and medium voltage resistance, and verifying the moisture resistance of the three-proofing coating; and inputting the change conditions of the standing-wave ratio and the output standing-wave ratio, performing comparative test, evaluating the influence degree of the three-proofing coating on the circuit, and making a test conclusion.
Description
Technical Field
The invention relates to a method for quickly verifying performance of a three-proofing coating for a printed circuit board.
Background
With the progress and development of the scientific and technological era, particularly, the electronic industry has more and more products, more and more powerful performance and higher and more product requirements. Printed circuit board assemblies, which are important electronic components for electronic equipment, are required to have good electrical parameter properties and corrosion resistance. The protective performance of the PCB circuit board assembly directly affects the electrical performance of the system, particularly, electronic equipment working in severe environment conditions such as the field, the sea, the aviation and the like is used for a period of time, and system faults are often caused by the fact that the surface of the PCB circuit board assembly is not protected in place, such as high humidity and heat, high salt fog and easy corrosion, and ignition is easy to happen under the conditions of airborne high altitude and low pressure, so that the normal work of the whole electronic system is greatly affected. Circuit board assemblies are made by integrating various materials, salt spray, sand, fuel, acid, and other corrosive vapors and mold can cause electronic decay, conductor corrosion, and irreparable short circuits. In the use environment of modern electronic equipment, the corrosion of moisture, salt fog and mold to the electronic equipment is common, and the weather factor and the environmental condition both affect each other and act simultaneously, thus accelerating the damage to equipment and equipment, wherein the moisture is the most common and destructive main factor to the circuit board assembly. Excessive moisture can significantly reduce the insulation resistance between conductors of electronic products, accelerate decomposition of organic materials, reduce Q-factor, and corrode conductors. We often see that the metal part of the PCB is caused by the chemical reaction of copper, water vapor and oxygen which are not coated with three-proofing paint. Since electronic products often experience environments such as high temperature, vibration, humidity, salt fog, dust and the like, the circuit board and electronic components thereof may have problems such as corrosion, cracking, deformation, mildew and the like, resulting in product failure or invalidation. Particularly, electronic products working outdoors and at sea need to adapt to severe environments such as damp heat, mold, salt mist and the like, the reliability requirement is high, and if the printed circuit board is required to work normally, three-proofing coating is required to be carried out on the printed circuit board. In order to solve the quality problem caused by poor air-proof protection performance of the whole electronic product and the printed circuit board, the electronic product can resist the erosion of the external environment, prolong the service life, increase the mechanical strength and the reliability, and prevent the leakage short circuit and even breakdown between the printed wires when the air temperature suddenly changes to generate condensation, a layer of synthetic resin or polymer protective coating needs to be coated on the surface of the printed circuit board.
Three-proofing paint, also called electronic moisture-proof glue or three-proofing glue protective Coating, is called Conformal Coating in English. Three proofings, namely mildew resistance, moisture resistance and salt mist resistance, are mainly used for preventing corrosion. The three-proofing paint is a special coating coated on the surface of a circuit board, is a popular name, and has the effects of resisting vibration, insulating, reducing the design size of the circuit board and the like besides resisting mildew, moisture and salt mist.
The three-proofing paint is coated on the surface of a printed circuit board component and used for isolating a circuit from a severe environment and preventing the circuit from being influenced by the severe environment, so that the circuit is protected from environmental erosion, faults such as circuit failure, electric leakage and the like are caused, and the service life of an electronic product is prolonged. Under practical conditions, the circuit board is often subjected to corrosion from harsh environments and working conditions, such as chemical, vibration, high-dust, salt mist, humidity, high temperature and other environments, so that various faults occur in the circuit of the circuit board, such as fracture open circuit failure, corrosion failure, electromigration failure, insulation failure, component failure and the like. The circuit board is coated with a layer of conformal coating with a protection effect, so that the printed circuit board and electronic devices thereof can be effectively isolated from the working environment, the circuit is protected from being damaged, the reliability of the circuit board is improved, the safety coefficient of the circuit board is increased, the service life of the circuit board is ensured, in addition, the conformal coating is insulating, the electric leakage can be prevented to a certain extent, the product is allowed to have higher power and closer distance between the printed boards, and the purpose of miniaturization of elements can be met.
The three-proofing paint can be divided into five major classes of acrylic resin (acrylic type ar), epoxy resin (epoxy type er), silicone (silicone type sr), polyurethane (urethane type ur) and parylene (parylene type xy) from the chemical composition. The solvent-containing acrylic resin three-proofing paint has the advantages that the curing process is relatively simple, the paint does not react with air, and the curing is carried out by volatilization of the solvent; the moisture-proof effect is good, and the viscosity adjustment is flexible; rework is also easier; the cost is also relatively low. But the protective layer is too thin after being cured, the content of the volatile solvent is very high due to the curing mode, and the working environment needs to have a good ventilation system; viscosity maintenance is difficult, and there is a case of tack-back under high temperature and high humidity. The three-proofing paint can be used for common electronic products.
The epoxy resin three-proofing paint has good moisture resistance, salt mist resistance and chemical resistance, can resist high temperature of 150 ℃, is wear-resistant and has good dielectric property. However, the epoxy resin film is difficult to repair, and the epoxy resin film must be removed by physical means before the epoxy resin film is repaired, which may damage the devices and the board cards. In addition, the potential high internal stress of the coating can damage the fragile elements, and the fragile elements need to be protected before coating; has a higher risk of chloride ion content; the double components are complex in proportion, and the viscosity is not doubt maintained; the performance is not good at low temperature and the curing shrinkage rate is high. Such three-proofing paints are not used in many applications.
The organic silicon three-proofing paint is a coating material with soft elasticity and good flexibility; the working temperature range is wide, the high temperature of 200 ℃ can be resisted, and the moisture-proof and ultraviolet-resistant performances are good; the repair is easy; and has remarkable electrical insulation property, lower surface energy and good wettability with the base material. But the mechanical strength is low, the scratch resistance is not good, and the adhesion with the substrate is poor. The three-proofing paint is suitable for high-heating elements, such as high-power high-frequency circuit boards with more resistors, and can be applied to aviation, navigation, military industry and radar control systems.
The polyurethane three-proofing paint is one of the solvent-based three-proofing paints which is commonly used, and is also called polyurethane alkyd resin three-proofing paint. The main curing principle is that the coating is cured by chemical reaction with oxygen in the air, and the formed polymer coating has good acid resistance, alkali resistance and excellent moisture resistance. But the complete curing process is longer, the VOC content is higher, the yellowing is easy at high temperature, and the galvanized screw is easy to corrode. The three-proofing paint is widely applied at present, and can be applied to industries such as automobile industry, industrial control electronic instruments and meters, power communication and the like.
The poly-p-xylene three-proofing paint is used for cracking the polymer in vacuum and depositing on the surface of a product to form a uniform coating, and can be used as a special protective coating in the electronic field. The micron film deposited in vacuum has uniform thickness, excellent acid resistance and corrosion resistance, is the most effective protective coating material for high-frequency elements, high-density assemblies and high-insulation assemblies at present, has the ageing resistance of more than thousand years at normal temperature, and is widely applied to the fields of aerospace, precious cultural relics, silicon rubber, sealing elements, magnetic materials, microelectronics, sensors, biological hospitals and the like. The investment in expensive vacuum coating equipment is also its greatest disadvantage.
In general, a three-proofing coating for coating should have the following characteristics: the paint has the characteristics of water resistance, moisture resistance, dust prevention, acid, alkali and alcohol corrosion resistance, mildew resistance, aging resistance and the like; the protective film has good adhesion and flexibility to printed circuit boards and components, can generate compact protective films on the surfaces of various printed circuit boards, component packaging materials, metal and nonmetal materials and welding spots, and can not cause the surfaces of the printed circuit boards, metal coatings, welding fluxes and the components to discolor, wrinkle and corrode. Good electrical properties (higher volume resistivity, lower dielectric constant and loss tangent, etc.); has good physical and mechanical properties (adhesive force, heat resistance and the like). The coating should be polymeric to reduce pinholes upon solvent evaporation. The curing temperature of the coating is low, and the cured coating is colorless and transparent; it should have good workability and fast curing speed.
Because important electronic components need to have good corrosion resistance and electrical parameter performance, the protective performance of a circuit board assembly directly influences the electrical performance of the whole circuit system, particularly electronic equipment working under severe conditions of field, spaceflight, navigation and the like, after the circuit board assembly is used for a period of time, system faults are often caused due to the fact that the surface protection of the circuit board assembly has problems, such as the problems of easy corrosion under high salt spray, high humidity and heat and high impact vibration and easy ignition under low air pressure conditions of airborne high altitude, and the like, so that the normal work of the whole electronic system is greatly influenced. The three-proofing paint has various types, and the quality of the three-proofing paint directly influences the three-proofing protection effect of the electronic component and the reliability of an electronic product. The performance of three-proofing coatings has been the focus of research by process designers. The general research method is to adopt a certain coating process to manufacture a process sample piece, apply the existing environmental test method to verify the three-proofing performance, and judge the quality of the three-proofing performance of the coating according to certain characteristic parameters. The research method has a certain screening effect on the performance of the protective coating, but the performance test methods only aim at single performance, for example, the influence of thickness on the protective coating is not considered, and simultaneously, different standards have different requirements on sample pieces. Generally, the verification test of the three-proofing performance of the protective coating of the printed circuit board still does not form a universal method, and the execution is difficult to balance. When the three-proofing coating is authenticated, various performance parameter indexes are generally required to be tested, and if the adopted test standards are different, the verification result has larger uncertainty. Aiming at the three-proofing performance verification of the protective coating, most standards only specify a damp-heat test method, and the method requirements are different. If the three-proofing performance of the protective coating of the printed circuit board is verified and optimized, the method specified by the existing standard is scattered and not uniform, different sample pieces need to be prepared for different performances, the manufacturing period is long, the relevance of different performance tests is poor, the influence of comprehensive factors on the performance of the coating cannot be reflected, and the practicability and accuracy of the result are poor.
In many cases of failure of printed wiring board components subjected to three-proofing protection, the failure of performance degradation and corrosion or cracking and the like due to mismatch of three-proofing coatings and other materials is very large. When the general three-proofing coating is used for surface protection of a printed circuit board assembly with higher working frequency, performance deterioration of devices can be caused, and phenomena that the actual performance of the system is greatly different from the original design, such as central frequency deviation, phase noise increase and the like, can occur. It has been found from previous studies that organic materials such as surface protective coatings are generally susceptible to aging and metallic materials are susceptible to rusting in hot and humid environments, mold environments, and salt spray environments. The realization of the functional performance index of the product is seriously influenced. Various standards are established abroad for printed circuit boards, and some standards specify damp heat, mould and salt spray test methods. Firstly, a standard test sample needs to be prepared, and then a proper test method is adopted to carry out test assessment. Under the condition that no specific three-proofing environmental test standard of a printed circuit board coating exists at home and abroad, circuit components of some products are often selected for electrical performance verification in the traditional electrical performance verification, and the test result difference is large due to different process parameters such as the formula, the spraying frequency, the spraying thickness, the baking temperature and the like of the coating. In actual evaluation, the type and conditions of an environmental test are generally selected according to the working conditions of the component product, including various environments such as damp heat, salt mist, high and low temperature, vibration, industrial gas and the like, and then the compatibility is evaluated by testing whether the coating performance and the electrical performance of the circuit board component are reduced before and after the environmental test and whether the component under the coating is corroded. However, the method has the defects of insufficient verification coverage, high verification cost, long verification period and the like. Only after strict test and authentication and optimization, the coating material with good protection performance can be selected, and the reliability of the product is improved.
Disclosure of Invention
Aiming at solving the actual performance indexes of various conformal coatings for the complete machine of electronic products and the three proofings of printed circuit boards, the invention provides a method which is simple, convenient, efficient, stable and reliable in quality and can quickly verify the performance of the three proofings coating for the circuit boards, aiming at solving the problems of more performance verification and preferable manufacturing samples, high verification cost, long verification period and the like of the three proofings coating of the current printed circuit board.
The above object of the present invention can be achieved by the following steps: a method for rapidly verifying the performance of three-proofing paint of a printed circuit board assembly is characterized by comprising the following technical steps: firstly, designing and manufacturing an integrated verification printed circuit board for three-proofing paint coating and a low-noise amplifier circuit component for evaluating the influence degree of three-proofing paint on a circuit, and dividing the integrated verification printed circuit board into four parts: the testing device comprises a comb circuit used for testing insulation resistance, a Y-shaped circuit used for testing dielectric withstand voltage and breakdown voltage, eight square copper-clad graphs used for thickness measurement and two rows of bonding pads used for verifying three-proofing performance of welding spots; then, carrying out integrated spraying process verification, coating thickness test, coating adhesion test, insulation resistance test, medium voltage resistance test, gain test, standing wave test and three-proofing capability of a welding spot on a sample piece; in the verification integrated spraying process, the manufacturability is verified according to the film forming condition of the coating in the spraying process and the appearance state of the cured coating, the coating process parameters are adjusted by testing the thickness of the coating, and in the coating thickness test, a thickness gauge is used for testing the thickness of the coating of the integrated verification printed circuit board which is coated; in the coating adhesion test, a hundred-grid knife is used for carrying out the coating adhesion test by adopting a grid cutting method, and the coating adhesion is verified; in an insulation resistance test, after electrifying lmin to two leading-out ends of the comb-shaped circuit, measuring a resistance value by using a high resistance meter to represent the insulation resistance of the comb-shaped circuit and the coating, measuring the leakage current of the Y-shaped circuit by using 1500V test voltage and frequency of 50Hz in a medium voltage resistance test, and then adding a large voltage to measure the breakdown voltage; the quality of the performance of the paint is conveniently evaluated through the test results; testing gain and standing wave, then carrying out a damp-heat test, a salt spray test and a mould test according to relevant standards, detecting the appearance state after the damp-heat test, the salt spray test and the mould test, observing the corrosion condition of a welding spot under the coating by visual observation or a quintuplet magnifier, and verifying the protection capability of the coating on the welding spot; then, performing an insulation resistance test and a medium voltage withstanding test, and evaluating the moisture resistance of the three-proofing coating; testing gain and standing wave, and evaluating the influence degree of the coating on the circuit performance by comparing the gain of the low-noise amplifier circuit component before and after coating the three-proofing paint, and inputting the change conditions of the standing wave ratio and the output standing wave ratio; this associates each authentication item. Through comparison and test, different three-proofing coatings can be evaluated and optimized, the influence degree of the three-proofing coatings on circuits and the quality of the three-proofing coatings are evaluated, and a test conclusion is drawn.
Compared with the prior art, the invention has the following beneficial effects:
high speed and high efficiency. The invention adopts the integrated verification printed circuit board to integrate the items of spray coating process verification, coating thickness test, adhesive force test, medium voltage resistance test, insulation resistance test, welding spot three-proofing capability test and the like, one sample piece can complete the verification items of various sample pieces, the manufacturing cost of the sample pieces is saved, and the manufacturing period of the sample pieces is shortened;
the low-noise amplifier is an active circuit and is generally formed by connecting multi-stage amplifying circuits, the microwave frequency band comprises circuits with various distributed parameters such as an interstage matching circuit, a biasing circuit, a feedback loop and the like, the performance of various devices on the circuits can change along with the different characteristics of a three-proofing coating, so that the noise coefficient and the linearity of the devices are influenced, the circuits are more sensitive to the performance change of the three-proofing coating, and the low-noise amplifier circuit component verifies the influence of the coating on the circuit performance and verifies the protection capability of the coating on the circuit component. The method has the advantages that integrated spraying process verification, coating thickness test, adhesive force test, medium voltage resistance test, insulation resistance test and welding spot three-proofing capability test can be integrated and verified on one integrated verification printed circuit board, and the graphic manufacturing of the integrated verification printed circuit board is in accordance with GJB 362B-2009 rigid printed board general Specification; the influence degree of the three-proofing coating on the circuit can be evaluated by adopting the typical circuit, the quality of the electrical performance of the three-proofing coating is determined, the circuit components of some products are prevented from being selected for electrical performance verification, and the problems of insufficient verification coverage, high verification cost, long verification period and the like exist.
The verification process is comprehensive. Multiple verification tests are carried out on one sample, all verification projects are better correlated, and different Brilliant three-proofing coatings can be clearly evaluated and optimized through comparison tests; the three-proofing capability of the coating under different thicknesses can be measured; the insulation resistance and the dielectric withstand voltage capability of the coating under different thicknesses can be measured; the medium withstand voltage and the insulation resistance before and after the three-proofing test and in the test are tested, the change conditions of the medium withstand voltage and the insulation resistance are analyzed, and the electrical property and the moisture resistance of the coating can be fully verified. Through the verification items, the comprehensive performance and the proper coating thickness of the coating can be quickly obtained, and a reference can be provided for selecting the coating with excellent performance for the complete machine of electronic products and the three prevention of the printed circuit board.
The invention is suitable for the rapid verification test of the performance of the three-proofing coating.
Drawings
FIG. 1 is a flow chart of the present invention for verifying the performance of a printed circuit board assembly.
Fig. 2 is an enlarged view of the "comb" circuit of the test insulation resistance in the integrated verification printed board of the present invention.
Fig. 3 is an enlarged view of a "Y" shaped circuit for testing insulation resistance in the integrated verification printed board of the present invention.
FIG. 4 is a circuit schematic of an exemplary circuit assembly of the present invention
Fig. 5 is a diagram of an input-output interface of an exemplary circuit assembly of the present invention.
In the figure: 1 is used as a comb-shaped circuit for testing insulation resistance, 2 is used as a Y-shaped circuit for testing dielectric withstand voltage and breakdown voltage, 3 is used as eight square copper-clad patterns for thickness measurement, and 4 is used as a bonding pad for verifying the three-proofing performance of a welding spot.
The present invention will be further described below by selecting a specific process for verifying the performance of a three-proofing coating as an example.
Detailed Description
See fig. 1-5. According to the invention, the method for rapidly verifying the performance of the three-proofing coating of the printed circuit board assembly has the following technical characteristics: firstly, designing and manufacturing an integrated verification printed circuit board for three-proofing paint coating and a low-noise amplifier circuit component for evaluating the influence degree of three-proofing paint on a circuit, and dividing the integrated verification printed circuit board into four parts: the testing device comprises a comb circuit used for testing insulation resistance, a Y-shaped circuit used for testing dielectric withstand voltage and breakdown voltage, eight square copper-clad graphs used for thickness measurement and two rows of bonding pads used for verifying three-proofing performance of welding spots; then, carrying out integrated spraying process verification, coating thickness test, coating adhesion test, insulation resistance test, medium voltage resistance test, gain test, standing wave test and three-proofing capability of a welding spot on a sample piece; in the verification integrated spraying process, the manufacturability is verified according to the film forming condition of the coating in the spraying process and the appearance state of the cured coating, the coating process parameters are adjusted by testing the thickness of the coating, and in the coating thickness test, a thickness gauge is used for testing the thickness of the coating of the integrated verification printed circuit board which is coated; in the coating adhesion test, a hundred-grid knife is used for carrying out the coating adhesion test by adopting a grid cutting method, and the coating adhesion is verified; in an insulation resistance test, after electrifying lmin to two leading-out ends of the comb-shaped circuit, measuring a resistance value by using a high resistance meter to represent the insulation resistance of the comb-shaped circuit and the coating, measuring the leakage current of the Y-shaped circuit by using 1500V test voltage and frequency of 50Hz in a medium voltage resistance test, and then adding a large voltage to measure the breakdown voltage; the quality of the performance of the paint is conveniently evaluated through the test results; testing gain and standing wave, then carrying out a damp-heat test, a salt spray test and a mould test according to relevant standards, detecting the appearance state after the damp-heat test, the salt spray test and the mould test, observing the corrosion condition of a welding spot under the coating by visual observation or a quintuplet magnifier, and verifying the protection capability of the coating on the welding spot; then, performing an insulation resistance test and a medium voltage withstanding test, and evaluating the moisture resistance of the three-proofing coating; testing gain and standing wave, comparing the gain of the circuit component of the low-noise amplifier before and after coating three-proofing paint, inputting the change conditions of the standing wave ratio and the output standing wave ratio, and evaluating the influence condition of the coating on the circuit performance; this associates each authentication item. Through comparison and test, different three-proofing coatings can be evaluated and optimized, the influence degree of the three-proofing coatings on circuits and the quality of the three-proofing coatings are evaluated, and a test conclusion is drawn.
Firstly, designing and manufacturing an integrated verification printed circuit board and a low-noise amplifier circuit assembly, wherein the integrated verification printed circuit board is an epoxy glass fiber copper-clad plate or a glass fiber reinforced polytetrafluoroethylene copper-clad plate; and coating a three-proofing coating on the integrated verification printed circuit board by adopting a spraying method.
The method is characterized in that a three-proofing coating is coated on the integrated verification printed circuit board by adopting a spraying method, wherein the spraying air source is 0.2 MPa-0.4 MPa, the caliber of a spray gun is 0.3mm, the spraying distance is 10 cm-20 cm, the spraying speed is 12 m/min-15 m/min, the coating thickness is generally controlled between 30 mu m-150 mu m, the coating is carried out at least twice, and the thickness of the coated integrated verification printed circuit board is tested by using a thickness tester.
And (4) carrying out a coating adhesion test by using a hundred-grid knife by adopting a grid cutting method, wherein the test grade of the coating adhesion of the printed board is not lower than grade 1.
And (3) carrying out a damp-heat test, a salt spray test and a mould test according to relevant standards, wherein the damp-heat test can be carried out according to the requirements of GJB150.9A-2009 part 9 of environmental test method of military equipment laboratories, namely a damp-heat test, and 5.6.2 test conditions are a high-temperature high-humidity section: the temperature is 60 ℃, and the relative humidity is 95%; low-temperature high-humidity section: the temperature is 30 ℃, and the relative humidity is 95 percent; and (3) test period: 24h is a period, which is 10 periods and longer (according to the product requirement); the salt spray test is carried out according to the requirements of GJB 150.11A-2009 part 11 of military equipment laboratory environment test method, namely salt spray test, and the test conditions are as follows: the concentration of the salt solution is 5 +/-1 percent (NaCl), the pH value of the salt solution before and after atomization is 6.5-7.2 (35 +/-2 ℃), and the period is 48 hours per cycle, wherein the spraying time is 24 hours, the drying time is 24 hours, and the two cycles are 96 hours or longer (according to the product requirement); the mold test was performed as GJB150.10A-2009 "military equipment laboratory environmental test method part 10: the requirements of the mould test are carried out, mould test strains: aspergillus niger, aspergillus flavus, aspergillus versicolor, penicillium funiculosum, chaetomium globosum, test duration: 28 days (28 cycles); after a damp-heat test, a salt spray test and a mould test, observing and grading the corrosion condition and the appearance of the base material of the sample piece, particularly observing and evaluating the corrosion condition of a welding spot below the coating, wherein the coating is required to have no bubbling and shedding, all matrixes and welding spots have no discoloring corrosion, and the mildew resistance grade of the base material and the coating is 0-l, so that the protection capability of the coating is verified.
Before and after the damp-heat test and the salt spray test, a medium withstand voltage test and an insulation resistance test are respectively carried out to verify the dielectric property of the coating. Measuring the leakage current of a Y-shaped circuit by using 1500V test voltage and frequency of 50Hz in a medium voltage resistance test, wherein the leakage current is required to be less than or equal to 10mA, then increasing the voltage, and measuring the breakdown voltage which is required to be not more than 3 KV; in an insulation resistance test, after two leading-out terminals of the comb circuit are electrified lmin, the insulation resistance of the coating is measured by a high resistance meter, and the insulation resistance before and after the test is required to be higher than 1.5 multiplied by 1012Ω。
The electrical performance test is carried out on the coated typical circuit assembly before and after a damp-heat test and a salt spray test, the circuit assembly and a base material are not corroded after the test, and a coating is not foamed, so that the protection capability of the coating on the circuit assembly is verified; gain is tested before and after the three-proofing paint is coated, the change conditions of the input standing wave ratio and the output standing wave ratio are input, the index change value is required to be not more than 10%, and the influence of the coating on the circuit performance is verified.
See fig. 2. The comb-shaped circuit for testing the insulation resistance in the integrated verification printed board is composed of a series of unconnected wires, the width and the distance of each wire are equal, each wire is communicated with each other at intervals to form a positive electrode or a negative electrode of a conductive comb tooth, leakage current between the positive electrode and the negative electrode is measured after a certain voltage is applied, the insulation resistance of a coating sample is obtained, and the coating performance with high insulation resistance is better.
See fig. 3. The Y-shaped circuit for testing the insulation resistance in the integrated verification printed board is composed of two wires with different edges, the width and the distance of the wires are equal, when a certain voltage is applied, the discharge current is tested, the voltage is increased to form a breakdown discharge phenomenon, and the breakdown voltage is recorded.
See fig. 4. The low noise amplifier is generally formed by connecting multistage amplifying circuits, and the microwave frequency band comprises circuits with various distributed parameters, such as an interstage matching circuit, a bias circuit, a feedback loop and the like. The whole circuit has the functions of voltage division, current limitation, feedback, choking, blocking and the like by using discrete devices such as a resistor, an inductor, a capacitor and the like besides the transistor, as shown in the figure, inductors L1 and L2 connected with the drain of the transistor are choking inductors, Rg with high resistance value provides stable bias voltage for the transistor, and the performances of the surface-mounted devices can change along with different characteristics of coating media, so that the noise coefficient and the linearity of the devices are influenced.
The foregoing is directed to the preferred embodiment of the present invention and it is noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.
Claims (10)
1. A method for rapidly verifying the performance of three-proofing paint of a printed circuit board assembly is characterized by comprising the following technical steps: firstly, designing and manufacturing an integrated verification printed circuit board for three-proofing paint coating and a low-noise amplifier circuit component for evaluating the influence degree of three-proofing paint on a circuit, and dividing the integrated verification printed circuit board into four parts: the testing device comprises a comb circuit used for testing insulation resistance, a Y-shaped circuit used for testing dielectric withstand voltage and breakdown voltage, eight square copper-clad graphs used for thickness measurement and two rows of bonding pads used for verifying three-proofing performance of welding spots; then, carrying out integrated spraying process verification, coating thickness test, coating adhesion test, insulation resistance test, medium voltage resistance test, gain test, standing wave test and three-proofing capability of a welding spot on a sample piece; in the verification integrated spraying process, the manufacturability is verified according to the film forming condition of the coating in the spraying process and the appearance state of the cured coating, the coating process parameters are adjusted by testing the thickness of the coating, and in the coating thickness test, a thickness gauge is used for testing the thickness of the coating of the integrated verification printed circuit board which is coated; in the coating adhesion test, a hundred-grid knife is used for carrying out the coating adhesion test by adopting a grid cutting method, and the coating adhesion is verified; in an insulation resistance test, after electrifying lmin to two leading-out ends of the comb-shaped circuit, measuring a resistance value by using a high resistance meter to represent the insulation resistance of the comb-shaped circuit and the coating, measuring the leakage current of the Y-shaped circuit by using 1500V test voltage and frequency of 50Hz in a medium voltage resistance test, and then increasing the voltage to measure the breakdown voltage; the quality of the performance of the paint is conveniently evaluated through the test results; testing gain and standing wave, then carrying out a damp-heat test, a salt spray test and a mould test according to relevant standards, detecting the appearance state after the damp-heat test, the salt spray test and the mould test, observing the corrosion condition of a welding spot under the coating by visual observation or a quintuplet magnifier, and verifying the protection capability of the coating; then, performing an insulation resistance test and a medium voltage withstanding test, and evaluating the moisture resistance of the three-proofing coating; testing gain and standing wave, comparing the gain of the circuit component of the low-noise amplifier before and after coating three-proofing paint, inputting the change conditions of the standing wave ratio and the output standing wave ratio, and evaluating the influence condition of the coating on the circuit performance; associating each verification item; through comparison and test, different three-proofing coatings are evaluated and optimized, the influence degree of the three-proofing coatings on circuits and the quality of the three-proofing coatings are evaluated, and a test conclusion is drawn.
2. A method for rapidly verifying the performance of a three-proofing coating for a printed circuit board assembly as recited in claim 1, wherein: the integrated verification printed circuit board is an epoxy glass fiber copper-clad plate or a glass fiber reinforced polytetrafluoroethylene copper-clad plate, and a three-proofing coating is coated on the integrated verification printed circuit board by adopting a spraying method.
3. A method for rapidly verifying the performance of a three-proofing coating for a printed circuit board assembly as recited in claim 1, wherein: coating a three-proofing coating on the integrated verification printed circuit board by adopting a spraying method, wherein a spraying air source is 0.2-0.4 Mpa, the caliber of a spray gun is 0.3mm, the spraying distance is 10-20 cm, the spraying speed is 12-15 m/min, the coating thickness is controlled between 30-150 mu m, the coating is carried out at least twice, and the thickness of the coating of the integrated verification printed circuit board after coating is tested by a thickness tester.
4. A method for rapidly verifying the performance of a three-proofing coating for a printed circuit board assembly as recited in claim 1, wherein: and (4) carrying out a coating adhesion test by using a hundred-grid knife by adopting a grid cutting method, wherein the test grade of the coating adhesion of the printed board is not lower than grade 1.
5. A method for rapidly verifying the performance of a three-proofing coating for a printed circuit board assembly as recited in claim 1, wherein: the damp-heat test conditions are high-temperature and high-humidity sections: a temperature of at least 60 ℃ and a relative humidity of at least 95%; low-temperature high-humidity section: a temperature of at least 30 ℃ and a relative humidity of at least 95%; with 24h as one test period: at least 10 cycles and longer depending on the product requirements.
6. A method for rapidly verifying the performance of a three-proofing coating for a printed circuit board assembly as recited in claim 1, wherein: the salt spray test conditions were: the concentration of the salt solution is 5 +/-1 percent (NaCl), the pH value of the salt solution before and after atomization is 6.5-7.2, the temperature is 35 +/-2 ℃, the period is 48 hours per cycle, wherein the spraying time is at least 24 hours, the drying time is at least 24 hours, and the two cycles are at least 96 hours and longer according to the product requirements.
7. A method for rapidly verifying the performance of a three-proofing coating for a printed circuit board assembly as recited in claim 1, wherein: the mold test species for mold test included: aspergillus niger, aspergillus flavus, aspergillus versicolor, penicillium funiculosum and chaetomium globosum, the duration of the test being at least 28 cycles.
8. A method for rapidly verifying the performance of a three-proofing coating for a printed circuit board assembly as recited in claim 1, wherein: after a damp-heat test, a salt spray test and a mould test, observing and grading the corrosion condition and the appearance of the base material of the sample piece, observing the corrosion condition of a welding spot below the coating, wherein the coating is required to have no bubbling and shedding, all the matrixes and the welding spots have no discoloring corrosion, and the mildew-proof grade of the base material and the coating is 0-l grade.
9. A method for rapidly verifying the performance of a three-proofing coating for a printed circuit board assembly as recited in claim 1, wherein: respectively performing medium voltage withstand test before and after a damp-heat test and a salt spray test, verifying the dielectric property of the coating by an insulation resistance test, measuring the leakage current of a Y-shaped circuit by using 1500V test voltage and frequency of 50Hz in the medium voltage withstand test, wherein the leakage current is less than or equal to 10mA, increasing the voltage, and measuring the breakdown voltage which is required to be less than or equal to 3 KV; in an insulation resistance test, the insulation resistance of the coating is measured by a high resistance meter after two leading-out terminals of the comb circuit are electrified lmin, and the insulation resistance before and after the test is higher than 1.5 multiplied by 1012Ω。
10. A method for rapidly verifying the performance of a three-proofing coating for a printed circuit board assembly as recited in claim 1, wherein: the comb-shaped circuit for testing the insulation resistance in the integrated verification printed board consists of a series of unconnected wires, the width and the interval of each wire are equal, each wire is communicated with each other at intervals to form a positive electrode or a negative electrode of a conductive comb tooth, and the leakage current between the positive electrode and the negative electrode is measured after voltage is applied to obtain the insulation resistance of a coating sample; the Y-shaped circuit for testing the insulation resistance in the integrated verification printed board is composed of two wires with different edges, the width and the distance of the wires are equal, when voltage is applied, discharge current is tested, the voltage is increased to form a breakdown discharge phenomenon, and breakdown voltage is recorded.
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