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Many electronic components are designed on the PCB circuit board, and these components are easy to affect their performance when the PH value is too high, such as insulation deterioration, spontaneous short circuit, power loss and so on. After uniform coating of Conformal coatings, a protective film can be formed on the surface of components, which can improve the stability of circuit board, increase its safety factor and prolong its service life. How to inspect the Conformal coatings after coating?

Before applying the Conformal coatings, the circuit board shall be cleaned first, and then applied with the Conformal coatings after baking dry. The Conformal coatings applied on the board can be seen with the naked eye whether the adhesion is strong and whether the transparency is OK. Whether the brushing is uniform, blistering or whitening. After the Conformal coatings is fully cured, sprinkle a little water on the surface of the board to test whether it can play the effect of waterproof and moisture-proof. In addition, the effect of anti-corrosion and anti salt fog can not be seen immediately. After a certain period of time, the board will be damaged in the regular pollution. Conformal coatings can reflect its protective value.

The test standards after the application of Conformal coatings are as follows:

1. Adhesion (refer to GB / t9286-1998 standard: Cross cut experiment method, Level 0 (maximum)

2. Salt spray test (refer to GB / t1771-2007, GJB150, standard: verify the corrosion resistance of the product. The standard is 72h and the limit test is 1000h)

3. Water absorption (refer to GB / t1738-1979 standard: verify the protection and safety performance of the product)

4. Insulation resistance in humid environment (refer to ipc-tm-6502.6.3.4a standard: verify the insulation safety of products)

5. Mildew resistance (refer to ipc-tm-6502.6.1, GJB150, standard: 28 day mold test, level 0 is the highest)

6. Weather resistance / cold and hot shock test (refer to ipc-tm-6502.6.7.1a, GJB150, standard: IPC Standard 100 cycles, limit test up to 600 cycles)

7. Acid and alkaline resistance test (refer to gb1763-1986 standard: no abnormality of paint film)

8. Breakdown strength (refer to gb1981.2-2003 standard: verify the insulation performance of the product)

9. Corrosion resistance (refer to ipc-tm-6502.6.15 standard: the test sample is free of corrosion)

10. Odor requirements (enterprise defined standards: small odor, no irritating and unpleasant odor; no interference to gas detector parts)

Many customers have bubbles when using the three proofing paint. The reasons for this phenomenon are generally caused by the fact that the circuit board is not cleaned or dried, and there is dust and humidity on the circuit board. If the material has bubbles from the nozzle, factors such as coating process pressure, material viscosity, nozzle model, humidity and so on need to be considered. If bubbles appear after passing through the furnace, please carefully adjust the furnace temperature curve and the traveling route of the nozzle.

If we pay attention to the following five points when using three proofing paint, we can reduce the probability of bubbles.

1. Before using the three proofing paint, remove the dust, moisture and oil on the surface of the object coated with the three proofing paint to ensure that no corrosive residue remains on the surface of the object, so that the three proofing paint of PCB circuit board can adhere to the circuit board well, which is conducive to give full play to the three proofing (moisture-proof, salt fog proof and mold proof) performance of the three proofing paint of circuit board.

2. When applying with brush coating method, the area of three proofing paint brush coating of PCB circuit board should be larger than the area occupied by the device, so as to ensure that the device can be fully covered.

3. When brushing the three proofing paint of PCB circuit board, try to ensure that the objects to be brushed can be placed flat. After brushing, there should be no dew to ensure that the brushing is flat, and there should be no exposed places. The thickness of brushing can be about 25 ~ 50 microns according to different requirements. If there are higher requirements, secondary coating can be carried out.

4. If the immersion method is adopted for coating, ensure that the coated object is vertically immersed in the coating tank (note that the connector cannot be immersed unless carefully covered), immerse it for about 1 minute, and then take it out slowly. The immersion speed should not be too fast to avoid excessive bubbles.

5. After the coating is completed, the heating method can be used to accelerate the curing of the three proofing paint of PCB circuit board. The heating temperature should not be too high, and it is better to be within 80℃.

Epoxy adhesive usually refers to the adhesive made of epoxy resin as the main body. Epoxy resin adhesive usually also includes epoxy resin curing agent, otherwise the adhesive will not cure. After curing in operation, foaming may occur, which may be caused by the following two reasons:

First, bubbles are generated during glue mixing or filling. Due to the viscosity of glue or the difficulty of mixing method, air is brought into the glue solution. The viscosity of the glue is high, and the bubbles are difficult to eliminate. If the glue viscosity is small and the glue solidifies slowly, the bubbles will gradually rise to the surface and disappear automatically.

The second is the bubbles in the curing process. There are other reasons for bubbles in the curing process: too fast curing speed, high exothermic temperature, large curing shortening rate of glue, too many solvents and plasticizers in glue, etc., which will only produce bubbles in the curing process. In order to solve these problems in the curing process, the whole glue formula needs to be adjusted. In order to eliminate bubbles during adjustment and filling, vacuum pump, heating, diluent or defoamer can be used.

The thermal conductivity of ordinary silica gel is poor, and the thermal conductivity is usually only about 0.2w/m · K. However, the thermal conductivity can be improved by mixing thermal conductive filler in ordinary silica gel. Commonly used thermal conductive fillers include metal powders (such as Al, Ag, Cu, etc.), metal oxides (such as Al2O3, MgO, BeO, etc.), metal nitrides (such as sin, AlN, BN, etc.) and non-metallic materials (such as SiC, graphite, carbon black, etc.). Compared with metal powder filler, although the thermal conductivity of metal oxide and metal nitride is poor, it can ensure the electrical insulation performance of thermal conductive potting adhesive.

Another major factor determining the thermal conductivity of potted silica gel is the manufacturing process. The temperature control, pressure, filler and the feeding sequence of various additives in the production process of liquid potting adhesive will also play a decisive role in its thermal conductivity. For example, if the vacuum pressure fails to meet the requirements, too many bubbles will be generated in the raw material, which will directly affect the service performance of potting adhesive. Excessive thermal conductive filler can not only improve the thermal conductivity, but also directly affect the adhesion and fluidity of potting adhesive. Therefore, the potting silica gel with high thermal conductivity and excellent comprehensive performance can be obtained by optimizing the type and amount of filler and the ratio of filler to other additives.

Since the most widely used fields of potting adhesive are high temperature and high pressure environments such as power supply, electronic components and outdoor electrical equipment, the insulation strength and temperature resistance of potting adhesive are highly required. In addition, many electronic industries have UL flame retardant grade requirements for potting adhesive, which is required to be V0 grade. Generally, the working temperature of thermal conductive potting adhesive is -50℃ ~ +240℃, while high temperature resistant potting silica gel can withstand 1200℃ or even higher.

There are many kinds of adhesives with different properties. Many factors need to be considered when selecting adhesives in order to achieve the ideal bonding effect. Proper selection of suitable adhesive can prolong product life, maintain efficiency and reduce cost. In general, the following factors should be considered when selecting adhesives for electronic industry:

Ⅰ Select the adhesive according to the chemical properties of the bonding substrate:

1. Adhesives with strong polarity shall be selected for bonding polar materials (such as steel, aluminum, nickel, ceramics, etc.), such as epoxy resin adhesive, polyurethane adhesive, acrylate adhesive, inorganic adhesive, etc.

2. Acrylate adhesive and unsaturated polyester adhesive shall be selected for bonding weak polar materials and non-polar materials (such as paraffin, asphalt, ABS / plastic, polyethylene / PE, polyethylene, etc.).

Ⅱ Select the adhesive according to the physical properties of the bonding substrate:

1. Thermosetting resin adhesives with high strength, high hardness and not easy to deform can be selected for bonding brittle and rigid materials (such as ceramics, glass, cement and stone), such as epoxy resin adhesive, phenolic resin adhesive and unsaturated polyester adhesive.

2. Adhesive with good elasticity and certain toughness shall be selected for bonding elastic and ductile materials (such as rubber, leather, plastic, film, etc.). Such as epoxy resin adhesive, polyurethane adhesive, rubber adhesive, polyvinyl acid ethyl ester adhesive, etc.

3. for bonding porous materials (such as foamed plastics, sponges, fabrics, etc.), adhesives with high viscosity shall be selected, such as epoxy resin adhesive, polyurethane adhesive, polyacrylic acid monoester adhesive, rubber adhesive, hot melt adhesive, etc.

Ⅲ Select the adhesive according to the use conditions and environment:

1. When the bonded part is subjected to uneven peeling force and pulling force, the adhesive with good toughness can be selected, such as rubber adhesive, polyurethane adhesive, etc.

2. When the adhesive is subjected to uniform pulling force and shear force, hard and brittle adhesive can be selected, such as epoxy resin, acrylic adhesive, etc.

3. When the adhesive is used in the sealed environment without oxygen or isolated from air, anaerobic adhesive can be selected.

4. When water resistance is required for bonding parts, epoxy resin adhesive, acrylic adhesive, etc. shall be selected; When the oil resistance is good, choose epoxy or silicone adhesive.

5. Select different adhesives according to the service temperature of the bonding parts. For example, epoxy resin is suitable for use below 120℃, and rubber adhesive is suitable for use below 80℃; Organic silica gel is suitable for use below 200℃; Inorganic glue is suitable for use above 500℃.

6. Select adhesives according to different processes: the pouring adhesive usually adopts solvent-free and low viscosity adhesive; Paste and paste adhesives are often used for sealing.

7. Select adhesives with different properties according to the special requirements of bonding parts: for example, functional adhesives shall be selected for conductivity, heat conduction, high temperature resistance and low temperature resistance.

Ⅰ Civil and commercial applications

Coating materials provide protection for electronic circuits in household appliances against:

1. Water and detergent (washing machine, dishwasher, bathroom products, outdoor electronic LED screen)

2. Adverse external environment (outdoor display screen, anti-theft and fire alarm devices, etc.)

3. Chemical environment (air conditioner, dryer)

4. Harmful substances in office and home (computer, copy)

5. Civil and commercial lighting (LED lighting)

6. All other circuit boards that need to be protected by coating materials

Ⅱ Automobile industry

The automotive industry requires coating materials to protect the circuit from the hazards of the following situations, such as gasoline evaporation, salt spray / brake fluid, etc. The application of electronic system in automobile is growing rapidly, so the use of coating materials has become the basic requirement to ensure the long-term reliability of automobile electronic devices. Such as ECU / lamp controller, vehicle sensor, electric vehicle battery control unit BMU, vehicle door lock / window controller, etc.

Ⅲ Aerospace

Due to the particularity of the use environment, the aviation and aerospace environment has very strict requirements for electronic equipment, especially under the condition of rapid pressurization or decompression, it is still necessary to maintain good circuit performance. Therefore, coating materials are widely used. Such as: aviation instrument panel / engine control system, radar control system, aviation airborne power supply / communication support system, sonar / photoelectric system, etc.

Ⅳ Navigation ship

Whether fresh fresh water or salty sea water will cause harm to the electrical circuit of ship equipment. The use of Tianxiang technology three proofing paint can maximize the protection of equipment on the water and even submerged and underwater. Such as weather radar / shipborne radar, shipborne power supply / direction control system, lighting system / communication support, sensors, etc.

Ⅴ Medical life and health

The coating material can protect the medical electronic equipment from the erosion of external chemicals and special use environment, and ensure its continuous stability. Such as: CT / B-ultrasound, electrocardiograph, rehabilitation equipment / fitness equipment, operating table / medical lighting, etc.

Ⅵ Rail transit and industrial control

Coating materials can protect motor cars and subways from external rain and freezing weather, and ensure the stable and safe operation of traffic. In industrial control, due to the harsh application occasions, coating materials must be used to ensure the stability of electronic circuit boards in humid or desert areas with great difference between cold and heat. Such as on-board power supply / communication signal system, motor control system, Metro PSD / gate / ticketing system, industrial computer / process control board, etc.

Ⅶ New energy / smart grid

New energy systems such as solar, wind or nuclear energy generally need to be deployed in areas with sufficient sunlight or strong wind. These areas generally have a bad environment, and the control unit of smart grid generally needs to be in these places. Therefore, coating materials are required to ensure the safe operation of these equipment for a long time. Such as inverter, energy storage system, wind energy motor, relay protection system, etc.

Potting glue is a kind of glue widely used in industrial manufacturing. According to the actual application of products and different glue materials, electronic potting glue has a variety of classifications. In terms of materials, epoxy resin potting glue is the most widely used.

The main function of potting epoxy AB glue is to strengthen the overall performance of electronic components and wrap some components and circuits, so as to make electronic components have certain waterproof and moisture-proof performance, so as to improve the resistance of electronic components to external impact and vibration, improve the insulation between internal components and circuits of electronic components, and also have certain heat conduction and heat dissipation, which is conducive to the miniaturization and lightweight of electronic products.

Epoxy AB glue for potting includes hard glue and soft glue. The colors include transparent, black, blue and other colors. According to the mixing ratio, there are 1:1, 2:1 and 10:1.

The viscosity of epoxy glue at room temperature is low, so it is easy to fill the gap of epoxy glue at room temperature.

Normal or medium temperature curing, moderate curing speed, and the curing process is relatively controllable; Epoxy resin AB glue basically has no colloid after curing, with flat surface, good luster and high hardness; The cured product has good acid-base resistance, moisture-proof, water-proof, oil-proof and dust-proof performance, which can meet the requirements, ensuring that the product has a certain waterproof grade; The cured product of epoxy AB glue has good insulation, light specific gravity, good toughness, compression resistance, high bonding strength and other electrical and physical properties.

The liquid epoxy resin composite potting glue is potted into the devices with electronic components and circuits through the gluing machine or dispensing machine, and solidified into a polymer insulation material with good performance under normal temperature or heating conditions. Epoxy potting adhesive can strengthen the integrity of electronic devices and improve the resistance of potted products to external impact and vibration. Epoxy potting adhesive can insulate the internal components and circuits well, which is conducive to the miniaturization and lightweight of devices. Epoxy potting adhesive can avoid direct exposure of components and circuits, so that electronic products have good waterproof and moisture-proof performance.

As we all know, potting adhesive plays a very important role in the electronic industry. Its selection will directly affect the performance of electronic products. However, there are many kinds of electronic potting adhesive in the market. How to choose the potting adhesive suitable for yourself?

From the function selection of potting glue

1. Whether it conforms to product characteristics and filling or bonding process characteristics.

2. Whether heat conduction flow or semi flow is required. Among the main categories of potting adhesives, epoxy potting adhesives generally have poor thermal conductivity and are generally used for more waterproof functions. Silicone potting adhesive has general waterproof durability, and pays more attention to thermal conductivity, insulation and shockproof performance.

3. Use environment and product type. Before curing, the electronic insulation potting adhesive is liquid and has fluidity. The viscosity of the adhesive varies according to the material, performance and production process of the product.

From the selection of potting adhesive performance parameters

1. Thermal conductivity: compared with other potting adhesives, the main characteristics of additive silicone potting adhesives are thermal conductivity and flame retardancy.

2. The waterproof effect of potting adhesive with good waterproof and adhesion will also be better. The condensation bonding potting adhesive can reach ipx7 waterproof level.

3. Hardness: condensation type transparent is about 20 hardness, black, white and gray are about 30 hardness, additive transparent is about 0~35 hardness, black, white and gray are about 0~70 hardness, the higher the hardness, the greater the specific gravity. When the hardness is 20~30, the density after mixing is about 1.02, and when the hardness is above 70, the specific gravity will reach about 1.6.

4. Flame retardancy. The additive type is better than the condensation type. The flame retardant level of condensation type is ul94v-1, and the additive type can reach UL94V-0.

5. Adhesiveness. The adhesiveness of condensation type is generally better than that of addition molding. Common ones can be bonded with PVC plastic, ceramic metal, ABS plastic, etc.

6. Both color and can play the role of potting and sealing. It is only transparent and suitable for products with light source, such as LED module, LED soft light strip, etc. Because the transparent can effectively spread the light rate, the black can't. In terms of application, for example, some parts of some IC circuit bare chips are sensitive to light, so black electronic potting adhesive can solve this problem. As another example, some cameras need flash links that need to accept external light, so they must use transparent packaging.

7. Thermal conductivity: the thermal conductivity of transparent potting adhesive is about 0.17~0.37, and that of black, white and ash is about 0.6~0.8.

8. Curing time requirements: adjust the curing time of potting adhesive by changing the formula composition, or heat up curing can be adopted.

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