Application of polyurethane potting sealant in PCB industry

June 17, 2022

Application of polyurethane potting sealant in PCB industry

    With the development of industry, the application of electronic components is more and more extensive. At the same time, the application of potting compounds, which play a key role in protecting electronic components, is becoming more and more common. Potting sealant can be found in various industries such as automotive electronics, military aviation, medical equipment, household appliances, power supplies, and new energy.

    Due to the existence of a large amount of moisture, oxygen, dust and mold in the external environment, electronic components exposed to air or some special acid-base environments for a long time are prone to oxidation and corrosion. Potting sealant can largely isolate the influence of the external environment on electronic circuits, thereby greatly extending the service life of electronic components.

    From the application side, the potting compound usually used for electronic components needs to have single or multiple functions such as sealing, potting, bonding, coating, and heat dissipation. There are many types of potting adhesives on the market. The mainstream products are mainly silicone potting adhesives, polyurethane potting adhesives, epoxy potting adhesives, UV potting adhesives, etc. The potting adhesives of different materials have different characteristics and uses. In this issue, let us delve into the "rules of use" of one of the most widely used potting compounds, polyurethane potting compounds.

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Features of Polyurethane Encapsulant

    Polyurethane encapsulant is a two-component AB sealant consisting of a curing agent or prepolymer with isocyanate groups, a hydroxyl polyol or prepolymer containing active hydrogen, and some functional additives and fillers. The mass ratio is usually 1-5:1. Since the molecular structure of the polyurethane itself contains both flexible and rigid segments, it can be adjusted in a wide range, so the hardness of the polyurethane potting compound can be as low as 5 Shore A, or as high as 70-80 Shore D. At the same time, the corresponding bulk tensile strength can be in the range of 0.5-15.0 MPa. The mechanical properties of polyurethane encapsulant are between silicone and epoxy, with moderate hardness, excellent waterproof performance and electrical insulation.

    In addition, the temperature range of polyurethane encapsulant is generally between -60 ℃ to 120 ℃, the high temperature resistance is not as good as that of silicone and epoxy, and the low temperature resistance is comparable to that of silicone, which is better than epoxy. Polyurethane potting adhesives have outstanding bonding properties and have good bonding effects on most substrates. Its bonding strength is higher than that of silicone, and it is not as strong as epoxy sealant and not easy to rework. Therefore, polyurethane encapsulants can be given priority to applications where adhesive performance is the main requirement. However, polyurethane encapsulant also has the disadvantage of excessive air bubbles. It is easy to generate bubbles during the two-component mixing process. Unlike silicone oil, which has a defoaming function, its own viscosity causes the bubbles to rise to the surface for a long time. Especially, the high-viscosity polyurethane encapsulant needs to be vacuumed to achieve defoaming.

Points for attention in the use of polyurethane potting sealant

    Due to the composition of the polyurethane potting compound, the isocyanate group in the curing agent is easily reacted with water vapor to generate CO2, so that gas remains in the colloid after curing. Bake to remove moisture. When mixing, it should be fully mixed according to the proportion recommended in the product specification. Otherwise, too many curing agent components will cause excess isocyanate groups to react with the infiltrated water vapor and generate CO2 gas, making the cured There are bubbles in the colloid, and if the curing agent component is too small, there will be insufficient curing or even no curing.

    It should also be noted that once the packaging material is opened, it is recommended that users use it up at one time or as soon as possible. Because the main agent is easy to absorb water, and the curing agent is easy to form skin after contact with water, both of which will cause problems such as foaming or adhesion and deterioration of waterproof performance of the cured adhesive.

    BAIYUN, who has been deeply involved in the sealant industry for 37 years, has developed high-quality two-component polyurethane products in the fields of power batteries, automobiles, electronic appliances, lighting, rail transit, etc. Adhesive solutions offer infinite possibilities for every customer who pursues perfection.

    At present, the precision of industrial manufacturing is constantly improving, and the performance requirements of adhesives in the industrial field are also getting higher and higher. BAIYUN will continue to develop and innovate in the field of polyurethane adhesives, assisting the high-quality development of Chinese manufacturing, and empowering beauty!