EMC electronic packaging glue stress release agent is mainly an additive added to change or improve certain characteristics of plastic packaging materials. Commonly used modified additives in molding materials include stress release additives, ion adsorption additives, etc. In terms of improving the performance of molding materials, stress release additives can reduce the elastic modulus, enhance flexibility and reduce the thermal expansion coefficient. The main commonly used stress release additives are silicon microspheres, acrylonitrile-butadiene rubber and polybutylene acrylate. Silicone elastic composite microspheres have become the most popular stress release additives due to their high purity and high temperature characteristics. The purpose of ion adsorption additives is to reduce the conductivity of any accumulated water vapor at the interface between the metal inside the potting body and the encapsulation material, thereby delaying the electrolytic corrosion degradation process.
Silicone rubber powder is a micro-powdered silicone rubber with a linear dimethyl polysiloxane cross-linked structure. Compared with ordinary rubber, silicone rubber has excellent heat resistance, cold resistance, and weather resistance, and can maintain elasticity in the temperature range of -50℃~250℃. If added to synthetic rubber, it can improve its smoothness, wear resistance, demoulding, heat resistance and cold resistance. In addition, it is also soft. If added to synthetic resin, it can improve its impact resistance and stress release. Silicone elastic composite resin microspheres are a kind of powder with silicone rubber microsphere powder coated with silicone resin. Silicone elastic composite microspheres are soft and have superior impact resistance. If added to epoxy resin, they give electronic potting materials EMC better stress release performance. However, due to the small particle size of silicone rubber microsphere powder and high viscosity, if it is to be evenly mixed and dispersed in other materials, strong stirring with special equipment is required, and its compatibility is not good. The silicone elastomer composite microspheres use organic resin to coat silicone rubber powder to effectively solve the above problems. Silicone elastomer composite microspheres have the superior characteristics of both silicone rubber and silicone resin powder. It has the excellent characteristics of not easy to bond, easy to disperse, and has lubricity, softness, impact resistance and compatibility.
Plastic internal stress refers to an internal stress generated during the plastic melting process due to factors such as the orientation of the macromolecular chain and cooling shrinkage. Almost all plastic products have internal stress to varying degrees, especially plastic injection products. The existence of internal stress not only causes plastic products to warp and crack during storage and use, but also affects the mechanical properties, optical properties, electrical properties and appearance quality of plastic products. To this end, it is necessary to find out the cause of internal stress and the way to eliminate internal stress, minimize the stress inside plastic products, and make the residual internal stress as evenly distributed as possible on the plastic products to avoid stress concentration, thereby improving the mechanical and thermal properties of plastic products.
There are many reasons for the generation of internal stress, such as the strong shearing effect on the plastic melt during processing, the orientation and crystallization effect during processing, the extremely difficult to achieve uniform cooling speed in various parts of the melt, the uneven plasticization of the melt, and the difficulty in demolding the product, which will all cause the generation of internal stress. The reduction and dispersion of plastic internal stress can be started from the design of raw material formula, the control of molding processing conditions (① barrel, mold temperature ② injection pressure, speed ③ holding pressure and time, etc.), and the heat treatment of plastic products. Among them, the raw material formula design can 1) select resins with large molecular weight, narrow molecular weight distribution, and low impurity content. 2) start with blending modification, enhancement modification, and nucleation modification.
Blending modification is the blending of resins that are prone to stress cracking with other suitable resins to reduce the degree of internal stress. For example, adding a small amount of silicone elastic composite microspheres to the epoxy resin of electronic potting material EMC can greatly release internal stress and reduce the degree of internal stress. It is a relatively economical and effective means to improve EMC internal stress.