In the process of potting adhesive application, most users have a defoaming process. The purpose is to ensure that there are no air bubbles and pores inside and on the surface of the colloid after the product is cured, so as not to affect the performance of the product. You may think that defoaming is a very simple operation. Open the vacuum box and pump it. I will talk to the majority of users about the consequences of this simple defoaming process and how to prevent abnormal defoaming of silicone potting sealants.
Silicone potting glue is used in all walks of life after curing, including electrical and electrical, military electronics, aerospace, communication equipment, automotive electronics, etc. All walks of life have special attention to performance, such as electrical performance, shock resistance and voltage resistance, Shrinkage expansion, waterproof and water absorption, sulfur resistance, acid and alkali resistance, etc. If the silicone potting compound is not properly vacuum defoamed in the first process of curing, there are air bubbles inside or outside the colloid, especially the air bubbles in the colloid, which will not be cured after curing. It was found that the performance of the silicone potting collagen was degraded, resulting in abnormal end products, minor rework, time-consuming, labor-intensive and financially consuming, and direct scrapping in serious cases. Therefore, it is necessary to propose preventive measures to avoid risks on process nodes. The specific influencing factors are as follows.
1 degree of vacuum
The degree of vacuum is determined by the power of the vacuum pump and the overall air tightness. With the extension of the service life of the vacuum pump, some parts will be aged and worn, the working power will be greatly reduced, and the pumping force will be reduced. No matter what kind of vacuum degassing box it is, there will be a trachea connected, and the air leakage of the trachea joint or the slight damage of the trachea will also lead to insufficient air extraction. Therefore, the inspection and maintenance of the equipment should be carried out regularly as daily work, including the sensitivity of the vacuum gauge. Because if the vacuum gauge is not a standard product, the sensitivity is low, and it always shows normal, which is also a potential work risk.
2 Deaeration process
The phenomenon that is easy to occur in the defoaming process is that the overflowing glue and bubbles are difficult to break and eliminate. The overflowing glue generally occurs in products with little glue filling or relatively full glue filling. For such products, the manual control box cannot directly operate at -0.1Mpa. Keep pumping down, you need to pay attention to observation, reduce the vacuum degree when the glue is almost full, repeat the operation, or reduce the vacuum degree to -0.08-0.09Mpa when the vacuum is vacuumed in the previous section, slowly pump the surface and upper layer first, when the pumping does not work Then use -0.1Mpa for pumping, so that it will not overflow.
Of course, there are also the factors of the glue itself. It is more aimed at manufacturers. The factors that affect the defoaming properties of silicone potting compounds in the process of research and development and optimization include density, viscosity, performance and dosage of defoamer, because mature Silicone encapsulant products have the function of self-discharging, which is easy to defoam, so the majority of users should manage and optimize equipment and processes to prevent product abnormalities caused by air bubbles.
