The potting glue is mainly composed of base resin, filler, curing agent, cross-linking agent and other additives. The filler and auxiliary agent are the main factors affecting the settlement of potting glue. Therefore, when designing the potting compound formula, it should be Considered in general, it is mainly from the perspective of packing. (based on the commonly used powder silicon powder in potting glue)
1. Particle size.
The same kind of thermally conductive filler, the finer the particle size, the better the sedimentation.
This is because the fine powder has a large specific surface area, a large surface hydroxyl group content, and strong hydrogen bonds between the particles, resulting in a large viscosity, thereby slowing the sedimentation of the filler, but the excellent anti-settling property caused by the gelation can cause potting The viscosity is high, so it makes no sense. Common potting compounds use different sizes of fillers for thickness matching. This compounding not only forms dense packing in the system, but also the addition of coarse powder can improve the thermal conductivity. More importantly, the coarse powder increases the viscosity of the system. The smaller, coarse and fine powders are matched with each other, and the viscosity of the system can be flexibly adjusted to adjust the sedimentation.
2. The amount of filler added.
Common fillers are inorganic powders. In the field of electronic potting, the common powder is silicon micropowder (see the figure below). Compared with silicone oil, the density is large and the surface active groups are small; the compatibility with silicone oil is poor, and as the standing time is prolonged, the inorganic powder gradually settles, causing oil powder to separate.
However, when the amount of powder added reaches a certain amount, the viscosity of the colloid increases sharply, and the sedimentation speed of the thermally conductive filler is slowed down, and the separation of the oil powder is weakened. However, if the viscosity is too high, it will affect the process performance of the heat-dissipating potting compound during foaming and potting, which is not worth the loss. Therefore, it is not possible to pursue excellent anti-settling properties and perform high filling.


(The picture shows the common physical properties of Haiyang silicon micropowder)
3. Surface properties of the filler.
The surface of the filler is coated with a surface treatment agent to introduce a non-polar oleophilic group on the surface of the powder particles, so that the modified powder has good wettability in the silicone oil, is easy to disperse uniformly, and is not easy to be bonded and aggregated between the particles, and the colloid The anti-settling property is enhanced. At the same time, the surface treatment process can reduce the polarity of the powder and reduce the interfacial tension between the powder and the silicone oil. The compatibility between the two is enhanced, and the colloidal viscosity is lower. Therefore, in the potting compound, the modified filler is better than the ordinary filler in terms of improving its anti-settling ability, and the viscosity does not increase.
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