Stress-free potting

Abstract

It is noted that totally stress-free potting is not theoretically possible, but stresses can be minimized by lowering the CTE (coefficient of thermal expansion) to match the CTE of the substrate material and lowering the shrinkage as much as possible. Since substrate materials usually have very low CTE, it is not possible to exactly match this with a potting compound. Shrinkage, CTE, and cost are best lowered by the addition of inorganic fillers, but viscosity and heat distortion (T/sub g/) are limiting factors. CTE and T/sub g/ of component materials can be related, because of the strong correlation between the two properties. Equations are given which may be used by the formulator to help bring the formulated product to the desired CTE and T/sub g/. Shrinkage may be retarded with a slower or lower-temperature cure, but is minimized by the addition of non-shrink, non-reactive materials to take up the available volume.<>