Humidity Resistivity of Cavity Package Sealed with Epoxy Adhesive Resin for Solid-State Images

Abstract

This paper presents humidity resistivity of a package with an optical glass window attached by epoxy adhesive resin.
The relative humidity in the cavity can be measured by a simple new technique, the procedure of which is to heat the package, cool the window glass by air spot blowing, and then measure the dew point. With this method, it is found that the water diffusion rate of the epoxy resin adhesive can be expressed by the general diffusion equation if the adsorption effect by the package inner surface is taken into account. The amount of water absorption by the inner surface can be estimated by Henry's law over the wide relative humidity range (0-about 50% RH). It is also found that a small amount of silicagel mixed with adhesive resin, which is used for mounting chips, delays the increase in humidity. This result leads to an improvement in the humidity resistance of the package.