Thermal Stress Analysis of Epoxy Encapsulants

The stresses produced by the epoxy resin during thermal shock may cause rupture of the component-to-ribbon welds in encapsulated welded modules. This investigation develops a mathematical model describing the stresses on component lead wires. Stresses are functions of the temperature-dependent mechanical properties of the epoxy, diameter of an epoxy slug in shear with the component lead wire, and temperature. Thermal stress indexes were established to predict the thermal-shock properties of epoxies. Strain-gage force-voltage transducers, simulating epoxy-encapsulated, cylindrical, electronic components, were used to measure stresses in modules. Good agreement was obtained between experimental data and theoretical results.