Ultrasonic Examination of Curing State of Thermosets Used for Plastic Encapsulated ICs and Contact State in Molding Processes.

Abstract

Changes in curing states of thermosetting resin during transfer molding processes are investigated. Contact conditions between a die and a resin specimen, and sound velocities in the resin strongly depend on the curing states. An ultrasonic examination is used to continuously measure the contact conditions and the varying sound velocities due to solidification during the molding processes. These factors are evaluated from the relative intensity and the time lag of ultrasonic waves reflected from the interface between dies (upper and lower) and a resin specimen. The experimental results clarify the changes in the contact ratios. The contact ratio is 0.55 at most in all the molding processes. The contact ratio and the curing states are also influenced by the molding temperature and the molding pressure. It has also been suggested that this measurement method is useful for inspecting the filling states of the resin in the cavity.