Effects of oxidation and plasma cleaning on the adhesion strength of molding compounds to copper leadframes

In this study, the effects of oxide thickness and plasma cleaning on the adhesion strength of molding compounds to copper leadframes have been analyzed. Leadframe pull-out tests and water contact angle measurements were performed to establish the correlation between the oxide thickness and the measured adhesion strength. The experimental results show that the adhesion strength is reduced as the heat treatment time of copper leadframes is increased. The contact angle measurements indicate that the surface contamination increases as the heat treatment time increases. The water contact angle increased from about 71° for the specimens with no heat treatment to about 85° for those with a 5 h heat treatment while the pull-out strength decreased by 43%. The load-displacement curve for the specimen with a thick oxide layer shows serration characteristics of a stick-slip motion and the interface is not chemically but frictionally bonded. The effect of plasma cleaning on the adhesion strength between the molding compound and the leadframe was also studied. To quantify the contaminants on the leadframe surface, water contact angle measurement and an atomic microscopic approach were utilized before and after plasma cleaning. Various mixtures of gases such as oxygen/argon and hydrogen/argon were studied for the plasma cleaning.