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 ad hesion strength of molding compounds to copper leadframes have been analyze d. Leadframe pull-out tests and water contact angle measurements were perfo rmed to establish the correlation between the oxide thickness and the measu red adhesion strength. The experimental results show that the adhesion stre ngth is reduced as the heat treatment time of copper leadframes is increase d. The contact angle measurements indicate that the surface contamination i ncreases as the heat treatment time increases. The water contact angle incr eased from about 71 degrees for the specimens with no heat treatment to abo ut 85 degrees for those with a 5 h heat treatment while the pull-out streng th decreased by 43%. The load-displacement curve for the specimen with a th ick oxide layer shows serration characteristics of a stick-slip motion and the interface is not chemically but frictionally bonded. The effect of plas ma cleaning on the adhesion strength between the molding compound and the l eadframe was also studied. To quantify the contaminants on the leadframe su rface, water contact angle measurement and an atomic microscopic approach w ere utilized before and after plasma cleaning. Various mixtures of gases su ch as oxygen/argon and hydrogen/argon were studied for the plasma cleaning.