Adhesion characteristics of copper alloys IC leadframe to mold resin

摘要

Adhesion to mold resin is one of the most important properties of leadframe materials in maintaining IC device reliability. This property may be determined by adhesion strength between copper alloy and its oxide film. The effects of copper alloy composition, the thickness of copper underplating and anti - tarnishing treatment were investigated respectively. Pure copper surfaces such as oxygen - free copper and copper-layered materials have better adhesion characteristics than other copper alloys. In case of copper alloys for leadframe without pure copper surface, C19400 alloy has better adhesion characteristics than Cu-Ni-Si alloy such as C70250. In order to avoid the effects of copper alloy composition, copper underplating must have enough to prevent the leadframe material from being oxidized. When oxide layer thickness proceeds to copper alloy over copper plating, adhesion strength between Cu-Ni-Si copper alloy system and its oxide film decreases abruptly. Anti - tarnishing treatment was quite effective in the actual production of copper leadframes. Benzotriazole (BTA) inhibitor with high thermal decomposition temperature may induce an exfoliation of copper oxide film. On the other hand, copper alloys covered by adsorptive inhibitor have better adhesion characteristics than BTA anti-tarnished copper alloys. By selecting the proper condition on the points above, the reliability of copper leadframes against exfoliation of mold resin can be maintained for mass production systems.