Adhesion strengths of epoxy molding compounds to gold-plated copper leadframes

In the present study, the effects of plasma cleaning on the adhesion strength of molding compounds to gold-plated copper leadframes are presented. Important process parameters such as the type of gasses used and the time exposed in air before molding are specifically evaluated. The leadframe pullout test is performed to measure interfacial bonding strengths. The liquid droplet test is used to measure contact angles and atomic force microscope (AFM) is employed to characterize quantitatively the roughness of modified surfaces to correlate with the bond strength measurements. The results indicate that plasma cleaning of leadframes has three major ameliorating effects, namely, surface cleaning due to the removal of contaminants, enhanced chemical compatibility with molding compounds and surface roughening with associated larger surface contact area for better mechanical interlocking. Exposure of plasma-cleaned leadframes in air before molding is detrimental to interface bond quality, a finding suggesting that molding operations should be carried out immediately after cleaning. The experimental results show that roughness on the nano-scale is an important surface characteristic that has a strong correlation with interface bonding strengths.