Bonding strengths at plastic encapsulant-gold-plated copper leadframe interface

The effect of plasma treatment on the adhesion strength of a moulding compound to a leadframe is evaluated on the basis of leadframe pull-out tests. The contact angle measurement method and atomic force microscopy are employed to quantitatively characterise the modified surface so as to correlate with the bond strength measurements. Process parameters including the type of gases used and the duration exposed in air before moulding are specifically studied. The results indicate that plasma treatments of leadframe have three major ameliorating effects, namely, clean surface due to the removal of organic contaminants, enhanced chemical compatibility with moulding compound and rough surface with associated larger surface contact area for better mechanical interlocking. Exposure of plasma treated leadframes in air before moulding is found detrimental to interface bond quality, recommending moulding operations immediately after treatment. It is also shown that roughness on the nanoscale is an important surface characteristic that has a strong correlation with the interface bond strength.