Electroless plating copper cones on leadframe to improve the adhesion with epoxy molding compound

Abstract

A simple method to increase the adhesion strength between leadframe and epoxy molding compound (EMC) was reported in this paper. Cone-structured copper film was deposited on copper-based leadframe sheets by electroless plating. SEM observation of the as-prepared film indicates that cone size distinctly depends on plating time. Adhesion strength between EMC and cone-coated leadframe was measured by button shear test (BST). Results show that when deposition time t≤120s, the adhesion strength increases rapidly with the growth of copper cones, when t >120s, although cones keep growing, the adhesion strength tends to level off. Average adhesion strength reaches maximum value of 33.80(±1.74) MPa, increased by 87% (57%~124%) when substrate was plated for 600s, compared with that of conventional leadframe. By observing leadframe side of fracture surface after destructive button shear test, two failure modes were proposed: failure at interface and inside EMC. It is assumed that the copper nano-cones structure could effectively increase the contact area of EMC and leadframe, which leads to mechanical interlocking. Such micro-nano structure and its unique property are expected to be applied in the practical industry.