A new approach in measuring Cu-EMC adhesion strength by AFM [electronics packaging applications]

The copper-epoxy molding compound (Cu-EMC) interface is known to be one of the weakest interfaces in an electronic package, exhibiting delamination during reliability testing. A thiol compound which bonds readily and forms a self-assembly monolayer (SAM) with copper is proposed to improve interfacial adhesion between copper and EMC. Conventional adhesion evaluation involves force measurement at macro-scale. However, inconclusive or even contradictory results are common in those tests because of uncontrollable surface conditions such as contamination and, in particular, roughness. To eliminate the roughness effect and reflect the true chemical bonding condition, a Si wafer was used as a substrate in the experiments. This study involves the use of an atomic force microscope (AFM) in characterizing the nano-scale adhesion force in the Cu-SAM-EMC system. Findings were used as the criteria in selecting an SAM candidate. A thiol compound having a carbonyl group is shown to be the best adhesion promoter from the measurements. The nano-scale AFM results are shown to be consistent with the results of macro scale shear tests. It has been demonstrated, with SAM treatment on a cleaned Cu surface, the fracture force between Cu-EMC samples is improved from 119 N to 195 N.