A New Approach in Measuring Cu–EMC Adhesion Strength by AFM

Copper–epoxy molding compound (Cu–EMC) interface is known to be one of the weakest interfaces in an electronic package exhibiting delamination during reliability test. 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 in macro-scale. However, inconclusive or even contradictive 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, an Si wafer was used as a substrate in the experiments. This study involves the use of an atomic force microscope (AFM) in characterizing the nanoscale adhesion force in a Cu–SAM–EMC system. Findings were used as the criteria in selecting a SAM candidate. A thiol compound having a carbonyl group is shown to be the best adhesion promoter from the measurement. The nanoscale AFM results are shown to be consistent with the result of macroscopic shear tests. It has been demonstrated, with SAM treatment on a cleaned copper surface, that the fracture force between Cu–EMC samples is improved from 119 to 195N.