High temperature degradation mechanism of conductive adhesive/Sn alloy interface

The Ag-epoxy conductive adhesive/Sn-10Pb coating interface was subjected to heat exposure at 150/spl deg/C for up to 1000 hours and the interface degradation was examined by metallurgical analysis. Preferential Sn diffusion from the Sn-Pb coating layer to the Ag-epoxy conductive adhesive layer occurs due to heat exposure. In contrast, Ag does not show any significant diffusion. Large voids are formed in the Sn-Pb coating layer and a thin gap is formed at the Ag-epoxy/Sn-Pb coating layer interface. Ag/sub 3/Sn is formed in the Ag-epoxy layer. A debonding band is formed from the free surface at the Ag-epoxy/Sn-Pb coating interface. The degradation due to heat exposure is attributed to these facts. An ideal interface structure for the Ag-epoxy/Sn alloy coating that does not lose interface connection was proposed. From the electrode, a diffusion barrier layer against the electrode is followed by a Sn alloy layer that can melt at repair temperatures, and finally a barrier layer against Ag-epoxy adhesive such as Cu or Ni is applied.