In-situ Observation and Modeling of Intermetallic Compound Growth Induced by Electromigration in Sn-2.5Ag Solder Joints with OSP and ENEPIG Surface Finish

The predicted growth behavior of intermetallic compound (IMC) induced by electromigration of a Cu/organic solderability preservative (OSP)/Sn-2.5Ag solder/electroless nickel electroless palladium immersion gold (ENEPIG)/Cu joint was calculated for a current density of 14 kA/cm 2 and current application time of 600 h and validated experimentally. Under as-reflow conditions, thin Cu 3 Sn and scallop-shaped Cu 6 Sn 5 layers were produced near the OSP interface, and a (Cu, Ni) 6 Sn 5 layer was formed near the ENEPIG interface. Cu 6 Sn 5 islands and Ag 3 Sn with a β-Sn matrix were formed in the solder. The mobilities of Cu, Ni, and Sn atoms at the OSP and ENEPIG interfaces were calculated, and a relationship was found between IMC thickness and current application time. Under electron flow from the OSP to ENEPIG interface, the predicted total thickness (26.6 μm) of the IMCs (Cu 3 Sn, Cu 6 Sn 5 , and (Cu, Ni) 6 Sn 5 ), was in agreement with the experimental value (24.7 μm). With electron flow reversed, the predicted IMC thickness (14.2 μm) was similar to the experimental value (13.2 μm). The application of current during electromigration only coarsened Cu 6 Sn 5 , regardless of the direction of electron flow. Finally, the Ni plating layer on the ENEPIG surface finish prevented the diffusion of Cu and suppressed electromigratory IMC growth by approximately 50%. Graphic abstract