LAUSR

Abstract Herein, we investigated the interfacial reactions of crystalline Pd (pure Pd) and amorphous Pd (Pd(P)) layers in thin electroless-Ni electroless-Pd immersion-Au (thin-ENEPIG) surface-finished printed circuit board with Sn-3.0Ag-0.5Cu (SAC305) solder joints reflowed at 260 °C for 10–180 s. After 20 s reflow, a thick (Pd,Au)Sn4 IMC was formed at the interface of the pure Pd joint, while thick AuSn4 and thin (Pd,Au)Sn4 IMCs were formed at the interface of the Pd(P) joint. After 30 s reflow, needle-type (Cu,Ni)6Sn5 IMC was mainly formed at the top-side interface of the pure Pd joint, while scallop-type (Cu,Ni)6Sn5 IMC was formed at the top-side interface of Pd(P) joints. Finally, the top-side (Cu,Ni)6Sn5 IMC of the pure Pd and the top- and bottom-side (Cu,Ni)6Sn5 IMCs of the Pd(P) joints coarsened with increasing reflow time up to 180 s. In the results of top-view SEM micrographs, the (Cu,Ni)6Sn5 IMCs on the Pd(P) joint were larger than those on the pure Pd joint for reflow times of 30–180 s. Therefore, P in the Pd layer was concluded to significantly affect the interfacial reactions and IMC morphology of the SAC 305 solder with ENEPIG joints during reflow reactions.