EFFECT OF ELECTROLESS Ni-P CONSUMPTION ON THE FAILURE MECHANISM OF SOLDER JOINTS DURING ELECTROMIGRATION

Abstract

The consumption of electroless Ni-P and its effect on the failure mechanism of solder joints during electromigration under a current density of 1.0×10 4 A/cm 2 at both 150 and 200 were investigated using line-type Cu/Sn/Ni-P solder joints. Before the electroless Ni-P was completely consumed, the microstructural evolution of the Sn/Ni-P interface (cathode) was the formation of Ni2SnP and Ni3P accompanied by the consumption of the electroless Ni-P. Ni atoms diffused from the electroless Ni-P into the Sn solder under electron current stressing. Most Ni atoms precipitated as (Cu, Ni)6Sn5 or (Ni, Cu)3Sn4 in the Sn solder, and few Ni atoms could arrive at the opposite Cu/Sn interface (anode). After the electroless Ni-P was completely consumed, the microstructural evolutions of the Sn/Ni-P interface (cathode) were the formation of voids and the transformation from Ni3 Pt o Ni2SnP. Furthermore, cracks that resulted from the propagation of voids significantly increased the current density through solder joints, and thus greatly enhanced the Joule heating of solder joints, resulting in the failure of solder joints by the fusing of Sn solder.