Interfacial Intermetallic Compound Grain Research Articles

Spalling behavior of interfacial intermetallic compounds in Pb-free solder joints subjected to temperature cycling loading

Morphological evolution of interfacial intermetallic compounds (IMC) subjected to thermal cycling loading was studied numerically and experimentally. In this study, the microstructure of Sn3.5Ag0.7Cu solder joint and its interfacial IMCs were investigated using Tape Ball Grid Array assemblies. Needle-type and hemispherical-type morphologies of interfacial IMCs were formed after reflow. During temperature cycling, the IMC grains ripened into large hemispherical-type and spheroidal-type morphologies and spalled into the solder joint. Finite element analysis showed that the spalling behavior was promoted by the geometrical changes of the IMC structure and the induced cyclic shear stresses during temperature cycling loading. For needle-type grains, the stress was concentrated at the tip of the IMCs, while the maximum shear stress was redistributed to the roots of the spheroidal-type grains.

Morphology and growth kinetics of intermetallic compounds in solid-state interfacial reaction of electroless Ni-P with Sn-based lead-free solders

A comparative study of solid/solid interfacial reactions of electroless Ni-P (15 at.% P) with lead-free solders, Sn-0.7Cu, Sn-3.5Ag, Sn-3.8Ag-0.7Cu, and pure Sn, was carried out by performing thermal aging at 150°C up to 1000 h. For pure Sn and Sn-3.5Ag solder, three distinctive layers, Ni3Sn4, SnNiP, and Ni3P, were observed in between the solder and electroless Ni-P; while for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders, two distinctive layers, (CuNi)6Sn5 and Ni3P, were observed. The differences in morphology and growth kinetics of the intermetallic compounds (IMCs) at the interfaces between electroless Ni-P and lead-free solders were investigated, as well as the growth kinetics of the P-enriched layers underneath the interfacial IMC layers. With increasing aging time, the coarsening of interfacial Ni3Sn4 IMC grains for pure Sn and Sn-3.5Ag solder was significantly greater than that of the interfacial (CuNi)6Sn5 IMC grains for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders. Furthermore, the Ni content in interfacial (CuNi)6Sn5 phase slightly increased during aging. A small addition of Cu (0.7 wt.%) resulted in differences in the type, morphology, and growth kinetics of interfacial IMCs. By comparing the metallurgical aspects and growth kinetics of the interfacial IMCs and the underneath P-enriched layers, the role of initial Cu and Ag in lead-free solders is better understood.