Effects of multiple reflows on interfacial reaction and shear strength of SnAgCu and SnPb solder joints with different PCB surface finishes

Authors

Ping Liu, Tianjin University, China
Pei Yao, University of WollongongFollow
Jim Liu, MFAL, Motorola, China

RIS ID

32373

Publication Details

Liu, P, Yao, P & Liu, J (2009), Effects of multiple reflows on interfacial reaction and shear strength of SnAgCu and SnPb solder joints with different PCB surface finishes, Journal of Alloys and Compounds, 470(1-2), pp. 188-194.

Abstract

The effects of multiple reflows (1, 2, 4, 6, 8, 10 numbers of reflow) on interfacial reaction and shear strength of Sn3.8Ag0.7Cu (SAC) and Sn37Pb (SP) joints were systematically investigated using electrolytic Ni/Au and organic solderability preservative (OSP) finished pad. In the case of OSP finished substrate, the well-known intermetallic compound (IMC) Cu₆Sn₅ was observed for both solders. While for the Ni/Au finished substrate, the IMC Ni₃Sn₄ and (CuNi)₆Sn₅ were formed on the interface of SP and SAC joints, respectively. With the increasing number of reflows, the thickness of IMCs on all reaction couples increased gradually and the IMC grain coarsened. The IMC growth kinetics showed that the interfacial IMC Cu₆Sn₅ was controlled by grain boundary diffusion and that the IMCs (Ni₃Sn₄ and (CuNi)₆Sn₅) near Ni layer had interactive diffusion control of grain boundary and volume diffusion. Moreover, IMC growth at Cu interface was faster than that at Ni interface, irrespective of the solder type. Shear test results showed that the shear force did not change much until eight numbers of reflow for each reaction couple. The ductile fracture indicated that the shear strength of solder joints could not be significantly influenced by the thickness and morphology of the interfacial IMC.