Growth of intermetallic compounds and brittle fracture behavior of Sn-Ag-Cu/ENIG joint with columnar Ni-P layer

Abstract

A growth of intermetallic compounds (IMCs) at the interface between electroless Ni/immersion Au (ENIG) and Sn-3.0Ag-0.5Cu (SAC305) solder and related brittle fracture behavior of solder joint with microstructure changes of electroless Ni-P was investigated. An amorphous columnar Ni-P and an amorphous structureless Ni-P surface finishes were used for the comparison. The (Cu,Ni)(6)Sn-5 IMC layers with a similar thickness were formed between solder and ENIG interface at the as-reflowed stage for both Ni-P surface finishes. During thermal aging, the interfacial IMC thicknesses for columnar Ni-P and structureless Ni-P increased up to 400 and 800 h, respectively, and then decreased with thermal aging time. This decrease of IMC thickness with thermal aging was due to spalling. The spalling rate of the columnar Ni-P sample was higher than that of the structureless sample. The shear strength decrease with aging time was lower for the columnar Ni-P sample than the structureless Ni-P sample. Brittle fracture for the columnar Ni-P sample was lower than for the structureless Ni-P sample.