Significant Inhibition of IMCs Growth between an Electroless Ni-W-P Metallization and SAC305 Solder During Soldering and Aging

Abstract

The formation and growth behavior of intermetallic compound (IMC) layers after introducing an electroless Ni-W-P metallization into the Sn-3.0Ag-0.5Cu (SAC305) solder joint during soldering and aging were investigated. The soldering was performed at 250 °C for 10 min, followed by air cooling and aging treatment at 150 °C up to 15 days. The results show that the scallop-like Cu6Sn5 IMC layer and planar-like Cu3Sn formed between solder and Cu substrate during soldering and aging. The Ni3P and (Ni,Cu)3Sn4 compounds were formed between electroless Ni-W-P layer and solder, and Cu substrate was not damaged and kept a smooth interface. When the isothermal aging treatment was applied, the total thickness of IMCs which formed at the SAC305/Cu and SAC305/Ni-W-P/Cu interface increased with increasing aging time. Kirkendall voids emerged at the Cu3Sn and the Ni3P layers, but the voids emerged at the Ni3P layer in the form of crack. The amount of Kirkendall voids increased and the crack elongated with increasing aging time. The Cu6Sn5 and (Ni,Cu)3Sn4 grains grew by merging adjacent grains. In the process of growth, the growing interfacial compounds filled the free space, and new columnar dendrite grain of (Ni,Cu)3Sn4 constantly generated during aging treatment. After 15 days aging, the Ni-W-P barrier layer was still remained, which indicated that the Ni-W-P layer can be a good barrier layer between the solder alloys and Cu substrate.