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.

Keywords

lead-free solder / intermetallic compound / electroless Ni-W-P / interfacial reaction / isothermal aging

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