Reliability of Die Attach on DBC Substrates With Different Ni Surface Finishes Using BiAgX Solder

Abstract

Ni plating is a commonly used barrier layer for direct bond copper substrates used in high-temperature and high-power applications. The Ni plating method can be electrolytic or electroless and the composition options include pure Ni, Ni:P, Ni–Co, or Ni:B. BiAgX solder paste is a promising lead-free solder for applications below 200 °C. The reactivity of these different Ni layers with the BiAgX solder paste has been compared. Specially the reaction to form NiBi3 during 200 °C storage and −55 °C to + 195 °C thermal cycling test. The initial shear strength of all these Ni plating is ~4.8 kg/mm2. A degradation in shear strength was observed in further aging. Among them, the electrolytic Ni:P plated samples had the lowest degradation. The reason of degradation is determined to be the formation of NiBi3 intermetallic, since it had been found in all the other Ni plating samples beside the electrolytic Ni:P. Similar results were observed in thermal cycling test.