Interfacial IMC growth of SAC305/Cu joint with a novel dual-layer of Ni(P)/Cu plating during solid-state aging

Abstract

A dual-layer barrier of electroless-plated Ni(P)/electroplated Cu was prepared as under-bump metallization (UBM) joined with Sn-3.0Ag-0.5Cu (SAC305) lead-free solder. The interfacial reaction and growth mechanisms of the intermetallic compounds (IMCs) formed between the SAC305 solder and the dual-layer UBM during reflow and isothermal aging at different temperatures were systematically investigated. It was found that only a single (Cu,Ni)6Sn5 IMC layer was observed between the SAC305 solder and electroless Ni(P) layer. At low aging temperature (150 °C), there was a very slow IMCs growth due to the protection of thin (Cu,Ni)6Sn5 layer, and the surface morphologies of interfacial (Cu,Ni)6Sn5 grains exhibited hexagonal-type rod-like. While during aging process of 180 °C temperature, most IMC morphologies of (Cu,Ni)6Sn5 grains exhibited scallop-like and only a small part of IMCs exhibited hexagonal-like. And these prism hexagonal-like IMCs gradually transformed into scallop-like morphologies with increasing aging time. When the aging temperature reached up to 210 °C, the IMCs had the fastest grow rate and almost all IMC morphologies of (Cu,Ni)6Sn5 grains exhibited scallop-like in every stage of reactions. Compared with the interfacial IMCs layer evolutions of the Sn-based solders with bare Cu or Ni(P)/Cu UBMs, the interfacial IMCs layer between the dual-layer of Ni(P)/Cu plating and solder possessed better thermal stability, indicating that the dual-layer of electroless-plated Ni(P)/electroplated Cu was a excellent diffusion barrier in the microelectronics packaging.