Fabrication of Ni–P coating film on diamond/Al composite and its soldering reliability

Although the diamond/Al composite is a good heat sink material due to its high thermal conductivity and low cost, its surface cannot be wetted directly for microelectronic packaging. Using modified electroless plating procedures and recipes, a glossy, continuous, and uniform Ni–P film was successfully fabricated on the diamond/Al composite surface for the first time with a bonding strength of 15.1 MPa. This Ni–P coating layer is solderable for both lead-free SAC305 and Sn63Pb37 alloys on Cu dummy chips. A continuous intermetallic compound (IMC) layer was formed at the interface without any crack or void defects, and the shear strength of both solder joints was in the range of 39.9–41.2 MPa. During thermal storage tests, the growth of IMC was slow at 125 and 150 °C, but it elevated sharply at 175 °C. According to growth kinetics analyses, a Ni element can hinder IMC growth. The diffusion activation energy (Q) of (Cu,Ni)₆Sn₅ was calculated as 62.6 kJ/mol in SAC305 and 97.7 kJ/mol in Sn63Pb37 solder joints. Both microstructures and mechanical properties of the solder joint using the Ni–P coated diamond/Al composite can satisfy the requirement of microelectronic industrial applications.