Influence of benzotriazole on electroplated Cu films and interfacial microstructure evolution of solder joints

Benzotriazole (BTA), a nitrogen-containing heterocyclic compound, was employed as a leveler to prepare Cu film. During electroplating, the concentrations of BTA were 0, 10, 20, 50, and 100 ppm. After electroplating, the Cu substrates were soldered by dip soldering with Sn3.0Ag0.5Cu (SAC305) solder at 250 °C for 10 s, then isothermal aging was conducted at 180 °C up to 240 h. The electroplated Cu (EPC) films and solder joints were characterized by scanning electron microscope (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and uniaxial micro-force test system. Experimental results showed that high concentration BTA (≥ 50 ppm) would lead to a reduction in the thickness of the EPC film. The surface roughness of the EPC film increased at first and then decreased with increasing BTA concentration. Additionally, the XPS patterns indicates that the Cu(I)-BTA complex could form on the copper surface. After soldering and thermal aging, for sample with low concentration of BTA (≤ 20 ppm), Cu–Sn intermetallic compound (IMC) was observed between the SAC305 solder and substrate. However, when the BTA concentration increased to 50 and 100 ppm. The Au coating and the Ni coating on the Kovar substrate would participate in interfacial reaction during the dip soldering process, resulting in the formation of single (Ni, Au, Cu)₆Sn₅ layer. The growth rate of the (Ni, Au, Cu)₆Sn₅ IMC was significantly lower than that of the Cu–Sn IMCs. Moreover, the incorporated impurities segregated and the doping of Au and Ni resulted in the decrease of shear strength at first and then increase as the BTA concentration increased.