A simple, cyanide-free, slightly acidic, chloride-based solution has been developed for the electrodeposition of Sn-0.7wt%Cu solder films. The solution contains only one additive (tri-ammonium citrate) other than the metal salts and is stable for more than 36 days. The optimum citrate concentration is 0.30 mol/L for 0.22 mol/L of SnCl2•2H2O. The addition of 0.003 mol/L of CuCl2•2H2O to this solution can produce near eutectic (Sn-0.7 wt% Cu) deposits, on Au, Ni or Cu substrates, at current densities of 10-12.5 mA/cm2. Plating rates are in the 20-27.5 μm/hr range at room temperature. Copper is evenly distributed (~0.7wt%Cu) through most of the thickness, with slightly higher Cu levels at the solder/Ni interface. After solder reflow at 260°C, two phases are present, Sn plus either Cu6Sn5 for Cu substrates or (Cu,Ni)6Sn5 for Ni substrates.

The dissolution process of nickel in liquid Pb-free 87.5% Sn-7.5% Bi-3% In-1% Zn-1% Sb and 80% Sn-15% Bi-3% In-1% Zn-1% Sb soldering alloys has been investigated by the rotating disc technique at 250-450°C. The temperature dependence of the nickel solubility in the solders obeys a relation of the Arrhenius type cs = 4.94 × 102 exp (-39500/RT) % for the former alloy and cs = 4.19 × 102 exp (-40200/RT)% for the latter, where R is in J mol-1 K-1 (8.314 J mol-1 K-1) and T in K. The solubility values of nickel in the alloys differ considerably, while the dissolution rate constants are rather close. The data presented can be used to evaluate (i) the thickness of the dissolved portion of the solid nickel material during soldering, (ii) the extent of saturation of a solder with nickel and (iii) the effect of dissolution on the growth rate of intermetallic layers at the Ni-solder interface.