Correlation between intermetallic thickness and roughness during solder reflow

The evolution of Cu-Sn and Ni-Sn intermetallic compound (IM) morphologies d uring isochronal reflow of a PbSn solder with Cu and electroless-Ni was inv estigated. The root mean square roughness of the Cu-Sn and Ni-Sn IM layers exhibited a linear dependence on average thickness, with gradients (alpha) of 0.33 and 0.65, respectively. The difference in alpha values was attribut ed to different thickness distributions resulting from morphological dissim ilarity of the IM layers. The apparent activation energies for growth and r oughness evolution of both IM were found to be similar and suggest that bot h IM thickness and roughness evolution are controlled by the same mechanism .