Controlling Cu electroplating to prevent sporadic voiding in Cu3Sn

One reliability concern, when soldering to a Cu surface finish, is the sporadic mechanical degradation of solder joints due to the formation and growth of voids within the interfacial Cu₃Sn intermetallic compound (IMC) layer and at its interface with the Cu pad structure. Excess organic impurity incorporation during Cu electroplating has been shown to cause this problem. The level of impurity incorporation is found to depend greatly on interactions between the plating additive chemistry and the plating process parameters. A general picture has been developed, based upon the parabolic adsorption behavior of organic molecules on metal electrodes in aqueous plating solutions as a function of the applied potential. Thus the propensity for voiding, in soldering and subsequent thermal aging, can be manipulated by varying a range of plating parameters. The mechanistic understanding required to devise practical control is outlined. Any remaining research required for the formulation of step-by-step process guidelines is identified.