Interfacial voiding in solder joints formed with Sn-Ag-Cu solder alloys and electroplated Cu was examined as a function of the plating solution chemistry and parameters. Galvanostatic Cu plating of *10 lm thick Cu films was performed in a commercially available plating solution, and in model generic plating solutions. Analysis of the current voltage behavior along with Secondary Ion Mass Spectrometry studies of organic impurity content of two plated and a wrought copper samples, yielded a conclusion that for certain chemistry solutions (e.g., H 2 SO 4 + CuSO 4 + Cl -+ PEG) and current density ranges above 2.5 mA cm -2 , organic impurities were incorporated into the growing Cu. Solder joints were produced with a variety of electroplated Cu samples. These joints were, then, annealed at a temperature of 175°C for 1 week, cross sectioned and examined. In general, it was observed that interfacial voiding in laboratory electroplated Cu layers was qualitatively similar to the unexplained voiding observed in some industrially plated Cu products. More specifically, it was found that the propensity for voiding could be correlated with specific electroplating parameters that in turn were associated with significant incorporation of organic impurities in the Cu deposit.

The microstructure of the Sn-Ag-Cu solder is examined by optical microscopy and scanning electron microscopy (SEM) for various compositions near the ternary eutectic for different cooling rates from the solder melt. Focus is on the size and orientation of Sn grains as indicated by cross-polarized, light optical microscopy, and pole figures from x-ray diffraction. We find that both composition and cooling rate have strong influences on Sn grain size, with Sn grain size increasing an order of magnitude as Cu concentration increases from 0% to 1.1%. Cyclic growth twinning, with twinning angles near 60°, is observed in Sn-Ag-Cu alloys near the composition Sn-3.9Ag-0.6Cu.

The sporadic voiding phenomenon in Cu 3 Sn intermetallic compound (IMC) formed during thermal aging, sometimes referred to as "Kirkendall voiding", has been found to lead to degradation of solder joint reliability in board level shock testing. It was suggested that the voiding phenomenon resulted from the incorporation of specific impurities in the copper during electroplating. In this study, Cu samples were electroplated from a generic suppressor-brightener additive system using a rotation disk electrode (RDE) apparatus. Overpotential during plating, surface morphology and the propensity for voiding of plated samples were investigated. Galvanostatic (constant current density) plating was conducted at 10 mA/cm 2 sequentially up to 18 hours. The solution exhibited dependences of overpoential and voiding propensity on bath aging, due to the breakdown of the organic additives. Cu samples were also plated in the current density range of 0.8-40 mA/cm 2 . In the 10-20 mA/cm 2 , current density range, a fine-grain, smooth, deposit surface was observed, accompanied by an especially low voiding level of samples plated in that range.

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