A study of the effects of solder volume on the interfacial reactions in solder joints using the differential scanning calorimetry technique

The differential scanning calorimetry (DSC) technique was employed to understand the interfacial reactions during soldering by simulating the soldering process as well as analyzing the interfacial reactions. The measurement of peak temperatures and heat involved provides useful information about the interfacial reactions, such as the amount of intermetallic compounds (IMCs) formed and the amount of Cu dissolved. Tin-plated Cu balls with different Sn thicknesses were used to investigate the solder-volume effect. As the Sn-layer thickness decreases, the amount of the IMC formed during reflow increases in general. This suggests IMC formation depends on the Sn volume. In addition, a Ni layer (electroless and electroplated), introduced as a diffusion barrier between Cu and Sn, was found effective in reducing Cu out diffusion. The results from the DSC study were confirmed by conventional metallography, scanning electron microscopy (SEM), and energy dispersive x-ray (EDX) techniques.