The proposal describes an innovative R & D program to improve solderability of electronic components by controlling the formation, growth and oxidation of Cu-Sn intermetallic compounds (IMC). The rate and extent of IMC growth depends, among other factors, on the microstructure of the finish plate on the Cu substrate. Differences in microstructure such as porosity, grain boundaries, fissures, delamination and other defects, provide variable paths for solidstate diffusion of Sn and oxidants to Cu substrate. These results in different rates of solderability degradation on aging. Three different types of plating and thickness will be used to produce different types of microstructures. These will include: (1) Electroplate at 3 levels of current densities to get 1, 3 and 6 um thickness; (2) Hot tin dip coating using 3 different coating cycles to produce 1, 3 and 6 um finish; and (3) Solder reflow of electroplated samples. Finish thickness and composition will be measured by XRF and microsection. Solderability at various stages of aging will be measured quantitatively by SERA. "Dip and Look" and wetting balance methods will be used as required. Accelerated aging will be accomplished by: (1) Steam aging below 95 degrees C; (2) Controlled heating in inert atmosphere; and (3) Anodic oxidation of samples in SERA apparatus. Microstructure will be determined using optical microscopy as well as modern surface science techniques (SEM, TEM, AUGER/ESCA) as needed. This part will be performed at the Center for Materials Characterization, University of North Texas, Denton, Texas.
