Kinetics of Thermocompression Bonding to Organic Contaminated Gold Surfaces

The kinetics of thermocompression gold ball bonding were studied for gold metallization contaminated with organic films. The contaminants studied were residual photoresist and atmospheric contamination. For gold metallization contaminated with organic films, thermo-compression gold bonding is a two-stage process. The first stage occurs within a fraction of a second and results from the mechanical disruption of barrier films by shear displacements at the faying surface. Bonding during this initial stage is a strong function of the interface temperature, the bonding force, and the contaminant films. The second stage involves growth of the metal-metal interfaces by a sintering phenomenon. Growth of bonds by sintering also occurs in the absence of external loads though at a decreased rate. Analysis of the rate data leads to the conclusion that the growth mechanism follows a parabolic rate law and, in the absence of external loads, exhibits an activation energy of approximately 11 kcal/mole. Under high external loads, the rate of second-stage growth exhibited little temperature dependence, indicative of a stress-assisted process. Bond growth rates for the atmospherically contaminated metallization were an order of magnitude higher than that for the photoresist contaminated samples.