A comparison of infrared- and torch-soldering of Au-Pd and Co-Cr metal-ceramic alloys using a high-fusing solder.

PURPOSE

The purpose of this study was to compare the bond strengths and fracture modes of soldered joints formed by infrared and gas-oxygen torch heating of a high-fusing, gold-based solder in two metal-ceramic alloys.

MATERIALS AND METHODS

Pairs of half-dumbbell-shaped specimens of either an Au-Pd or a Co-Cr alloy were positioned with a 0.25-mm gap and were joined using a high-fusing, gold-based solder by either gas-oxygen torch heating or infrared heating. The resulting specimens were subjected to a heat treatment that simulated ceramic firing. Each specimen was fractured in tension at a loading rate of 0.5 cm/min, and its bond strength was measured. The halves of the specimen were rejoined using the other heating method and were heat treated, and the specimen's bond strength was again measured. Fractured cross-sections were examined at a magnification of 40x to determine the following: the fracture mode (adhesive, cohesive, or mixed); the percentage of adhesive fracture; the presence or absence of voids, porosities, or flux inclusions; and the percentage of the cross-section that was discolored.

RESULTS

Three-factor analyses of variance showed that neither the heating method, the particular specimen tested, nor the order of testing significantly affected the bond strength (P < .05). For each alloy, significantly fewer infrared-heated joints than torch-heated joints contained voids, porosities, or flux inclusions visible at 40x (chi 2 test, P < .05). All fractures were either entirely cohesive in the solder or mixed cohesive and adhesive. When infrared heating was used, entirely cohesive fractures occurred more frequently in the Au-Pd alloy specimens than in the Co-Cr alloy specimens (chi 2 test, P < .05). The coefficients of variation of the bond strengths for the infrared-heated joints were smaller than those for the torch-heated joints.

CONCLUSIONS

Although the two heating methods produced solder joints that had strengths that were not significantly different, infrared-heated joints showed less scatter in bond strengths. It was suggested that, in the hands of most technicians, fewer infrared-heated joints would contain defects visible at a magnification of 40x. The presence of such defects may increase the probability of in vivo failure caused by cyclic stresses.