[Study on postsoldering of Ni-Cr ceramic alloys. Effect of soldering temperature and atmosphere]

The effects of soldering temperatures and atmospheres on tensile strength of solder joints were investigated for two types of Ni-Cr ceramic alloys and one type of gold solder for postsoldering. Each alloy and the gold solder were soldered with fluoride flux in an electric furnace in three different temperatures and four different atmospheres. Of the three different temperatures, one was just over the liquidus point of the solder, another 50 degrees C higher than the liquidus point and the other 100 degrees C higher than the liquidus point. Of the four different atmospheres, one was under vacuum, another under vacuum with a 6 l/h argon gas flow, another under vacuum with a 12 l/h argon gas flow and the other under vacuum with a 24 l/h argon gas flow. Tensile strength testing was performed at the solder joints. The fracture surface was observed by EPMA. Wettability of the liquid solder on each alloy was performed by the sessile drop method in high-purity argon gas. The surface tension and the contact angle of the liquid solder on MgO were determined by the sessile drop method in high-purity argon gas. The soldering was performed in the furnace used for the sessile drop method in high-purity argon gas. The results are summarized as follows. The tensile strength of UNI METAL-solder joints was significantly affected by the soldering temperature (p less than 0.01). However, the effect of the soldering atmosphere on the tensile strength was small. The effect of the soldering temperature and atmosphere on the tensile strength of Victory II-solder joints was small. Each alloy had a different adequate soldering temperature. With the increase in the soldering temperature, the diffusion layer of the solder joint interface increased, but no correlationship between the atmosphere and the diffusion layer thickness was observed. Fracture patterns of UNI METAL-solder joints were mixed adhesive-cohesive fractures with a large cohesive area. Fracture patterns of Victory II-solder joints were mixed adhesive-cohesive fractures with a large adhesive area. It was possible to perform the soldering without flux in the furnace used for the sessile drop method in a strictly controlled atmosphere of high-purity argon gas. Wettability of the liquid solder on UNI METAL was better than on Victory II. The surface tension of the solder used was 505.9 dyn/cm at 1000 degrees C. The contact angle of the solder used was 163.0 degrees at 1000 degrees C.