| Alumina-copper substrate was fabricated by active metal brazing with Ag-Cu-Zr alloy. The microstructure of the Al₂O₃/Cu pint was investigated by using SEM, EDX and EPMA. The bond strength for the bulk shaped pint was evaluated by shear test. The reaction product was identified as ZrO₂ with a monoclinic structure. The reaction layer thickness was nearly constant(∼4㎛) in the brazing temperature range of 785-850℃ because the content of Zr in the brazing alloy was consumed in the reaction with bonded copper. The shape of the brazement was irregular and also the width of the brazement was decreased with increasing the temperature because of the diffusion of Cu in the filler metal. The joint strength was abruptly decreased at the brazing temperature higher than 800℃ due to a decrease in the width of the brazement. The pint of a brazement with ∼140㎛ width, which was formed by brazing at 800℃ for 30min, showed the highest fracture strength(∼96㎫). In the alumina-copper substrate, the fillet width and morphology of the pint edge strongly affected the physical properties of the joint. To obtain a sound substrate pint, the brazing temperature lower than 800℃ was required. The substrate brazed at 745℃ did not form the crack during 50 thermal cyclic fatigue. |
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