Plasma sprayed copper-nickel-indium coatings on titanium alloys: A. Koutsomichalis, H. Badekas (National Technical University of Athens, Athens, Greece). Mater. and Manuf. Processes, vol 10, no 5, 1995, 1087–1092

Abstract

Copper substrates have been widely used to mount semiconductor device chips due to their high electrical and thermal conductivity. To achieve high heat conduction, solders are utilized to bond the chip on the substrate. Soft and ductile solders such as indium and lead–tin alloys are often used to help release the stress developed in a bonded structure through plastic deformation and strain. In the solder joint, a major concern is the formation of intermetallics caused by the diffusion of copper atoms from the substrate to the joint. The growth of intermetallics makes the solder joint less ductile and less capable of releasing stresses. Prevention of copper diffusion is needed in applications where the solder joint must remain soft and ductile. On the other hand, in applications where creep movement cannot be tolerated, hard solders such as AuSn eutectic alloy should be considered. In this paper, we report a barrier metallization technique on copper substrates to block copper atoms from diffusing into the solder. Indium was selected as the solder medium in this study because of its increasing applications in many photonic devices such as laser diodes and photonic switches. Other solders such as lead–tin alloys can be also used with the metallization process. The metallization consists of Ni buffer layer and Cr blocking layer. The solder joint is fabricated by the fluxless bonding technology. After accelerated aging test at 130°C for 100 h, no sign of copper diffusion through the metallization is detected using energy dispersive X-ray (EDX). If 90°C is the maximum temperature of the solder joint during device operation, the corresponding time for no copper diffusion is 107 500 h, or 12.3 years. This result shows that the metallization process developed in this research is, indeed, very effective.