Low Temperature Transient Liquid Phase (LTTLP) Bonding for Au/Cu and Cu/Cu Interconnections

The Low Temperature Transient Liquid Phase Diffusion Bonding (LTTLP) process has been used to reduce the residual stresses and hence, improve the thermal fatigue performance of bonds between dissimilar electronic packaging materials. Aluminum oxide plated with either gold or copper has been bonded to copper heatsinks at temperatures less than 160°C, using In-Sn eutectic solders. After two hours at the bonding temperature, Cu/In-Sn/Cu joints exhibit a remit temperature in excess of 470°C and provide static strengths up to four times greater than the original solder bonds. Au/In-Sn/Cu joints do not exhibit a high remit temperature due to the formation of a stable Au-In-Sn phase which melts below 130°C. Both types of joints exhibited acceptable thermal fatigue performance for the conditions which were studied.