JOINING OF ALN TO CU USING IN-BASE ACTIVE BRAZING FILLERS

Brazing of aluminum nitride (ALN), which is a good ceramic substrate i n high power electronic applications, to copper was investigated using In-base active fillers. Compositions of brazing fillers were chosen a s In-1 wt. % Ti (IT1), In-19 wt. % Ag-2 wt. % Ti (LAT2), In-15 wt. % T i (IT15), and In-52 wt. % Ag-20 wt. % Cu-3 wt. % Ti (ACIT3). Brazing, operation was performed in vacuum at temperatures of 650-900 degrees C . The brazing fillers showed good wetting on AlN and led to a strong b ond between ALN and braze alloy. From the microstructural analysis, no evidence of reaction layer was clearly found at the interface under t he experimental brazing conditions. The composition of brazing alloy l ayer changed into Cu9In4 phase due to the extensive dissolving of Cu f rom base metal. Bond strength, measured by 4-point bend test, was obta ined as high as 23-30 kgf for the Cu/AlN/Cu joint brazed with 1T15 and ACIT3 fillers, and shown to be nearly constant even when the temperat ure was varied within 700-800 degrees C. Most of the fracture appeared to proceed through the interior of the AlN ceramic. Based on the expe rimental results, it is believed that a strong bonding between AlN and braze alloy can be achieved without the apparent forming of a Ti-rich reaction layer at the interface.