Joining of AlN to Cu Using In-base Active Brazing Fillers

Brazing of aluminum nitride (AlN), which is a good ceramic substrate in high power electronic applications, to copper was investigated using In-base active fillers. Compositions of brazing fillers were chosen as In–1 wt.% Ti (IT1), In–19 wt.% Ag–2 wt.% Ti (IAT2), In–15 wt.% Ti (IT15), and In–52 wt.% Ag–20 wt.% Cu–3 wt.% Ti (ACIT3). Brazing operation was performed in vacuum at temperatures of 650–900 °C. The brazing fillers showed good wetting on AlN and led to a strong bond between AlN and braze alloy. From the microstructural analysis, no evidence of reaction layer was clearly found at the interface under the experimental brazing conditions. The composition of brazing alloy layer changed into Cu9In4 phase due to the extensive dissolving of Cu from base metal. Bond strength, measured by 4-point bend test, was obtained as high as 23–30 kgf for the Cu/AlN/Cu joint brazed with IT15 and ACIT3 fillers, and shown to be nearly constant even when the temperature was varied within 700–800 °C. Most of the fracture appeared to proceed through the interior of the AlN ceramic. Based on the experimental 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.