Bonding behavior of copper thick films containing lead-free glass frit on aluminum nitride substrates

The present work indicates through thermodynamic considerations that the calcium, barium-borosilicate glass, which was selected as the bonding agent in copper paste, is chemically compatible to aluminum nitride (AlN) substrate. Meanwhile it implicates the scarce of reactivity which results in poor adhesion strength between the copper thick film and the AlN substrate. However after pre-oxidized treatment on AlN substrate, the adhesion strength was improved significantly by about 1 kg/mm2 (at 20 vol.% glass frit) than that of the untreated AlN substrate, due to the improved reactivity of the glass frit. The adhesion strength is also demonstrated being affected by frit content and firing temperature. The optimum value (1.85 kg/mm2) was obtained when the copper paste (containing 20 vol.% glass frit) was printed on the pre-oxidized AlN substrate and subsequently fired at 850 °C.