Bonding behavior of Cu/CuO thick film on a low-firing ceramic substrate

Abstract

The adhesion strength between a low-firing substrate consisting of an alumina/glass composite and a copper thick film was affected by the addition of cupric oxide and glass frit to the copper paste in a new co-firing process. An interlayer, 3–4 μm in thickness, was produced in the metal-ceramic interface during the new co-firing process due to the diffusion of copper. At the same time, the adhesion strength was improved by controlling the cupric oxide content. The addition of about 3 wt.% glass frit (softening point = 670 °C, based on the calcium-barium borosilicate glass composition) to the metal paste resulted in highest adhesion strength of 3 kg/mm2 with a shift of the debonding site toward the ceramic substrate within the interlayer. The shift of the debonding site could be observed by comparing the ratios of Al2O3/Cu and Ca concentration at the test pad areas on the substrate after debonding. The shift of the debonding site is attributed to the migration of glass frit into the interfacial region. The migration of glass frit occurred easily when the softening point of the glass frit was compatible with the new co-firing process, regardless of how much frit was used.