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 mu m 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 degrees C, based on the calcium-barium borosilicate glass composition) to the metal paste resulted in highest adhesion strength of 3 kg/mm(2) 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.