Characterization of glass-ceramic to metal bonds

Abstract

Glass-ceramic thick films were deposited on copper and copper/invar/copper substrates by screen printing and subsequent firing in a belt furnace. One lithium-zinc silicate glass and two lithium-aluminosilicate glasses were deposited. Microstructures of the coatings and the coating/substrate interfaces were studied using optical and electron optical techniques. SEM was used to investigate the glass-ceramic microstructure and EPMA to characterize chemical composition across the interface. Crystalline phases were identified using X-ray and electron diffraction. The lithium-aluminosilicate glass-ceramics were composed of lithium disilicate, β-spodumene and quartz crystals in residual glass. Lithium disilicate and quartz were the only crystals identified in the lithium-zinc silicate glass-ceramic. In all the samples copper diffused extensively through the glass-ceramic during firing and formed Cu2O precipitates in the glass-ceramics adjacent to the interface. Strong adhesion between the glass-ceramic and the substrates is promoted by copper diffusion and oxide development at the glass-ceramic/substrate interface. The strongest bonds develop when the Cu2O forms as discrete particles rather than a continuous layer at the interface. Interfacial residual stress also influences the measured adhesion strength.