Field-assisted diffusion bonding and bond characterization of glass to aluminum

The bonding of glass wafers to aluminum foils in multi-layer assemblies was investigated by the field-assisted diffusion bonding process. Bonding was effected at temperatures in the range 350-450 degrees C and with an applied voltage in the range 400-700 V under a pressure of 0.05 MPa. The experimental parameters of voltage and temperature were the main factors in influencing the ionic current leading to the formation of the depleted layer. The peak current in three-layer samples (glass/aluminum/glass) during bonding is twice that for the case of the two-layer samples (aluminum/glass). SEM and EDS analyses showed the presence of transition layers near the glass/aluminum interface, and XRD data demonstrated the phase structure of the glass/aluminum interface. The tensile strength of the bonded material increased markedly with increasing temperature and applied voltage. Fracture occurred in the glass phase near the interface with the aluminum. Finite element analysis showed the residual deformation in three-layer samples to be significantly lower than in two-layer samples. The symmetry in three-layer samples resulted in the absence of strain, an important advantage in MEMS fabrication.