Anodic bonding to imperfect surfaces

The intimate surface contact necessary for anodic bonding of a metal to a glass is examined in terms of the electrostatic forces which promote this contact and surface imperfections which prevent this contact. Surface imperfections that are considered include foreign particles, isolated hillocks, and periodic curved and angular surfaces. With curved and angular surfaces, a critical voltage exists that causes spontaneous mating of the surfaces by elastic or plastic deformation. Below this voltage, intimate surface contact is achieved by viscous flow. For isolated hillocks and foreign particles, surface conformation generally occurs by viscous flow because of large stress concentrations at these imperfections. The resulting time required for intimate surface contact is a very sensitive function of the imperfection size.