Initiation toughness of silicon/glass anodic bonds

We describe an approach to characterize the initiation toughness (resistance to fracture initiation) of silicon/glass anodic bonds based on the universal stress stale that exists at the most common site of fracture initiation: the silicon/glass interface corner. The framework is universal in that it is independent of the bond size (area). It can be applied to rank bond initiation toughness as a function of processing parameters, and also used to design reliable bonds. In order to validate the theory we designed and fabricated relatively simple anodic bond test specimens and carried out a mechanical lest program to characterize bond initiation toughness. We find that while failure stresses vary significantly with bond area, the inferred initiation toughness is invariant with respect to bond area. We emphasize that the primary objective of this paper is not to develop the simplest, perhaps nondestructive, test possible. Instead it is to provide a rigorous mechanics-based framework to assess the initiation toughness of anodic bonds that can be used both to evaluate bond quality and to design reliable anodic bonds. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.