Abstract
A fracture-mechanics investigation of peeling of the insulating films and wiring metals in a redistribution layer was performed
on three types of photosensitive resins (polyimide, polybenzoxazole, and phenol) by using finite-element analysis with a simplified
three-dimensional structure of a semiconductor package. Based on the interfacial toughness of the insulating films on the wiring
metal, it was predicted that polyimide would peel the least in the temperature profiles of both the temperature cycling and the reflow
process. That result was correlated well with the interfacial toughness at ambient temperature or below. Also, the fatigue crack
propagation path after peeling had occurred was predicted, with the results that in any of the insulating-film materials, the ratio of
the driving force of the crack propagation to the fracture toughness was higher at the interface than in the insulating films and the
fatigue crack propagation path was at the interface. A statistical survey showed that in both the reflow process and temperature
cycling, insulating-film materials for the redistribution layer should be designed effectively for high interfacial fracture toughness at
ambient temperature or below, and also the insulating films should have high elastic modulus and low thermal expansion coefficient.
Consequently, polyimide is the most reliable material for the insulating films of the redistribution layer.
