Characterization of Bulk and Thin Film Fracture in Electronic Packaging

As semiconductor packaging technologies continue to scale, it drives the use of existing and new materials in thin layer form factors. Increasing packaging complexity implies that materials in thin layers are subject to nontrivial loading conditions, which may exceed the toughness of the material, leading to cracks. It is important to ensure that the reliability of these low-cost materials is at par or better than currently used materials. This in turn leads to significant efforts in the area of material characterization at the lab level to speed up the development process. Methods for testing and characterizing fracture-induced failures in various material systems in electronic packaging are investigated in this paper. The learnings from different test methods are compared and discussed here. More specifically, different fracture characterization techniques on (a) freestanding “thin” solder-resist films and (b) filled “bulk” epoxy materials such as underfills and epoxy mold compounds are investigated. For thin films, learnings from different test methods for measuring fracture toughness, namely, uniaxial tension (with and without an edge precrack) and membrane penetration tests, are discussed. Reasonably good agreement is found between the various thin film toughness test methods; however, ease of sample preparation, fixture, and adaptability to environmental testing will be discussed. In the case of filled epoxy resin systems, the single-edge-notched bending (SENB) technique is utilized to obtain the fracture toughness of underfills and mold compounds with filler materials. Learnings on different methods of creating precracks in SENB samples are also investigated and presented.