Analysis of Adhesion and Fracture Energy of Nano-Particle Silver in Electronics Packaging Applications

Nano-particle silver (NPS) conductors are increasingly being investigated for package level electronics applications. Unlike traditional thick film materials and conductive inks, nano-particle conductors often do not incorporate compounds to promote interfacial adhesion such as binders used in thick films and polymer adhesives used in conductive inks as these adhesion promoters can degrade the electrical performance. The NPS is concerned with low adhesion to most of processed polymer surface such as liquid crystal polymer (LCP), polyimide, and benzocyclobutene (BCB). Moreover, the adhesion mechanism of NPS has not been identified yet. Thus, as a first step to identify NPS adhesion mechanism and thus, to improve NPS adhesion, quantitative measurement of the adhesion strength of NPS is necessary. Since conventional adhesion test methods are not directly applicable to thin (similar to 2 mu m) NPS film adhesion test, a new adhesion test method is developed in this paper to estimate the adhesion strength of NPS films. The newly developed adhesion test method is called modified button shear test (MBST) because it modifies the conventional button shear test and integrates the generally known die shear test. The MBST is used for measuring not only interfacial bond strength, but also interfacial fracture energy. The interfacial bond strength in tension and the interfacial fracture energy of NPS with LCP substrate measured by MBST are 24.4 MPa and 17.2 J/m(2), respectively. The MBST is generic in nature and can be extended to other thin films adhesion test for measuring interfacial bond strength and interfacial fracture energy.