There is growing interest in using anisotropically conductiveadhesives (ACAs) not only for interconnections between LCDs and PCBs butalso in higher current contacts such as flip chip and rigid-flexinterconnects, for example in automotive applications. 1/f noisemeasurements are a common diagnostic tool for investigation of chipmetallization lifetime. Resistance fluctuations (which mean noise) areinduced by electron mobility fluctuations due to, for example,scattering on moving atoms (electromigration). Another noise source isresistance fluctuations that are dominated by current constriction in apoint contact. Both mechanisms play a role in ACA contacts. A technologyto prepare anisotropically conductive interconnections with only a fewconducting particles per contact to separate different failuremechanisms and to realize the noise measurements is presented. Samplesare exposed to current, and noise is measured before and after thesedamaging processes. Measurements show that anisotropically conductivecontacts exhibit a transition from mixed film/spot contact behaviour tofilm dominated contacts when the gap between the contact pads isincreased, transgressing the diameter of the conducting particles. Aftercurrent damaging, we find a noise spectrum consisting of a 1/f portionand an additional 1/f2 component, which is relaxed during afollowing zero current period. The increase in noise power afterdamaging is significantly higher than the increase of resistance. Thetests were carried out on FR-4 substrates with Cu traces and Ni/Aumetallization. Adhesives were filled with Au particles
展开▼
