Four isotropically conducting adhesives were used to form lap joints between copper fingers which had been prepared with four surface metallizations (Cu, Au, Pd, and PdNi). A micromechanical tester was used to perform pull and fatigue tests on the 16 adhesive/finish combinations. The micro-ohm resistance change was measured during both the pull and fatigue tests. The similarities and differences between the mechanical strength, fatigue life, and resistance change for the 16 adhesive/finish combinations have been reported, and conclusions were made about relative motion between silver particles, and the fracture interfaces.

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A commercial Hitachi anisotropic conducting film (ACF) was used to form the electrical interconnection between aluminum pads on a glass plate substrate, and electrolysis tin coated copper pads on a polyimide flexible circuit. These interconnections were aged over 1,400 hours at 85°C and 79% relative humidity. Throughout the thermal aging period a variety of electrical properties were measured. Electrical resistance of the ACF bonds was monitored in situ providing a continuous record of the resistance increase toward failure. The specimens were periodically brought back to ambient and dried out to monitor the resistance recovery and how other electrical properties were affected due to aging. A continuous resistance monitoring during the temperature ramp provided the temperature coefficient of resistance as a function of aging. The other electrical properties measured at ambient conditions were the voltage coefficient of resistance, both at low currents and at high currents, where self-heating occurred, the magnitude of l/f noise, and the thermopower. As will be explained, each of these electrical properties provides an independent measurement of critical interconnection parameters. IntroductionAnisotropic conducting adhesive (ACA) films are currently the primary method to interconnect flat panel displays to external flexible circuits. Initial products have emerged and research is continuing on the use of ACA films for direct chip attach to circuit boards. ACAs have the advantage in fine pitch applications of eliminating the difficult registration problem between the interconnecting pad and the solder balls. ACAs also act as an underfill eliminating a separate underfill process needed for some applications. Other advantages are that the processing for ACAs require lower bonding temperatures, and are lead free. Tests by independent researchers [ 13 and ACA manufacturers [2] have demonstrated the reliability of the joints formed using ACA. The literature, however, is still lacking a satisfactory quantitative understanding of the conduction mechanism through all the redundant interfaces, and a consistent and complete understanding of the failure mechanisms for commercial products.Many flat panel displays use aluminum metallurgy on the bonding pads. Because the displays that prompted this study had aluminum, and tungsten clad aluminum pads, the test vehicles used in this study had aluminum contact pads and traces. The hard oxide coating present on aluminum and tungsten surfaces represents special challenges for the formation of stable mechanical contacts that are electrically conducting. Articles have indicated that these contacts are