Anisotropic conductive adhesive films for flip-chip interconnection onto organic substrates

We have developed new anisotropic conductive adhesive films (ACFs) for flip-chip interconnection to organic substrates such as printed wiring boards (PWBs). In order to reduce thermal and mechanical stress and strain induced by CTE (coefficient of thermal expansion) mismatches between chip and organic substrate, the elastic modulus of the ACF adhesive resin was lowered. In addition, the ACF adhesion strength was enhanced by optimizing the adhesive resin formulation. As a result, the modified ACF in flip-chip interconnection between gold bumps of a chip and Ni/Au coated pads on an FR-4 PWB shows stable contact resistance of lower than 10 m/spl Omega/ even after exposure to various environmental tests such as a thermal cycling test (-55/spl deg/C/+125/spl deg/C, 1000 cycles) and a pressure cooker test (121/spl deg/C, 2 atm, 168 hr) following an IR reflow treatment (twice). In addition, the excellent connection reliability was confirmed by in-situ measurement of contact resistance on a thermal cycling test (-55/spl deg/C/+125/spl deg/C, 1,000 cycles) and a high temperature humidity test (85/spl deg/C/85%RH, 1,000 hr) following IR reflow treatment (twice).