Microwave modeling and characterization of anisotropic conductive adhesive flip-chip interconnection

Microwave model and high-frequency measurement of the ACF hip-chip interconnection is investigated using a microwave network analysis. The test IC was fabricated using a 1-poly and 3-metal 0.6 mu m Si process with an inverted embedded microstrip structure. As flip chip bumps, electroless Ni/Au plating was performed on test IC chips and as an interconnect material, Several ACFs were prepared and flip-chip bonded onto the Rogers(R) RO4003 high frequency organic substrate. S-parameters of on-chip and substrate were measured separately at a frequency range of 200 MHz to 20 GHz using a microwave network analyzer HP8510 and cascade probe. Also the cascade transmission matrix conversion was performed. The same measurements and conversion were conducted on the test chip mounted substrates at the same frequency range. Then impedance values in hip-chip interconnection were extracted from cascade transmission matrix. The extracted model parameters of the 100 mu m x 100 mu m interconnect pad show that the resistive increases due to skin effect up to 8 GHz. And beyond this frequency, conductive loss of epoxy resin also increases. Reactance is dominantly affected by inductances of Ni/Au bumps and conductive particles in the ACF interconnection at whole measured frequencies. ACF flip chip interconnection was performed only below 0.1 nH. The effects of different conductive particle materials on electrical behavior in GHz were investigated. Different particle materials in ACF show difference in the reactance and resistance behavior up to 12 GHz and in the resonance frequency. Our results indicate that the electrical performance of ACF combined with electroless Ni/Au bump interconnection is comparable to that of solder joint.