Flip chip interconnection using anisotropic conductive adhesives for RF and high frequency applications

Anisotropic conductive adhesives have been considered and evaluated as promising interconnect materials for flip chip assembly in the applications for low cost, high-density and high speed interconnection packages. In this paper, we have evaluated and compared several flip chip interconnects using anisotropic conductive adhesives at RF and high frequency range. The performances of highspeed circuits are limited by package interconnect discontinuity doe to large inductance and resistance in the high frequency range. This discontinuity is determined by the interconnection geomehy and materials used. For bumps on the IC, Au stud, Au electroplated and electroless Ni/Au were used, and for the interconnection adhesives, two kinds of ACFs with different dielectric constant were used. The high kequency measnrements were performed on the test flip chip vehicles using different bonding materials to evaluate high frequency model parameters based upon ACF flip chip model and network analysis. We applied these ACFs flip chip technologies to the assemblies of passive device using RF IPD (Integrated Passive Device) and active device using RF active MMIC device on RF module to demonstrate real applications of ACF interconnection at RF and high frequency range, and compared the results with those of flip chip assembles using conventional methods such as solder ball interconnection. The reliability of ACF flip chip interconnects was also investigated by various environmental tests, such as thermal cycling test (-55 OC/+125 "C, 1000 cycle), high temperature humidity test (85 'C/85%RH, 1000 hours) and high temperature storage test (150 OC, dry condition) to evaluate the effect of environmental attacks on the electrical stability of ACF flip chip assemblies.