Journal of the Microelectronics & Packaging Society Vol. 12, No. 1, p. 9-16. 2005 9 Flip Chip Assembly Using Anisotropic Conductive Adhesives with Enhanced Thermal Conductivity Myung Jin Yim*, Hyoung Joon Kim and Kyung Wook Paik Center for Electronic Packaging Materials (CEPM) Deptartment of Materials Science and Engineering, KAIST 373-1, Kusong-dong, Yusong-gu, Taejon, 305-701, Korea Abstract: This paper presents the development of new anisotropic conductive adhesives with enhanced thermal conductivity for the wide use of adhesive flip chip technology with improved reliability under high current density condition. The continuing downscaling of structural profiles and increase in inter- connection density in flip chip packaging using ACAs has given rise to reliability problem under high current density. In detail, as the bump size is reduced, the current density through bump is also increased. This increased current density also causes new failure mechanism such as interface degradation due to inter- metallic compound formation and adhesive swelling due to high current stressing, especially in high current density interconnection, in which high junction temperature enhances such failure mechanism. Therefore, it is necessary for the ACA to become thermal transfer medium to improve the lifetime of ACA flip chip joint under high current stressing condition. We developed thermally conductive ACA of 0.63 W/m·K thermal conductivity using the formulation incorporating 5 μm Ni and 0.2 μm SiC-filled epoxy-based binder system to achieve acceptable viscosity, curing property, and other thermo-mechanical properties such as low CTE and high mod- ulus. The current carrying capability of ACA flip chip joints was improved up to 6.7 A by use of thermally conductive ACA compared to conventional ACA. Electrical reliability of thermally conductive ACA flip chip joint under current stressing condition was also improved showing stable electrical conductivity of flip chip joints. The high current carrying capability and improved electrical reliability of thermally conductive ACA flip chip joint under current stressing test is mainly due to the effective heat dissipation by thermally con- ductive adhesive around Au stud bumps/ACA/PCB pads structure. Key words: Flip chip, anisotropic conductive adhesives, thermal conductivity, current carrying capacity 1. Introduction Flip chip technology has been widely used to meet the package requirements of increasing density and higher electrical performance for electronic devices to be still smaller, shorter and thinner. Flip chip bonding is also more effective in dissipating the heat from high density IC due to short thermal path than conventional plastic mold package 1) . Especially, flip chip assembly using Anisotropic Conductive Adhesives (ACAs) has been gaining much attention for its simple and lead-free process- ing as well as cost effective packaging method. ACAs do not need additional underfill and poten- tially can be processed in much shorter times than the conventional solder/underfill method, and already successfully implemented in the package methods of reliable direct chip attach such as Chip- On-Glass (COG), Chip-On-Film (COF) for flat panel displays and Chip-On-Board (COB) for mobile electronics 2-5) . ACAs consist of mixtures of conductive particles *Corresponding author E-mail: myungjin@kaist.ac.kr