ABSTRACT
Flip-chip technology has emerged as a high-density, high-performance interconnection method. A revolutionary technology to attach flip-chip devices without solder bumps or balls and underfill uses anisotropic conductive adhesive films (ACFs). Conductive adhesives avoid the toxicity and environmental concerns of lead and chlorofluorocarbon-based flux cleaners, but also have technological advantages over tin-lead (Sn/Pb)-based solder interconnects: (1) the lower curing temperature required for the adhesive reduces joint fatigue and stress cracking problems, enabling the use of heat-sensitive or non-solderable materials; (2) fewer processing steps enable an increase in production throughput; (3) the higher flexibility and the closer match in the coefficient of thermal expansion (CTE) enable a more compliant
connection, while minimizing failures and (4) the smaller filler particle size facilitates finer line resolution [1]. Anisotropic conductive adhesives can also provide short electrical paths, good horizontal gap insulation, low joint stress and sufficient mechanical adhesion. Moreover, no cleaning/flux is required, secondary underfill is not necessary, and placement of the anisotropic conductive adhesives is not critical.
2. ACF Bonding Process
