Recent advances on anisotropic conductive adhesives (ACAs) for flat panel displays and semiconductor packaging applications

Anisotropic conductive films (ACFs) consist of conducting particles and adhesive polymer resins in a film type and have been widely used for the flat panel display module to be high-resolution, light weight, thin profile and low power consumption in forms of out lead bonding (OLB), flex to printed circuit board bonding (PCB), chip-on-glass (COG) and chip-on-film (COF) in last decades. As the interconnection pitch between driver IC and flex is decreasing, ACF materials have been evolved to meet the fine pitch capability, low-temperature curing and strong adhesion requirements. Multi-layered ACF structures such as double and triple-layered ACFs were developed for the same reason. Flip chip technology has been well-known as one of the solutions to meet today's semiconductor packaging needs of miniaturization of package size as well as reduction in interconnection distance, resulting in high electrical performance. Especially, flip chip assembly using anisotropic conductive adhesives (ACAs) has been gaining much attention for its simple and lead-free processing as well as cost-effective packaging method. High mechanical reliability, good electrical performance at high-frequency range and effective thermal conductivity for high current density are the required properties for the ACF material for wide use in the flip chip application. In this paper, an overview on the principles, recent development and applications of ACF materials for flat panel displays and semiconductor packaging applications, with focus on the fine pitch capability, low-temperature bonding process, electrical/mechanical/thermal performance and wafer level package using ACFs are described.