Electrical conductive film for Flip-Chip Interconnection based on Z-axis conductors

The development of new Anisotropic Conductive Film for high density Flip-Chip Interconnection has met with growing interest over the last few years. ACF provides promising solutions for bumpless chip connection to high density printed circuit board. Standard ACF are composed of a resin film containing randomly dispersed fine metallic particles or metal-coated polymer balls. These ACF find their applications mainly in LCD display despite their high resistivity. One enhancement which has been clearly identified is the concept of a vertical interconnection sheet with structured Z-axis conductors instead of particles. The main advantage of Z-axis ACF compared with standard ACF is the possibility to achieve lower pitch and pad area. Moreover, Z-axis ACF achieves a better electrical contact. LETI has been involved in Z-axis ACF technology since 1990 and different film structures have been developed. The purpose of this paper is to present an overview of the results obtained.