Recent advances in Anisotropic Conductive Adhesives (ACAs) technology: Materials and processing

Abstract

New ACA materials and processing technologies innovation have been made at various advanced packaging applications such as FOB, FOF, COF, COG, TSP (Touch Screen Panel) and 3D-TSV (Through Silicon Via) assemblies. In ACA materials innovation, noble nanofiber ACA materials with conductive particles incorporated polymer nanofiber finally solve the electrical shortage and unstable contact resistance problems of less than 20 micron ultra-fine pitch COG and COF interconnection, because conductive particle movement can be significantly limited by polymer nanofibers. In addition, new solder ACA materials can significantly solve the current handling capability and reliability limitation of conventional ACAs, because solder ACFs form solder alloy metallurgical joints rather than physical contact based joints of conventional ACFs with metal conductor particles. And new epoxy based photo Active(PA)-ACFs are also introduced to reduce the ACF bonding temperature down to 110 C. In addition, there were progresses made in the area of ACA processing technologies too. New vertical ultrasonic ACA bonding technology provides less than 3 seconds ACA bonding time, reduced assembly thermal damage, good adhesion strength, good contact resistances, and reliability compared with the conventional thermo-compression bonding method. The ultrasonic ACA bonding method has been successfully adapted at the touch screen panel(TSP), FOB and FOF assembly applications. Another ACA processing innovation is the invention of the wafer-level ACA process which significantly reduces the number of processing steps resulting in low cost COB, COF, COG assemblies using ACAs. Furthermore, this wafer-level ACA processing method can be successfully extended to the 3D-TSV vertical interconnection applications too.