A study on low temperature curable anisotropic conductive films (ACFs) with photo-active curing agents (PA-ACFs)

Abstract

Anisotropic conductive films (ACFs) have been widely used for various electronic packaging and interconnection applications, due to its low temperature process, smaller package size, and compatibility with many substrate materials. Recently, low temperature curable ACFs are strongly demanded for many applications, because of their high productivity, cost effectiveness, and good reliability. Furthermore, to prevent thermal deformation of polymer substrates having low glass transition temperature (Tg) such as polyethylene terephthalate (PET) substrates in the touch screen panels (TSPs), the bonding temperature should be lower than that of the conventional ACFs bonding temperatures. Therefore, acrylic resin based or thermoplastic resin based ACFs have replaced high temperature curing epoxy resin based ACFs for lower temperature bonding applications. Since lower temperature curable ACFs are getting more and more important, more research is focused on developing low temperature curable ACFs which is lower than 120 ºC. However, there are two barriers to overcome in order to obtain low temperature curable ACFs. First barrier is the shelf life of ACFs. Crosslinking systems that could be cured at low temperature below 120 °C within a few seconds already exist, but they have no latent curing behavior at room temperature or freezer storage conditions. In order to commercialize, the shelf life of ACFs should be over one month at room temperature and six months at freezer storage conditions. Second barrier is the low limit of on-set temperature of ACFs curing. This is due to the temperature of solvent drying process. To avoid the curing of ACFs resin, solvent drying should be performed below the curing on-set temperature during the film coating process. In other words, curing on-set temperature should be higher than the solvent drying temperature. In this thesis, low temperature curable anisotropic conductive films with photo-acitve curing agents (PA-ACFs) were investiga...