Flip chip attachment using anisotropic conductive adhesives and electroless nickel bumps

Flip chip attachments provide the highest interconnection density possible, which makes this technology very attractive for use with liquid crystal display (LCD) packaging methods. This technology stimulated the development of new interconnection techniques, such as anisotropic adhesives. However, several factors have hindered the wide use of this technology. These factors include the availability and costs of bumped wafers. IZM and TU-Berlin have addressed both of these concerns by establishing a wafer-bumping facility which uses electroless nickel bumps. The combination of anisotropic adhesives and electroless nickel bumps has the potential for a low-cost chip on glass (COG) and chip on flex (COF) bonding technology. In this paper, two types of anisotropic adhesives were studied with an emphasis on the properties of COG and COF interconnections. The electrical and mechanical performance of the adhesive bonds was studied by evaluating initial contact resistance and mechanical adhesion as a function of temperature and humidity.