The fine pitch direct bonding technology for chip interconnection

We have developed new direct bonding technology using anisotropic conductive film (ACF) connections between two chips. We applied this bonding technology in ultra fine pitch interconnections at 40 /spl mu/m between an LED array and a driver IC, and realized a minimized LED print head. The key point of direct bonding technology is assurance of connection reliability which can be improved by two important factors. One is the elastic recovery quantity of conductive particles between the connection electrodes, and the other is the adhesive strength of the chip bonding area. As a result of analysis with particular attention paid to these factors, we found two further features: (1) an elastic recovery quantity usually obtained by using soft conductive particles which was included in ACF, in the case of electrodes with variable form and hardness; (2) adhesive strength increased when accompanied with a rise in the curing temperature. We tested this technology by interconnection of 192 connection pads lined in 40 /spl mu/m pitch, and achieved good bonding reliability in temperature and relative humidity cycling tests. This new bonding technology is effective in ultra-fine pitch direct bonding, so that this technology can be widely applied to various types of device chip. In this paper, the details of the technology and the connection reliability are reported.