| abstract |
A very low stress attachment method for attaching a microelectronic device to a flexible substrate comprises use of a photo initiated anisotropic conductive adhesive, preferably an infrared photo initiated anisotropic paste, which can be applied to the bonding terminals of a microelectronic device. The flex circuit is then aligned with the corresponding pads on the device. The flex circuit is then biased against the microelectronic device and the infrared photo initiated anisotropic adhesive is exposed to infrared light by means of a dual purpose light guide that presses against the back side of the polyimide flex circuit and simultaneously receives and guides light energy from an Nd: YAG laser to the back side of the polyimide flex circuit. Light energy from the laser passes through the polyimide substrate and between the circuit tracks of the flex circuit to excite the photo initiator of the photo initiated ACA material, thereby causing it to cure. Preferably the ACA material is a dual cure epoxy such that the photo initiator is required only to begin the polymerization process and a secondary (low-temperature thermal or preferably cationic) polymerization carries the cure through the bulk of the material. |