Laser ablation of anisotropic conductive adhesive

A laser ablation process has been developed and optimized for the rework of anisotropic conducting adhesive bonds. Ablative photodecomposition of the adhesive matrix and simultaneous removal of the conductive particles is a dry, controllable, and readily implemented alternative for removal of these materials and preparation of the substrate for reprocessing. The ultraviolet absorption spectrum was evaluated, and ablation results evaluated at both /spl lambda/=193 nm and /spl lambda/=248 nm. The /spl lambda/=193 nm wavelength was determined to be optimal for complete adhesive removal and minimal thermal damage to the substrate. A systematic evaluation of the fluence level, angle of incidence, and cumulative exposure established the parameter range between complete adhesive removal and substrate damage. The surface topology of reworked samples showed little change from the original, but a resistance increase was observed for the rebonded circuits. This process appears superior to competing methods because it is both dry and restores the bonding surface to nearly original condition.