Laser/infrared evaluation of TAB innerlead bond integrity

The feasibility of using laser/infrared technology as a noncontact and nondestructive inspection technique to assess tape automated bonded (TAB) inner-lead bond integrity was studied. Chip-on-tape samples with well-bonded inner leads and opens or lifted leads were evaluated. The peak thermal signals obtained during thermal decay after the laser was shut off were evaluated. For a given laser power and exposure time, good bonds and opens generated distinctly different infrared (IR) signatures during thermal decay. Typically, good bonds emitted peak amplitudes which were nominally two to five times lower than those for opens. These were attributed to the superior thermal dissipation properties of well-bonded interconnects as well as to the IR detector configuration in the inspector system. The IR signal modulations observed for well-bonded samples could be explained by the thermal mass/conductance variation associated with circuit metallization patterns on the silicon chip. The results showed that the technique investigated in this study could be adapted as an inprocess inspection scheme for detection of opens or lifted leads. However, refinements are still needed to improve the technique´s capability