Redistribution of pads on a singulated IC die using laser direct-write ablation

The use of laser direct-write technology is demonstrated for rapid turnaround redistribution of pads on known good integrated circuit dice. The technology, which is suitable for rapid prototyping of advanced electronic packages, employs an automated laser ablation system with wavelength at 355nm to pattern thin copper films to form the interconnect and vias in the polyimide interlevel insulator. The ablation tool is designed to directly accept the CAD data and write the metallization and via level patterns with excellent (/spl plusmn/3/spl mu/m) layer-to-layer registration. This process is maskless and, except for cleaning steps, does not require patterning by wet chemical etching. The implementation of a change in the design can be done rapidly and involves modifying the CAD data, downloading it to the laser ablation tool, and fabricating a part according to the new design. This paper illustrates the use of laser direct-write ablation for fabrication of via chain test structures and redistribution of pads on functional integrated circuits on singulated dice. Comparable electrical test results were obtained between structures fabricated using laser ablation technology and those fabricated on full 150-mm diameter wafers using conventional photolithography and etch processes.