Laser Milling Techniques for Stacked Die Package Applications

Abstract

Ultraviolet (UV) lasers can be used as microsurgery tools to deprocess electronic packages to expose the device and internal package features. A UV laser milling tool was characterized for various applications on multiple die stacked packages to assist in fault isolation and failure analysis. Laser milling procedures evaluated were package delayering to expose traces, trace cutting so that fails can be isolated between the die and package, wire bond exposure and cutting, multiple stacked die exposure through mold compound decapsulation and device milling. Results show excellent selectivity of the laser in removing organic material without etching copper traces at multiple layers in the organic package. Mold compound removal above the die was limited to within ~15 microns of the die surface to prevent any die damage. Mold compound decapsulation outside the die area to expose multiple layers of wire bonds for probing and inspection was developed after overcoming issues related to wire damage. In conclusion, laser milling procedures developed and evaluated show that the technique has a unique advantage in performing local package microsurgery with minimal damage or change in the global stress state of the package.