Localizing power to ground shorts in a chips-first MCM by scanning SQUID microscopy

We demonstrate that scanning SQUID (Superconducting Quantum Interference Device) microscopy is a fast and easy method for finding the location of power-to-ground shorts in a series of chip-first MCM (multi-chip module) samples. Previous work has shown that the scanning SQUID microscope is capable of locating shorts in a C4 chip carrier and a ball grid array package, however the physical analysis was not performed to verify the (presumed) fail locations. In the present work, shorted areas in a chips-first MCM were located by SQUID microscopy and confirmed by mechanical cross-sectioning. When a short in a second MCM was found by SQUID microscopy and repaired with a laser, the power-to-ground resistance increased by more than a factor of 1000, bringing the part within specification. Techniques such as emission microscopy were unsuccessful in detecting the shorted current paths in these devices. Thus scanning SQUID microscopy is the only known method for locating and repairing defects in this product.