Magnetic Field Imaging Using a "SQUID" for Fault Isolation

Recent work with a commercial instrument based on a SQUID sensor shows that magnetic field imaging can be very effective in isolating defect shorts in packages and dies. This technique is especially beneficial when the defect is buried under layers of metal, Si, or encapsulation materials. Many of these defects can be imaged for coarse localization without any deprocessing of the sample. SQUID sensors can produce weak current images even in the presence of background current five orders of magnitude stronger. This high sensitivity also enables effective imaging with much lower currents than thermal techniques.