Nondestructive identification of cusil braze material by neutron activation analysis

Abstract

Neutron activation analysis was used as a nondestructive technique to positively distinguish between cusil (28% Cu, 72% Ag) and silver braze material bonding electrical leads to the substrate of an LSI. The SLL californium-252 source was used to activate LSI samples and a small volume Ge(Li) spectrometer was used to observe the characteristic radiations. Based on these results, it is concluded that an exposure of the braze material for twenty-four hours to a thermal neutron flux of 10 7</ neutrons/cm2/sec will produce sufficient activation to positively identify the cusil braze parts. Thermal neutron fluxes of this order, and large exposure areas, are available at nuclear reactor facilities- Using a large volume Ge(Li) gamma-ray spectrometer to observe the characteristic radiations from copper-64, the counting interval per part would be approximately 100 sec. The neutron sensitive LSI chips can be shielded with cadmium foil to reduce the thermal neutron fluence to an insignificant level.