The reliability study of laser trimmed resistor components

A process model was established to understand the formation of stresses within the silica overlayer using TFR (thin-film resistor) laser trimming. The stresses were calculated using a thermal inclusion model. The stress resulting from laser trim created delaminations lead to cone crack formation. The cracks and delaminations were examined by fracture mechanics and reliability experiments. Based on the morphology, the cracks were treated as those generated by a flat, elastic punch loading on free surfaces. These types of cracks possess equilibrium lengths and are stable. The strength of silica containing such cracks was calculated as a function of crack length. It was found that the stresses required to propagate the cracks to failure were very large, well above any stresses likely to be generated in usage. There were no failures observed during the reliability experiments. Therefore, the cracks and delamination are not a reliability concern under normal usage conditions