Handling wrong mapping: A new direction towards better diagnosis with low pin convolution compressors

Diagnosis with a modern day low pin convolution compressor is difficult. Generally, it is done in two steps. In the first step, known as failure mapping, failures are mapped to the scan cells from the faulty responses recorded at compressor outputs on the Automatic Test Equipment (ATE). In the second step, normal scan diagnosis - cone tracing and fault simulation - is used to identify the faulty gate/pin/net. Accurate failure mapping is extremely important for successful diagnosis. Unfortunately, due to aliasing and presence of don't cares in the response, no mapping algorithm can guarantee that mapping will always be correct for convolution compressors. In this paper, we proposes a new technique which can handle incorrect mappings (the first step of diagnosis). This feature is shown to provide significant improvement over previous methods. Combining the new proposed techniques to the prior algorithms, we have achieved scan level diagnosis accuracy (99.8%) in a compression environment with extreme low pin compressors.