DFT Digest

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[editors note: This post is second in a regular series of featured contributions from Stephen Pateras of LogicVision]

One of the most common questions I get about logic BIST is “how can it possibly guarantee the coverage of specific faults if it’s random pattern based?” Well the answer, of course, is that it can’t… But that, it turns out, is irrelevant. Because in the real world, you can only afford a certain amount of test time. And so the relevant question becomes: “What percentage of real defects can you cover in a fixed amount of time?” This is where the high-throughput aspect of logic BIST comes into play. And this is where I like to use my paint brush versus spray gun analogy.