Test gains importance as perfection recedes

Is the test engineer a hero or a villain? That's a question I posed back in 2002, concluding that test adds as much value as any other aspect of a product's journey from concept to customer: Test is a vitamin (a healthy boost to the economical production of a quality product), not an aspirin (a treatment for some unforeseen illness).

As I noted in my 2002 column, perfect designs and defect-free production are impossible goals, and efforts to approach them are prohibitively expensive. In fact, as designs become more complex, perfection is receding, not coming closer. Anne Gattiker, program chair for this year's International Test Conference and research staff member at the IBM Austin Research Lab, commented during a recent interview, "It used to be that people would do worst-case design. Designers would guarantee that their chips would work at all of the worst-case corners. But with increasing variability, they just can't afford to do that anymore. So, instead of trying to guarantee that 100% of their chips will work, they play a nasty trick on [test engineers] and only guarantee that 90% will work."

In addition, she said, "Technology has become so complex that we now have design and process interactions. There's so much pattern dependence and neighborhood dependence that it's almost impossible to get all the models right and all the test structures right the first time."

In such an environment, she said, "It's becoming more and more important for test not to just separate good chips from bad chips or good boards from bad boards, but to provide feedback to the fabrication process to help improve manufacturing yields, speed yield-learning ramp-up, and improve debug and time to market."

The theme of this year's ITC (October 24–26, Santa Clara, CA) is "Getting more out of test," and presentations will aim to help test engineers do more than separate good parts from bad parts. Getting more out of test, said Gattiker, will require efforts from EDA companies as well as test-equipment vendors. On the EDA side, she said, vendors need to enhance defect-localization and diagnosis software, while ATE needs to adapt to its role as a data-collection engine. Gattiker emphasized, "Only at test does the rubber meet the road. When you do a real test of your real product—that represents the first look you get with no modeling and no effort to be representative—it's the real thing."

"ITC to address expanding test role" (interview with Anne Gattiker)

"Hero or villain," Test & Measurement World, June 2002.