As IC design sizes continue to double every 18 to 24 months, those charged with testing the finished product are challenged on multiple fronts. Test-data volume and testing time are expanding, while manufacturing throughput is reduced. The International Technology Roadmap for Semiconductors (ITRS) predicts that by 2008 the industry will need 200 times more test-data volume compression, with the requirement growing exponentially over the next five years.
In the latest iteration of its TestKompress automatic test-pattern generation (ATPG) tool, Mentor Graphics' Xpress technology ups the compression ante from 80 to 90 times previous versions to well over 100 times. Additionally, the tool uses new compression algorithms that enable it to achieve the same test quality with fewer patterns.
Historically, logic built-in self-test (BIST) schemes have struggled with handling unknown states in the design (referred to as X states). X states, of which there can be many in uninitialized memory, confound tests because they're unknown logic values. They're traditionally dealt with through the addition of additional so-called "top-up" test patterns that bypass compression circuitry.
Mentor's X-masking technology adds selection logic before the X compaction stage, enabling test engineers to decide which paths to observe. Furthermore, a new Xpress compactor enhances the ability to examine faults in the presence of X states (see the figure).
With the ITRS data in mind, Mentor's roadmap for test compression encompasses developmental technology that allows higher levels of compression without the need for changes in the scan architecture. It essentially involves a cascade of compactors.
TestKompress Xpress is available for beta evaluation and will be in production in the fourth quarter release of TestKompress, scheduled to ship in November.
Mentor Graphics www.mentor.com
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