Defect simulator cuts mixed-circuit test time

The solution satisfies the growing defect-coverage measurement requirement for automotive ICs set by Tier1 automotive suppliers.

Tessent DefectSim works with Mentor’s Eldo and Questa ADMS circuit simulators to measure the effects of opens, shorts, extreme variations, and user-defined defects modelled within a layout-extracted or schematic netlist.

A number of techniques are used to reduce total simulation time by many orders of magnitude, compared to sequential simulation of every defect in a flat layout-extracted netlist, without reducing simulation accuracy or limiting the type of test.

Among the techniques is a new statistical method called likelihood-weighted random sampling that minimises the number of defects to simulate and more accurately indicates outgoing chip quality.

“In mixed-signal automotive ICs, about 80% of the defects found in returned ICs are in the analogue circuitry. The quality of analogue circuitry is traditionally guaranteed using functional tests while the fault coverage remains unknown. A few years ago, we identified several ways to improve defect coverage of analogue tests but the main gap towards improvement was the absence of an automated fault simulation tool” said Wim Dobbelaere, director of test and product engineering at ON Semiconductor. “We had an extensive collaboration with Mentor during the development of Tessent DefectSim. We evaluated the tool on several automotive ICs and concluded it is a highly-automated and flexible solution that guides improvements in test and design-for-test techniques and allows us to measurably improve the defect coverage of analogue tests.”

“We used DefectSim to investigate a simpler, faster structural test for an analogue circuit that we manufacture,” said Peter Sarson, test development manager at the division Full Service Foundry, ams AG. “DefectSim showed us that the new test has defect coverage equal to that of our specification-based test, and now we only need to validate the new test in production. This tool paid for itself in one project.”

Tessent DefectSim can also measure a circuit’s tolerance to defects. Defect tolerance is a measure of a circuit’s ability, in the presence of defects, to either continue to operate within acceptable operational limits or to transition into a safe state. This metric is very important in automotive applications as it directly relates to long term reliability.