Low overhead delay testing of ASICs

Delay testing has become increasingly essential as chip geometries shrink. Low overhead or cost effective delay test methodology is successful when it results in a minimal number of effective tests and eases the demands on an already burdened IC design and test staff. This work describes one successful method in use by IBM ASICs that resulted in a slight total test pattern increase, generally ranging between 10 and 90%. Example ICs showed a pattern increase of as little as 14% from the stuck-at fault baseline with a transition fault coverage of 89%. In an ASIC business, a large number of ICs are processed, which does not allow for the personnel to understand how to test each individual IC design in detail. Instead, design automation software that is timing and testability aware ensures effective and efficient tests. The resultant tests detect random spot timing delay defects. These types of defects are time zero related failures and not reliability wearout mechanisms.