Method of improving logical built-in self test (LBIST) AC fault isolations

A system, apparatus and method of isolating a plurality of limiting logical cones in a chip during a logical built-in self test (LBIST) are provided. An LBIST is performed on the chip in order to locate a first latch that fails the test. Particularly, latches on the chip are arranged in a plurality of scan chains wherein each latch holds data for a logical cone. The LBIST is performed on one scan chain at a time. Once the first latch is located, a first limiting cone (i.e., the cone for which the first latch is holding data) may be isolated. After isolating the first limiting cone, the data from the first latch is masked out and the LBIST is repeated on the scan chain. The data is masked out in order to facilitate the identification of any other latch that may fail the test. Again, if another latch fails the test a corresponding limiting cone may be isolated.