Stabilizing the GO-PATH by evaluating DTIF files for a “don´t care status”

The Digital Test Interchange Format (IEEE P1445-DTIF) is a mechanism for logic data interchange between the automatic test system (ATS) and the unit under test (UUT). This paper will describe conflicts between theoretical logic and actual logic data that may occur periodically in test programs using DTIF format, causing a good UUT to fail when tested. Many of the factors associated with these types of problems will be addressed, a number of which are not illustrative of circuit operation. The paper will begin with a discussion of the variability of UUT functionality on a specific ATE based on factors like: impedance, timing, windows, and drive potential. This variability causes sporadic or intermittent measurements such that, given the same stimulus, they sometimes pass and sometimes they fail. An example of this variability is that of power supply capacitance between the ATE and UUT. After compensating for or correcting these variable UUT functionality factors, a measurement may still continue to be sporadic. Such a failure that cannot be stabilized causes the associated tests to become useless and causes considerable testing problems ranging from wasted staff, time, and material resources. In particular, needless UUT repair actions that do not alter test results cause excessive wear on the UUT and significantly reduces its useful life. Sporadic failures must be corrected and the test sequences must be stable and repeatable to effect proper repair and reduce the frustration level of the repair technician. The mechanism to remove sporadic failures from the test program when normal procedures fail to isolate the problem will be presented on the basis of evaluating the ability to detect such tests and to alter their characteristics based upon well-defined criteria. This will include a discussion of the specific criteria that must exist and the methods that should be used to alter the appropriate files to eliminate sporadic failures. The paper will conclude with an evaluation of the DTIF files with respect to their applicability to the fault detection and functionality of the UUT