It is a well-known phenomenon that test power consumption may exceed that of functional operation. ICs have been observed to fail at specified minimum operating voltages during structured at-speed testing while passing all other forms of test. Methods exist to reduce power without dramatically increasing pattern volume for a given coverage. We present case study information on ATPG- and DFT-based solutions for test power reduction.

Minimizing power consumption in scan testing: pattern generation and DFT techniques

Scan-based at-speed testing is a key technology to guarantee timing-related test quality in the deep submicron era. However, its applicability is being severely challenged since significant yield loss may occur from circuit malfunction due to excessive IR drop caused by high power dissipation when a test response is captured. This paper addresses this critical problem with a novel low-capture-power X-filling method of assigning 0's and 1's to unspecified (X) bits in a test cube obtained during ATPG. This method reduces the circuit switching activity in capture mode and can be easily incorporated into any test generation flow to achieve capture power reduction without any area, timing, or fault coverage impact. Test vectors generated with this practical method greatly improve the applicability of scan-based at-speed testing by reducing the risk of test yield loss

Low-capture-power test generation for scan-based at-speed testing

At-speed scan is a key technique in modern IC testing. One of its drawbacks, with respect to functional tests, is its excessive power consumption leading to voltage drop and frequency degradation. This paper discusses the frequency and power correlation between At-speed scan and functional tests. The influence of voltage drop on frequency is demonstrated by silicon measurements and supporting simulation results. The localized nature of the voltage drop as well as impedance component analysis are presented. Additionally, the need for power aware scan patterns is also discussed. Suggestions for achieving a higher correlation between At-speed scan and functional patterns, with respect to power consumption, are offered.

Frequency and Power Correlation between At-Speed Scan and Functional Tests

An embodiment is directed to extended test coverage of complex multi-clock-domain integrated circuits without forgoing a structured and repeatable standard approach, thus avoiding custom solutions and freeing the designer to implement his RTL code, respecting only generally few mandatory rules identified by the DFT engineer Such an embodiment is achieved by introducing in the test circuit an embodiment of an additional functional logic circuit block, named “inter-domain on chip clock controller” (icOCC), interfaced with every suitably adapted clock-gating circuit (OCC), of the different clock domains The icOCC actuates synchronization among the different OCCs that source the test clock signals coming from an external ATE or ATPG tool and from internal at-speed test clock generators to the respective circuitries of the distinct clock domains Scan structures like the OCCs, scan chain, etc, may be instantiated at gate pre-scan level, with low impact onto the functional RTL code written by the designer

Apparatus for at-speed testing, in inter-domain mode, of a multi-clock-domain digital integrated circuit according to BIST or SCAN techniques

The delay fault test pattern set generated by timing unaware commercial ATPG tools mostly affects very short paths, thereby increasing the escape chance of smaller delay defects. These small delay defects might be activated on longer paths during functional operation and cause a timing failure. This paper presents an improved pattern generation technique for transition fault model, which provides a higher coverage of small delay defect that lie along the long paths, using a commercial no-timing ATPG tool. The proposed technique pre-processes the scan flip-flops based on their least slack path and the detectable delay defect size. A new delay defect size metric based on the affected path length and required increase in test frequency is developed. We then perform pattern generation and apply a novel pattern selection technique to screen test patterns affecting longer paths. Using this technique will provide the opportunity of using existing timing unaware ATPG tools as slack based ATPG. The resulting pattern set improves the defect screening capability of small delay defects.

Timing-based delay test for screening small delay defects

The authors describe new strategies where at-speed scan tests can be applied with internal PLL. They present techniques for optimizing ATPG across multiple clock domains and methodologies to combine both stuck-at-fault and delay-test vectors into an effective test suite.

T. Rinderknecht

Papers

High-frequency, at-speed scan testing