Modeling Dynamic Parasitic Loading Effects on Scan Network Timing Margins
Dynamic parasitic extraction during ATPG shift prevents false timing violations by accounting for state-dependent capacitance and power rail collapses.
Scan Shift Timing
Test Parameter
A critical clock configuration governs the movement of test data through a circuit’s internal shift registers during boundary scan and wafer testing. In digital assemblies, scan shift timing ensures that stimulus vectors are loaded into flip-flops without setup or hold violations. This timing profile must be slower than the functional clock to accommodate the long routes of the scan chains across different board zones.
It prevents false test failures caused by timing margin issues rather than physical manufacturing defects.
Frequency Optimization
Test engineers balance the scan frequency against the total test time to maximize throughput on automated test equipment. Running the shift clock too fast induces ground bounce and voltage droop because thousands of flip-flops switch simultaneously. This high switching activity draws massive peak currents that do not occur during normal operation, causing artificial voltage drops.
By optimizing the clock period, the system delivers stable test results without extending the duration of the test run.
Error Mitigation
Hold time margins are verified through post-layout simulation to guarantee that clock skew does not corrupt the scan data. When skew exceeds the design margin, the scan chain fails to shift patterns correctly, making diagnostics impossible. Clock tree synthesis tools prioritize scan path routing to resolve these errors early in the layout process.