Test-Mode SDC: Mechanism

Mechanism to understand

Mechanism for Test-Mode SDC focuses on test SDC completeness, false test-path violations, test constraint audit score. The goal is to convert metric movement into mechanism, owner, and release decision.

Dedicated test SDC captures scan clocks, test enables, and exceptions needed to analyze shift and capture behavior correctly. Think of DFT as a quality pipeline where setup quality determines what silicon evidence means.

• Identify where controllability/observability is introduced.

• Identify legal constraints and mode assumptions.

• Identify failure class: architecture, constraints, physical, or silicon.

Layered view

DFT CLOSURE FLOW - Test-Mode SDC

scan/test architecture
        |
        v
ATPG constraints + fault models
        |
        v
pattern generation + compression
        |
        v
timing/power/physical validation
        |
        v
silicon diagnosis and release signoff

Debug rule: always state metric, run tags, and owning team with any claim.

Test SDC contract

test clocks + test enables + mode exceptions
    -> shift/capture timing checks
    -> legal test closure

Layer responsibilities

DFT OWNERSHIP LAYERS - Test-Mode SDC

layer              owns                         failure mode
----------------   --------------------------   -------------------------
rtl/architecture   scanability hooks            uncontrollable logic
atpg/constraints   legal pattern intent         aborts, low coverage
physical/clocking  chain route + test clocks    shift hold/timing escapes
tester/program     pattern apply integrity      false binning / bad fails
quality signoff    release criteria             escapes or schedule slip

DFT deep dive

Test signoff fails when shift/capture timing and test power are treated independently.

Concept diagram

TEST SIGNOFF LOOP

test SDC -> shift/capture timing -> power-aware ATPG -> IR validation -> release

Metric graph

TEST CURRENT

functional current  baseline
scan shift current  peak-risk zone

Reports and artifacts

• test-mode STA report

• shift/capture split

• test power IR map

• waiver tracker

Mini case study

At-speed patterns passed timing but failed in production due to peak shift IR; staggered capture and power-aware fill resolved.

Debug branches

• Tag test and functional corners separately

• Check hold in shift mode

• Correlate fail bins with power hotspots

Senior review question

Ask: what evidence proves this DFT decision is safe for production?

Key takeaways

• State metric, lot/corner context, and pattern tag with every claim.

• Treat timing, power, and quality as one signoff problem.

Common pitfalls

• Chasing coverage without legality checks.

• Ignoring test-power side effects of pattern changes.

• Debugging silicon without reproducible tags.

Mechanism deep dive

Dedicated test SDC captures scan clocks, test enables, and exceptions needed to analyze shift and capture behavior correctly.