Test-Mode SDC: Design Space

Design space exploration

For Test-Mode SDC, release options trade quality, tester cost, and schedule risk.

Option A - conservative

• Conservative quality: helps debug confidence

• Risk: higher test cost

• Validate with: first production ramps

Option B - balanced

• Balanced release: helps quality and cost

• Risk: needs discipline

• Validate with: mainstream products

Option C - aggressive

• Aggressive schedule: helps faster closure

• Risk: escape risk

• Validate with: late tapeout pressure

Option D - architecture change

• Architecture change: helps long-term quality

• Risk: schedule hit

• Validate with: chronic recurring failures

DESIGN SPACE - Test-Mode SDC
quality <-> tester cost <-> schedule

Design pitfalls

• No ownership for quality gap

• Fixing one metric while regressing another

Tradeoff curve

BEFORE / AFTER - Test-Mode SDC

metric quality
  ^
  |                    --- release target
  |      o regressed
  |           o baseline
  |                o after fix
  +-------------------------------> closure iteration

Prove quality, timing, and test-power all moved safely.

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.

Principal DFT review addendum

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

Metric: test SDC completeness, false test-path violations, test constraint audit score