4.5 Environmental & Burn-in Testing
Simulating real-world conditions.
Environmental and burn-in testing is a production screen that catches “infant mortality”—the early failures on the bathtub curve—before a customer ever plugs in. It isn’t design qualification; it’s a consistency check that proves the build, parts, and process are holding steady. The method is simple in spirit: run units hot, under real load, through planned power cycles (including brief “brownouts,” i.e., voltage dips), and sometimes at controlled humidity (RH = relative humidity) while they actually do work. Profiles stay light but repeatable and are tied to the SKU, so results flow into MES (manufacturing execution system) as clean data rather than hunches. With clear pass/fail limits and safe racks or chambers, burn-in turns surprises into statistics—and ships hardware that’s already had a hard day at the office.
4.5.1 Why do this?
To flush out early-life failures (Chapter 16’s bathtub curve) and prove the unit survives heat, time, and power cycling before it meets a customer. We’re not qualifying the design (16.3)—we’re screening production and validating build consistency.
4.5.2 What counts as “environmental & burn-in”
- Thermal stress: elevated ambient, thermal cycling, controlled ramps.
- Electrical stress: constant load, power cycling, brownout/surge profiles.
- Humidity (if applicable): steady RH or damp heat (only if parts are rated).
- Operational soak: exercise fans, I/O, radios, storage—work while hot.
- (Light vibration/transport shake belongs in 21.3 for harnesses; only include if your product spec requires.)
4.5.3 Typical burn-in profiles (pick the lightest that works)
Start aggressive at NPI/ECOs (100% units), then taper to sampling when FPY is stable and field data supports it.
4.5.4 Chambers, racks & fixtures (keep it safe and uniform)
- Burn-in racks: dedicated power distribution with current limit/fusing, airflow management, cable strain relief, interlocks.
- Chambers: uniform airflow, monitored temp (±2 °C band), dew-point control to avoid condensation (see 25.5.6).
- Loads: electronic loads, fan trays, network generators, RF attenuators/shield box if radios run.
- Scripts: station launches the right recipe by SKU/Variant scan—no manual tweaks.
4.5.5 What to monitor (and how to decide pass/fail)
Log to MES by unit SN at 1–60 s cadence (pick a rate that shows trends without swamping storage):
- Power: input current & voltage, inrush peaks on each cycle.
- Thermals: hottest sensor/heatsink ΔT; fans RPM & tach faults.
- System health: watchdog resets, error counters, crash logs, throughput (Eth/USB), storage SMART.
- I/O activity: periodic loopbacks, LED/display keep-alive, relay/PWM chatter.
- Pass if:
- No trips/resets/crash logs.
- Currents within golden bands; no rising trend.
- Hottest T ≤ spec − margin (set a 5–10 °C guard).
- All scheduled checks pass on the final cycle.
- Fail fast: any smoke/odor, repeated watchdog, fan stall, over-temp, or unplanned power draw spike.
4.5.6 Thermal cycling & humidity (do it without causing damage)
Thermal cycling (production screen)
- Ramps ≤ 5 °C/min; dwell 10–30 min at highs/lows you can justify (not HALT extremes).
- Cycle count: 3–10 within the burn-in window for rugged products.
Humidity (only if the design & labels allow)
- 40 °C / 85% RH for 2–8 h as a stress screen (not qualification).
- No condensation: keep chamber setpoint > dew point of the unit’s guts; avoid rapid door-open shocks.
- After humidity segments, let units stabilize to room before any Hipot/IR (25.2) to avoid false fails.
4.5.7 Power cycling & brownouts (catch marginal power paths)
- Cycle count: 5–20 over the burn-in; include cold start and hot restart.
- Brownout dip: briefly drop input to the edge of spec (e.g., −20%) and recover; unit should not latch up or corrupt storage.
- Inrush: capture peaks; compare to golden so swollen caps/failing soft-start stand out.
4.5.8 Safety & ESD in hot environments
- Racks/chambers have E-stop, thermal cutouts, and door interlocks.
- High temp reduces glove grip—use rated cable boots and strain relief.
- Radios on? Follow RF safety and local RF rules (use shield boxes/attenuators).
4.5.9 Data & traceability (what to store)
Bind to SN:
- Profile ID (temps, durations, ramp rates), recipe version, rack/chamber ID.
- Time-series summaries: max current, max temp, min volt, cycle counts, fan RPM min.
- Event logs: resets, errors, throttle events, protection trips.
- Final PASS/FAIL and reason codes; any rework ticket ID.
4.5.10 Acceptance cues (fast table)
4.5.11 Common traps → smallest reliable fix
4.5.12 Pocket checklists
Before
- SKU/Variant scanned → correct profile loaded
- Rack/chamber ID recorded; interlocks & E-stop OK
- Loads/network scripts ready; fans unobstructed
- Ambient/chamber sensors read sane; dew-point margin OK (if humidity)
Run
- Start log: V/I/T, RPM, heartbeat up
- Hold at temp; run I/O/throughput tasks
- Execute power cycles & brownouts per plan
- Watch trend tiles; fail fast on trips/resets/over-temp
After
- Cooldown to room; post-burn-in FCT re-run
- Safety tests (25.2) if required post-soak—after stabilization
- Results & summaries to MES by SN; fails to NG-QUAR with reason