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4.5 Environmental and Burn-in Testing

Environmental andBurn-In burn-in testingTesting is thea stagehigh-stress, whereaccelerated hiddenaging weaknessesprocess are forcedapplied to showfinished themselveselectronic systems to deliberately induce failure in weak components before athe product reaches the field.customer. ByThis stressingprocess unitsis withmandatory heat,for load,high-reliability powerproducts cycling,(IPC Class 3) as it filters out Infant Mortality — the high initial failure rate observed early in a product's life due to manufacturing defects or latent component flaws. A successful burn-in ensures a stable, reliable product upon shipment.

4.5.1 Protocol Mandate and sometimesStressors

humidity, this process screens out early-life failures that slip past functional and safety checks. Unlike design qualification, its purpose

Burn-in is not toa provesimple newfunctional conceptstest; butit toinvolves validatesimultaneous manufacturingapplication consistencyof environmental and componentelectrical reliabilitystress under controlled, repeatable conditions. With profiles tiedtailored to the SKU and results bound to serial numbers, burn-in replaces guesswork with statistics, turning reliability into a measured outcome.

4.5.1 Why do this?

To flush out early-life failures (Chapter 16’product'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.class.


A)
Mandatory


4.5.2 What counts as “environmental & burn-in”

Stressors
  • Thermal stress:Stress: elevatedElevated ambient,ambient temperature and periodic thermal cycling,cycling controlled(ramps ramps.≤ 5˚C/min).
  • Electrical stress:Stress: constantConstant load,dynamic load (near-max duty) and controlled power cycling, brownout/surge profiles.
  • Humidity (iftypically applicable):5 – 20 steadycycles) RHto ortest dampinrush heatand (only if parts are rated).sequencing.
  • Operational soak:Soak: exerciseThe fans,unit must be functionally exercised: fans running, storage R/W active, I/O,O radios,periodically storage—workchecked, whileand hot.network throughput verified.
  • (LightBrownout vibration/transportDips: shakeBriefly belongsdropping ininput 21.3voltage forto harnesses;the onlyedge include if your productof spec requires.(e.g., -20%) to verify the unit does not latch up or corrupt storage.


4.5.3

B) Typical burn-in profilesProfiles (pickStarter Ranges)

Profiles must be specific to the lightestSKU that(Stock works)

Keeping Unit) and scaled based on complexity and environment.

Product classClass

Duration

Ambient

Load profileProfile

ExtrasPower Cycles

Consumer/officeOffice

2–2 – 4 h

40–40 – 45 °˚C

50–80% duty; periodic I/O pokepoke.

3–3 – 5 power cycles

Industrial indoor

4–8 h

45–55 °C

70–100% duty; PWM/relay chatter

5–10 cycles; brownout dips

Outdoor/ruggedIndustrial/Rugged

8–8 – 24 h

55–55 – 65 °˚C (per spec)

Near-max duty; RF/network activeactive.

Periodic5 – 10 cycles + thermal ramps (±10 °C), power cycles

Compute/network

8–24 h

45–55 °C rack/flow

CPU/NET stress (≥80%); storage R/W

Throughput check each hourramps.

Mandate:Start aggressiveTesting must start aggressively at NPI/ECOsNew Product Introduction (100% units)NPI), then taper to a sampling plan only when First Pass Yield (FPY) is stable and field data supports it.


4.5.42 Chambers,Chamber racks & fixtures (keep it safeIntegrity and uniform)Monitoring

The uniformity of the test environment and the continuous logging of health metrics are critical for valid results.

A) Chamber and Fixture Requirements

  • Chamber Control: The chamber must maintain uniform airflow and monitored temperature (± 2˚C band).
  • Racks and Power: Burn-in racks: must have dedicated power distribution with current limit/limits/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 hotcable restartstrain relief.
  • Brownout dipSafety:: 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 haverequire mandatory E-stop, thermal cutouts, and door interlocks.
  • High temp reduces glove grip—useThe ESD strap must be OFF during HV tests; rated cable boots must be used in hot zones.

B) Monitoring Mandates

Monitoring must be automated, high-cadence, and strain relief.

  • Radios on? Follow RF safety and local RF rules (use shield boxes/attenuators).

    • 4.5.9 Data & traceability (whatlogged to store)

    the

    BindMES to(Manufacturing SN:Execution System).

    • Log Rate: Data must be logged at a rate sufficient to capture transient failures (e.g., 1 – 60 second cadence).
    • Monitored Health Metrics:
      • Power: Input current (including inrush peaks), voltage, and power consumption trends.
      • Thermals: Hottest sensor/heatsink ∆T (Delta Temperature); fan RPM and tach faults.
      • System: Watchdog resets, error counters, crash logs, and storage SMART data.

    4.5.3 Acceptance Criteria and Failure Response

    Acceptance is based on continuous stability and reaching a defined thermal margin, not just simple functionality.

    A) Pass/Fail Criteria

    • Stability: Zero watchdog resets, crash logs, or unexpected power spikes. Current must be flat or settling (no rising trend).
    • Thermal Margin: The hottest monitored temperature (Tmax) must remain below the specified limit minus a margin (e.g., Tmax ≤ Spec - 5˚C guard band).
    • Critical Failures: Any smoke/odor, repeated watchdog, or unplanned power draw spike must trigger a fail fast response.

    B) Data Traceability and Rework

    • Data Bind: The log must bind the Profile ID (temps, durations, ramp rates), recipeTime-series versionsummaries (max current, min RPM), rack/chamberand ID.Event logs (resets, errors) directly to the unit Serial Number (SN).
    • Failure Response: All burn-in failures trigger immediate Corrective and Preventive Action (CAPA) investigation. The focus must be on finding the process flaw (e.g., incorrect torque application, component batch issue), not just component replacement.
    • Humidity Rework:Time-series summaries:If using humidity stress, units must be stabilized to maxroom current, max temp, min volt, cycle counts, fan RPM min.
    • Event logs: resets, errors, throttle events, protection trips.
    • Final PASS/FAILtemperature and reason codes;before any reworkHi-Pot/IR tickettesting ID.to avoid false fails from condensation.


    Final

    4.5.10 Acceptance cues (fast table)Checklist

    AreaMandate

    AcceptCriteria

    RejectVerification Action

    Mortality Filter

    Unit subjected to thermal and power cycling per profile (e.g., 40˚C to 55˚C).

    Test profile ensures product is aged past the early failure phase.

    Stability

    Zero watchdog resets/crash logs; current flat or settling.

    Log current and resets at a high cadence (e.g., 1 – 60 s).

    Thermal marginGuard Band

    Hottest temperature TTmax ≤ Spec −- 5–105˚C °Cmargin.

    Near/overContinuous spec;logging of temperatures; log confirms no thermal throttlingthrottling/over-temp.

    Power Stress

    StabilityProfile includes power cycling and brownout dips.

    CurrentInrush flatpeaks orcaptured settling

    Risingand currentverified trend,against oscillationsthe golden limit.

    Contamination

    Resets/errorsIf humidity is used, dew point controlled; unit stabilized before safety tests.

    None

    Watchdog/crashAudit logsprevents presentfalse Hipot fails due to condensation/moisture.

    Traceability

    FansTime-series summaries (current, temp, cycles) linked to the unit SN.

    RPMMES withinrecords window

    Stall,profile noisyID bearings,and tachfinal error

    Powerreason cycles

    All clean boots

    Latch-ups, long boot drifts

    Humidity (if used)

    Post-soak IR/Hipot PASS

    False fails from condensation; actual shortscodes.


    4.5.11 Common traps → smallest reliable fix

    Trap

    Symptom

    First move

    “Cook and hope” (no monitoring)

    PASS but field returns

    Log current/temps/resets; set guard bands

    Over-aggressive humidity

    Hipot fails, corrosion risk

    Control dew point; dry to room before safety tests

    Same profile for every SKU

    Over/under screen

    Profiles by SKU/Variant; scale load/temp

    Long test on main line

    Takt killer

    Side loop racks; ping-pong fixtures

    Manual recipe edits

    Inconsistent stress

    Scan-to-recipe; lock scripts; version in MES

    Power cycling via mains switch

    Nuisance surges

    Use programmable PSU; timed sequences

    Hot cables sagging

    Intermittents

    Strain relief; high-temp cable boots; route supports



    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



    When implemented with discipline, burn-in testing raises confidence that shipped hardware will survive real-world use without early surprises. The benefit is fewer field returns, stronger customer trust, and production lines that can scale without carrying hidden risks.


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