Case Studies: From Failure to Solution — Full Retrospectives of 35 Real Scenarios

ProblemTwo years after a power module batch shipped, devices would shut down on protection after running for a while; teardown and retest restored normal operation, but the fault reappeared after dozens of hours powered.

根因The hole-wall copper provided a mobile metal source; a 40V differential with 0.005-inch spacing converts to an electric field gradient exceeding 5V/mil; insufficient coupling agent treatment at the glass fiber/resin interface formed capillary channels crawling along glass fiber bundles; post-process cleaning with water-soluble flux was compressed, leaving ionic residue above the control line. This is interface-type cumulative failure — incoming inspection tests bulk properties, while CAF tests interface properties.

MeasuresHole-wall to inner-layer spacing in high-potential-difference areas increased from 0.005 inches to over 0.012 inches; post-process cleaning restored and tightened, with ionic contamination controlled within 1.56 μg/cm² sodium chloride equivalent; 85℃/85%RH, rated bias, 500-hour accelerated verification sampling added for work-in-progress and inventory boards, written into laminate qualification specifications.

ProblemA base station board after one year in service showed slow signal margin decline and rising bit error rates on some channels, while all routine tests still judged it qualified.

根因The resistance drop was not a cliff but a slow staircase with fluctuation, indicating a migration pathway was gradually forming; cross-sections along the highest potential gradient showed intermittent dotted copper deposits at glass fiber bundle junctions, not yet connected into through filaments; energy spectroscopy confirmed the deposit was mainly copper, with silicon enrichment around the channel, proving migration occurred along the glass fiber surface.

MeasuresIncoming material decisions upgraded from binary pass/fail judgment to actionable graded handling; the evaluation system was written into enterprise standards, with subsequent new platform laminate selection following the same process; the collaboration point moved earlier, with TMC participating in stack-up and material selection reviews.

ProblemAn engine bay control unit showed intermittent functional anomalies during endurance testing; after removing the housing, gray-green deposits were visible locally on the board — dendritic metal crystals under the microscope.

根因Total ionic content across three sample groups did not differ dramatically, but failed units showed higher concentrations of organic acid radicals and halide ions; crystals grew from cathode to anode, mainly copper; matrix experiments showed that at the same contamination level, 6-mil spacing failed extensively, 10-mil significantly reduced failures, and 50-mil almost never failed. This is composition–spacing–condition coupled failure.

MeasuresCleanliness standard changed from "total quantity" to "composition + threshold," with separate limits for halide ions and specific organic acid radicals; zoning control by spacing, with stricter limits for high-risk areas below 10 mils; 168-hour accelerated verification made a mandatory pre-mass-production item for every new project.

ProblemDuring a European client's factory audit, when asked whether the laminate was halogen-free, procurement showed supplier compliance certificates — but compliance certification and halogen-free requirements are two different things, with entirely different lists and limits.

根因Of the laminates with all six certificates in order, only two were truly halogen-free; the three marked Tg 170 measured 172℃, 168℃ and 151℃ respectively — the third deviating by 19℃, a mid-Tg material passed off as high-Tg; in thermal stress cross-verification, the 151℃ laminate delaminated after solder float; three batches of the same spec showed inter-batch Tg variation approaching 8℃.

MeasuresSwitched from certificate review to a dual track of "certificate + measurement," with Tg and halogen content sampled from every batch; procurement specification rewritten into verifiable clauses (Tg no lower than 170℃ per DSC sampling, Td compliant, halogen subject to arbitration method results); measurement reports consolidated into factory audit response materials.

ProblemA smart home appliance main control board saw delamination suddenly approach 10% during the second reflow of double-sided assembly — several hundred scrapped boards per day at that day's capacity.

根因Ultrasonic imaging showed visible blistering was just the tip of the iceberg — large-area separation existed across multiple interlayers, propagating along the resin/glass fiber interface; concurrent damage — some plated through-hole wall copper cracked at the board's mid-thickness; simulated 30℃/70%RH storage without vacuum packaging for 7 days reached nearly half the material's saturation moisture content.

MeasuresStandardized baking of inventory and in-line laminates at 120℃/4 hours; reflow profile re-tuned, ramp rate in the preheat zone pressed below 1.5℃/s with an added soak plateau near 150℃; Z-axis CTE and Tg added to every batch sampling and compared against baseline batches.

ProblemEquipment deployed in outdoor cabinets on the southern coast, with year-round high temperature and humidity and condensation from day-night temperature swings — field failure rate reached 22% after six months of operation.

根因More than half of the failed units returned to normal after drying, proving the failure was reversible and moisture-related; east- and south-facing cabinets failed noticeably more than north-facing ones — sunlight heating plus nighttime cooling condensation formed a daily temperature/humidity cycle that doesn't exist in standard testing; interface bond strength dropped by more than 30% as moisture content rose.

MeasuresA "high temperature/humidity soaking + rapid cooling condensation + high temperature drying" cyclic profile was designed for verification; low-moisture-absorption materials were evaluated and introduced; conformal coating applied at critical locations, with cabinet orientation and heat dissipation optimized.

ProblemA body control module showed several intermittent open circuits during vehicle endurance verification, traced to the plated through-holes of an eight-layer board — the hole-wall copper fractured at mid-height.

根因The crack was located mid-hole-wall, through the copper layer, with fatigue characteristics at the fracture surface, initiating on the copper's inner side and propagating outward; stress peaked at board mid-thickness where Z-axis expansion stress is greatest, and the inherent distribution of electroplating made hole copper thinnest there; in control experiments, samples with high-ductility plating processes survived thousands of cycles intact.

MeasuresThermal cycling conditions were redefined, with the criterion changed from "continuity" to "resistance change not exceeding 10% of initial value"; critical networks switched to parallel via or staggered-layer layouts; procurement specifications specified "minimum thickness" rather than "average thickness."

ProblemSecond- and third-order stacked micro-via products passed all electrical tests, then went open after reflow.

根因At about 210℃, stacked via resistance suddenly jumped to open; cooling to about 180℃ it suddenly recovered — this reversible characteristic was the decisive evidence for the mechanism; high-temperature cross-sections showed a clear gap at the bonding interface between the micro-via bottom copper and the lower target pad; about 27% of micro-vias in samples stacked three or more layers cracked after thousand-order cycling.

MeasuresAcceptance criteria upgraded from "passing static electrical test" to dual qualification of "static electrical test + dynamic temperature cycling resistance monitoring"; when mixed lamination is required, the CTE difference between core and build-up materials must be controlled within 3ppm/℃; laser drilling parameters, desmear process and electroless copper coverage capability were jointly reviewed with the board manufacturer.

ProblemA millimeter-wave front-end module showed good metrics at prototype stage, but system margin became insufficient during production ramp: the link budget computed fine, measured insertion loss was too high, and bit error rate worsened at high temperature.

根因Production boards' insertion loss was noticeably higher than early prototype boards, differing by nearly 30% at 28GHz; loss separation showed dielectric loss was close between the two — the difference came almost entirely from conductor loss; production boards' copper surface roughness parameters were about twice those of prototype boards — material switch changed from low-profile grade to standard grade.

MeasuresProcurement specifications explicitly designate the copper foil grade and require suppliers to note the actual model with delivery; roughness effects incorporated into simulation models — based on actual measured topography rather than simple correction factors; inner-layer brown oxide parameters jointly adjusted with the board manufacturer.

ProblemA 25Gbps high-end switch backplane's link eye was nearly closed at prototype stage, with bit error rates too high to establish a link.

根因The client's simulation used 50Ω, while measured average impedance was around 48Ω, deviating about 4%; cross-sections showed signal vias left approximately 1.8mm of dangling stubs below the inner-layer routing, connected to no network; impedance deviation traced — simulation used the supplier's "process value" Dk of 3.48, while the measured "design value" was close to 3.66.

MeasuresBack-drilling removed the stubs; stub length requirements and inspection methods fixed into the board manufacturer agreement; simulation switched to measured Dk/Df with temperature coefficients considered; frequency-domain verification of complete links including vias written into all high-speed product acceptance specifications.

ProblemAn intelligent driving camera module showed functional anomalies mid-way through the OEM's tightened thermal shock verification before pre-installation mass production, located to main chip BGA solder joint cracking.

根因Failures were highly concentrated at the four corners of the BGA array, especially the outermost ring farthest from the chip center; at about 1600 cycles, micro-cracks appeared at the corner solder ball's upper interface; by 1900 cycles some solder balls had fully separated; the interface intermetallic compound layer was excessively thick — hard and brittle, becoming the preferred crack path; solder ball microstructure showed tin phase precipitation and coarsening.

MeasuresReflow profile redone — lowering peak temperature and shortening time above liquidus while ensuring wetting and solder ball collapse; three reflow parameters brought under process control and periodically verified with measurement boards; underfill solutions evaluated for high-reliability positions.

ProblemA vehicle-body flip-chip packaged product showed several functional interruptions during road trials; repaired units tested intermittently connected electrically.

根因Damage evolution showed three clear stages — minor edge interface separation (electrically normal) → separation advancing along the interface toward the center (occasional parameter fluctuation) → cracks through (connection interrupted); modal testing found the first natural frequency falling exactly within the frequency band where real-vehicle road trial vibration energy is most concentrated — resonance; heavier components near the failure area with relatively thin board thickness.

MeasuresMove the board's first natural frequency out of the main vibration energy band — increase board thickness or add local stiffeners, adjust support point positions, move heavy components away from the board center where amplitude is greatest; vibration testing changed from "standard profile compliance" to a "real-vehicle profile + enhanced profile" combination.

ProblemA handheld product showed functional anomalies during drop verification before the standard drop count was even completed.

根因Dye-stained areas showed fracture occurred between the pad and the substrate — substrate cohesive failure, not solder joint separation; the substrate itself cracked; the client used non-solder-mask-defined pads, relying entirely on copper foil adhesion for copper-substrate bonding; in control experiments, solder-mask-defined samples lived noticeably longer, with failure mode shifting from substrate cratering to solder joint cracking itself.

MeasuresPads in high-risk areas (board edges, corners, large components) changed to solder-mask-defined or hybrid definition, letting the solder mask overlap the pad edge slightly; assembly line strain sources mapped — routing changed from V-score to milling, fixture support points redistributed, screw torque capped; a prevention plan based on strain thresholds established.

ProblemAfter reflow of a certain batch, some pads blackened and solder wetting was poor.

根因Blackened pads showed granular rough topography at 40x magnification, entirely different from the bright flatness of normal pads; the nickel layer showed clear corrosion morphology, penetrating along grain boundaries and locally through; energy spectroscopy showed phosphorus content in corroded areas significantly higher than normal areas; ion chromatography detected free phosphate species; process traceability found that after immersion gold bath maintenance, bath activity was high while immersion time had not been adjusted accordingly.

MeasuresIncoming inspection changed from "thickness only" to thickness + metallurgical state (phosphorus content, corrosion morphology, shear force); immersion gold time must be reconfirmed after bath maintenance; high-reliability platforms uniformly adopted surface finish solutions with barrier layers.

ProblemProducts used many pure-tin-plated components and connectors, with latent random short-circuit risks and unpredictable growth timing.

根因Multiple tin whiskers were found — straight, bent and helical forms, from tens of microns to nearly a millimeter long; density highest at lead roots and plating edges, with bent deformation zones several times denser than flat areas; cross-sections showed the intermetallic compound between the tin layer and copper substrate was locally thick and locally thin — direct evidence of uneven stress distribution.

MeasuresProducts classified and controlled by risk level; high-risk products prioritized nickel-barrier plating, eliminating the main stress source at its origin; in-service products unable to change plating adopted conformal coating as a physical barrier; plating type confirmation written into mandatory component selection inspection items.

ProblemThe internal void rejection line was set at 25%, but both rejecting and accepting by this line caused problems — false rejections and false acceptances existed simultaneously.

根因2D X-ray projects the entire solder ball's voids onto one plane, unable to judge vertical position; voids of the same volume weaken strength far more at the interface than at the center; cracks tend to propagate along interface-type voids — voids act as pre-planted crack sources; process traceability found the failed batch's preheat ramp was too fast, trapping volatiles at the interface.

MeasuresPreheat zone re-tuned for insufficient volatile escape — longer preheat time, lower ramp rate; pad solderability added to incoming inspection, with longer-stored boards requiring solderability confirmation or baking before use; high-risk products sampled with 3D tomography.

ProblemProducts passed all functional tests before shipment, but developed batch intermittent failures after months of client use.

根因On both sides of the separation surface — smooth spherical on the solder ball side, solder paste retaining its independent shape on the pad side — both showed "free surface" morphology, meaning they had never melted together; the interface intermetallic layer was extremely thin, under one micron, directly proving almost no metallurgical reaction; oxides were detected on failed solder ball surfaces, and some devices in inventory exceeded recommended storage periods.

MeasuresA moisture sensitivity level management system established — clarifying storage conditions and post-opening exposure time limits, first-in-first-out, and baking of overdue devices by level; reflow profiles re-tuned for large components to ensure corner solder balls fully melted; solderability testing before placement.

ProblemProducts used many 01005 components (0.4mm × 0.2mm, weighing about 0.04mg), with a tombstone rate of about 5%.

根因Tombstoning is essentially "two ends out of sync"; a considerable proportion of solder joints showed solder paste volume differences exceeding 10% between ends; placement offset at some locations exceeded a dozen microns; temperature differences between ends exceeded 3℃ across board regions; pad design was asymmetric — one end connecting to large copper areas (heat sinks), the other to thin traces; locations with all three factors stacked had tombstone rates several times those with single factors.

MeasuresSolder paste volume and placement precision control tightened; pads redesigned for thermal symmetry, with thermal isolation on ends connecting to large copper areas; step stencils adopted to improve solder paste volume consistency; an SPI–placement–reflow closed-loop feedback established.

ProblemA high-end motherboard in mass production saw edge solder joint cold solder and open joints; X-ray showed failures concentrated at the four corners and edges of the BGA, with center solder joints normal.

根因Near reflow peak temperature, BGA area warpage reached 0.68% of board length — for large BGAs, this converts to tens of microns of edge height difference, while solder ball collapse is typically also in the tens of microns — meaning warpage was enough to pull edge solder balls out of the paste; failed corner solder joints showed typical "stretching" morphology in cross-sections; this laminate's modulus dropped noticeably at peak temperature.

MeasuresHigh-Tg materials evaluated and introduced — warpage at reflow peak temperature dropped significantly, with edge height difference compressed to less than half the original; reflow carriers with flattening function introduced to the production line; high-temperature warpage measurement methods established and made mandatory for new product introduction.

ProblemAfter introducing the crimp process on a new platform, hole-wall damage, pad lifting and excessive contact resistance appeared.

根因Hole diameter tolerances were oversized with some holes undersized — the elastic pin pressed back against the hole wall, splitting the copper barrel, breaking inner-layer connections and lifting pads; cross-sections showed three types of damage, all caused by excessive interference; severely damaged holes could show normal initial contact resistance, degrading only after temperature cycling and vibration.

MeasuresCrimped hole finished diameter tolerances and plating thickness requirements redefined per connector supplier specifications, written into manufacturing drawings and procurement specifications; a first article verification mechanism established — each batch of boards and connectors requires cross-section inspection and retention force testing on first articles; minimum spacing rules between crimped holes, board edges and adjacent BGAs clarified.

ProblemWith continuous bumping and vibration during vehicle driving, connector terminals backed out and made poor contact, with lighting and sensor signals occasionally interrupting; faults were hard to reproduce in the field, repaired units tested fine back at the factory, and after-sales repair rates stayed persistently high.

根因The single-lock structure's retention force margin was insufficient — under long-term alternating loads, the latch wore and gradually retreated; terminal lance-to-housing fit clearance was oversized, with insufficient axial constraint; crimp height fluctuated, causing fretting wear as terminals moved slightly within housings, raising contact resistance.

MeasuresAdded secondary anti-withdrawal clips (TPA/secondary lock) to strengthen axial constraint; terminal lances improved to increase retention force within housings; crimp height and pull-out force windows locked, with 100% terminal retention force inspection added.

ProblemOutdoor industrial control equipment exposed long-term to rain and condensation — connector interface water ingress caused short circuits and poor insulation, with frequent equipment downtime; the original product's IP rating couldn't meet field conditions, facing full batch replacement.

根因Seal material had high compression set, with rebound failure after long-term use; no stress relief at the rear — water wicked along conductors via capillary action as cables swung; strip length and assembly tolerances were out of control, making the sealing surface effectively useless.

MeasuresSwitched to silicone seal housings matched with compression; optimized rear stress relief structure; standardized stripping and assembly processes with 100% air tightness inspection.

ProblemTerminal crimp height control was unstable, with some points exceeding contact resistance limits; equipment heated up during high-current operation, with ablation risks; manual visual sampling had high miss rates, accumulating rework and customer complaint costs.

根因Crimp dies wore out, with insufficient crimp height CpK; parameters not locked by wire gauge/batch, with no confirmation at changeover; manual sampling couldn't cover fluctuations and micro-resistance anomalies.

MeasuresCrimp dies replaced or optimized with parameters locked; online crimp height monitoring + micro-resistance sampling introduced; wire stripping and terminal insertion SOPs standardized, with first article–patrol–last article three-stage closed loop.

ProblemEngine bay harnesses operated long-term at high temperature — connector plastic housings gradually aged and embrittled, terminal surfaces oxidized, signals intermittent, worsening over time and hard to predict.

根因Housing material's temperature rating didn't match actual bay temperature — molecular chain degradation and embrittlement after thermal aging; terminal plating oxidized faster at high temperature, forming oxide films on contact surfaces; harnesses ran close to heat sources, with local temperatures above datasheet assumptions.

MeasuresHigh-temperature plastic housings replaced with reselection based on measured conditions; terminal plating upgraded for oxidation and high-temperature resistance; routing optimized to avoid direct heat exposure with added thermal insulation.

ProblemAt ports and coastal outdoor sites, salt spray and moisture corroded terminals, drifted contact resistance, and intermittently cut signals; routine testing struggled to reproduce it, and field maintenance was frequent.

根因Insufficient plating thickness or pores/cracks let salt spray penetrate, forming galvanic corrosion; housing sealing structure failed to block effectively, allowing moisture ingress and retention; plating at crimp edges was scratched, exposing bare copper as the corrosion starting point; standard salt spray duration was insufficient to cover field accumulation effects.

MeasuresTerminal plating thickness and corrosion-resistant plating systems upgraded; housing sealing structure optimized to reduce moisture ingress; crimp process optimized to control plating damage; extended NSS + humidity cycling verification implemented.

ProblemNew energy passenger vehicle high-voltage power harnesses — vehicle bumping plus high/low temperature alternation degraded terminal contact stress, with loaded temperature rise over limit; each passed standalone temperature rise or vibration testing, and only combined environments exposed the fault.

根因Temperature cycling caused spring stress relaxation and creep — insufficient creep resistance in the copper alloy reduced retention force; fretting wear and oxide films pushed resistance up, with Joule heating raising temperature further, forming a "resistance rises → heating worsens → creep accelerates" positive feedback loop.

MeasuresHigh-voltage terminal spring structure optimized to increase long-term contact normal force; high-creep-resistance copper alloy selected to suppress high-temperature stress relaxation; crimp process and plating integrity control optimized.

ProblemBefore submitting complete units for third-party certification, the client's internal pre-compliance found temperatures high at kettle-body/handle seams, but readings varied widely across batches and measurement points — unable to tell whether it was a measurement method issue or a product issue.

根因Temperature rise points were placed by experience at "where it feels hottest," missing the two truly hottest spots behind the seam and inside the handle — readings naturally ran low; thermocouple attachment methods varied, with attachment pressure differences introducing 3–5K fluctuation; the ball pressure indentation on plastic near current-carrying terminals approached the limit — a tight heat-resistance grade selection, not process variation.

MeasuresTemperature rise measurement points fixed at 12 locations per standard clauses with drawings to lock them in, making readings comparable across people and batches; thermocouples uniformly attached by aluminum foil tape spot-welding, eliminating attachment differences; plastics around current-carrying parts switched to higher heat-resistance grades with tightened ball pressure sampling.

ProblemDuring the certification body's abnormal testing, temperature kept climbing after the protection action; the client had only verified normal operation internally, never covering the "protection device fails first" path.

根因The thermal cut-off and thermostat were in series in the same circuit — the path where both failed simultaneously was never evaluated; after the protection action, residual power was still supplied via bypass circuits, with temperature rising about 18K within 7 seconds of power-off; the housing plastic was near its heat deflection temperature in this range, and repeated cycles would leave permanent indentations.

Measures"Protection device failure" written into the internal verification checklist as an independent test item; heating circuit changed to dual independent protection in separate physical locations; housing material's heat deflection temperature raised one grade with 30-cycle verification.

ProblemThe PCB's primary-to-secondary spacing met the design drawing's calculations, but the measured path along the insulation surface was insufficient, and electric strength broke down after humid heat treatment.

根因The design drawing calculated by straight-line distance, while the actual path detoured along slot walls and component bodies — measured nearly twice the drawing; slot width was insufficient, with the creepage path inside the slot calculated continuously along the slot bottom; no isolation slot was cut beneath bridging components between primary and secondary, becoming a hidden bridging point.

MeasuresDrawings redone based on measured paths, with slot width given an extra 0.4mm margin above the standard minimum; isolation slots added beneath bridging components, switched to horizontal placement; electric strength after humid heat treatment listed as a sampling item for every batch.

ProblemThe client made energy efficiency declarations based on driver parameters provided by the supplier — measured input power exceeded the rating, dropping the energy efficiency grade by two levels.

根因The driver datasheet gave typical values under ideal loads, while the complete lamp's actual operating point deviated significantly; power factor worsened at low load — exactly the range included in energy efficiency testing; standby power of multi-output models exceeded limits when accumulated.

MeasuresBefore declaration, measure once at the complete lamp's actual operating point — do not trust driver typical values; a separate internal control line for power factor in the low-load range; standby power measured through the complete unit's full circuit with hard disconnection in the circuitry.

ProblemA handheld tool housing softened and deformed locally after temperature rise pre-compliance — the client initially judged it injection molding batch variation.

根因The housing's recycled material blending ratio had risen, with measured heat deflection temperature about 12℃ below the datasheet rating; in glow-wire testing, this batch ignited noticeably faster than the control batch; the deformation was located directly above the hottest internal component — a combination of selection and structure.

MeasuresHousing material switched to virgin resin with the grade locked, and heat deflection temperature sampling added to incoming inspection; thermal insulation and ventilation clearance added between internal heat-generating parts and the housing; drop and temperature rise combined into a combined verification item.

ProblemAfter months of wear, users saw charging contacts corrode and buttons fail — repairs concentrated in summer and among high-frequency exercise users.

根因Sweat seeped through housing seams, forming electrolyte films between contacts, with metal ions migrating and depositing; ultrasonic weld line width was uneven, with local unfused areas forming capillary channels; charging contact plating wore through after repeated friction, becoming the corrosion starting point.

MeasuresUltrasonic weld line width and energy windows locked with 100% air tightness inspection; contacts switched to corrosion-resistant plating systems with increased thickness; complete-unit artificial sweat + temperature/humidity cycling combined verification added.

ProblemThe complete unit passed regular-face drop testing, but field repairs were dominated by "functional anomalies after drops" — which the laboratory could never reproduce.

根因Standard drops only cover regular faces, while actual drops land mainly on corners and edges, concentrating impact energy; battery pack clips momentarily disengaged and re-engaged under angled impact, with contact interruptions recorded as "functional anomalies"; the motor was already heated under load before drops, reducing housing toughness.

MeasuresCorner/edge oriented drops and loaded pre-heating before drops added; secondary locking added to battery pack clips; post-drop judgment changed from "can it power on" to "continuous loaded operation + uninterrupted current waveform."

ProblemAfter two years of field operation, power modules failed — yet laboratory testing at constant temperature and full load ran the full 1000 hours without any anomaly.

根因Condensation formed inside during overnight shutdown segments, cycling once per day — constant-temperature full-load testing erased this cycle entirely; thermal interface material between power module substrates and heat sinks was pumped out and gradually dried under thermal cycling; control board protective coating absorbed water during condensation segments, degrading insulation.

MeasuresA "night shutdown + cooling condensation + daytime full load" day-night cycle added to the verification profile; thermal interface material switched to anti-pump-out grades with specified coating thickness; control board coating thickened in critical areas with coating integrity checks.

ProblemImage transmission occasionally interrupted during low-temperature flights, with everything normal on retest at room temperature — the fault remained unlocatable for a long time.

根因At low temperature, plastic housing contraction reduced connector contact normal force, and combined with rotor vibration produced microsecond-level intermittent disconnections — uncatchable by ordinary multimeters and patrols; the disconnection duration was shorter than the image transmission link's reconnection criterion, manifesting as "one frozen frame"; harnesses stiffened at low temperature, transmitting vibration stress directly to connectors instead of being absorbed by the cable.

MeasuresConnectors switched to high-normal-force springs with added latches; stress relief bends reserved in harnesses for low-temperature segments; low temperature + vibration + µs-level intermittent disconnection monitoring triple-combined added to verification items.