Skip to main content

3.3 Soldered and Ultrasonic Terminations

EnvironmentalWhile crimping is the standard for high-volume termination, soldering and lifeultrasonic testingwelding turnsare mandatory for specific high-reliability or high-current applications. These processes create a wiremetallurgical harnessbond fromrather than a lab-builtmechanical assemblyone. intoHowever, athey provenintroduce fieldthermal survivor.variables By— exposingheat, samplesflow, and solidification—that mechanical crimping does not. Controlling these thermodynamics is essential to bending,prevent vibration,brittle heat,joints, humidity,insulation melt-back, and corrosivelatent agents,failures thesecaused testsby uncover the weaknesses that only appear after long use or harsh conditions. Running electrical checks before and after each stress cycle ensures that performance, insulation, and contact integrity remain intact. The process transforms durability from an assumption into measurable proof, tailored to the product’s real operating environment.wicking.

3.3.1 WhatSolder thisCups: provesThe Manual Interface

Solder cup terminations are common in military (MIL-DTL) and whenheavy toindustrial run it)

  • Design/qualification: “Will this harness survive its world?” Run at NPI or when materials change (wire, boots, backshells, overmold).connectors.
  • Process monitoring: “Are builds consistent?” Run smaller samples perUnlike quarterPCB or per vendor shift (sleeve, resin, contacts).
  • Failure analysis: reproducesoldering, the customer’sheat environmentsource tois seemanual, and the breakthermal andmass fixof the mechanism.
connector

Alwayscup bookendis exposures with electrical checks: Continuity → Resistance (Kelvin on power) → IR → Hipot (3.1), plus visuals.significant.


A)

Process Mandates

  • 3.3.2Pre-Tinning: TestThe planningwire strand end must be pre-tinned (foursolidified) decisionsbefore first)insertion.
      Inserting loose strands invites splaying and poor wetting inside the cup.
    1. SpecimensThermal Transfer:: exactThe PN–Rev–Variant;iron routetip themmust heat the cup, not just the wire. Solder is fed into the cup to form a molten pool before the wire is fully seated.
    2. Cleaning: If liquid flux is used, the assembly must be cleaned to remove corrosive residues from inside the connector housing.

B) Workmanship Standards (IPC/WHMA-A-620)

  • Wetting: The solder must show positive wetting to the wire and the inner wall of the cup over at least 75% to 100% of the circumference (depending on a board to final install clamp spacing and bend radiiClass).
  • Instrumentation:Fill continuity glitch monitor (≥1 kHz), Kelvin taps on power/grounds, thermocouplesLevel: onSolder suspectshould joints.be visible at the cup entry.
    • Class 2: Solder may be slightly recessed or slightly convex.
    • SuccessClass criteria3:: defineSolder must follow the contour of the cup entry. limits up front (drops, ΔR, ΔT, IR/Hipot, cosmetic).
    • SequenceOverfilling (typical):spillage onto the outside of the cup) is a Defect.
  • Wicking: Solder wicking up the wire is unavoidable but must be controlled.
    • Limit: Wicking must not extend to the point where the wire needs to flex (e.g., the connector strain relief clamp). It must stop short of the insulation.
  • Sleeving: Because solder joints are rigid and brittle (fatigue prone), Baselineshrink sleeving →is Flex/Torsionmandatory →to Vibrationprovide →strain Temp/Humidityrelief cyclesand →insulation Chemical/Ingresssupport (ifimmediately relevant)behind →the Final electrical.cup.

3.3.2 Splices: Ultrasonic vs. Crimp

KeepSplicing onejoins unittwo asor more wires into a controlsingle (noelectrical exposure) to compare drifts.node.


A)

3.3.3Ultrasonic Flex & bend cycling (where most field issues start)

Welding

Setups

Ultrasonic
  • Mandrelwelding bend:uses wraphigh-frequency overmechanical vibration to scrub metal surfaces together, creating a radiussolid-state =metallurgical design minimumbond (static:cold ≥6×weld) OD;without dynamic:adding ≥10× OD unless high-flex cable).
  • Rolling flex / drag-chain: for motion-class cables.
  • Torsion: clamp ends; twist ±90–180° about axis.

Starter profiles (tune to product)

Class

Mandrel bend

Rolling flex

Torsion

Office/benign

5k cycles, 30 cpm

—

±90°, 2k cycles

Machine bay

20k cycles, 30–60 cpm

200–500k cycles at chain radius

±180°, 10k cycles

High-flex chain

—

1–5 million at vendor-rated radius

±180°, 50k cycles

Monitor & limits

  • Continuity glitches >1 ms = fail; ≤3 blips <1 ms allowed (log).
  • ΔR end-to-end ≤ 10–20% vs baseline (Kelvin on power).
  • No jacket cracks, sleeve retreat,solder or shieldcrimp breakouts.


3.3.4 Vibration (find loose pins, fretting, bad clamps)

Replicate the installed clamp scheme on the shaker; first clamp before first bend.

Screening sweep (find resonances)

  • Sine 5→200 Hz, 0.5 g, 2 oct/min, 3 axes; dwell 1 min at peaks if needed.

Random vibration starter (industrial)

  • 10–500 Hz, overall 3–5 grms, 3 axes, 30–60 min/axis (tune to product/vehicle spec if provided).

Pass indicators

  • 0 continuity opens >1 ms during any axis.
  • No bent/broken contacts or backshell loosening.
  • Post-test IR ≥ limit and Hipot PASS (21.1).


3.3.5 Temperature cycling & thermal shock

Temperature cycling (air-to-air)

  • Range: −40 → +85 °C (or your product limits), ramp ≤ 5 °C/min, dwell 30 min at extremes, 50–100 cycles.
  • Monitor continuity at extremes if possible.

Thermal shock (two-chamber)

  • −40 ↔ +85/105 °C, transfer ≤ 30 s, dwell 10–15 min, 50–100 cycles.

Pass

  • No cracks in boots/overmolds, label legible, ΔR ≤ 10–20%, IR/Hipot PASS.
  • Shield bonds intact (< 0.1 Ω end-to-end or to chassis point).

3.3.6 Humidity & moisture

Insulation resistance loves to fall when wet. Prove your materials.

Damp heat steady state (starter)

  • 40 °C / 95% RH, 96 h; unpowered, then 1 h dry at room conditions → run IR/Hipot.

Damp heat severe (materials-permitting)

  • 85 °C / 85% RH, 168–500 h (verify jacket/adhesive ratings first).
  • Acceptance: IR ≥ 10–100 MΩ (per product), boots/labels still adhered, no green corrosion.


3.3.7 Chemicals, UV, salt fog (if the environment demands it)

Chemical splash/soak

  • Fluids: oil/coolant/IPA/brake fluid/cleaners from your use-case.
  • Method: 24–72 h soak or periodic splash at room temp; then flex 2k cycles on mandrel.
  • Pass: no swelling >10%, no softening/cracks, labels legible, IR/Hipot PASS.

UV/outdoor

  • UV exposure (lamp/arc) ≥ 100 h; then bend test. Pass = no embrittlement/cracking; print still readable.

Salt fog

  • 5% NaCl, 35 °C, 48–96 h; focus on backshells/lugs. Pass = no red rust on stainless, minor cosmetic only on plated, continuity unchanged.


3.3.8 Ingress (IP) & washdowns

  • IP54 spray: multi-angle spray 5–10 min; IR/Hipot afterward.
  • IP67 dunk: 1 m / 30 min with mated seals; look for bubbles; post IR/Hipot.
  • Washdown: if applicable, run spray with detergent and relabel legibility check.


3.3.9 Mate/unmate life & latch strength

Cycle per expected service.

Mating cycles

  • 50–100 cycles for general purpose; ≥500 if field-serviceable.
  • Track contact resistance (per pin) every 25 cycles; drift ≤ 50 mΩ from baseline.

Latch/CPA pull

  • Pull at rated direction; latch must hold ≥ spec without damage; visual OK after test.


3.3.10 What to record (tie to SN, not a notebook)

  • Profile IDs (flex/vibe/temp), dates, operator, fixture IDs.
  • Baseline and post-exposure: Continuity/shorts, Kelvin R, IR/Hipot, shield bond Ω, photos.
  • Real-time: glitch timestamps, ΔT at connectors, resonance notes.
  • Disposition (PASS/REWORK/FAIL) with mechanism if failed (e.g., “shield wire break at bend after 12k cycles”).

Store with the harness SN (20.5) so RMAs find it in seconds.barrels.


  • 3.3.11 Starter acceptance table (tune to your spec)

Test

Pass (starter)

Flex / torsion

0Application: opensPreferred >1 ms;for ΔRhigh-current ≤battery 20%; no jacket/shield damage

Random vibration

0 opens >1 ms/axis; no mechanical damage

Temp cycle / shock

Visual OK; IR ≥ limit; Hipot PASS; ΔR ≤ 20%

Humidity

IR ≥ 10–100 MΩcables (perEVs) product);and labelsgrounding intactpoints where minimum resistance is required.

  • Process Monitoring:Chemicals Quality is controlled by the machine parameters, not operator skill.

    • No cracks/swelling >10%; labels readable; electrical PASS

    Salt fog

    No functional corrosion; continuity unchanged

    IP67

    • Energy (ifJoules): claimed)The total energy delivered to the weld.

  • Collapse Height:No leaks;The IR/Hipotfinal PASSheight post-testof the welded "nugget."

  • Validation:Mating life

    • ContactThe ΔRmachine must output a ≤ 50 mΩPass/Fail based on the Energy and Height window. Destructive Peel Tests are required at setup to verify the bond strength exceeds the wire strength.

    B) Crimp Splices (Butt and Parallel)

    • Parallel Splice: Wires enter from the same side.
    • Butt Splice: Wires enter from opposite sides.
    • Risk: The primary risk is wire placement. In a blind butt splice, it is difficult to verify that both wire ends are fully seated in the crimp zone.
    • Process Control: Use splices with an inspection window in the insulation to verify wire presence. Pull testing is mandatory during setup.

    3.3.3 Heat Shrink Application: The Environmental Seal

    Heat shrink tubing provides insulation, strain relief, and environmental sealing. It is not just "plastic tubing"; latchit intactis an engineered component that must be fully recovered to function.


    A) Material Selection

    • Single Wall: Provides electrical insulation and color coding only. Not waterproof.
    • Dual Wall (Adhesive Lined): Contains an inner layer of hot-melt adhesive. Mandatory for any splice or termination requiring an environmental seal.

    B) Application and Inspection

    • Recovery: The tubing must be heated until it has fully shrunk onto the substrate (no wrinkles or loose spots).
    • Adhesive Flow: For dual-wall tubing, a ring of adhesive must be visible at both ends of the tube. This confirms the glue has melted and flowed, creating a seal.
    • Positioning: The tubing must overlap the wire insulation by a defined minimum distance (e.g., wire diameter or 6 mm) to ensure strain relief.
    • Defects:
      • Scorching/Charring: Excessive heat degrades the polymer (brittle).
      • Piercing: The underlying terminal or wire strands must not poke through the tubing wall.

    3.3.12Final CommonChecklist: trapsSoldered →and smallestSealed reliable fixTerminations

    TrapMandate

    SymptomCriteria

    FixVerification Action

    Solder Cup Fill

    TestingSolder visible at the entry, fully wetting cup and wire; no spillage on “freethe cable”exterior.

    UnrealisticVisual failures

    Replicateinspection clamp(10x). distancesVerify andsolder first-benddoes positionnot exceed the cup rim diameter.

    Wicking Limit

    WrongSolder radiuswicking inmust flexstop testbefore the wire enters the strain relief zone.

    EarlyTactile breaks

    Usecheck: designWire minremains radiusflexible (orbehind vendor-ratedthe radiusrigid forsoldered high-flex)area.

    Ultrasonic Weld

    NoWeld glitchnugget monitormust meet Height and Energy targets.

    IntermittentsMachine unseen

    Addlog ≥1verification; kHzdestructive continuitypeel loggingtest duringat motionshift start.

    Seal Integrity

    HipotDual-wall rightheat aftershrink humiditymust show a visible ring of adhesive at both ends.

    FalseVisual fails

    Stabilize/drycheck toconfirms roomthe conditionsenvironmental beforeseal IR/Hipotis active.

    Tubing Quality

    OvercookingNo heat-shrinkcharring, inburning, cyclesor splitting of heat shrink.

    BrittleVerify stiffheat zones

    Controlgun heat;settings keepand stiffnozzle zonedistance; shortreject (20.4)burnt assemblies.

    Splice Position

    GenericSplices chemicalsmust be staggered in the harness to prevent a large "snake swallow" bulge.

    PassDimensional incheck lab, fail in field

    Test actual fluids used byof the customer

    Fixtureharness loosensbundle ondiameter shaker

    Pinagainst damage,the false faults

    PM clamps & nests; torque audit before each rundrawing.


    3.3.13 Pocket checklists

    Setup

    • Specimens PN–Rev–Variant; board-mounted with real clamp spacing
    • TC and Kelvin leads on suspect points; glitch logger armed
    • Success limits posted; control unit set aside

    Run

    • Flex/drag-chain to target cycles; log glitches/ΔR
    • Vib: sine sweep then random 3 axes; no opens >1 ms
    • Temp/humidity per profile; stabilize before electrical retest
    • Chemical/UV/salt/IP as required

    Closeout

    • Post-test Continuity, Kelvin R, IR, Hipot recorded
    • Visuals & photos (boots, labels, overmold, shields)
    • Failures tagged with mechanism; samples archived


    When harnesses are qualified under controlled environmental stresses and results are logged with traceable detail, reliability is no longer left to chance. The outcome is fewer failures in service, stronger confidence in design choices, and production that delivers durability as a standard feature.


    Back to top