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2.2 Complex Cable Preparation

SolderingProcessing complex cables requires a fundamental shift in wiremindset harnessfrom simple connectivity to geometric integrity. For coaxial, shielded, and ribbon cables, the physical structure of the assembly isdetermines lessits aboutelectrical routineperformance. A crushed dielectric changes impedance; a nicked shield compromises EMI protection; and morea abouttorn precisionribbon cable insulation leads to latent short circuits. Preparation in this stage involves precise, multi-layer material removal where mechanicaltolerance crimpsstacks cannotare reach.measured Itin bridgesmicrons, not millimeters.

2.2.1 Coaxial Cable: Multi-Stage Precision

Coaxial stripping is not merely removing insulation; it is the gapsequential inexposure legacyof connectors,concentric PCBlayers interfaces,(Jacket, Shield, Dielectric, Center Conductor) without disturbing the layer beneath.

A) The Rotary Stripping Mandate

Manual stripping with V-blades is prohibited for coaxial cables. Programmable Rotary Strippers are mandatory to ensure concentricity and shielddepth terminations,control. butThe demandsblades carefulcut controlthrough the material while rotating around the cable axis, preventing the "crush and tear" effect of heat,clamp-style flux,blades.

B) The Stepped Strip Profile

The strip profile typically follows a 3-step sequence. Each step has specific defect risks:

  1. Jacket Removal: The blade must cut the outer jacket without scoring the underlying braid. Defect: Severed shield strands reduce screening effectiveness.
  2. Shield/Braid Cut: The blade cuts the metal braid. Defect: Long, loose strands ("whiskers") capable of causing shorts, or uncut strands that prevent connector seating.
  3. Dielectric Removal: The most critical step. The blade must remove the dielectric without touching the center conductor.
    • Risk: "Ringing" the center conductor (scoring it circumferentially) creates a stress concentration point where the pin will snap under vibration.
    • Dielectric Residue: Any foam/plastic residue left on the center pin interferes with soldering or crimping.

C) Concentricity Checks

Coaxial cables are rarely perfectly round. The stripping machine must feature concentricity adjustment to offset the blades relative to the cable center. Setup validation requires microscopic inspection to ensure the cut depth is uniform around the entire circumference.

2.2.2 Shield Management: Preserving the Faraday Cage

Shielded cables (braid or foil) rely on 360-degree coverage to block EMI. Handling the shield during preparation is the most labor-intensive and supportdamage-prone step.

A) Braid Handling Techniques

Once the jacket is stripped, the braid must be manipulated without breaking strands.

  • Brushing: Rotating nylon or brass brushes are used to comb the braid strands out straight. Mandate: Brush speed and pressure must be controlled to prevent tearing the fine shield wires.
  • Unpicking: For high-reliability manual assembly, the braid is unpicked strand-by-strand using a non-metallic pick to avoid creatingdamage.
  • Folding/Windowing: brittleIf weakthe points.shield Whenis pairednot being terminated (floating), it must be folded back and covered with strainshrink relieftubing. techniquesIt likemust boots,never clamps,be andsimply heat-shrink,cut solderflush becomeswithout notinsulation, justas afraying bond,will butcause ashorts.
durable

B) safeguardFoil againstShields

vibration,

Foil flex, and long-term fatigue. Selectively applied, it turns vulnerable joints into compact, sealed connections that endure years of service.

2.2.1 Should you even solder?shields (quickAluminized decision)

Mylar)

Useare crimps by default. Choose solder only when it brings a clear advantage.

Solder is a good choice when…fragile.

  • Solder-cups/turretsRemoval: areFoil should be scored and peeled, not scraped.
  • Drain Wire: The drain wire (which maintains electrical continuity for the onlyfoil) interfacemust not be nicked during jacket stripping.

2.2.3 Ribbon and Flat Flex: Separation Mechanics

Flat Ribbon Cables (legacy/mil1.27 connectors, some sensors).mm

  • You need a sealed, inline splice orpitch) and Flat Flexible Cables (FFC) require separation (slitting) to terminate individual conductors. The challenge is maintaining insulation integrity between the split wires.shield

    bond

    A) Scribing and Separation

    Separation is performed using a solderslitting sleevedie or a scribing wheel.

    • Depth Control: The blade must penetrate the "web" (controlled,the repeatable).plastic between conductors) without touching the conductor insulation itself.
    • Defect – "Shiners":You’re makingIf flyingthe leadsseparation tool cuts too close to the wire, it exposes the copper sidewall (a PCB"shiner"). This is an immediate safety reject as it creates a potential short circuit path.
    • Defect – Tearing: and can anchorPulling the wireribbon mechanicallycable nearby.apart by hand without a scribe line results in jagged, torn insulation (stress whitening), significantly reducing dielectric strength.

    B) Notching

    For daisy-chain applications, a "notch" is punched out of the ribbon cable edge to key the connector.

    • Tooling:Field repairNotching must be compactdone andwith youa cansharp addpunch-and-die strainset. relief.
    Dull

    Avoidtooling solder (choose crimp/ferrule) when…

    • The joint willcauses flexdelamination, or vibrate (robot arms, engine bays). Solder creates a stiff wick zone that breaks strands.
    • The conductor terminates under a screw/pressure clamp. Do not tin stranded wire for screw terminals—use a bootlace ferrule.
    • High current lugs or ring terminals are needed—usewhere the manufacturer’s crimp.


    2.2.2 Common soldered terminations (how to do them right)

    A) Solder-cup connectors (plugs, circulars)

    1. Prep: strip to the drawing (no nicked strands), lightly pre-tin the cup (not the wire).
    2. Support: clamp the cable/backshell so the cup sees no cable weight.
    3. Heat & feed: tip sized to the cup; heat the cup, not the insulation. Feed solder until the cup is full and a small meniscus forms; no solder balls.
    4. Inspect: smooth, concave fillet; no exposed bare strands; wicking under insulation ≤ 2 mm.
    5. Strain relief: install the backshell boot or adhesive heat-shrink after cooling.

    B) Wire to PCB (flying lead, THT pad)

    • Anchor first: tie-down, clamp, or adhesive within 50–80 mm of the pad.
    • Form: route so the first bend is after the anchor, not at the pad.
    • Solder: wet both pad and wire; 95% fill on plated-through holes; trim flush; clean flux if required.
    • Relief: finish with heat-shrink over the exit or a dab of approved adhesive on the wire body, not the joint.

    C) Solder sleeves (splices, shield bonds)

    • Pick ID & shrink ratio for the jacket OD; for shields, use sleeves with preform ring + flux.
    • Hot-air tool, correct nozzle; heat until solder ring fully flows and adhesive extrudes at the ends; no burning of jacket.
    • Shield 360°: for braided shields, fan evenly under the sleeve; for foil, ensure drain contact.
    • Inspect: continuous fillet around 360°, clear adhesive bead both sides, wires centered (no skew).

    D) Lap/inline solder splices (only if spec requires; sleeves preferred)

    • Stagger splices by ≥ 30 mm across a loom.
    • Twist lightly, solder through capillary action (no blobs), cover with adhesive heat-shrink.


    2.2.3 Heat-shrink: selection & application

    Choose

    • Material: polyolefin is default; dual-wall (adhesive-lined) for sealing/strain relief; clear when you need to see the joint.
    • Ratio: 2:1 for snug fits; 3:1 or 4:1 to bridge boots or mixed diameters.
    • Length rule: cover the joint + 1–2× wire OD beyond each side (sleeves: per spec).

    Apply

    • Pre-cut lengths; mark position from a datum (backshell/boot).
    • Use hot air, not an open flame; move the nozzle to avoid scorching.
    • Shrink from middle outward to push adhesive to the ends; let cool undisturbed.

    2.2.4 Strain-relief best practices (make the joint live long)

    • First clamp before first bend: place a cushioned clamp 50–80 mmseparates from the backshell/joint.
    • Serviceconductor, loop:allowing leave 80–120 mm where the product needs movement; gauge it on the nailboard.
    • Boots: use molded or adhesive heat-shrink boots on backshells/branches; avoid zip-ties over bare insulation.
    • Keep the stiff zone short: limit solder wicking under insulation to ≤ 2 mm; if longer, reject or re-terminate.
    • Route away from edges: add grommets/edge guardsoxidation and sleevesmoisture (19.4) anywhere the cable can rub.
    • Potting (only if spec’d): pot over the relief, not over the solder fillet alone; allow drip-free cure before handling.
      ingress.


    Final
    Checklist:

    2.2.5Complex WhatCable “good” looks like (acceptance cues)Preparation

    FeatureMandate

    AcceptCriteria

    RejectVerification Action

    Wetting/filletRotary Processing

    Smooth,Coaxial concave,cables wetsmust cup/pad/wirebe evenlystripped using Rotary machines.

    Dull/grainy,Visual balls,check icicles,confirms voidsclean, square cuts with no crushed dielectric.

    WickingCenter Conductor Integrity

    ≤Zero 2 mmscoring underor insulation"ringing" allowed on the center pin.

    >Microscopic 2inspection mm,(10x) jacketof melted,the stiffcenter longconductor sectionafter dielectric removal.

    ExposedShield strandsIntegrity

    NoneNo beyondsevered spec;braid lightstrands brushduring okjacket in cupsstripping.

    StrandsCheck splayed,for whiskers,loose sharpmetallic spikesdebris in the stripping machine and "whiskers" on the cable.

    Heat-shrinkDielectric Cleanliness

    FullyCenter recovered;conductor adhesivemust beadbe bothfree endsof (dual-wall)dielectric residue.

    ColdVisual spots,check gaps,ensuring scorchedthe orcopper splitsurface is bright and clean for termination.

    SolderRibbon sleeveSeparation

    PreformSlitting fullymust flowed 360°; wiresbe centered in the web; zero exposed copper ("shiners").

    PartialVisual melt,inspection off-center,of nothe adhesiveseparated flowwire sides for insulation integrity.

    StrainBraid reliefManagement

    Clamp/bootBraid installed;must nobe bendcombed ator jointbrushed without excessive strand loss.

    WireCompare bendsthe atvolume cup/sleeve;of nothe anchor

    combed

    Tugpigtail test: after cool-down,to a firmreference pull inline shows no movement. For quantitative checks, use the pull-force table from 20.1.7 as the minimum baseline for that AWG.


    2.2.6 Flux, alloy, and heat (keep it predictable)

    • Flux: no-clean or RMA for harness work; never acid flux. Clean if customer/spec requires.
    • Alloy: match plant standard (SnPb vs SAC). Use the same alloy as the mating hardware when practical.
    • Heat: temperature-controlled iron/hot air; tips matchedsample to the joint mass. Too hot = burnt jacket; too cold = grainy joints.



    2.2.7 Common traps → quickest reliable fix

    Trap

    Symptom

    First move

    Tinned wire under screw terminal

    Loosens over time (creep)

    Use bootlace ferrule or proper clamp lug

    Long pigtails on shields

    EMI failures

    Use solder sleeves or 360° backshells; keep pigtails ≤10 mm

    No mechanical support

    Broken joint at fillet

    Add clamp/boot/service loop; move first bend away

    Overheated sleeve

    Burnt jacket, brittle wire

    Lower temp, move nozzle, shrink from middle out

    Pre-tinned wire for cups

    Excess wicking, cold joints

    Tin the cup, not the wire; insert bare strands

    Solder blobs on splices

    Stiff, cracks later

    Rework: remove excess, ensure capillaryshield flow,density coveris with maintained.adhesive HS



    2.2.8 Pocket checklists

    Before you solder

    • Right termination method (crimp vs solder) chosen for the environment
    • Wire strip per drawing; strands intact; parts supported
    • Sleeves/boots sized & pre-cut; hot-air/iron temps set

    During

    • Heat the metal, not the insulation; fillet forms smoothly
    • Wicking checked (stop ≤ 2 mm under jacket)
    • Install heat-shrink from middle out; adhesive visible (dual-wall)

    After

    • Tug test pass; no bends at the joint; clamp within 50–80 mm
    • Visuals: no spikes/balls; sleeve fully recovered; labels undamaged
    • Log lot/tool/operator if required; stamp module PASS



    By reserving solder for the cases where it adds real value and reinforcing every joint with proper relief, manufacturers prevent fatigue failures and EMI issues while keeping assemblies clean and consistent. This disciplined approach ensures soldered terminations remain strong, quiet, and dependable in the field.

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