5.3 Cable & Harness Assembly (IPC/WHMA-A-620)

Cable assemblies are the "nervous system"system of the product. Failures hereThey are often intermittentbuilt by hand, making them the most variable and difficultfailure-prone tocomponent diagnose.in the BOM. IPC/WHMA-A-620 governsis the qualitystandard ofthat crimps,separates insulations,a reliable connection from an intermittent field failure. If a crimp is bad, the resistance increases, heat generates, and solderingthe ofconnector wires.melts.

Crimping Criteria (The Gas-Tight Seal)

A crimp is not a fold; it is a cold-weld. The goal is to compress the copper strands into a solid mass, eliminating oxygen to prevent corrosion.

Critical Visual Attributes:

• Bellmouth: The flared endtrumpet shape at the entry of the crimp terminal that prevents the metal edge from cutting the wire.crimp.
  • Requirement: VisibleMust bellmouthbe requiredvisible at the wire-entry end. It prevents the sharp metal edge from slicing the wire strands during vibration.
• Conductor Brush: The wire strands of wire sticking outextending past the crimp.crimp barrel.
  • Target: Visible strands (flush to 1x wire diameter).
  • Defect: No strands visible (risk of partial"short crimp)crimp" or strandsempty extending into the mating area.barrel).
• Insulation Crimp: The strain relief grip.
  • Target: Fully supports the insulation without piercing it.
  • Defect: Insulation fullycrimped supportedinto andthe grippedconductor withoutbarrel being(conductivity pierced.risk).

Pro-Tip: Crimp height is a proxy for compression. A "Go/No-Go" gauge is useless if the tool wears out. Measure Crimp Height with a micrometer at the start of every shift.

IDC (Insulation Displacement Connection)

Used for ribbon cables. The blades slice through insulation to contact the core.

Alignment Rules:

• IF the connector is misaligned (cocked) -> THEN Reject. Uneven pressure leads to open circuits.
• IF the wire is cut or strands are broken -> THEN Reject.

Strain Relief & Routing

A harness is a dynamic structure. It moves, vibrates, and expands.

Mechanical Logic:

• Cable Ties: Must be tight enough to hold but not deformsecure the wirebundle without crushing the insulation.
  • Spacing:Rule: EveryIf 100mmthe -tie 300mmleaves dependinga ondeep harnessimpression, diameter.it is too tight.
  • Tail Cut:Safety: Tails must be cut flushflush. withA noprotruding sharp edgestail (safetyis hazard).a "blood draw" hazard for the installer.
• Bend Radius:
  • Static: MinimumMin bend5x radiuscable isdiameter.
  • Dynamic (Flexing): Min 10x the cable diameterdiameter. toViolating preventthis guarantees internal conductor fatigue.fatigue and breakage.

Final Checklist

FeatureControl Point	CriteriaCritical Requirement	VisualNon-Negotiable CheckRule
Pull Force	Per UL 486A / Wire Gauge.	Destructive test at setup (3-5 pcs).
Crimp Height	PerWithin Mfr Spec (±0.05mm).	MicrometerWrong Check
Bellmouth	Visible	Entryheight side= ofWrong crimp
Pull Force	Per UL 486A	Destructive Test (Sample)compression.
Continuity	<100% 2Electrical OhmsTest.	No "sample testing" for open/short.
Pinout	100% ElectricalMap TestVerification.	Wrong pinout = Blown PCB.
Labeling	Legible & Permanent.	Missing label = Unidentifiable part.