4.6 Complex Cable Preparation

Processing complex cables requires a fundamental shift in mindset from simple connectivity to geometric integrity. For coaxial, shielded, and ribbon cables, the physical structure of the assembly determines its electrical performance. A crushed dielectric changes impedance; a nicked shield compromises EMI protection; and a torn ribbon cable insulation leads to latent short circuits. Preparation in this stage involves precise, multi-layer material removal where tolerance stacks are measured in microns, not millimeters.

4.6.1 Coaxial Cable: Multi-Stage Precision

Coaxial stripping is not merely removing insulation; it is the sequential exposure of concentric layers (Jacket, Shield, Dielectric, Center Conductor) without disturbing the layer beneath.

The Rotary Stripping Mandate

Manual stripping with V-blades is prohibited for coaxial cables. Programmable Rotary Strippers are mandatory to ensure concentricity and depth control. The blades cut through the material while rotating around the cable axis, preventing the "crush and tear" effect of clamp-style blades.

The Stepped Strip Profile

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

• Jacket Removal: The blade must cut the outer jacket without scoring the underlying braid.
  Defect: Severed shield strands reduce screening effectiveness.
  
• 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.
  
• 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.

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.

4.6.2 Shield Management: Preserving the Faraday Cage

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

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 damage.
• Folding/Windowing: If the shield is not being terminated (floating), it must be folded back and covered with shrink tubing. It must never be simply cut flush without insulation, as fraying will cause shorts.

Foil Shields

Foil shields (Aluminized Mylar) are fragile.

• Removal: Foil should be scored and peeled, not scraped.
• Drain Wire: The drain wire (which maintains electrical continuity for the foil) must not be nicked during jacket stripping.

4.6.3 Ribbon and Flat Flex: Separation Mechanics

Flat Ribbon Cables (1.27 mm pitch) and Flat Flexible Cables (FFC) require separation (slitting) to terminate individual conductors. The challenge is maintaining insulation integrity between the split wires.

Scribing and Separation

Separation is performed using a slitting die or a scribing wheel.

• Depth Control: The blade must penetrate the "web" (the plastic between conductors) without touching the conductor insulation itself.
• Defect – "Shiners": If the separation tool cuts too close to the wire, it exposes the copper sidewall (a "shiner"). This is an immediate safety reject as it creates a potential short circuit path.
• Defect – Tearing: Pulling the ribbon cable apart by hand without a scribe line results in jagged, torn insulation (stress whitening), significantly reducing dielectric strength.

Notching

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

• Tooling: Notching must be done with a sharp punch-and-die set. Dull tooling causes delamination, where the insulation separates from the conductor, allowing oxidation and moisture ingress.

Final Checklist: Complex Cable Preparation

Mandate	Criteria	Verification Action
Rotary Processing	Coaxial cables must be stripped using Rotary machines.	Visual check confirms clean, square cuts with no crushed dielectric.
Center Conductor Integrity	Zero scoring or "ringing" allowed on the center pin.	Microscopic inspection (10x) of the center conductor after dielectric removal.
Shield Integrity	No severed braid strands during jacket stripping.	Check for loose metallic debris in the stripping machine and "whiskers" on the cable.
Dielectric Cleanliness	Center conductor must be free of dielectric residue.	Visual check ensuring the copper surface is bright and clean for termination.
Ribbon Separation	Slitting must be centered in the web; zero exposed copper ("shiners").	Visual inspection of the separated wire sides for insulation integrity.
Braid Management	Braid must be combed or brushed without excessive strand loss.	Compare the volume of the combed pigtail to a reference sample to ensure shield density is maintained.