Causes of Bad Insulation

The following table shows some of the causes of bad insulation, how a Cirris tester will report insulation errors, and measures you can take to catch insulation errors sooner and prevent them from occurring again. 

Cause of Bad InsulationPossible Errors*Countermeasure / Process Change
Extraneous wire
  • Short
Guided assembly
Learn more about guided assembly here.
Mis-registration in IDC connectors (tines have destroyed insulation).
  • Short
  • Intermittent Short
  • Dielectric Breakdown
Inspect cable
Solder bridges
  • Short
  • Intermittent Short
  • Dielectric Breakdown (When a small air gap exists)
Inspect cable
Wire insulation that has been damaged and pierced due to compression (cable ties, strain reliefs), heat (heat shrinking, soldering), or stripping (to inner conductors during outer jacket or shield removal).
  • Short
  • Intermittent Short
  • Dielectric Breakdown (When a small air gap exists)
Learn more about compression errors here.
Loose strands of wire outside of termination, including braided or foil shielding.
  • Short
  • Intermittent Short
  • Dielectric Breakdown
Inspect cable
Loose metal particles such as metal flake or cut strand of wire.
  • Short
  • Intermittent Short
  • Dielectric Breakdown
Inspect cable
Combination of leakage and arcing between layers of insulation.
  • (Partial) Dielectric Breakdown
Look for non-homogeneous (more than one kind) of insulation. You may need to change sensitivity or else use a different cable.
Burn/carbon trail from breakdown; also some flux residue.
  • Short (only with severe carbon trails)
  • IR Failure, Dielectric Breakdown
Learn more about flux problems here.
Ionic contamination like salt or RMA flux on connector body.
  • IR Failure
Learn more about flux problems here.
Hydroscopic plastics/insulators that absorb moisture in humidity.
  • IR Failure
Experiment by checking IR before and after drying connectors or cable in an oven to determine if they are absorbing water. Check manufacturer's specs. PTFE and other Teflon wire types have excellent properties in humidity.
Plywood, paint and most phenolic materials (as often used in fixturing), but only if used as an insulator for connections.
  • IR Failure
Learn more about material choices here.
Test fixturing to the device under test that has any of the problems above.
  • Short
  • Intermittent Short
  • IR Failure
  • Dielectric Breakdown
 Inspect fixturing

*Based on severity, test may or may not detect defect. Tests are not 100% effective in detecting all of the defects.