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Charring of Wire Insulation

Question: We have an ongoing debate regarding the charring of wire insulation. IPC-A-610E is very clear on the topic. Aside from overheating damage to the PCB, what other dangers does this pose? Do you have any white papers on the topic? Thank you for the help.

Answer: Burning the insulation during the wire stripping operation can create other problems. Charred insulation as you mentioned is a defective condition as defined in IPC/WHMA-A-620, Page 3-9, Section 3.5.

The charring means the insulation has been burnt and the burnt material is left behind. This charring is carbon and conductive, so depending upon how secure it is to the wire, it can fall off and create a short. Additionally, if the wire is charred during the soldering operation, it will impact the insulation clearance dimension and that will also create a potential problem with insulation clearance.

If the insulation is stripped during the stripping operation, the problem can be destroying the solderability of the wire, where it will not solder or, cannot be tinned, due to the oxidation on the wire strands. This oxidation is very difficult to removed and since only RMA or ROL0 fluxes can be used to tin the wires, this flux is not strong enough to remove these oxides and will not allow the solder to wet the wire strands.

Another reason for not doing this or burning the insulation, is that the toxic fumes it creates are detrimental to the operators stripping the wires. This is especially true of Teflon insulation.

So yes, there are many reasons for not burning the insulation off the wire when stripping the wire and I hope this provides some insight for you.

We don’t have any white papers, but would suggest doing a web search on the NASA web site and on the general web for burnt insulation and its effects and I am sure more information can be found.