Electrical Contact Resistance

[hkymstr]

Here is the issue. We are currently applying chem film, Class 3 to parts that need low electrical resistance. Our supplier applies chem film to our parts and our receiving and inspection department will only accept a part if they can "see" the chem film. This results in parts with much to high electrical contact resistance due to much chem film on the part. The part is then rejected and the chem film reapplied, yes, a very inefficient way of doing things. I am trying to identify a process that will allow inspection to pass a part by a quantitative number rather than an subjective opinion on whether or not the chem film has been applied.

My question is, is there any way to measure the contact resistance of the chem film, other than that in the MIL spec 5541 and 81706? Going by MIL-C-5541 and MIL-C-81706 there is a method, but very impractical for manufactured parts.

 

[Sparweb]

A) If the film changes the colour of the part slightly, would a "color-card" help? Inspectors could line up the appropriate stripe with the part, give it a score from 1 to 10, and if within an acceptable range that suits everybody's requirements, it gets passed on to you.

B) Give the inspectors a device to measure the electrical resistance of the part before they pass it, and guidelines on the pass/fail criteria.


Steven Fahey, CET