Exact meaning / interpretation of "Plating Thickness" specification

A. Hi, Janhavi. While a specifier should certainly try to avail himself of the expertise of his platers, it is the specifier's job to decide what specifications are to be met.

The specification must be clear as to what is required. If it doesn't say "minimum thickness" or "average thickness", I would think that a plating shop can make an excellent case that 17-30 microns is compliant with an 18 micron specification. I would also say that the difference between 17 and 18 microns is so small that the measurement method starts getting into it. How can the buyer strongly assert that the part is surely not 18 microns without destroying the part?

The usual way to write such a thickness specification might run something like this: "Complete visible plating coverage required on entire part, with 18 micron minimum thickness on any surface which can be touched with a 3/4" dia. ball, and 30 micron absolute maximum thickness anywhere."

Note that I am just using your numbers for the example, not suggesting that this is a good specification for the part in question. Good question, and I hope others will chime in.

Regards,

A. Remember that the tighter the tolerance is, the more that it will cost you.
Also, you get a dog bone effect in most plating where the edges are a much higher current density area, so will plate much heavier than the center. Therefore you have to get with the plater and find out what it will cost you to be very specific about the job. If you do not specify, then you get "average" thickness.

A. Just to emphasise on what Ted has already stated, I am one of those people that write the specifications. A good specification will always include either a minimum average or a thickness range. It should also define where measurements should be taken, on a metric side I normally specify that it should be able to be touched by a 19 mm hemispherical end.

If the specification is unclear it is better to go back to the specifier and ask them what they really want.

Anyone rejecting 17 microns for an 18 micron minimum average probably doesn't understand the nature of measurement. Now if they were rejecting because a particular dimension was out of tolerance I could understand it.