I am hoping to get some inputs from both designer and
manufacturers of PCB's on this topic. The issue is when customer specifies
finish copper thickness where is the thickness most important. We have several
designs with ground area and isolated pads and traces. The customer calls out
for finished copper of 0.0026" and does not specify where measurement is to be
taken. The total ground area is 15.84 square inches and the total circuit area
is 3.36 square inches. Plating up the ground to meet this thickness is almost
impossible without the circuits dramatically over plating and holes in this area
becoming undersized. I have done some calculations of the current carrying
capacity of the trace verses the ground area and the ground can carry 100
times more current carrying capacity than the trace. My question is why
would the ground and the trace have to have the same copper thickness? Or does
it? My QA department is rejecting everything because the ground does not
meet the specification of minimum .0026" while the traces are .0038" to .0042".
This is becoming a major problem causing many rejects due to over plate, under
etch, traces shorting.
Yes the use of 2oz copper foil would make this easier but
have any of you gotten a quote lately on 2oz copper foil. Would
appreciate your inputs
Scott B. Westheimer