Re: Measuring PC Board Copper Thickness
- From: Ross Herbert <rherber1@xxxxxxxxxxxxxx>
- Date: Mon, 26 Feb 2007 05:48:05 GMT
On Mon, 26 Feb 2007 17:27:00 +1300, Terry Given <my_name@xxxxxxxx>
wrote:
greaterMulti-layer pcb's are a different story. Usually copper layers on
these boards aren't very thick at all. If heavy currents are to be
carried you might parallel tracks on several layers to achieve
overall copper thickness for those connections which require it.
or find somebody who makes heavy-copper multi-layer PCBs
Yep, that's an option if the situation warrants the expense.
If you really could get 8oz or 10oz laminate as you say, the copper
would be more than 1/16" thick.
yep. and looking edge-on, there was hardly any FR4 visible. When Dan
gave me a blank PCB, my immediate reaction was something like "Fuck
Me! how much copper is in this damn thing", it felt just like a 100mm
x 100mm x 2mm piece of copper (which it very nearly was)
When 99% of the tracks on most pcb's
don't carry any appreciable current, why would you want tracks say
10mil wide by 1/16" high sitting on the board?
A PCB I designed in early 2002 uses a 1-4-4-1 Oz 4-layer PCB, for
exactly this reason. It has TQFP144s, 1206 quad-packs etc, as well as
a planar magnetic transformer and inductor for the 50W 2.8V on-board
SMPS. Admittedly we only built 30,000 or so of them....
That's a viable qty to amortise the cost I think.
The thicker the copper
on the board the greater the cost and the greater the waste copper
during etching. No laminate manufacturer would make material with
copper this thick.
FFS dont mention that to whomever makes the PCBs for Syncor, lest the
entire company cease to exist!
Yeah, it does depend on the requirement I suppose. I did a bit of
digging and came up with this piece of current news
http://www.pcb007.com/anm/templates/feat_article.aspx?articleid=13951&zoneid=143&v=design
I didn't go into the article too deeply but it seems that at least one
manufacturer has cracked the problem of plating heavy (up to 6oz)
copper for thermal plane application on multi-layer boards.
and why would you want to etch off much of the copper? its there for
electrical and thermal reasons.....
Yes, quite true. Depending on track density requirements you may have
to reduce the track width to a minimum in some areas and in others you
might want to keep the tracks widely separated. Thermal planes are a
slightly different question but still introduce other problems. There
is also the question of emi/rfi susceptibility - too much copper is
not always good. I would guess than on many practical boards as much
as 40 - 50% of the total copper volume has to be etched away. This
would mean as much as 4oz per sqft of pcb using 8oz copper laminate
would disappear into the etching bath. That would soon saturate the
etchant so you would need a really efficient means of replacing the
etchant quickly to do a big run of fairly large boards. Automated pcb
manufacturing plants could handle it easily but smaller manufacturers
might find it a bit daunting. Increases the costs dramatically.
.
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