Measuring PC Board Copper Thickness

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Couldn't you just inspect these visually???

With a suitable inspection microscope, you should be able to determine the copper thickness. To speed things up, maybe you could put a special trace on the PCB in a convenient location for initial accept / reject purposes...

I've used 1 and 2 oz copper before, never 6. (?) So that said, I really don't have experience here, but the approach seems reasonable. I'll be curious to see what others have to say...

-mpm

Couldn't you just inspect these visually???

With a suitable inspection microscope, you should be able to determine the copper thickness. To speed things up, maybe you could put a special trace on the PCB in a convenient location for initial accept / reject purposes...

I've used 1 and 2 oz copper before, never 6. (?) So that said, I really don't have experience here, but the approach seems reasonable. I'll be curious to see what others have to say...

-mpm

Add a waste strip to the pcb that can be removed and micosectioned /cut it in half and measure the thickness.This is a common test for plating thickness in vias/through holes.

Micrometer? Measure a copper-free area and then a nearby trace. Or just measure the resistance of a trace, with a power supply and any decent DVM.

Right, when you ask for X ounce copper, you ususlly get less, often much less. I have one fab note that says

START WITH 2 OZ COPPERCLAD.

I have another that specifies maximum sheet resistance as 600 uohms/square, with test traces. The best we've actually measured on these boards is around 700.

Get used to it, I suppose.

John

Do you really need to do more than just spot check during incoming inspection?

Fairly low resistances can be checked pretty easily with a Kelvin connection-- four test points (pogo pins, a little header or whatever) capable of a few A, set a lab supply to limit at 1A or 5A or whatever, and measure the voltage on the other two test points. Typical 100uV resolution on a cheap DVM gives you 20-100uOhm resolution. A 250 mil wide 6oz copper track an inch long has something like 300uOhm resistance, so that ought to be plenty. Or buy the fancy micro- ohmmeter if it sounds like more fun.

Best regards, Spehro Pefhany

In this instance the traces are more like fill areas which may read nice in bulk across small areas but still have scant clad in areas. I would like something that could show that the copper is 6 oz and uniform across a 4"x6" area.

In the end it probably will come down to the vendor providing breakaways with each board so we can crunch a bunch of numbers. Then verifying with a small sample of actual boards measured in several spots.

Thanks to all, Ed V.

Presumably you want it to carry current, not merely shield something. If so, drive a current through it and measure the V drop.

The sheet resistance technique preferred by NIST is based on four points in a square, probing a sheet larger than the point spacing. AC current is applied to NE and SE corners, and AC voltage drop is measured across NW and SW corners. It requires a substantial unetched area, and that means waste, usually.

Since the specification is oz/sq. in, another obvious way to proceed is to punch out a known area, of 100% coverage with copper, weigh, and etch the copper off and weigh again. A hole punch and access to a good balance would suffice (and unlike the sheet-resistance meter, you can find lots of other uses for the balance).

In either case, you can calibrate against a known sample and look at ratios, so absolute accuracy is of minor importance.

You can also just mill or route an edge and optically scope the cross section. Edmund sells a decent little 50x handheld microscope with a measurement graticule.

John

Just my opinion: The test point resistance method would seem to be easier to implement for automated testing. Microscopes, micrometers and other such techniques will work fine for sampling incoming parts, but its going to be more time consuming for higher volume testing.

Damn! I though this thread was about scantily clad broads, not boards.

Well, if it is any consolation, thin boards can be *curved*!

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Some other techniques in use are eddy current measurements, beta backscatter, and x-ray fluorescence. See eg

What about basing it on heat, since that's his failure mode? In my mind, you're the "heat guy" based on your experience. So, known heat source pressed against the center, infra red thermometer readings at 4 spots x distance from the center and y time after heat applied? Doable? Useful? Too bulky? (You'd have to do it in a regulated ambient environment)

Ed

I'd expect that would be hard to calibrate. And it would tangle up copper on different layers.

John

A lab I used to code for had this really nifty laser height guage on a machine... impressively accurate. Take a one-d scan, no problem at all if the board is tilted, just look for the bumps above the general slope.

Problem is you'd get the thickness of the trace + solder mask. So you'd have to leave the mask off in strategic areas for testing.

Sorry I don't remember who made it. Bet it wasn't cheap either.

As far as I am aware the maximum copper thickness available is 2oz.

If you require the copper to carry heavy currents you have to either widen the copper tracks or fit heavy bus-bar strips to the copper tracks to increase current carrying capacity.

I normally add a test rig, for 4-wire measurements, on each layer, on a break-off (there usually is one). then a lab psu and a half-decent DMM suffice.

Some PCB vendors provide a nice section, in a clear plastic gunk that acts like a lens. very nice.

Cheers Terry

which suggests a nice accurate scale. the PCB weight may correlate fairly well with the total amount of deposited copper?

Cheers Terry

problem

either

heavy.

Multi-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 greater overall copper thickness for those connections which require it.

As far as single sided or double-sided pcb laminates are concerned you can get laminate up to 0.5" thick. BUT, the copper plating is still

If you really could get 8oz or 10oz laminate as you say, the copper would be more than 1/16" thick. When 99% of the tracks on most pcb's don't carry any appreciable current, why would you want tracks say

or find somebody who makes heavy-copper multi-layer PCBs

All I really care about is the amount of copper on the PCB when it turns up at inwards goods.

yep. and looking edge-on, there was hardly any FR4 visible. When Dan gave me a blank PCB, my immediate reaction was something like "F*ck Me! how much copper is in this damn thing", it felt just like a 100mm x

When 99% of the tracks on most pcb's

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....

The thicker the copper

FFS dont mention that to whomever makes the PCBs for Syncor, lest the entire company cease to exist!

and why would you want to etch off much of the copper? its there for electrical and thermal reasons.....

Cheers Terry