copper thickness test

W

Winfield Hill

Guest
PCB copper is thicker than predicted by the weight
rating (e.g. 1 or 2 oz), for top and bottom layers,
because through-hole plating adds to its thickness.
A 2mm-wide 1cm-long trace to check for 2oz copper,
measured 1.06 mR, compared to a calculated 1.2 mR.
Kelvin setup, natch, 2cm trace with taps at 1cm.

I have received 2 oz copper when the default 1 oz
was expected, and also 1oz when 2 oz was specified.


--
Thanks,
- Win
 
Winfield Hill <winfieldhill@yahoo.com> wrote in
news:qvhum002nfn@drn.newsguy.com:

PCB copper is thicker than predicted by the weight
rating (e.g. 1 or 2 oz), for top and bottom layers,
because through-hole plating adds to its thickness.
A 2mm-wide 1cm-long trace to check for 2oz copper,
measured 1.06 mR, compared to a calculated 1.2 mR.
Kelvin setup, natch, 2cm trace with taps at 1cm.

I have received 2 oz copper when the default 1 oz
was expected, and also 1oz when 2 oz was specified.
Click to expand...

Gotta keep those dirty fab houses in line!
 
On 13 Jan 2020 06:26:08 -0800, Winfield Hill <winfieldhill@yahoo.com>
wrote:

PCB copper is thicker than predicted by the weight
rating (e.g. 1 or 2 oz), for top and bottom layers,
because through-hole plating adds to its thickness.
A 2mm-wide 1cm-long trace to check for 2oz copper,
measured 1.06 mR, compared to a calculated 1.2 mR.
Kelvin setup, natch, 2cm trace with taps at 1cm.

I have received 2 oz copper when the default 1 oz
was expected, and also 1oz when 2 oz was specified.
Click to expand...

I sometimes measure trace resistance to estimate copper thickness. "1
oz" copper usually turns out to be less, maybe 3/4 oz.

Possibly plated copper doesn't conduct as well as the pure stuff,
which would distort my resistance:thickness calculation, but my bottom
line is that I seldom get the expected conductivity of 1 oz copper.

Maybe if a pcb house puts various boards on a panel, and different
boards have different requirements, not all can be right.


--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Monday, January 13, 2020 at 9:26:30 AM UTC-5, Winfield Hill wrote:
PCB copper is thicker than predicted by the weight
rating (e.g. 1 or 2 oz), for top and bottom layers,
because through-hole plating adds to its thickness.
A 2mm-wide 1cm-long trace to check for 2oz copper,
measured 1.06 mR, compared to a calculated 1.2 mR.
Kelvin setup, natch, 2cm trace with taps at 1cm.

I have received 2 oz copper when the default 1 oz
was expected, and also 1oz when 2 oz was specified.
Click to expand...

I would assume this was a low quantity prototype run? It may have been combined with other designs. The plating is not small, I think it is typically half an ounce or so. Any particular specs that would make the plating thicker, like small diameter with extra plating time to assure plating in the small holes. Generally something like copper thickness is a minimum, not a max.

Then there is the accuracy of the trace width. Did you check that?

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
 
Rick C wrote...
On Monday, January 13, 2020, Winfield Hill wrote:
PCB copper is thicker than predicted by the weight
rating (e.g. 1 or 2 oz), for top and bottom layers,
because through-hole plating adds to its thickness.
A 2mm-wide 1cm-long trace to check for 2oz copper,
measured 1.06 mR, compared to a calculated 1.2 mR.
Kelvin setup, natch, 2cm trace with taps at 1cm.

I have received 2 oz copper when the default 1 oz
was expected, and also 1oz when 2 oz was specified.

Then there is the accuracy of the trace width.
Did you check that?
Click to expand...

Hmm, looks a little on the wide side. At any rate,
it's easy to see it was indeed made with 2oz copper.


--
Thanks,
- Win
 
On 13 Jan 2020 11:52:21 -0800, Winfield Hill <winfieldhill@yahoo.com>
wrote:

Hmm, looks a little on the wide side. At any rate,
it's easy to see it was indeed made with 2oz copper.
Click to expand...

I take a small section of the board and etch half of it in ferric
chloride. Then I compare the etched and non-etched sections with a
ten-thou micrometer. Other methods are available.

--

No deal? No problem! :-D
 
Cursitor Doom wrote...
On 13 Jan 2020, Winfield Hill wrote:

Hmm, looks a little on the wide side. At any rate,
it's easy to see it was indeed made with 2oz copper.

I take a small section of the board and etch half of
it in ferric chloride. Then I compare the etched and
non-etched sections with a ten-thou micrometer.
Other methods are available.
Click to expand...

Argghh! I'll go for one of the other methods.


--
Thanks,
- Win
 
"Winfield Hill" wrote in message news:qvj8af01eou@drn.newsguy.com...
Cursitor Doom wrote...

On 13 Jan 2020, Winfield Hill wrote:

Hmm, looks a little on the wide side. At any rate,
it's easy to see it was indeed made with 2oz copper.

I take a small section of the board and etch half of
it in ferric chloride. Then I compare the etched and
non-etched sections with a ten-thou micrometer.
Other methods are available.

Argghh! I'll go for one of the other methods.
Click to expand...

Wikipedia says that 1 oz copper is about 35 um thick, and that the density
is 8.96 g/cm^3, so 1 oz copper should weigh 0.031 g/cm^2. Grab a scale that
can weigh to 0.01 g, cut a 10 cm^2 piece of single sided pcb, and weigh it
before and after etching it bare and you should have an answer good to about
5%. Use a better scale and/or a bigger piece of pcb if you need more
accuracy.

--
Regards,
Carl Ijames
 
Carl wrote...
"Winfield Hill" wrote...
Cursitor Doom wrote...
On 13 Jan 2020, Winfield Hill wrote:

Hmm, looks a little on the wide side. At any rate,
it's easy to see it was indeed made with 2oz copper.

I take a small section of the board and etch half of
it in ferric chloride. Then I compare the etched and
non-etched sections with a ten-thou micrometer.
Other methods are available.

Argghh! I'll go for one of the other methods.

Wikipedia says that 1 oz copper is about 35 um thick, and
that the density is 8.96 g/cm^3, so 1 oz copper should
weigh 0.031 g/cm^2. Grab a scale that can weigh to 0.01 g,
cut a 10 cm^2 piece of single sided pcb, and weigh it before
and after etching it bare and you should have an answer good
to about 5%. Use a better scale and/or a bigger piece of
pcb if you need more accuracy.
Click to expand...

Double ARRGGHH! Not that method!


--
Thanks,
- Win
 
"Winfield Hill" <winfieldhill@yahoo.com> wrote in message
news:qvj8af01eou@drn.newsguy.com...
I take a small section of the board and etch half of
it in ferric chloride. Then I compare the etched and
non-etched sections with a ten-thou micrometer.
Other methods are available.

Argghh! I'll go for one of the other methods.
Click to expand...

No need to etch, peel is easy. Can also measure the peeled off material
directly -- remember to hit it with a cigarette lighter to burn off the
soldermask (the copper oxides are negligible thickness, as you can tell from
their rainbow colors when this is done quickly enough).

Though if you're going to etch, you can also do some analytical chemistry
once you're there. For example, cut a coupon of known size (PCB with bare
or plated copper), etch it, then titrate the solution. Uh, neutralization
of the etchant followed by precipitation (as whatever will precipitate, CuO
or Cu metal perhaps) might be okay, in which case you get a gravimetric
answer (i.e., you weigh the precipitate). There might be a good redox
titrant for copper, I don't know offhand (exposure to air complicates that,
too). Spectrophotometric can be good, making sure the copper is in a known
complex (e.g. diluted enough for tetraaquo, or paired with say EDA to get a
stronger color?), impurities being a major downside. Can always make a
dilutions and perform fancier analyses like atomic absorption (your sample
gets aspirated into an oxyacetylene flame, then light from a hollow-cathode
lamp is shined through it), or various mass spectrometry methods (of which
ICP-MS is the most sensitive?).

Or sand and polish a section, and use a dimensional microscope to measure
the plating thickness edge-on. Nice way to measure trace width and etch
shape, too.

Or ultrasound I guess, if you absolutely need nondestructive testing. Or
eddy current testing, if you have large enough contiguous (pour/plane)
areas. Or x-rays, as long as you know the transmittance of bare board
versus 1-4 layers of copper. Or neutron activation and gamma spectroscopy.
Or...

Note that these all have various and worse errors than direct measurements;
you can make some assumptions about the properties of the materials involved
(e.g., acoustic velocity and impedance for ultrasound; resistivity for eddy
currents; absorbance of copper versus glass for x-ray; activation and decay
of copper, silicon and other elements for neutron; etc.), some of which
aren't all that obvious (of these, the resistivity of stressed (as-plated,
non annealed) copper is probably the furthest out there).

Can also just feel it, but your sense of touch is easily fooled by the
sharpness of the edge, and a nice soft soldermask edge feels different from
a sharp cut metal edge (with or without burr as the case may be!). So it
may take some practice^Hcalibration to get there. For modestly sharp
corners, a touch threshold under 1 mil seems pretty typical to me, so >=
0.5oz is fair game.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/
 
On 2020-01-14, Winfield Hill <winfieldhill@yahoo.com> wrote:
Carl wrote...

"Winfield Hill" wrote...
Cursitor Doom wrote...
On 13 Jan 2020, Winfield Hill wrote:

Hmm, looks a little on the wide side. At any rate,
it's easy to see it was indeed made with 2oz copper.

I take a small section of the board and etch half of
it in ferric chloride. Then I compare the etched and
non-etched sections with a ten-thou micrometer.
Other methods are available.

Argghh! I'll go for one of the other methods.

Wikipedia says that 1 oz copper is about 35 um thick, and
that the density is 8.96 g/cm^3, so 1 oz copper should
weigh 0.031 g/cm^2. Grab a scale that can weigh to 0.01 g,
cut a 10 cm^2 piece of single sided pcb, and weigh it before
and after etching it bare and you should have an answer good
to about 5%. Use a better scale and/or a bigger piece of
pcb if you need more accuracy.

Double ARRGGHH! Not that method!
Click to expand...

Etch a known area and performa a titration on the solution.


Nah... encapsulate a fragment in resin grind a flat edge and use a microscope...

--
Jasen.
 
Tim Williams wrote...
No need to etch, peel is easy. ...
Click to expand...

OK, now there's a good idea, almost easier
than getting out the milli-ohm-meter. This
method might benefit from a ready-to-strip
exposed trace, without solder mask.


--
Thanks,
- Win
 
On 14 Jan 2020 03:16:15 -0800, Winfield Hill <winfieldhill@yahoo.com>
wrote:

Tim Williams wrote...

No need to etch, peel is easy. ...

OK, now there's a good idea, almost easier
than getting out the milli-ohm-meter.
Click to expand...

Tim's titration method? Are you serious?
--

No deal? No problem! :-D
 
Cursitor Doom wrote...
Winfield Hill wrote:
Tim Williams wrote...

No need to etch, peel is easy. ...

OK, now there's a good idea, almost easier
than getting out the milli-ohm-meter.

Tim's titration method? Are you serious?
Click to expand...

What, no? Use an Xacto knife to peel away
a layer of PCB copper, and mic it.


--
Thanks,
- Win
 
On 14 Jan 2020 07:01:38 -0800, Winfield Hill <winfieldhill@yahoo.com>
wrote:

What, no? Use an Xacto knife to peel away
a layer of PCB copper, and mic it.
Click to expand...

How do you do that? It's bonded to the substrate.

--

No deal? No problem! :-D
 
On 14 Jan 2020 03:16:15 -0800, Winfield Hill <winfieldhill@yahoo.com>
wrote:

Tim Williams wrote...

No need to etch, peel is easy. ...

OK, now there's a good idea, almost easier
than getting out the milli-ohm-meter. This
method might benefit from a ready-to-strip
exposed trace, without solder mask.
Click to expand...

I just connect a power supply (it's always on my bench) to a trace and
let it current limit. Then measure the voltage drop with my Fluke.
Just takes a minute. I do that to a trace that's long enough and wide
enough to make for good math. It's often my TDR test trace too; SMA on
each end for the current, and intermediate vias for voltage probing on
various layers. You can learn a lot doing that.

https://www.dropbox.com/s/nr79qsht1rxif30/Chimera_Test_Trace.jpg?raw=1

https://www.dropbox.com/s/0qhyst28jxz7f5v/28A909A_TDR_trace.JPG?raw=1

It's cool to include test traces on boards, and measure resistances,
impedances, and plane capacitances.





--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
 
On Tue, 14 Jan 2020 08:56:27 -0800, jlarkin@highlandsniptechnology.com
wrote:

It's cool to include test traces on boards, and measure resistances,
impedances, and plane capacitances.
Click to expand...

So would you say it's the best fun you've ever had in your entire
life, John? I'm looking for a new, challenging hobby.

--

No deal? No problem! :-D
 
On Tue, 14 Jan 2020 18:35:13 +0000, Cursitor Doom
<curd@notformail.com> wrote:

On Tue, 14 Jan 2020 08:56:27 -0800, jlarkin@highlandsniptechnology.com
wrote:


It's cool to include test traces on boards, and measure resistances,
impedances, and plane capacitances.

So would you say it's the best fun you've ever had in your entire
life, John? I'm looking for a new, challenging hobby.
Click to expand...

I have done a lot more enjoyable things, in and out of bed.

Skiing at Northstar last week, with a family of crazy Italians, was
probably more fun than measuring trace resistances. I taught three of
them to spin, and two to attempt some features in the terrain parks.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Tue, 14 Jan 2020 11:32:24 -0800, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

Skiing at Northstar last week, with a family of crazy Italians, was
probably more fun than measuring trace resistances. I taught three of
them to spin, and two to attempt some features in the terrain parks.
Click to expand...

Think I'd rather measure the trace resistances, but each to their own.
--

No deal? No problem! :-D
 
Winfield Hill wrote:
Cursitor Doom wrote...

I take a small section of the board and etch half of
it in ferric chloride. Then I compare the etched and
non-etched sections with a ten-thou micrometer.
Other methods are available.

Argghh! I'll go for one of the other methods.
Click to expand...

Find somebody at the fab and say, "I'll give you a barometer if you tell
me...."

But seriously, you can't etch it anyway after it's coated. Can we
assume the solder mask is a constant thickness across the board? If so
just use a micrometer on a section with foil and a section with no foil.

Or you could drop it off a building....
 
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