copper thickness test

[Dave Platt]

In article <qvjtl4$bnt$1@gonzo.revmaps.no-ip.org>,
Jasen Betts <jasen@xnet.co.nz> wrote:

Double ARRGGHH! Not that method!

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

I like it. Extra points for using especially-toxic, or explosive
reagents to perform the titration.

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

Carefully carve a trench down through the copper with a box cutter
until you just barely hit the FR-4. Carefully smooth off the burr at
the top of the trench. Jump into your Ant-Man suit, start reducing
your size, hop into the trench you've cut, fine-tune your size until
the top of your head is level with the top of the trench, then read the
size-reduction factor off of your suit's instruments. A bit of math
(knowing your own normal height) will tell you the thickness of the
copper.

 

"Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com> wrote
in news:qvlccr$kcc$1@dont-email.me:

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.

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....

Add a half mil for the adhesive used to bond to foil. Add 1 mil
(IIRC) for the mask. The PCB house can tell you the exact bonded
thickness of the mask.

Then measure the pcb at a location that is bare. Measure again
over a trace. Subtract.

 

[Steve Wilson]

Steve Wilson <no@spam.com> wrote:

Measuring thickness is easy. Here's an example for a thin aluminum film:

The resistance of a pure aluminum film 26 nanometers thick is
1.038 ohms per square.

This means you can have a ribbon of material 1 cm wide and 10 cm
long, and the resistance between the ends will be 10 * 1.038 = 10.38
ohms. The resistance is calculated as follows:

Ohms/square = Bulk Resistivity / Thickness

The bulk resistivity of pure aluminum is about 27e-9 Ohms, and the film
is 26 namometers thick. So the resistance is

Ohms/square = 27e-9 / 26e-9 = 1.038 ohms per square

Similarly, you can measure the resistance of the ribbon, and
determine the average thickness. The thickness is calculated as
follows:

Thickness = Bulk Resistivity / Ohms per square

For example, if you measure 10.38 ohms between the ends of a ribbon 1
cm wide and 10 cm long, the resistance is 10.38 / 10 = 1.038 Ohms per
Square. The thickness of the film is then

Thickness = 27e-9 / 1.038 = 26 nm

A Kelvin probe can be used to measure the resistance when it is very
low.

The next problem is to extend this to copper, and figure out the weight
from the thickness.

Resistivity

Aluminum : 2.65e-8
Copper : 1.68e-8

http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/rstiv.html

Copper Weight

The following is the formula for cpw (in oz) to thickness (in mils)
conversion:

Thickness(in oz) = thickness (in mils) /1.37

The following is the formula for thickness (in mils) to cpw (in oz)
conversion:

t (in mils) = t (in oz) * 1.37

Weight Thickness
1/2 Oz. .7 mils
1 Oz. 1.4 mils
2 Oz. 2.8 mils

https://baltimorehackerspace.com/2012/08/pcb-copper-weight-thickness-chart/

 

[Cursitor Doom]

On Tue, 14 Jan 2020 16:38:33 -0500, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:

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....

Indeed. I reckon peeling the stuff off and micing it will give an
erroneous oversize result. The most accurate method is to etch it
away. But if precision isn't an issue then fine I suppose.
--

No deal? No problem! :-D

 

[Steve Wilson]

jlarkin@highlandsniptechnology.com wrote:

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.

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.

Measuring thickness is easy. Here's an example for a thin aluminum film:

The resistance of a pure aluminum film 26 nanometers thick is
1.038 ohms per square.

This means you can have a ribbon of material 1 cm wide and 10 cm
long, and the resistance between the ends will be 10 * 1.038 = 10.38
ohms. The resistance is calculated as follows:

Ohms/square = Bulk Resistivity / Thickness

The bulk resistivity of pure aluminum is about 27e-9 Ohms, and the film is
26 namometers thick. So the resistance is

Ohms/square = 27e-9 / 26e-9 = 1.038 ohms per square

Similarly, you can measure the resistance of the ribbon, and
determine the average thickness. The thickness is calculated as
follows:

Thickness = Bulk Resistivity / Ohms per square

For example, if you measure 10.38 ohms between the ends of a ribbon 1
cm wide and 10 cm long, the resistance is 10.38 / 10 = 1.038 Ohms per
Square. The thickness of the film is then

Thickness = 27e-9 / 1.038 = 26 nm

A Kelvin probe can be used to measure the resistance when it is very low.

The next problem is to extend this to copper, and figure out the weight
from the thickness.

 

[John Larkin]

On Tue, 14 Jan 2020 23:09:37 -0000 (UTC), Steve Wilson <no@spam.com>
wrote:

jlarkin@highlandsniptechnology.com wrote:

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.

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.

Measuring thickness is easy. Here's an example for a thin aluminum film:

The resistance of a pure aluminum film 26 nanometers thick is
1.038 ohms per square.

This means you can have a ribbon of material 1 cm wide and 10 cm
long, and the resistance between the ends will be 10 * 1.038 = 10.38
ohms. The resistance is calculated as follows:

Ohms/square = Bulk Resistivity / Thickness

The bulk resistivity of pure aluminum is about 27e-9 Ohms, and the film is
26 namometers thick. So the resistance is

Ohms/square = 27e-9 / 26e-9 = 1.038 ohms per square

Similarly, you can measure the resistance of the ribbon, and
determine the average thickness. The thickness is calculated as
follows:

Thickness = Bulk Resistivity / Ohms per square

For example, if you measure 10.38 ohms between the ends of a ribbon 1
cm wide and 10 cm long, the resistance is 10.38 / 10 = 1.038 Ohms per
Square. The thickness of the film is then

Thickness = 27e-9 / 1.038 = 26 nm

A Kelvin probe can be used to measure the resistance when it is very low.

The next problem is to extend this to copper, and figure out the weight
from the thickness.

500 uohms/square is close for 1 oz copper.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Tue, 14 Jan 2020 16:38:33 -0500, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:

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.

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....

Part of the foil on common FR4 boards includes a terrible "black
oxide" adhesion treatment. It adds thickness but is a horrible
conductor. Skin effect is especially awful.

https://www.dropbox.com/s/m65gd96vs8j5qp8/PCB_foil_peel.jpg?raw=1

So measure resistance to get the effective low-frequency copper
thickness.





--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Tom Del Rosso]

Cursitor Doom wrote:

Indeed. I reckon peeling the stuff off and micing it will give an
erroneous oversize result. The most accurate method is to etch it
away. But if precision isn't an issue then fine I suppose.

If you etch it away, the glue could partly dissolve away too. And a
micrometer might compress the glue as well.

 

[Tom Del Rosso]

John Larkin wrote:

Part of the foil on common FR4 boards includes a terrible "black
oxide" adhesion treatment. It adds thickness but is a horrible
conductor. Skin effect is especially awful.

https://www.dropbox.com/s/m65gd96vs8j5qp8/PCB_foil_peel.jpg?raw=1

So measure resistance to get the effective low-frequency copper
thickness.

What if you peel some off and wash it in solvent to remove the mask from
the top and the glue from the bottom?

But since the real goal is to get the resistance you want, measuring
that is more direct than direct measurement of the thickness.

 

"Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com> wrote in
news:qvm12t$umd$2@dont-email.me:

Cursitor Doom wrote:

Indeed. I reckon peeling the stuff off and micing it will give an
erroneous oversize result. The most accurate method is to etch it
away. But if precision isn't an issue then fine I suppose.

If you etch it away, the glue could partly dissolve away too. And
a
micrometer might compress the glue as well.

No etch. Just take a reading and subtract the KNOWN mask
thickness.
One can assume the mask thickness better than the copper (obviously).

Another way is to get and keep handy some samples of 4oz 2oz 1oz,
and maybe even a cutaway of each.

With experience, one could tell easily by how difficult the peeled
strip is to bend or curl.

Or you could use a known cut strip size and use weight. Known
values for each copper weight sould allow you to peel a specifically
sized strip and simple weight it to tell what the copper oz weight
is.

 

[Jasen Betts]

On 2020-01-14, Cursitor Doom <curd@notformail.com> wrote:

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.

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

Heat it with a reducing flame (ie one with excess fuel) the resin will
let go long before the copper melts

The redusicng flame will prevent the copper from oxidising.


--
Jasen.

 

[Cursitor Doom]

On Wed, 15 Jan 2020 05:48:28 -0000 (UTC), Jasen Betts
<jasen@xnet.co.nz> wrote:

Heat it with a reducing flame (ie one with excess fuel) the resin will
let go long before the copper melts

The redusicng flame will prevent the copper from oxidising.

I'm oblig'd.
--

No deal? No problem! :-D

 

[legg]

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.

From JLPCB, you may have just inherited the weight of other
jobs, processed at the same time.

If you'd opted for ROHS, they'd have back-ordered you to the
1st of the month.

RL

 

[John Larkin]

On Wed, 15 Jan 2020 08:08:24 -0500, legg <legg@nospam.magma.ca> wrote:

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.

From JLPCB, you may have just inherited the weight of other
jobs, processed at the same time.

If you'd opted for ROHS, they'd have back-ordered you to the
1st of the month.

RL

Why do the Chinese proto board houses have such insane default
stackups?

https://jlcpcb.com/client/index.html#/impedance

0.1 mm between a layer 1 trace and a layer 2 ground plane! That makes
a 50 ohm trace 6 mils wide, and a 75 ohm trace impossible.





--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Lasse Langwadt Christense]

onsdag den 15. januar 2020 kl. 20.20.06 UTC+1 skrev John Larkin:

On Wed, 15 Jan 2020 08:08:24 -0500, legg <legg@nospam.magma.ca> wrote:

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.

From JLPCB, you may have just inherited the weight of other
jobs, processed at the same time.

If you'd opted for ROHS, they'd have back-ordered you to the
1st of the month.

RL

Why do the Chinese proto board houses have such insane default
stackups?

https://jlcpcb.com/client/index.html#/impedance

0.1 mm between a layer 1 trace and a layer 2 ground plane! That makes
a 50 ohm trace 6 mils wide, and a 75 ohm trace impossible.

I doubt the Chinese proto houses are doing something that isn't common practice

and there are numerous app notes, saying that keeping the signal layer close
<5mil from the plane and impedance 50-60 Ohm is best for EMC/EMI/crosstalk

 

[Tim Williams]

"Jasen Betts" <jasen@xnet.co.nz> wrote in message
news:qvm93c$5qb$1@gonzo.revmaps.no-ip.org...

Heat it with a reducing flame (ie one with excess fuel) the resin will
let go long before the copper melts

The redusicng flame will prevent the copper from oxidising.

A hot air machine will do much better, or you can use a torch more carefully
than any relevance to its oxidation state. (The substrate bond weakens
*far* before the copper begins to oxidize aggresively, and further still
before carbon radicals in the flame will actively reduce the oxides.)

Also, once copper is hot enough that it can be reduced by the flame, it
oxidizes rapidly, so you can't exactly stop the flame. Rapid cooling can
minimize the oxidation (which since we're talking foil, should be fine
as-is, but water quenching isn't a bad idea either).

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

On Tue, 14 Jan 2020 15:59:01 +0000, Cursitor Doom
<curd@notformail.com> wrote:

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.

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

Peel up a bit and grab it with tweezers. Now pull and run a hot
soldering iron on the top of the trace, just ahead of the pull point.
The epoxy softens and the whole trace zips off easily.



--

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"

 

[Cursitor Doom]

On Fri, 17 Jan 2020 07:31:00 -0800, jlarkin@highlandsniptechnology.com
wrote:

Peel up a bit and grab it with tweezers. Now pull and run a hot
soldering iron on the top of the trace, just ahead of the pull point.
The epoxy softens and the whole trace zips off easily.

I'm oblig'd.

Incidentally, John, that quote on your sig about the triumph of
ignorance over reason or whatever it is, who is the author - PG
Woodhouse perchance? I really should read more Woodhouse.
--

No deal? No problem! :-D

 

[John Larkin]

On Fri, 17 Jan 2020 18:38:11 +0000, Cursitor Doom
<curd@notformail.com> wrote:

On Fri, 17 Jan 2020 07:31:00 -0800, jlarkin@highlandsniptechnology.com
wrote:

Peel up a bit and grab it with tweezers. Now pull and run a hot
soldering iron on the top of the trace, just ahead of the pull point.
The epoxy softens and the whole trace zips off easily.

I'm oblig'd.

Incidentally, John, that quote on your sig about the triumph of
ignorance over reason or whatever it is, who is the author - PG
Woodhouse perchance? I really should read more Woodhouse.

Instinct over Reason!

That was Dorothy Sayers, in one of the Lord Peter mysteries. She was
really smart. She invented the Guinness toucan.

https://vinepair.com/articles/history-guinness-toucan-ads/

Wodehouse was an amazing writer. A Damsel In Distress is astonishing,
especially the last three chapters.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Cursitor Doom]

On Fri, 17 Jan 2020 11:45:00 -0800, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

That was Dorothy Sayers, in one of the Lord Peter mysteries. She was
really smart. She invented the Guinness toucan.

https://vinepair.com/articles/history-guinness-toucan-ads/

Wodehouse was an amazing writer. A Damsel In Distress is astonishing,
especially the last three chapters.

Wodehouse - of course! It's been far too long; over 40 years since I
finished The Mating Season. His satirical observations on the English
class system are matchless. The Grossmiths' Diary of a Nobody came
close-ish, but.... not close enough.

--

No deal? No problem! :-D