Measuring PC Board Copper Thickness

[James Waldby]

....
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.

Some other techniques in use are eddy current measurements, beta
backscatter, and x-ray fluorescence. See eg
http://www.oicm.com/products/cmi95.php and links from
http://www.globalspec.com/Supplier/ProductAnnouncements/FischerTechnology

 

[Tony Williams]

What if it's the right thickness, but porous or some damn thing?
Might be better to measure the parameters that matter in the
application.

Agreed, in spades.

I had backplane busbar resistance problems a few
years ago and had a long conversation with the QA
inspector at the PCB house. Some time in, it
dawned on me that he was only interested in the
chemical process of plating-up. He was definitely
not interested in discussing the quality of the
deposited copper and he did not understand (or did
not want to understand) the importance of the word
'resistance'.

 

[ehsjr]

We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not.
[considering] micro resistance type systems.

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

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

 

[John Larkin]

We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not.
[considering] micro resistance type systems.

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

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

 

[[email protected]]

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.

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.

 

[Ross Herbert]

We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not. Actual fires at the customer.
Eeeeow!

Needless to say we would like to not do this anymore.

I have googled and found a couple of micro resistance type systems.
Seems reasonable enough but it will require adding test points and
then doing some kind of conformal coat touch up.

Anyone know a niftier approach? Ultasound imaging maybe?

Thanks,
Ed V.

As far as I am aware the maximum copper thickness available is 2oz.
6oz would be very costly even if you could get it and a real problem
for etching - a helluva lot of copper wasted especially as it would
only be required for the power rails on a board. The majority of
tracks wouldn't require more than 1oz or 2oz at the most.

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.
http://www.espbus.com/pcb_bus_bars.html

 

[Terry Given]

Add a waste strip to the



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.

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

 

[Terry Given]

As far as I am aware the maximum copper thickness available is 2oz.
6oz would be very costly even if you could get it and a real problem
for etching - a helluva lot of copper wasted especially as it would
only be required for the power rails on a board. The majority of
tracks wouldn't require more than 1oz or 2oz at the most.

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.
http://www.espbus.com/pcb_bus_bars.html

10Oz isnt that hard. And I've seen 8-layer 8-Oz PCBs too. extremely heavy.

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

Cheers
Terry

 

[Ross Herbert]

10Oz isnt that hard. And I've seen 8-layer 8-Oz PCBs too. extremely heavy.

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

Cheers
Terry

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
1oz or 2oz per sqft. The weight of the laminate itself is not what is
being referred to in the oz/sqft spec, only the copper itself.

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
10mil wide by 1/16" high sitting on the board? 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.

 

[Terry Given]

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.

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

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
1oz or 2oz per sqft. The weight of the laminate itself is not what is
being referred to in the oz/sqft spec, only the copper itself.

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

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 "**** 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....

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!

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

Cheers
Terry

 

[Ross Herbert]

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

Yep, that's an option if the situation warrants the expense.

yep. and looking edge-on, there was hardly any FR4 visible. When Dan
gave me a blank PCB, my immediate reaction was something like "****
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)



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.

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.

 

[Terry Given]

Yep, that's an option if the situation warrants the expense.




That's a viable qty to amortise the cost I think.

it was viable in 10+ quantities. a 1-4-4-1 pcb was IIRC NZ$3 more than a
1-2-2-1 ($12 or so total)

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.




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.

the biggest problem with heavy copper is the track-track spacing,
followed by screen printing the overlay.


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'd love to see you expand on this concept. I guess it depends what you
connect the copper to.

I would guess than on many practical boards as much

as 40 - 50% of the total copper volume has to be etched away.

I'd believe that. most PCB layouts I've seen have really sucked from an
EMI perspective. A simple test - hold blank pcb up to the light. if you
can see thru it, the layouts probably bad.

I try to keep as much copper as possible, after all I paid for it.

the heavy copper stuff I have done tends to have about 80-90% Cu, mainly
governed by track-track spacing and voltage creepage/clearnace

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.

Cheers
Terry

 

[Robert Baer]

We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not.
[considering] micro resistance type systems.

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.

Please forgive my ignorance, i seem to be unable to comprehend
"specification is oz/sq. in" in the proper units or scale factor or
something.
According to the handbook of chemistry, the specific gravity (AKA
density) of copper is from 8.93 to 8.95 grams per cubic centimeter; for
the purposes of my question, call it 8.94 grams per cubic centimeter.
If i have done my conversions correctly, that is about 5.167 ounces
per cubic inch.
So, if i have a square of copper on a PCB that is one inch by one
inch, it would have to be over ine inch thick to be 6 ounce "plating" (!!!).
And for some strange, unknown and incompernsible reason, that seems
to be incorrect by at least a few orders of magnitude.
So, pray tell, where is my error?

 

[Jim Yanik]

We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not.
[considering] micro resistance type systems.

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.

Please forgive my ignorance, i seem to be unable to comprehend
"specification is oz/sq. in" in the proper units or scale factor or
something.
According to the handbook of chemistry, the specific gravity (AKA
density) of copper is from 8.93 to 8.95 grams per cubic centimeter;
for the purposes of my question, call it 8.94 grams per cubic
centimeter.
If i have done my conversions correctly, that is about 5.167 ounces
per cubic inch.
So, if i have a square of copper on a PCB that is one inch by one
inch, it would have to be over ine inch thick to be 6 ounce "plating"
(!!!).
And for some strange, unknown and incompernsible reason, that seems
to be incorrect by at least a few orders of magnitude.
So, pray tell, where is my error?

maybe the spec is really oz/sq.ft.? (144 sq.in.)

a spec of oz/sq.IN. seems odd to me.

 

[Terry Given]

whit3rd wrote:

We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not.
[considering] micro resistance type systems.


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.

Please forgive my ignorance, i seem to be unable to comprehend
"specification is oz/sq. in" in the proper units or scale factor or
something.
According to the handbook of chemistry, the specific gravity (AKA
density) of copper is from 8.93 to 8.95 grams per cubic centimeter;
for the purposes of my question, call it 8.94 grams per cubic
centimeter.
If i have done my conversions correctly, that is about 5.167 ounces
per cubic inch.
So, if i have a square of copper on a PCB that is one inch by one
inch, it would have to be over ine inch thick to be 6 ounce "plating"
(!!!).
And for some strange, unknown and incompernsible reason, that seems
to be incorrect by at least a few orders of magnitude.
So, pray tell, where is my error?

maybe the spec is really oz/sq.ft.? (144 sq.in.)

a spec of oz/sq.IN. seems odd to me.

thats AIUI

Cheers
Terry

 

[Robert Baer]

whit3rd wrote:




We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not.
[considering] micro resistance type systems.



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.


Please forgive my ignorance, i seem to be unable to comprehend
"specification is oz/sq. in" in the proper units or scale factor or
something.
According to the handbook of chemistry, the specific gravity (AKA
density) of copper is from 8.93 to 8.95 grams per cubic centimeter;
for the purposes of my question, call it 8.94 grams per cubic
centimeter. If i have done my conversions correctly, that is about
5.167 ounces
per cubic inch.
So, if i have a square of copper on a PCB that is one inch by one
inch, it would have to be over ine inch thick to be 6 ounce "plating"
(!!!). And for some strange, unknown and incompernsible reason,
that seems
to be incorrect by at least a few orders of magnitude.
So, pray tell, where is my error?

maybe the spec is really oz/sq.ft.? (144 sq.in.)

a spec of oz/sq.IN. seems odd to me.

thats AIUI

Cheers
Terry

"AIUI"?? What does that mean? (not found in WikiPedia).

 

[Robert Baer]

whit3rd wrote:

We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not.
[considering] micro resistance type systems.


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.

Please forgive my ignorance, i seem to be unable to comprehend
"specification is oz/sq. in" in the proper units or scale factor or
something.
According to the handbook of chemistry, the specific gravity (AKA
density) of copper is from 8.93 to 8.95 grams per cubic centimeter;
for the purposes of my question, call it 8.94 grams per cubic
centimeter.
If i have done my conversions correctly, that is about 5.167 ounces
per cubic inch.
So, if i have a square of copper on a PCB that is one inch by one
inch, it would have to be over ine inch thick to be 6 ounce "plating"
(!!!).
And for some strange, unknown and incompernsible reason, that seems
to be incorrect by at least a few orders of magnitude.
So, pray tell, where is my error?

maybe the spec is really oz/sq.ft.? (144 sq.in.)

a spec of oz/sq.IN. seems odd to me.

Using square feet for area, and inches for thickness, the value is
fairly close.
Using 8.94 grams per cubic centimeter converts to 744 ounces per
foot*foot*inch, which gives 1.344 mils per ounce.
Snooping on the web, i see the "standard" for plating copper (at 20
amps per square foot, the nominal and recommended value) produces (after
conversion) 1.358 mils per ounce.
That means that the plated copper is less dense than pure copper and
thus may include the organic additives and "pinholes" (to use the term
loosely).
I found no reference that discussed the plated density of copper VS
current - even in crude terms; only that the "throwing power" is
increased at 10 amps per square foot.

 

[Terry Given]

whit3rd wrote:




We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not.
[considering] micro resistance type systems.




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.


Please forgive my ignorance, i seem to be unable to comprehend
"specification is oz/sq. in" in the proper units or scale factor or
something.
According to the handbook of chemistry, the specific gravity (AKA
density) of copper is from 8.93 to 8.95 grams per cubic centimeter;
for the purposes of my question, call it 8.94 grams per cubic
centimeter. If i have done my conversions correctly, that is about
5.167 ounces
per cubic inch.
So, if i have a square of copper on a PCB that is one inch by one
inch, it would have to be over ine inch thick to be 6 ounce "plating"
(!!!). And for some strange, unknown and incompernsible reason,
that seems
to be incorrect by at least a few orders of magnitude.
So, pray tell, where is my error?



maybe the spec is really oz/sq.ft.? (144 sq.in.)

a spec of oz/sq.IN. seems odd to me.

thats AIUI

Cheers
Terry

"AIUI"?? What does that mean? (not found in WikiPedia).

As I Understand It. YMMV (which took me years to figure out, I was too
ashamed to ask

C,
T

 

[arfa]

We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not.
[considering] micro resistance type systems.

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.

Please forgive my ignorance, i seem to be unable to comprehend
"specification is oz/sq. in" in the proper units or scale factor or
something.
According to the handbook of chemistry, the specific gravity (AKA
density) of copper is from 8.93 to 8.95 grams per cubic centimeter; for
the purposes of my question, call it 8.94 grams per cubic centimeter.
If i have done my conversions correctly, that is about 5.167 ounces
per cubic inch.
So, if i have a square of copper on a PCB that is one inch by one
inch, it would have to be over ine inch thick to be 6 ounce "plating" (!!!).
And for some strange, unknown and incompernsible reason, that seems
to be incorrect by at least a few orders of magnitude.
So, pray tell, where is my error?

In not simply asking "shouldn't that be oz/sq ft?" rather than carrying on like
a crazed pedant.

 

[John Popelish]

whit3rd wrote:




We have been literally burned by boards that are supposed to have 6
ounce copper and in fact do not.
[considering] micro resistance type systems.



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.


Please forgive my ignorance, i seem to be unable to comprehend
"specification is oz/sq. in" in the proper units or scale factor or
something.
According to the handbook of chemistry, the specific gravity (AKA
density) of copper is from 8.93 to 8.95 grams per cubic centimeter;
for the purposes of my question, call it 8.94 grams per cubic
centimeter. If i have done my conversions correctly, that is about
5.167 ounces
per cubic inch.
So, if i have a square of copper on a PCB that is one inch by one
inch, it would have to be over ine inch thick to be 6 ounce "plating"
(!!!). And for some strange, unknown and incompernsible reason,
that seems
to be incorrect by at least a few orders of magnitude.
So, pray tell, where is my error?



maybe the spec is really oz/sq.ft.? (144 sq.in.)

a spec of oz/sq.IN. seems odd to me.

thats AIUI

Cheers
Terry

"AIUI"?? What does that mean? (not found in WikiPedia).

Google [acronyms aiui].