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Measuring PC Board Copper Thickness

E

EdV

Jan 1, 1970
0
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.
 
M

mpm

Jan 1, 1970
0
We have been literally burned by boards that are supposed to have 6
ounce copper... Anyone know a niftier approach?  Ultasound imaging maybe?

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
 
T

TT_Man

Jan 1, 1970
0
Add a waste strip to the
We have been literally burned by boards that are supposed to have 6
ounce copper... Anyone know a niftier approach? Ultasound imaging maybe?

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.
 
J

John Larkin

Jan 1, 1970
0
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.


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
 
S

Spehro Pefhany

Jan 1, 1970
0
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.


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
 
E

EdV

Jan 1, 1970
0
On 22 Feb 2007 07:00:44 -0800, the renowned "EdV"


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.
 
E

Eeyore

Jan 1, 1970
0
EdV said:
I would like something that could show that the copper is 6 oz and
uniform across a 4"x6" area.

How would it be non-uniform ? Are you plating it to 6oz ?

Graham
 
E

EdV

Jan 1, 1970
0
How would it be non-uniform ? Are you plating it to 6oz ?

Graham

I am not certain exactly how it happens because I am not doing the
plating but I have heard about these two:

1. Chemical gradient in the bath because somebody forgot to turn on
the agitator.
2. Stuff dropped in the tank; pieces of pipe, tools,etc. that
interfere with electrical characteristics of the bath.

Nothing some good statistical methods shouldn't be able to wring out.
 
H

Homer J Simpson

Jan 1, 1970
0
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.

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


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J

Jim Yanik

Jan 1, 1970
0
I am not certain exactly how it happens because I am not doing the
plating but I have heard about these two:

1. Chemical gradient in the bath because somebody forgot to turn on
the agitator.
2. Stuff dropped in the tank; pieces of pipe, tools,etc. that
interfere with electrical characteristics of the bath.

Nothing some good statistical methods shouldn't be able to wring out.

ISTR NASA Tech Notes having some method for measuring coating thicknesses.
Ultrasound,IIRC,but I'm not 100% on that.
 
S

Spehro Pefhany

Jan 1, 1970
0
ISTR NASA Tech Notes having some method for measuring coating thicknesses.
Ultrasound,IIRC,but I'm not 100% on that.

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.


Best regards,
Spehro Pefhany
 
R

Rich Grise

Jan 1, 1970
0
I am not certain exactly how it happens because I am not doing the
plating but I have heard about these two:

1. Chemical gradient in the bath because somebody forgot to turn on
the agitator.
2. Stuff dropped in the tank; pieces of pipe, tools,etc. that
interfere with electrical characteristics of the bath.

Nothing some good statistical methods shouldn't be able to wring out.

Are you making these in-house, or is there really a vendor that's that
bad?

If they're in-house, clearly you need better process control - just
turning on the agitator and not dropping crap into the tank might
fix it. I've seen an ultrasonic thickness gauge, but used on a
piece with nothing behind it - I don't know if it could catch just
the copper and no FR4.

But, if you keep your anode/cathode in good shape and keep the
electrolyte fresh, you probably could keep track of thickness by the no.
of amp-hours the plating process took. This would have to be calibrated,
of course.

Good Luck!
Rich
 
F

Fred Bartoli

Jan 1, 1970
0
Spehro Pefhany a écrit :
What if it's the right thickness, but porous or some damn thing?

Then after the ultrasound scan you can go for an osteoporosis diagnosis.
 
W

whit3rd

Jan 1, 1970
0
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.
 
H

Homer J Simpson

Jan 1, 1970
0
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.

That's why you need to drive a current through it. Same reason you need to
load a battery to test it.

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J

John Larkin

Jan 1, 1970
0
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
 
P

Paul Hovnanian P.E.

Jan 1, 1970
0
EdV said:
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.

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.
 
R

Robert Baer

Jan 1, 1970
0
EdV said:
I am not certain exactly how it happens because I am not doing the
plating but I have heard about these two:

1. Chemical gradient in the bath because somebody forgot to turn on
the agitator.
2. Stuff dropped in the tank; pieces of pipe, tools,etc. that
interfere with electrical characteristics of the bath.

Nothing some good statistical methods shouldn't be able to wring out.
Well, tell them to keep Frankenstein from drinking it and then peeing
in it!
 
R

Robert Baer

Jan 1, 1970
0
Fred said:
Spehro Pefhany a écrit :



Then after the ultrasound scan you can go for an osteoporosis diagnosis.
Fosamax anyone?
 
R

Robert Baer

Jan 1, 1970
0
Paul said:
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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