[EE] Measuring PCB copper weight?

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[EE] Measuring PCB copper weight?

Neil
Is there a simplish way to figure out or measure the copper weight on an
existing PCB?

I'm asking because I'm redoing a layout for someone and I did not do the
original circuit design, so was planning to use the same trace widths as
on the original board, but I'll need to know the copper weight to order
a prototype board.
If I have to redo the math on current etc, that opens up another can of
worms as I don't have all of the specs otherwise.
And the copper does feel thicker than usual.

Thanks.




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Re: [EE] Measuring PCB copper weight?

Clint Jay
Micrometer? The thickness of the copper should be a giveaway

On Wed, 3 Feb 2021, 16:01 Neil, <[hidden email]> wrote:

> Is there a simplish way to figure out or measure the copper weight on an
> existing PCB?
>
> I'm asking because I'm redoing a layout for someone and I did not do the
> original circuit design, so was planning to use the same trace widths as
> on the original board, but I'll need to know the copper weight to order
> a prototype board.
> If I have to redo the math on current etc, that opens up another can of
> worms as I don't have all of the specs otherwise.
> And the copper does feel thicker than usual.
>
> Thanks.
>
>
>
>
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Re: [EE] Measuring PCB copper weight?

Spehro Pefhany
Measure the resistance of a known width/length trace?

If you don’t have a 4-wire ohmmeter, put a known fairly large (but not large enough to cause too much heating too quickly) current through the trace and measure the mV drop inwards of where the current is injected.

Best regards, SP

> On Feb 3, 2021, at 12:00 PM, Clint Jay <[hidden email]> wrote:
>
> Micrometer? The thickness of the copper should be a giveaway
>
>> On Wed, 3 Feb 2021, 16:01 Neil, <[hidden email]> wrote:
>>
>> Is there a simplish way to figure out or measure the copper weight on an
>> existing PCB?
>>
>> I'm asking because I'm redoing a layout for someone and I did not do the
>> original circuit design, so was planning to use the same trace widths as
>> on the original board, but I'll need to know the copper weight to order
>> a prototype board.
>> If I have to redo the math on current etc, that opens up another can of
>> worms as I don't have all of the specs otherwise.
>> And the copper does feel thicker than usual.
>>
>> Thanks.
>>
>>
>>
>>
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>> http://mailman.mit.edu/mailman/listinfo/piclist
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Re: [EE] Measuring PCB copper weight?

Neil
In reply to this post by Clint Jay
I have calipers w/0.01" resolution here, but not sure if that will be
accurate enough, especially with soldermask, which I'll have to scrape
off.  I can't measure pads as that will have a plating on it.
Google tells me that 1-oz is 1.4 mils thick, so I guess I could run out
and get a better caliper or micrometer for this.  Even harbor freight
calipers should be good enough for this I guess.



On 2/3/2021 11:54 AM, Clint Jay wrote:

> Micrometer? The thickness of the copper should be a giveaway
>
> On Wed, 3 Feb 2021, 16:01 Neil, <[hidden email]> wrote:
>
>> Is there a simplish way to figure out or measure the copper weight on an
>> existing PCB?
>>
>> I'm asking because I'm redoing a layout for someone and I did not do the
>> original circuit design, so was planning to use the same trace widths as
>> on the original board, but I'll need to know the copper weight to order
>> a prototype board.
>> If I have to redo the math on current etc, that opens up another can of
>> worms as I don't have all of the specs otherwise.
>> And the copper does feel thicker than usual.
>>
>> Thanks.
>>
>>
>>
>>
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>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist
>>

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Re: [EE] Measuring PCB copper weight?

Spehro Pefhany
Micrometer would be much better than calipers (~10x). Repeatability of calipers is in the one thou range.

Best regards, SP

> On Feb 3, 2021, at 1:02 PM, Neil <[hidden email]> wrote:
>
> I have calipers w/0.01" resolution here, but not sure if that will be
> accurate enough, especially with soldermask, which I'll have to scrape
> off.  I can't measure pads as that will have a plating on it.
> Google tells me that 1-oz is 1.4 mils thick, so I guess I could run out
> and get a better caliper or micrometer for this.  Even harbor freight
> calipers should be good enough for this I guess.
>
>
>
>> On 2/3/2021 11:54 AM, Clint Jay wrote:
>> Micrometer? The thickness of the copper should be a giveaway
>>
>>> On Wed, 3 Feb 2021, 16:01 Neil, <[hidden email]> wrote:
>>>
>>> Is there a simplish way to figure out or measure the copper weight on an
>>> existing PCB?
>>>
>>> I'm asking because I'm redoing a layout for someone and I did not do the
>>> original circuit design, so was planning to use the same trace widths as
>>> on the original board, but I'll need to know the copper weight to order
>>> a prototype board.
>>> If I have to redo the math on current etc, that opens up another can of
>>> worms as I don't have all of the specs otherwise.
>>> And the copper does feel thicker than usual.
>>>
>>> Thanks.
>>>
>>>
>>>
>>>
>>> --
>>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>>> View/change your membership options at
>>> http://mailman.mit.edu/mailman/listinfo/piclist
>>>
>
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Re: [EE] Measuring PCB copper weight?

Clint Jay
In reply to this post by Neil
I'd perhaps ignore the soldermask and measure bare substrate then copper
and subtract the difference working on the assumption that soldermask
should be fairly consistent. If that gives wildly varying results then
scrape away.

On Wed, 3 Feb 2021, 17:59 Neil, <[hidden email]> wrote:

> I have calipers w/0.01" resolution here, but not sure if that will be
> accurate enough, especially with soldermask, which I'll have to scrape
> off.  I can't measure pads as that will have a plating on it.
> Google tells me that 1-oz is 1.4 mils thick, so I guess I could run out
> and get a better caliper or micrometer for this.  Even harbor freight
> calipers should be good enough for this I guess.
>
>
>
> On 2/3/2021 11:54 AM, Clint Jay wrote:
> > Micrometer? The thickness of the copper should be a giveaway
> >
> > On Wed, 3 Feb 2021, 16:01 Neil, <[hidden email]> wrote:
> >
> >> Is there a simplish way to figure out or measure the copper weight on an
> >> existing PCB?
> >>
> >> I'm asking because I'm redoing a layout for someone and I did not do the
> >> original circuit design, so was planning to use the same trace widths as
> >> on the original board, but I'll need to know the copper weight to order
> >> a prototype board.
> >> If I have to redo the math on current etc, that opens up another can of
> >> worms as I don't have all of the specs otherwise.
> >> And the copper does feel thicker than usual.
> >>
> >> Thanks.
> >>
> >>
> >>
> >>
> >> --
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> >> View/change your membership options at
> >> http://mailman.mit.edu/mailman/listinfo/piclist
> >>
>
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Re: [EE] Measuring PCB copper weight?

Neil
In reply to this post by Spehro Pefhany
Hmmm... I would've expected this to require a very accurate meter, but
this seems relatively doable.. on the gerber, I can find traces with no
hidden branches (it's a 4-layer board), and over 10" long, so if I run
~3A through it I should get a somewhere in the order of 0.24V (if it's
2oz), which is very measurable with the DMM I have here.

Thanks.



On 2/3/2021 12:05 PM, Spehro Pefhany wrote:

> Measure the resistance of a known width/length trace?
>
> If you don’t have a 4-wire ohmmeter, put a known fairly large (but not large enough to cause too much heating too quickly) current through the trace and measure the mV drop inwards of where the current is injected.
>
> Best regards, SP
>
>> On Feb 3, 2021, at 12:00 PM, Clint Jay <[hidden email]> wrote:
>>
>> Micrometer? The thickness of the copper should be a giveaway
>>
>>> On Wed, 3 Feb 2021, 16:01 Neil, <[hidden email]> wrote:
>>>
>>> Is there a simplish way to figure out or measure the copper weight on an
>>> existing PCB?
>>>
>>> I'm asking because I'm redoing a layout for someone and I did not do the
>>> original circuit design, so was planning to use the same trace widths as
>>> on the original board, but I'll need to know the copper weight to order
>>> a prototype board.
>>> If I have to redo the math on current etc, that opens up another can of
>>> worms as I don't have all of the specs otherwise.
>>> And the copper does feel thicker than usual.
>>>
>>> Thanks.
>>>
>>>
>>>
>>>
>>> --
>>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>>> View/change your membership options at
>>> http://mailman.mit.edu/mailman/listinfo/piclist
>>>
>> --
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>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist
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Re: [EE] Measuring PCB copper weight?

Bob Blick-5
In reply to this post by Neil
Peel off a trace and do the same to a PC board with known copper, and compare.

Friendly regards, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of Neil
Sent: Wednesday, February 3, 2021 7:58 AM
To: Microcontroller discussion list - Public.
Subject: [EE] Measuring PCB copper weight?

Is there a simplish way to figure out or measure the copper weight on an
existing PCB?

I'm asking because I'm redoing a layout for someone and I did not do the
original circuit design, so was planning to use the same trace widths as
on the original board, but I'll need to know the copper weight to order
a prototype board.
If I have to redo the math on current etc, that opens up another can of
worms as I don't have all of the specs otherwise.
And the copper does feel thicker than usual.

Thanks.



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Re: [EE] Measuring PCB copper weight?

Perry Curling-Hope
In reply to this post by Neil
Micrometer
Scrape off the solder mask to reveal the tin.
Perhaps try a few solvents, might be lu ky.
Remove some tin with wick.
Clean up
Take your measurements
On 03 Feb 2021 6:01 PM, "Neil" <[hidden email]> wrote:

> Is there a simplish way to figure out or measure the copper weight on an
> existing PCB?
>
> I'm asking because I'm redoing a layout for someone and I did not do the
> original circuit design, so was planning to use the same trace widths as
> on the original board, but I'll need to know the copper weight to order
> a prototype board.
> If I have to redo the math on current etc, that opens up another can of
> worms as I don't have all of the specs otherwise.
> And the copper does feel thicker than usual.
>
> Thanks.
>
>
>
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
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Re: [EE] Measuring PCB copper weight?

Alan Pearce
In reply to this post by Bob Blick-5
Shouldn't need to peel a trace from a known board.

standard inner trace thickness is one ounce copper which is 35 microns
nominal thickness.
Outer trace could be one ounce copper or two ounce copper which is
nominally 70 microns thick.

If you want 2 ounce copper it is normally plated up from 1 ounce copper
these days. Unless there is a special reason for it (typically current
carrying capacitor or thermal reasons) it is normal to use 1 ounce
copper.

Personally I would just design the board, and get an initial batch made
with 1 ounce copper, and do some kelvin resistance measurements as
already suggested, to compare the new PCB with an old one. If the
variance is too large then the original PCB is probably 2 ounce copper.

Even if both PCBs are made with the same weight of copper I wouldn't be
surprised to find a difference in resistance of 10%. The variability of
the etching process can result in significant differences in etch
undercut and track width, especially if you are pushing track
width/spacing specifications of the PCB manufacturer.

If you need defined impedance tracks these always need to be specified
in the documentation supplied to the PCB manufacturer so they can
control their process to suit the requirements.




On Wed, 3 Feb 2021 19:59:23 +0000
Bob Blick <[hidden email]> wrote:

> Peel off a trace and do the same to a PC board with known copper, and
> compare.
>
> Friendly regards, Bob
>
> ________________________________________
> From: [hidden email] <[hidden email]> on behalf of
> Neil Sent: Wednesday, February 3, 2021 7:58 AM
> To: Microcontroller discussion list - Public.
> Subject: [EE] Measuring PCB copper weight?
>
> Is there a simplish way to figure out or measure the copper weight on
> an existing PCB?
>
> I'm asking because I'm redoing a layout for someone and I did not do
> the original circuit design, so was planning to use the same trace
> widths as on the original board, but I'll need to know the copper
> weight to order a prototype board.
> If I have to redo the math on current etc, that opens up another can
> of worms as I don't have all of the specs otherwise.
> And the copper does feel thicker than usual.
>
> Thanks.
>
>
>

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Re: [EE] Measuring PCB copper weight?

Dmitriy Kiryashov-2
In reply to this post by Spehro Pefhany
 2nd on this approach as most practical and least messy.

Using 4x wires DMM with under 2 mOhm "residual" resistance left and knowing trace width will allow to reverse calculate copper thickness quickly.

You will only need to carefully remove / scratch off insulation from couple of spot above that copper trace in question at some distance from each other
( so you total measured trace resistance will be above 20 mOhm at least )

     On Wednesday, February 3, 2021, 09:14:16 AM PST, Spehro Pefhany <[hidden email]> wrote:  
 
 Measure the resistance of a known width/length trace?

If you don’t have a 4-wire ohmmeter, put a known fairly large (but not large enough to cause too much heating too quickly) current through the trace and measure the mV drop inwards of where the current is injected.

Best regards, SP

> On Feb 3, 2021, at 12:00 PM, Clint Jay <[hidden email]> wrote:
>
> Micrometer? The thickness of the copper should be a giveaway
>
>> On Wed, 3 Feb 2021, 16:01 Neil, <[hidden email]> wrote:
>>
>> Is there a simplish way to figure out or measure the copper weight on an
>> existing PCB?
>>
>> I'm asking because I'm redoing a layout for someone and I did not do the
>> original circuit design, so was planning to use the same trace widths as
>> on the original board, but I'll need to know the copper weight to order
>> a prototype board.
>> If I have to redo the math on current etc, that opens up another can of
>> worms as I don't have all of the specs otherwise.
>> And the copper does feel thicker than usual.
>>
>> Thanks.
>>
>>
>>
>>
>> --
>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist
>>
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Re: [EE] Measuring PCB copper weight?

V G-2
In reply to this post by Neil
On Wed, Feb 3, 2021 at 11:08 AM Neil <[hidden email]> wrote:

> Is there a simplish way to figure out or measure the copper weight on an
> existing PCB?
>
> I'm asking because I'm redoing a layout for someone and I did not do the
> original circuit design, so was planning to use the same trace widths as
> on the original board, but I'll need to know the copper weight to order
> a prototype board.
> If I have to redo the math on current etc, that opens up another can of
> worms as I don't have all of the specs otherwise.
> And the copper does feel thicker than usual.
>

If a destructive test is possible, you can get an exact answer by
dissolving it in ferric chloride and measuring the mass.
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Re: [EE] Measuring PCB copper weight?

Jesse Lackey
In reply to this post by Dmitriy Kiryashov-2
Just a minor LOL/Sigh, I got some boards made at JLCPcb, they have trace
antennas for RFID, a 55mm spiral square of 6mil wide track.  I was
having problems not seen on a proto pcb made in the USA.  After some
head scratching and fiddling and calculating, the trace antenna is 380
inches long, and with 1 Oz copper it measured close to 30 Ohms, as
expected, on the proto.  The pcb from JLCPcb is 44 Ohms, i.e. 30% less
copper than the standard for 1 Oz.

Never seen that before.

Now they want me to measure the thickness.  Ya right.

J


Dmitriy Kiryashov wrote:

>   2nd on this approach as most practical and least messy.
>
> Using 4x wires DMM with under 2 mOhm "residual" resistance left and knowing trace width will allow to reverse calculate copper thickness quickly.
>
> You will only need to carefully remove / scratch off insulation from couple of spot above that copper trace in question at some distance from each other
> ( so you total measured trace resistance will be above 20 mOhm at least )
>
>       On Wednesday, February 3, 2021, 09:14:16 AM PST, Spehro Pefhany <[hidden email]> wrote:
>  
>   Measure the resistance of a known width/length trace?
>
> If you don’t have a 4-wire ohmmeter, put a known fairly large (but not large enough to cause too much heating too quickly) current through the trace and measure the mV drop inwards of where the current is injected.
>
> Best regards, SP
>
>> On Feb 3, 2021, at 12:00 PM, Clint Jay <[hidden email]> wrote:
>>
>> Micrometer? The thickness of the copper should be a giveaway
>>
>>> On Wed, 3 Feb 2021, 16:01 Neil, <[hidden email]> wrote:
>>>
>>> Is there a simplish way to figure out or measure the copper weight on an
>>> existing PCB?
>>>
>>> I'm asking because I'm redoing a layout for someone and I did not do the
>>> original circuit design, so was planning to use the same trace widths as
>>> on the original board, but I'll need to know the copper weight to order
>>> a prototype board.
>>> If I have to redo the math on current etc, that opens up another can of
>>> worms as I don't have all of the specs otherwise.
>>> And the copper does feel thicker than usual.
>>>
>>> Thanks.
>>>
>>>
>>>
>>>
>>> --
>>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>>> View/change your membership options at
>>> http://mailman.mit.edu/mailman/listinfo/piclist
>>>
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Re: [EE] Measuring PCB copper weight?

RussellMc
On Tue, 23 Feb 2021 at 15:27, Jesse Lackey <[hidden email]>
wrote:


> The pcb from JLCPcb is 44 Ohms, i.e. 30% less
> copper than the standard for 1 Oz.
>
> Specifying copper weight, and laminate thickness & material is "a really
good idea".


                   Russell
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Re: [EE] Measuring PCB copper weight?

Bob Blick-5
In reply to this post by Jesse Lackey
I bet the free ballpoint pen more than made up for the error :-(

Thanks for the heads-up, I've had non-critical hobby boards from them before.

Friendly regards, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of Jesse Lackey
Sent: Monday, February 22, 2021 6:26 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Measuring PCB copper weight?

Just a minor LOL/Sigh, I got some boards made at JLCPcb, they have trace
antennas for RFID, a 55mm spiral square of 6mil wide track.  I was
having problems not seen on a proto pcb made in the USA.  After some
head scratching and fiddling and calculating, the trace antenna is 380
inches long, and with 1 Oz copper it measured close to 30 Ohms, as
expected, on the proto.  The pcb from JLCPcb is 44 Ohms, i.e. 30% less
copper than the standard for 1 Oz.

Never seen that before.

Now they want me to measure the thickness.  Ya right.

J

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