From Newsgroup: sci.electronics.design

We did a big JLC order and inclued a bunch of 6" square pieces of
double-side gold-plated 1oz copper FR4, for dremeling prototypes.

I sheared off a strip and measured its resistance. The result
corresponds to 0.7 oz copper. I've seen worse.

Maybe most of their boards start out 0.7 and get plated up some, when
they plate the vias.

Copper *is* expensive lately.

https://www.dropbox.com/scl/fi/q6obxr1rkiozcttqldmsn/JLCPCB_Copper.jpg?rlkey=wlj6oppktx4p5gztgkp431kzn&raw=1



John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
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From Newsgroup: sci.electronics.design

On 13/10/2025 20:42, john larkin wrote:

We did a big JLC order and inclued a bunch of 6" square pieces of
double-side gold-plated 1oz copper FR4, for dremeling prototypes.

I sheared off a strip and measured its resistance. The result
corresponds to 0.7 oz copper. I've seen worse.

Maybe most of their boards start out 0.7 and get plated up some, when
they plate the vias.

The resistivity of the plated copper may not be what you expect for
bulk copper, either due to impurities or internal stress.
Have you checked the weight?

John

Copper *is* expensive lately.

https://www.dropbox.com/scl/fi/q6obxr1rkiozcttqldmsn/JLCPCB_Copper.jpg?rlkey=wlj6oppktx4p5gztgkp431kzn&raw=1

John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

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From Newsgroup: sci.electronics.design

On Mon, 13 Oct 2025 12:42:45 -0700, john larkin <jl@glen--canyon.com>
wrote:

We did a big JLC order and inclued a bunch of 6" square pieces of
double-side gold-plated 1oz copper FR4, for dremeling prototypes.

I sheared off a strip and measured its resistance. The result
corresponds to 0.7 oz copper. I've seen worse.

Maybe most of their boards start out 0.7 and get plated up some, when
they plate the vias.

Copper *is* expensive lately.

<https://www.dropbox.com/scl/fi/q6obxr1rkiozcttqldmsn/JLCPCB_Copper.jpg?rlkey=wlj6oppktx4p5gztgkp431kzn&raw=1>

Electroless coatings are usually of higher bulk resistivity than
electroplated, and electroplated also varies with how it's done.

If the copper and gold have higher bulk resistivity due to impurities,
won't that translate into a thinner coating than actual if one
computes assuming ideal purity?

Joe
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From Newsgroup: sci.electronics.design

On Mon, 13 Oct 2025 20:57:37 +0100, John R Walliker
<jrwalliker@gmail.com> wrote:

On 13/10/2025 20:42, john larkin wrote:

We did a big JLC order and inclued a bunch of 6" square pieces of
double-side gold-plated 1oz copper FR4, for dremeling prototypes.

I sheared off a strip and measured its resistance. The result
corresponds to 0.7 oz copper. I've seen worse.

Maybe most of their boards start out 0.7 and get plated up some, when
they plate the vias.

The resistivity of the plated copper may not be what you expect for
bulk copper, either due to impurities or internal stress.
Have you checked the weight?

I'd assume that the base copperclad is mechanically fabricated, not
plated. The ENIG is plated, but that's microinches. Maybe the rolled
foil has higher resistivity than virgin bulk copper, stress or
something.

I don't have a good way to check the weight of the copper.

0.7 oz electrical equivalent isn't bad. Just good to know. We
sometimes care about trace resistance.

John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
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From Newsgroup: sci.electronics.design

On 14/10/2025 7:00 am, Joe Gwinn wrote:

On Mon, 13 Oct 2025 12:42:45 -0700, john larkin <jl@glen--canyon.com>
wrote:

We did a big JLC order and inclued a bunch of 6" square pieces of
double-side gold-plated 1oz copper FR4, for dremeling prototypes.

I sheared off a strip and measured its resistance. The result
corresponds to 0.7 oz copper. I've seen worse.

Maybe most of their boards start out 0.7 and get plated up some, when
they plate the vias.

Copper *is* expensive lately.

<https://www.dropbox.com/scl/fi/q6obxr1rkiozcttqldmsn/JLCPCB_Copper.jpg?rlkey=wlj6oppktx4p5gztgkp431kzn&raw=1>

Electroless coatings are usually of higher bulk resistivity than electroplated, and electroplated also varies with how it's done.

If the copper and gold have higher bulk resistivity due to impurities,
won't that translate into a thinner coating than actual if one
computes assuming ideal purity?

It is not impurities that raise the resistance, but structure of the
metal. Electroplating grows crystals of metal and the current flows from crystal to crystal, following a longer path than it would take if the
crystals were bashed together.

I've often wondered if a pulsed laser could be used to briefly melt a
local spot of surface crystals into the liquid phase without heating a
large enough volume to get the substrate too hot.

--
Bill Sloman, Sydney

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From Newsgroup: sci.electronics.design

john larkin <jl@glen--canyon.com>wrote:

We did a big JLC order and inclued a bunch of 6" square pieces of >double-side gold-plated 1oz copper FR4, for dremeling prototypes.

I sheared off a strip and measured its resistance. The result
corresponds to 0.7 oz copper. I've seen worse.

Maybe most of their boards start out 0.7 and get plated up some, when
they plate the vias.

Copper *is* expensive lately.

https://www.dropbox.com/scl/fi/q6obxr1rkiozcttqldmsn/JLCPCB_Copper.jpg?rlkey=wlj6oppktx4p5gztgkp431kzn&raw=1

Looks like 'auto-pen' that stamp top right :-)
It still misses te date, needs some work!
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From Newsgroup: sci.electronics.design

On Tue, 14 Oct 2025 08:11:18 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

john larkin <jl@glen--canyon.com>wrote:

We did a big JLC order and inclued a bunch of 6" square pieces of >>double-side gold-plated 1oz copper FR4, for dremeling prototypes.

I sheared off a strip and measured its resistance. The result
corresponds to 0.7 oz copper. I've seen worse.

Maybe most of their boards start out 0.7 and get plated up some, when
they plate the vias.

Copper *is* expensive lately.

https://www.dropbox.com/scl/fi/q6obxr1rkiozcttqldmsn/JLCPCB_Copper.jpg?rlkey=wlj6oppktx4p5gztgkp431kzn&raw=1

Looks like 'auto-pen' that stamp top right :-)
It still misses te date, needs some work!

It's a rubber stamp ordered from Amazon.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
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