# Need help with ID of material on board



## R Glover (Feb 17, 2013)

I'm new to this site, I've learned a lot on here, thanks for all of the input by so many.
I have some boards that have a silver coating over the PCB. Does anybody know what this coating is? One guy said it was Tin Lead coat, I heat it to 860 & it doesn't melt. 

I have searched this site & did a Google search with no success. I would imagine that it's been brought up on this forum before, but I can't find it.

Thanks,
Rube


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## MMFJ (Feb 17, 2013)

R Glover said:


> I'm new to this site, I've learned a lot on here, thanks for all of the input by so many.
> I have some boards that have a silver coating over the PCB. Does anybody know what this coating is? One guy said it was Tin Lead coat, I heat it to 860 & it doesn't melt.
> 
> I have searched this site & did a Google search with no success. I would imagine that it's been brought up on this forum before, but I can't find it.
> ...


your picture shows a 'complete' board, however, you state you heat it to 860 (presumably degrees Fahrenheit?), which would melt all the solder and several other metals (http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html as a reference for temps of metals http://www.rfcafe.com/references/electrical/solder.htm for various solders).

Did you first depopulate the board before/as you heat it to 860? Just not clear on your steps.

I am pretty sure this type board has been discussed many times on the forum (it looks like a fairly common board from some telecom/datacom equipment in the early-mid 80s) - I didn't find a direct post on it yet, but search a bit, I'm sure it is there.


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## R Glover (Feb 17, 2013)

MMFJ said:


> R Glover said:
> 
> 
> > I'm new to this site, I've learned a lot on here, thanks for all of the input by so many.
> ...




I did not heat the entire board, just a small spot on the bare board, trying to melt the silver coating.


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## Marcel (Feb 17, 2013)

Melting point of silver is 960°Chttp://en.wikipedia.org/wiki/Silver
I have never seen silver over copper plating, but there is almost nothing that does not exists.
Try if it is magnetic. Then it is nickel or nickel alloy.


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## necromancer (Feb 17, 2013)

some better pictures of the top and bottom pluss the front would be nice


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## g_axelsson (Feb 17, 2013)

Silver plating on copper is common among newer electronics as a substitute for solder plate. The problem with modern lead free solders for surface treatment it is that it isn't as easy to have it flow and the higher melting point is problematic.
I know there are silver plated boards as I have ordered it myself for several of my PCB designs.

Older, pre rohs-compatibility boards, usually have HASL (hot air surface leveling) treated surfaces, basically it is dipped in solder and any excess is blown away by hot air.

This board clearly have a tin/led solder surface.

Göran


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## resabed01 (Feb 17, 2013)

Older boards such as this were often full plated with tin. This was a cheaper alternative than gold but accomplished almost the same result.
The copper traces on a PCB needs to be covered with something. Bare copper traces will quickly corrode to green fuzzy dust so the manufacturer had a few choices.
Solder mask the board to expose only the solder pads for soldering. Plate the traces with a inert metal or fully cover the copper traces with tin/lead solder.

Tin was cheap to use, corrodes relatively slow and is wetted to solder very easily.


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