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Imm Silver tarnish?

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Imm Silver tarnish? | 27 August, 2008

We have an immersion silver board that has a brown discoloration after processing. It's not flux residue, that normally doesn't cause this condition. Elemental analysis shows less than 1% sulfur, and I thought silver sulfide is more a black color. The supplier doesn't add the anti-tarnish sheets because it messes with our destacker. Anyone else seen brown tarnish on Imm Ag boards?

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Imm Silver tarnish? | 29 August, 2008

We saw this one time when we were trying to develop some lead-free product. It ended up being copper migration. Some of the pads had a brown discoloration and those that did would not wet very well. Your elemental analysis would have shown if there was copper though.

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Imm Silver tarnish? | 30 August, 2008

Some immersion silver [IAg] products can go brown with aging. On a newly plated board, we expect you to see Ag, C, & O. The amount will vary according to supplier and thickness.

Questions are: * How uniform is the brown coloration of the IAg on the pads and across the board? * You say, "... board that has a brown discoloration after processing." What type of processing is that? Is discolored prior to this processing? * Is MacDermid Sterling the product name of the IAg on your board? * How thick is your IAg?

IPC-4553, Specification for Immersion Silver Plating for Printed Circuit Boards specifies a minimum of 5 uinch, typically 8 � 12 uinch, as measured on a 60 X 60 thou pad.

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Imm Silver tarnish? | 2 September, 2008

Colorization is relatively uniform across the board.

"Processing" is first pass reflow.

I belive MacDermid is the ImmAg supplier.

Plating thickness has not been determined, our XRF is being revitalized.

Elemental analysis did show a large copper peak on one of the pads (smaller peak on a different part).

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Imm Silver tarnish? | 2 September, 2008

MacDermid Sterling seems to take-on a brownish tint in high dew points. Look at figure 3, p14 here:

We not so sure that it's fatal.

That you see Cu makes us nervous.

Since your XRF is doinked, how are you doing your elemental analysis?

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Imm Silver tarnish? | 3 September, 2008

Elemental is by SEM/EDX.

The brown coloration does resemble the 3 micron photo. Again, if I'm picking up copper (our Ag plating thickness requirements are 0.05 micron to 0.12 micron following IPC 4553), maybe we do have a porous silver plating.

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