In terms of losing solderability on the secondary side after a single trip through the reflow, I think you have immersion silver finish confused with immersion tin. Immersion silver does not usually degrade significantly after a single reflow excursion.
But again, it depends (ka-ching).
There are many immersion silver plating products, some not as good as others, and there is a huge variation amongst the plating companies that apply these products. Like any other plating, it depends on which product you use, and which plating company or PWB fabricator you use. Some IAg products have a much superior co-inhibitor that prevents tarnishing and oxidation.
Minor tarnishing (yellowing) of immersion silver has very little effect on the DPMO of a given PWB. Black areas caused by direct contact with sulfur-bearing desiccant packages, rubber bands, tape, paper (including the Moisture Indicator cards) are a completely different story; these will have significant impact on solderability, and the flux has little or no effect on this.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
Sent: Wednesday, February 09, 2011 8:33 AM
To: [log in to unmask]
Subject: Re: [TN] IPC-4553
Good point. Solderability depends heavily on your flux I would say. Those using a high activity, halide containing formulation would have an easier time than those with ROL0. Plus, the additional predicament is that the oxidation may be minor when the PCBs are received, and they solder just fine, but after 6 months or so in stock it is worse, or even after 1 trip down the reflow oven making Side 2 unsolderable.
-----Original Message-----
From: Jack Olson [mailto:[log in to unmask]]
Sent: Wednesday, February 09, 2011 9:11 AM
To: [log in to unmask]; Glidden, Kevin
Cc: Jack Olson
Subject: Re: IPC-4553
Good question.... and when looking at an actual board, how is one to determine
visually if we are looking at "staining" or "oxidation/corrosion"? Inquiring minds
want to know.
(many would say that even oxidized boards are solderable and acceptable.
right? I think I just read that somewhere...)
Jack
.
On Tue, 8 Feb 2011 09:20:44 -0500, Glidden, Kevin
<[log in to unmask]> wrote:
>Morning everyone,
>I have a question on IPC-4553, specifically, section 3.1 "Visual", and
specifically regarding staining of immersion silver. The text states "The
coverage shall be complete and the finish shall be uniform on the surface to be
plated (see Figures 3-1 through 3-5 for properties visually identified with IAg
plated surfaces)" Figure 3-1 shows 'Example of Uniform Plating", with no
staining. Figures 3-2 through 3-5 show staining. Is this to imply (without text
to support) that any staining of immersion silver is determined to be non-
uniform and therefore a defect?
>Thanks.
>
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