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Subject:
From:
David Hillman <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, David Hillman <[log in to unmask]>
Date:
Tue, 12 Jul 2016 08:55:12 -0500
Content-Type:
text/plain
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text/plain (100 lines)
Hi folks - I agree with George's assessment. The critical parameter is not
letting the IMC oxidize. Once the original solder is removed as George
detailed, then re-tinning with the 95/5 alloy right away is key process
step.

Dave Hillman
Rockwell Collins
[log in to unmask]

On Tue, Jul 12, 2016 at 8:50 AM, George Wenger <[log in to unmask]>
wrote:

> Hi Mary Grace,
>
> If your Sn95/Ag5 solder wets the wiring and components after SN63/Pb37
> removal I wouldn't be concerned about the integrity of the solder joint.
>
> However, the concern I would have is the ability for the Sn95/Ag5 solder
> after wicking away the standard solder. I'm not a real fan of using solder
> wick. When you solder to a component that has copper terminations the
> "glue" that keeps the solder attached to the copper is copper-tin
> intermetallic compound (IMC) that forms between the copper and solder.
> Solder wick is a very good means of removing all of the molten solder from
> a copper termination and it leaves behind the copper-tin IMC that doesn't
> melt at soldering temperature. So if the reason you are removing the
> SN63/Pb37 solder and re-soldering with Sn95/Ag5 solder is to make the
> solder joint Pb-Free then solder wick is the method you would want to use.
> The other method to remove the old solder would be to use a "solder
> sucker". This method sucks away a lot of the molten solder (i.e., takes off
> most of but not all of the molten solder) and leaves a small amount of old
> solder on top of the copper-tin IMC. When you re-solder the Sn95/Ag5 should
> wet the component termination very well. If you removed the Sn63/Pb37
> solder with a solder wick the copper-tin IMC is then on the outside surface
> of the component termination and is exposed to the environment and it can
> readily oxidize. The problem with oxidized copper-tin IMC is that the
> oxidized IMC can't be reduced with standard soldering fluxes and the
> surface will not wet well with solder. It may be that you can wick off the
> old solder and re-solder immediately with the new solder and get good
> wetting because the IMC hasn't had time to oxidize. If you do soder wicking
> at one station and then at some later time do re-soldering at another
> station you will probably find solderability issues.
>
>
> Regards,
>
> George Michael Wenger
>
> George M. Wenger
> Failure Signature & Characterization Lab LLC
> 609 Cokesbury Road, High Bridge, NJ 08829
> (908) 638-8771 (Home) (732)-309-8964 (Cell)
> [log in to unmask]
>
> ----- Original Message -----
>
> From: "Mary Grace Keenan" <[log in to unmask]>
> To: [log in to unmask]
> Sent: Tuesday, July 12, 2016 8:15:08 AM
> Subject: [TN] Using high temp solder after removing standard solder
>
> I have a question regarding using the high temp solder after removing
> standard solder Sn63/Pb37. After wicking away the standard solder, we need
> to re-solder the wiring and components using the high temp solder
> (Sn95/Ag5). We are concerned that the integrity of the solder joint and the
> temperature rating may be negatively affected. Is this a legitimate
> concern? Any suggestions?
>
>
> Regards,
> Mary Grace Keenan, Quality Assurance Manager
> Taber Industries
> 455 Bryant St.
> North Tonawanda, N.Y. 14120
> [log in to unmask]
> Phone (716) 694-4000 Ext.134
> Fax (716) 694-1450
>
>
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