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) 
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----- 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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