Gregg, 

While I am not an industry guru I do frequently come into contact with 60-40 and 63-37 interactions.  I repair a lot of vintage boards circa 1968, made before 63-37 was widely available, at least to my knowledge.   
Our preference is that where repairs need to be made remove the old 60-40, clean the area, and solder using 63-37.   Most of the vintage boards have the traces reflowed as well, so we usually allow at least a pad diameter of clean re-soldered 63-37 overlap.  Our engineering group has evaluated this and agrees with using this method.  
I do have a roll of 60-40 to use just in case an overriding document requires it's use.   

The 60-40 appears dull and lusterless after 40+ years but the 63-37 is bright and shinny following replacement. 
I also find that we have fewer fracture faults with properly applied 63-37 then the oxidized 60-40 of yesteryear, whether that is age or material related or both I know not.  

I have yet to see a problem using this methodology in the past 30 years.   

Pat  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gregg Owens
Sent: Tuesday, March 12, 2013 3:43 PM
To: [log in to unmask]
Subject: [TN] Mixing Solders

I have an industry friend who asked me the following question and I did not have a good enough reply. So I thought I would put it out there on TechNet.

What are the possible problems with tin dipping a gold plated contact with 63/37 then soldering it in a (PCB) board using 60/40 solder ?



2.    What arguments could I use to move away from using the 60/40 and use just the 63/37 for the product (i.e. Do you believe one has any benefit over the other)?



3.    Are you aware of any problems mixing the solder types ? (63 / 37 and 60 / 40)

Your thoughts and comments are appreciated.

Gregg Owens

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