Remember that the industry has been soldering to ~ pure tin for years
with Sn/Pb solder, prior to ROHS. 

As for the intermetallics, when you solder with SnPb you may get
quantitatively less CuSn intermetallics because of the lower quantity of
tin and typically lower soldering temperatures.  I think you could say
that with 63/37 you would theoretically get less erosion of the metallic
surfaces. 

Data to support the soldering to Matte Tin with 63/37?  I suspect that
SolderTec may have that sort of information. Sorry but I don't. I'm sure
they've done some type of study, although it may got back to the
international Tin Research days.

Rich K / GTS

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of - bogert
Sent: Tuesday, August 07, 2007 6:44 PM
To: [log in to unmask]
Subject: [TN] Soldering pure matte tin plated component leads using
Sn63Pb37 solder

August 7, 2007

Many component manufacturers because of RoHS regulations have changed
their 
component lead finish to a pure matte tin finish.  Most of these folks
have 
also implemented some form of tin whisker mitigation (anneal after
plating, 
use a nickel flash, etc.).

It is my understanding that assembly level soldering of these component 
leads using the traditional Sn63Pb37 solders for wave soldering, or
reflow 
soldering using Sn63 based paste, with traditional RMA or Rosin based
L0/L1 
flux does not need to change the wave or reflow soldering profile 
temperatures since the matte tin plated component leads are considered 
solderable as a "drop-in" replacement for SnPb plated component leads.

Can folks confirm the above conclusion or otherwise provide comments?
Is 
there any technical information on soldering to matte tin plated leads
using 
Sn63 solder alloy at assembly?  Will the same intermetallics form as
when 
soldered to traditional Pb-bearing leads with Sn63 solder and FR4 board 
material?

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