windell747 wrote:
> One member, and electrical engineering lead, who is taking
> the lead role in instructing everyone how to solder, is insisting that
> 420degF is all that is needed to make leaded solder joints since the melting
> point for leaded solder is a little under 400degF. He says that his main
> reason for setting the temperature this low is to avoid the risk of
> over-heating the ICs. 
As you know, that is blatently wrong.

With typical soldering-iron soldering (not reflow), you need the joint 
to reach around 100*C higher than the melting/solidification point, so 
that the solder forms an alloy with each surface.  This alloy is 
*critical* to stable joints.  You can get away with less, but, 204*C 
(only 20*C above the solder melting point) is way low.

My soldering iron is typically set to around 600F.   I'm also doing 
really small joints - I.E. 1/8W resistors and dip leads. I do turn this 
up a bit if I am soldering large items.   If you look at most 
datasheets, you will find that the soldering lead temperatures are rated 
typically for at least 260*C for 10 seconds, which equates to 500*F, 
which is still well above the 420*F.   Setting at 600*F, and with good 
technique, I find I can be on and off the joint within a second or less, 
and the semi never even sees the 260*C.   IF you are really paranoid, 
using appropriate lead "heatsink clips" (not sure what they are really 
called), might be useful.

I also would be worried about non-activated Flux or trapped flux in the 
joints.   Part of heating the solder up to an appropriate temperature 
includes fully activating the flux.   If it isn't fully activated, you 
may end up with rosin chunks in the joint, which I would think would be 
bad.   I am assuming that you are using a rosin-type cored solder (R, 
RMA, or RA) - probably RMA.

The following URL's may help...

http://www.lautsprechershop.de/hifi/index_en.htm?/hifi/aka_loeten_en.htm
See also: http://www.elexp.com/t_solder.htm , the last part of the 
paragraph which says "Soldering iron temperature settings".
http://www.emtworldwide.com/article.aspx?ArticleID=8519

In short, you need enough heat to give you a good, solid joint, but not 
too much to destroy the part.   400*F doesn't even come close to hot 
enough.    500*F might be acceptable, but 600*F is even better....

-forrest
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