Werner,

A question that haunts me lately:

the solubility of Ni in Sn increases with the temperature. At lead-free temperatures, the solubility of Ni in Sn is already at higher values than in SnPb. On top of it, there is more Sn, less "impurities", so it should not matter whether we solder to Cu or Ni. Therefore Liquidus + 20 should be enough for both.

Where is the reasoning error?

Thanks,

Ioan

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Werner Engelmaier
Sent: Friday, November 17, 2006 7:29 AM
To: [log in to unmask]
Subject: Re: [TN] BGA anomaly


Hi Iain,
Perhaps you have not seen some of my previous responses, but...
For reflow soldering, the time-above-Solidus is not an important number for
solder joint quality; you are not making solder joints at or just above
Solidus. However, time-above-(Liquidus+20C [if soldering to Ni you need
Liquidus+30C]) is very important and should be 3 to 5 seconds or longer.
Unfortunately, paste vendors have been misleading their customers for a long
time with this "time-above-183" nonsense, that is now spilling over into the
LF-arena.

Werner

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