Hi Carey,
SOT-23's have leads made of Alloy 42 (42% nickel & iron). This material is
more difficult to solder to than are Cu alloys; everything else being equal
it needs to reach about 15C hotter during peak reflow or be at a lower
temperature for a longer time. As Dave indicates, slowing down the conveyor
in the reflow machine is a way of getting more heat to them; I prefer in most
cases to raise the set point in the peak reflow zone. But it really depends
on the mix of the components on the PWA which way to go or whether to raise
the set point some and slow down the conveyor. You should really measure the
reflow temperature profiles by instrumenting key locations on one assembly
with thermocouples.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask]

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