Hi Graham,
You are absolutely right, with the LF-solders, vapor phase soldering is the 
way to go, because of 
(1) assured uniform temperatures, everywhere, and 
(2) soldering just above Liquidus is possible avoiding the much higher peak 
reflow temperatures needed because of the thermal gradients resulting from all 
other heat transfer modes.

Unfortunately, this technically very elegant way of reflowing solder got a 
black eye in its earlt history, because oven manufacturers designed their oven 
improperly in terms in insufficient pre-heating capability [resulting in solder 
pooling up component leads] and insufficient sealing [resulting in expensive 
vapor fluid losses].



Werner

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