Ok, but to play devils advocate here:
Weller and others recommend HT. So it legitimately performs well. HT is 1/2 the price of LS. Let's assume that solvay doesn't have bigger margins on the LS product, but that might not be true given that they have no competitors (they do in heat transfer though: fluorinert, krytox, etc). If you have a sealed batch vapour phase system, then it is effectively a closed loop system so you should expect basically no losses except what sticks to the board.
I can see the that the LS would be better for an inline system which is perpetually open, but will the losses offset the savings from using HT in a batch oven?
I also think that having some lower boiling point fluids would be better; it will make the temperature gradient of the vapour cloud much less steep.
Can anyone shed any light on why fluid viscosity
really matters in a batch oven? I can't think of anything.
Also a lot of this kind of reeks of marketing:
"The latter defeats the purpose of moving towards lower environmental friendly lead-free soldering."
This makes sense superficially, but it doesn't really make technical sense. The lead-free soldering move had nothing to do with ozone or CFCs. We can of course argue all day if it is actually better for the environment
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/xwink.gif.pagespeed.ic.cldandycH0.png)
, but lead free (afaik) uses the same amount of fluxes, generates the same amount of gas, etc if not more due to the higher temps required.
The actual fluid losses aren't quantified. I'm pretty sure if it was a huge amount, they would use the figure to make their argument. They have a technical audience after all. Something like "in our testing, we found that HT losses were 250% greater than LS at 230C". After reading the technical detail in the PDF, I'd be willing to bet that they've done the test and didn't see an enormous difference.
In the slides, they state that Galden is not a CFC, not toxic, accidental spills/release is ok (even on food!), etc. But when it comes to LS vs HT, HT is pretty nasty stuff for the environment? Um
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif.pagespeed.ce.5xOqKkq0Co.gif)
tldr; do the losses by using HT really account for a doubling in price? My guess is no, or they would have been a little more technical about the whole thing.