Seems to be a common misconception. Maximum temperature is limited by Galden boiling point. However achieving an acceptable temperature profile is more difficult than in conventional oven. If you just heat it until PCB reflows, you will get a lot of tombstoning due to too steep temperature rise.
After my previous post I did a bit of research and also found mentions of this in a manual for a vapor phase reflow device. (Linked below). Unfortunately it's both legal and common to highlight advantages and at the same time swipe disadvantages of a certain process under the rug. It's quite misleading.
Controlling some temperature trajectory (which is important to prevent tombstoning) will be difficult with a system like this. The fluid has a high thermal mass, and a fixed temperature at it's boiling point.
This also explains why the PCB is held horizontally at a fixed distance from the fluid, and there is not a rack with 10 or so PCB's in the chamber.
Combining it with other heat sources such as IR to make the PCB itself follow a temperature profile is also difficult. If that stuff gets overheated it apparently decomposes in Gaseous Hydrogen fluoride (HF) and Fluorophosgene. I'm not a chemist, but that's nasty stuff. Any heating beyond it's boiling point should be avoided, which is only easily doable if the liquid reservoir itself is the only heated part.
https://en.wikipedia.org/wiki/Hydrogen_fluoridehttps://en.wikipedia.org/wiki/Carbonyl_fluoridehttps://static.eleshop.nl/mage/media/wysiwyg/downloads/misc/RK-10698_730.pdfI also do not understand what's so special about that liquid that justifies it's price. It only has to have a few simple properties.
* It's vapour drives away oxygen, which prevents corrosion.
* It's boiling point and condensation on the PCB brings in a lot of energy to bring it to that specific temperature.
* It should be non-toxic, and not react with the parts on the PCB.
I'm wondering why it is not simply done with water / steam.
You'd need a pressure vessel at around 3MPa, (And pressure vessels need complex certification) but that is not an extreme pressure, but still may be problematic for hermetically sealed parts such as crystals and MEMS sensors.
It's just a thought experiment.
I'd be curious to know more about possible liquids for this.