Electronics > Manufacturing & Assembly

Vapour Phase soldering machine interface

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Emil:
I’m developing a vapour phase soldering machine. It’s a desktop machine in a powder coated sheet metal enclosure, ~180*250mm maximum board size, target price point around $1k.

trevwhite:
Look forward to hearing more about it.

Doctorandus_P:
A small (Oled?) LCD with a rotary encoder and some push buttons to make it a standalone device is nice, and fairly low in cost. A big TFT is overkill for a device like this.
But overall vapor phase is quite simple. It's the fluid itself that regulates the temperature, so how much of a controller do you actually need?

With vapor phase the art is not in the electronics, but you have to design the box carefully.
You want the box to be hot, but can't heat the box itself too much because you really do not want to heat the vapor beyond it's boiling point.

The fluid for vapor phase soldering is quite expensive, so recovering as much of that stuff as possible is a good idea.

I had a look at the video Marko Reps made of his contraption, and what he misses is that if the temperature changes, gas is pushed out or pulled into the thing.

A good way to further limit vapor loss is to first make the lid air tight (as Marco already did) but then also make a hole, with some hose and put that through a heat exchanger (For example as used in the water block of CPU coolers) and mount it in such a way that condensate flows back into the chamber.

Marco also had problems with the horizontal lid, and drops falling from it. putting the (glass) lid under some angle will prevent drops from falling on your PCB.

If you really want to minimize fluid loss, then collect any condensate in a beaker, and heat that beaker, and combine that with some radiator that can cool the vapor in the camber at the correct time.

wraper:

--- Quote from: Doctorandus_P on October 29, 2021, 08:11:12 am ---But overall vapor phase is quite simple. It's the fluid itself that regulates the temperature, so how much of a controller do you actually need?

--- End quote ---
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.

Doctorandus_P:

--- Quote from: wraper on October 29, 2021, 08:16:05 am ---
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.

--- End quote ---

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_fluoride
https://en.wikipedia.org/wiki/Carbonyl_fluoride

https://static.eleshop.nl/mage/media/wysiwyg/downloads/misc/RK-10698_730.pdf

I 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.

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