Vapour Phase soldering machine interface

[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]

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?

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]

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_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.

[wraper]

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.

Water is not inert unlike Galden.

[Emil]

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?

I think it's necessary to control how quickly the temperature rises to avoid tomb stoning. This is actually a bit tricky.

With vapor phase the art is not in the electronics, but you have to design the box carefully.

Agreed. The first working version of my prototype actually had no electronics for control, just thermocouple amplifiers. It's probably 80% about managing temperatures and fluids. Which is why I did not start with the electronics.

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.

It’s important to keep as little heat as possible going anywhere other than into the liquid.
To heat galden above it's boiling range I think one of three things would need to happen: 1. Boil off all the liquid. 2. Heat the vapour rather than the liquid. 3. Significant pressure. My machine can't do 2 or 3 and 1 will be prevented by the controller, or a thermal fuse if the controller should fail. The fluid needs to be heated to 290C before it breaks down, so there is some room for error.

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

Agreed. I have not done any tests to quantify the liquid loss, but based on how much I have needed to top up during testing it appears to be minimal.   

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.

My prototype has a heat exchanger attached to a hole in the lid to allow air to move either way while galden is supposed to condense in the heat exchanger and drip back. I have not actually observed galden condensing in (or escaping from) the heat exchanger. I have not observed drops on the lid either. I think this is because the contained is high enough that the vapour doesn't rise to the lid during the short time at boiling temperature.

[Emil]

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.

I have added this option to the poll.

[GerardG]

Hello @Emil

Nice to see you make an effort on this. It sounds very good.

[lutkeveld]

I recently bought an Imdes vapour phase oven and the vapour seems to work well.
However, the electronics is just a mess and the mechanical construction is a 7/10.

It would be great if there was an open-source project for this.
I am planning on doing a redesign for the control circuitry of the Imdes, just as an hobby project.
Something with an oled and rotary encoder would be simple to use and have a BoM of under 20 dollars.

Once there is a simple piece of electronics for control and a mechanical engineer would redesign the construction a bit,
it seems that you can get pretty far with not too much effort.