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Vapor phase soldering – No more fear of SMD

Today we have steamed circuit boards… Or how to make your life easier with condensation soldering.

No, there will be no recipes presented now, or talk about cooking, although the latter is not quite correct. It is about a quite old method of reflow soldering: Vapor phase soldering or also called condensation soldering. With the vapor phase, SMD soldering is child’s play.

As recently as the early 1980s, this process had fallen into disrepute and into oblivion because of the use of chemicals that were not exactly environmentally friendly. It was not until the development of perfluoropolyethers that this process experienced a new renaissance.

But the really interesting thing is that you can very easily replicate it at home. And without the use of expensive machines or special tools.

Perhaps first of all, why exactly it goes. The perfluoropolyether, or also better known under the trade name Galden, is a slightly oily plastic that is liquid at room temperature. When this is heated, an inert gas is formed, which maintains the temperature quite accurately (there are different versions of Galden for different temperature ranges).

And in this gas, or steam, you can now solder circuit boards. The big advantage over the infrared reflow process (as used in most reflow ovens) is that everything heats up evenly. The color of the components does not play a role, in contrast to IR reflow. There is also no shadowing of large components. BGAs are also no problem, because this gas fills everything evenly.

I use Galden LS 230  (manufacturer is the company Solvay) for lead-free soldering. Where the number 230 stands for the temperature. And the really interesting thing is that you can work quite simply with the usual home remedies.

The setup for me looks like this:

Construction of a vapor phase “soldering system”

What is required?

I use an asparagus pot, along with a small induction cooktop from the discount store. What is then still needed is a thermometer. A suitable multimeter with a so-called thermocouple element is also sufficient.

An induction hob is important because the heat source is directly under the electrode and the pot does not have to be heated first. With a deep fryer, where the heating coils are not open (very important, because otherwise you need far too much Galden, because the heating coils must be completely covered) you can also use the vapor phase soldering. Gas in any case not, because not finely enough adjustable.

Such an induction hob costs around 25,. euros, a corresponding asparagus pot is already under 20 euros to have and the measuring device strikes again with 20 euros (if not already available). With not quite 75 euros one is thus there, at least almost.

Because, of course, the galden itself is still needed. And that is unfortunately not quite cheap. A container with 500gr is currently just under 100, – euros. The good news, however, is that you can probably solder 100,000 boards with it. Because the gas is almost not consumed.

If you take a tight pot, and also do not remove the lid in between (glass lid is best for curious noses) while the gas is still in the pot, then you can probably work with the Galden for life. Sure, a small whiff is always lost, but it’s so little that you still won’t notice any loss after several tries.

A pot of asparagus because you need a vessel as high as possible, but not wide. The higher the better, the less Galden can escape to the top. And the asparagus pots have a corresponding grid insert, which is ideal for placing the sinker in. Because, of course, the sinker must not be placed in the liquid Galden.

2 boards with a spacer in the grid insert of the asparagus pot

The temperature sensor should be fixed about 2 cm above the board. Since I now even steam-cure 2 boards at the same time, I have attached two sensors.

The Galden itself is filled into the pot until it is sufficiently covered. 5-10mm is quite sufficient.

Hint!

And here also the only warning that must be given: Never leave the bottom of the pot uncovered at any point. If the Galden gets hotter than 230 degrees, hydrofluoric acid is formed, which is extremely dangerous. It is no problem if a drop of Galden should drip onto the hot induction field, etc. The temperature is not sufficient for this. The temperature is not sufficient for this. If the bottom of the pot is sufficiently covered and the gas cannot escape constantly, it is not possible to reach a suitable temperature even with the highest setting so that hydrofluoric acid could form.

This is similar to boiling water. Once it boils and there is a sufficient amount in the pot, it stays at 100 degrees. No matter how hot you then set the hotplate, it stays at 100 degrees. And, of course, this is also true with the Galden.

I recommend using the hob at a fairly low power anyway. You can not run temperature curves, unlike in the reflow oven. The gas does not form until the galden reaches 230 degrees. So you can not heat the gas slowly.

However, if you now set the induction field to low power, it takes longer for the liquid Galden to heat up. However, the liquid gives off heat towards the top. And this can be used to prevent the cold boards from immediately coming into contact with the hot steam.

You have to do some testing. I always set the induction hob that I use to a temperature of 80 degrees. Whereby these 80 degrees are somewhat misleading. Because basically only the power can be controlled, but not the temperature itself.

Watch the temperature

And so you can then slowly watch the temperature rise.

Thermometer for temperature control

The upper value indicates the temperature above the lower board, and the second value for the upper board. Here you can see very well how the hot Galden alone slowly heats up the board.

You can watch as the gas slowly forms.

The Galden vapor slowly begins to form.

Now it gets exciting. From here on, it only takes a few moments. The temperature continues to rise and the steam becomes denser and denser until you can almost or even no longer see the boards.

The Galden gas has completely filled the pot

Now just watch the thermometer, and once 230 degrees is reached, turn off and remove the pot from the induction hob.

The correct temperature is reached

Because now the necessary temperature for the lead-free solder is reached and the soldering itself is already completed. The whole process from heating to reach 230 degrees takes 4-5 minutes, depending on the power.

Put the pot down from the hob because the induction hob itself is still very hot, and this only delays the cooling down unnecessarily.

And since the boards should also not be cooled down too quickly, I recommend simply waiting until the gas has cooled down again to the point where the steam has completely disappeared. This way you also have the lowest losses of Galden. If you open the pot lid beforehand, the steam escapes, which is accompanied by a small loss of Galden.

By the way, it smells like warm plastic during the process. This is perfectly normal, because as mentioned at the beginning, Galden is a liquid plastic.

Ready “cooked” the boards are now ready

Fertig

When everything has cooled down, the basket insert can be removed from the pot. The boards themselves are basically clean. There is only a very thin film of Galden on the boards, which can be easily washed off if necessary.

Ready for the next swing

The Galden can now be filled back into the bottle for the next use. Because you can use Galden over and over again. From time to time it will be necessary to run the Galden through a coffee filter, because over time dirt particles (which are in the air and especially the circuit boards) collect in the liquid.

I took two more close-up pictures showing how neatly the components are soldered.

No short circuits or dispersed solder

Side view of a 0805 size capacitor

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As you can see from the pictures, the soldering points have been neatly executed. In addition, a few tips as far as the preparation is concerned.

It is important to work with a stencil. If you apply the solder paste manually, the result is rarely satisfactory afterwards. Above all, this quickly leads to the so-called tombstone effect. The forced uneven application of the solder paste leads to temperature differences. This can then lead to one side already being liquid, while the other side has not yet melted. And if this is the case, then a lighter component will line up on the melted side due to the surface tension of the liquid solder.

Also, when designing the circuit board, care should be taken to ensure that there are appropriate thermal differences. For example, one should avoid connecting one side of a component directly to a large copper surface.

But also a good solder paste is very important. In my experience, the cheap ones from any auction websites or former booksellers are not the best. I personally like to use the solder pastes from Felder. These are not much more expensive, but easier to process and the result is also convincing.

If you want to work with leaded solder paste, you can do so with Galden LS 200. Here, the point at which the vapor forms is already at 200 degrees. Otherwise, everything said above also applies here.

I hope you enjoy making them!

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