When you are into electronics and fabricating your own pcb's you want to have a reflow oven in your lab.
A quick search online tells you to open up your wallet and grab 500€ for a decent small oven unless you go half that price and find one in China paying way too much on shipping and tax.
Since we like to make things ourselves and there is a ton of info on how to make one yourself, we found ourselves on the 'diy-road'.
Did I also mention that we like to put an arduino in everything? And we're not the only ones in the world. Rocket scream has developed a nice shield for our preferred dev board. Their reflow oven controller shield has everything we need. A nice interface, PID control and open source code. You only need a solid state relay (SSR) for switching the power to the heating elements and K-type thermocouple (high temperature sensor).
Which oven to buy?
For extra advice on buying an oven, read this post. Your oven needs to heat at a minimum rate of 3°C per second.
How to build one?
Since I'm going to talk about our improvements, I'll send you to Rocket Scream's tutorial how to build one.
To be clear, you'll need to void the warranty of the oven to build it like ours. It can be done without, but then you would need to control it externally.
Front panel design
Finishing a build like this needs a custom frontpanel. I designed another one that accepts the reflow controller shield. The slt file of the panel can be found here. Having our own Ultimaker 3D printer, makes it quite easy to create this kind of object in a couple of hours.
What, Why? Reflowing is a delicate proces that needs precise temperature control. In this case the PID control is doing a great job. But our oven is merely capable of following the right temperature curve.
Our first try was moving all the heating elements to the top, which was not a big improvement.
Trying to improve and not getting a good result simply makes us try harder, much harder. Out went the heating elements. Off to the world wide web learning about heating possibilities and we found the following options:
- Ceramic heaters (slower heating, more efficient in radiating heat)
- Quartz heaters (fast heating, ideal solution for overhead heating)
Because we needed fast heating up to 250°C, we went with 2 1000W Quartz Elements. This adds an extra 700 Watt to our 1300W oven, which is not a problem as long as the SSR (solid state Relay) can handle it.
Hence the power and the improved heat-up time, the PID values for pre-heat were off. Overshooting a lot. Less "I" to compensate the overshoot and we even managed to get a bit more boost.
Another thing to do would be reducing the volume of the oven. We are not going to produce big pcb's, so we could add some insulation to the walls of the oven. Because we removed the bottom heating elements we have all the space underneath the tray, which we don't use. We could fill this space up with some extra insulation. (Not yet implemented)
At the moment the cooling stage is not following the correct curve. If we're reflowing and we're reaching the cooling fase, we'll open up the oven. Still the cooling is going too slow.
Adding active cooling is on our next list of improvements. Still thinking about a good implementation. Will be updated, when we finish this addition.