I have done a few PCBs using the reflow process. To apply the solder-paste using a stencil one requires some sort of fixture to hold the PCB.
So far I helped myself with other PCB Material which I glued on the table to get to the same height. This is okay when only one PCB needs to be made. However, when doing multiple PCBs on after another, the position needs to be constant for every board.
So I designed a simple spring loaded fixture to hold the PCB in place. Its made out of 1.5mm acrylic.
Using a pizza oven for reflow soldering has already been done a million times by hackers/makers all over the world. You can even buy a ready made reflow controllers for such setups. Still, I will present my approach here since it is a little bit different from others I have seen so far.
Most setups use a relay to switch the heating element on/off. Some designs use a SSR and even have elaborate features like zero-crossing-detect. However, I didnt want to mess around with mains voltage. Thats why I decided to use a DMX512-Dimmer do control the heating element. When you think about it, its just another kind of lamp. So why not use a device made to control lamps?
The actual control is done with a Raspberry-Pi. I used a “max6667” Thermocouple amplifier from ebay which is interfaced via SPI. Fortunately there was enought sample code available on the net, I only had to do a litte copy&paste to get it running. I did modify the code to use the py-spidev library. My sourcecode is attached to this post. I also used python to run the PID-Temperature-Loop. Since that code is really ugly I wont publish it now 😀
Here is a picture of the complete Setup:
I did label some of the Items on the picture:
As mentioned above, a PID-Algorithm was used to control the temperature. The Profile is rather slow, but it does work. I might add insulation to the oven to allow faster heating.
Modified max6667-lib: max6667
