Recently I’ve been working on a collaborative project with my friend Ed. His electronic work has been held back by a range of disappointing soldering results from his reflow oven. Having been supplied with a T962 oven for a project, he immediately found it frustrating to work with – Boards were inconsistently soldered and a lot of manual work was needed to create reliable circuits. The results were also badly affected by the ambient conditions. While an irritation, it was not the end of the world for building prototypes and one-off circuits.
As he moved into producing short runs of electronics, however the combination of an oven only large enough for one board and the corrections needed proved impractical to continue. He bought a larger T962A oven – big enough for four of the boards he was using at a time. Having discussed his problems, we were both looking forward to a smoother production process. Unfortunately the bigger oven proved to be even worse, a little investigation revealed that the temperature displayed on the controller was wildly different from the temperature the boards we subjected to – now not only were the boards not soldered consistently, they were coming out burnt as well!
After a little discussion, we concluded that the control of an oven wasn’t all that complicated – there are basically only two outputs to control and the need to sense the temperature. The oven was soon in pieces. We discovered a few shortcomings in it’s build quality – once the earth connections were secure and the thermocouple was more sensibly installed, we set to work building a controller. Ed took charge of the control side of the software and the electronics, while I worked on the user interface.
We were keen to re-use the existing case – with an LCD display mounted on the front and four buttons for the user we came up with a simple process which allowed navigation to load and save temperature profiles, adjust the parameters for the heating / cooling of the board and initiate the cycle. Working on a clean object-orientated model allowed me to build an easy-to-configure, user-friendly menu system. Once the software was running happily on an Arduino, it was loaded onto the controller’s processor. The solid-state relay controlling the heating element was easy to control, the temperature was read with the existing thermocouple connected to an all-in one chip. Adding a second SSR allowed for fine control of the oven’s fan, by running it at a slow speed through the cycle, much more even temperatures were seen.
Overall, with a new controller and a little care over the way the oven was put together, we ended up with a very usable reflow oven that was easy to configure for specific board weights and various electronic components.