08/07/2019 at 08:58 •
07/20/2019 at 13:39 •
New SMD practice boards have come, along with some lower temp paste.
I've updated my oven const to run the different heat profile for this paste, I also programmed a slower pre-heat ramp so the solder could de-gas a bit more calmly.
Overall I think the new result is good. There was some bridging on the SOP package, but was easily fixed with an iron + flux. The 0603's are pretty ropey, but I think there was far too much paste for these parts. I think if I had a stencil for these boards, the result would be much better.
07/16/2019 at 08:10 •
To test the oven I bought a SMD practice board that came with all the required components. This would be a cheap, expendable board that I could test my reflow chops on.
I am glad I did this, because it was a complete disaster! All of the components popped off like popcorn somewhere during my pre-head/soak @ about 100c. Looking at the data, I get the feeling that temperature climb was way too steep, and 100c is suspiciously the boiling point of water, so paste could have been contaminated and the popping was gas violently escaping.
Another possible issue was my hand application of paste was quite heavy, as I do not have a stencil for these test boards.
Will buy some more boards and different paste to try.
07/11/2019 at 00:00 •
To hook the oven up quickly I used this majorly dangerous setup. Going forward I will come up with something much safer, but I don't think I have enough bits lying around right now to do anything else.
With it working I ran my test program that I wrote over the weekend, and the first results look pretty promising!
This is the reflow profile I was aiming for as a test:
And this is what I got:
Not bad! The oven doesn't seem to be able to cool down too rapidly, but I think that's probably the best problem to have with a project like this. I was worried that the oven wouldn't be able to ramp up quite as fast as it does.
I can solve the cooling problem with a little fan and opening the door a little.
I've bought a SMD training board which comes with an assortment of SMD packages to practice with, will post some photos of how that goes.
07/10/2019 at 23:50 •
The oven I intend to use has arrived, along with some heat reflecting high temperature tape.
I set to work on taking it apart so I could install the thermocouple. Turns out there were some pre-existing holes left over from the factory that it threaded through perfectly. Just a bit of the heat tape to secure it in place. Side note: this kind of cheap folded metal construction has lots of sharp edges, be careful!
While I had the oven apart I used the tape to insulate the front glass a bit, as well as some pretty big seams in inner body construction.
Now needs hooking up to my breadboard and solid state relay.
07/09/2019 at 22:47 •
Here's the first version of the reflow ovens brain, I've thrown this together while I wait for the oven to arrive.
So far it has:
- Teensy LC for running reflow logic
- Adafruit AD8495 breakout for temperature sense
- Decent length k-type thermocouple
- 4-18v switched, 240v load solid state relay
Teensy LC doesn't output 5v, so I've dropped in a simple 5v charge boost and switching the 5v to SSR using a simple NPN relay (relay-ception)
I've gone for this oven from Amazon. I hope my house doesn't burn down.