Toaster Oven: Reflow SMD Soldering…
There’s a special place in my workshop for the toaster oven, that place is on the workbench. Using an toaster oven to reflow circuit boards is both fast and easy. When you find an oven on sale at Walmart for $17, it’s also very cheap. The other things you’ll need are solder paste, a syringe applicator, some SMD parts and a circuit board. The whole process is just three steps:
- Apply solder paste to PCB
- Place parts according to schematic
- Bake for 5 minutes on high
You might find the solder paste to be quite difficult to squeeze out of the nozzle, a bit like a golf ball and a garden hose or something like that. We could all use a bigger nozzle, but instead I used a couple of pieces of wood and an old hinge to come up with this lever action below. It now comes out in a hurry and without the muscular fatigue, my hands are free for other more important tasks.
Here we have the circuit board with the solder paste applied, a little dab on each pad. The board is a switch mode boost power supply. For the controller chip, a long thin line of paste is applied as the pads are much too small to apply individually. When the solder paste liquifies, magical surface tension will clear the bits between pins. The same technique works for QFN and most other packages, smear on the paste, apply heat and let surface tension do it’s business.
Now that the paste is applied, the parts go on according to the schematic. The part numbers increment with a left-right top-bottom order such that it is easier to locate the part by table. The passives are mostly 0603 size with a few 10uF ceramics in 0805 scattered about, the transistors are SOT-23 and the remaining packages are particular to the part. Placement goes quickly and not much concern is given to accuracy. Here’s the PCB with the parts on, ready to bake.
The final step is baking, it goes in the oven for about five minutes on full blast which is a little more than the time it takes to liquify the solder. The magical surface tension pulls everything into place and with the right amount of paste any bridged pins will clear. The toaster oven is an IR radiant type with glowing heaters on top and bottom. This step is shown in video.
And after it comes out, a quick visual inspection reveals everything has placed well and there is no bridging between adjacent pins. The only thing left to do is apply power and make sure it works…