This week we take a look at the 946A+ solder reflow hot plate from our last Shenzhen equipment haul. There’s a ton of no-name 946A+ out there, ours happens to be D-GOLD. They’re all pretty similar, and run about $50 in Shenzhen.
Using a kitchen hot plate is a common hack for DIY reflow soldering, even SparkFun has used them. This is the industrial version, actually intended for reflow soldering and board preheating. The difference is the big block of metal surrounding the heating element, it has more thermal mass and and spreads the heat more evenly than a lightweight kitchen hot plate can.
Many people prefer these to a reflow soldering oven because the PCB is exposed and you can tweak the component positioning on the fly. The downside is that the solder paste heat profiles can’t really be adhered to, at least without constant attention. Our strategy is to preheat the board to a lower temperature, then ramp it up to let the solder melt.
To demonstrate how it works, and compare to the reflow oven demo, we’ll use Sjaak’s RGB controller PCB as a test. We applied the solder paste with the solder paste dispenser, and manually placed the hand-full of parts on the board.
For more than one board you might speed things up with a solderpaste stencil. Generally the board and stencil require some kind of frame and unwieldy rig, but the Stencil8 board is a great alternative. Thanks to Arachnid Labs for arranging it.
We’re using ancient Mechanic Paste solder paste, a standard lead/tin mix. We’ll borrow from the reflow oven profile and start off at 180C. After the plate warms up the PCB goes on. After a few seconds it warms and the flux starts to activate. Now we crank the temperature to 240C and watch for the grey solder paste to melt into shiny solder.
When the plate reaches 240C we turn it off and let the board cool naturally for 10 minutes, like the natural cool phase of the reflow oven. After 10 minutes the board comes off, slightly charred. We probably cooked it a little too hot and long, but the result is perfectly usable.
This is way more involved than the reflow oven, and there’s always the looming hazard of an exposed hot metal plate to fall into. Overall we still prefer the reflow oven for one-offs, but definitely see the appeal of the hot plate in a small workshop.