kevinhub88 over at the Black Mesa Labs writes:
Black Mesa Labs has been using a $20 hot plate for a year now for soldering QFN ICs to PCBs. Only issue so far has been the size ( 10″x10″x3″ ) and thermal mass of the thing as it consumes precious microscope work area and unfortunately stays quite hot for 30+ minutes after a quick 4 minute reflow job. BML boards are mostly 1″x1″, so a 800W hot plate with a 6″ diameter heating surface is overkill for most jobs.
Wanting something much smaller for a typical BML PCB – stumbled across this 24V DC heating element on Amazon for only $14. It is rated for 24V at 5-7 ohms ( or 4.8Amps ). A surplus 19.5V DC 5A laptop power brick laying around BML seemed like a perfect match for this element. BML has safety rules avoiding designs above 48V – so the 100Watt 20V DC supply coupled with the 24V element seemed like a great way to make a lot of heat in a small surface area in a short amount of time.
Details at Black Mesa Labs project page.