1″ 100W hot-plate for SMT reflow


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.

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  1. Nice small heating element. That small board with dual MOSFETs for doing the 100W PWM looks nice, wonder if it might be made available for purchase on Tindie etc.?

  2. I got one myself. Resistance is 4.3 ohms cold (23 C) and rises to about 10 ohms at 300 C. Driving it with a constant 2.5 A, it goes from 23 C to 300 C in just under 60 seconds and it takes 15 V at 1.53 A to maintain 300 C steady state. These measurements are with a fine-wire thermocouple attached with kapton tape, and with the element hanging from the leads in still air, not otherwise touching anything. I was able to use it to reflow solder on a small test PCB (but then quickly burned the board on the bottom side, due to a too-fast too-hot temperature ramp)

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