1″ 100W hot-plate for SMT reflow

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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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3 Comments

  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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