Miniware Mini Hot Plate (MHP30)

The latest addition to my toolkit is a mini hot plate designed for electronics work at a small scale. This is the Miniware MHP30, purchased from Adafruit as their product #4948. Emphasis of this product is on “small”, as the actual heating area is a square only 30cm (approx. 1 1/4″) on a side. The hot plate unit itself is dwarfed by its power supply that came in the same box. This is a USB-C supply that, through the magic of USB Power Delivery protocol, can deliver up to 65 Watts. (20V @ 3.25A)

I believe MHP30 was designed for reworking surface mount electronics, focusing energy just on the portion of the board that needed fixing. I’ve wished for this kind of capability in the past, for example when I wanted to remove a voltage-divider resistor. I bought a hot-air rework station which was useful, but I was sometimes stymied by boards with a large heat dissipating ground plane. I found that I could help my hot air gun by heating up circuit boards with an old broken clothes iron. That experiment represented a bluntly crude version of what this little focused heating plate promises to do.

The first test run was to remove an already-ruined LED module from a dead LED bulb. I tried to remove this LED with a hot-air gun. Not the small electronics hot-air rework station kind of hot-air gun, one of those big units sold for paint stripping. Now armed with the proper tools, I could successfully remove what remained of this LED module.

The next test was more challenging. I wanted to see if this hot plate could heat up multiple legs of a through-hole part allowing me to pull it from a circuit board and do so without damaging the more heat-sensitive plastic portions. The test subject was a DC power barrel jack from a dead Ethernet switch.

One reason this is difficult is due to the air gap caused by the through-hole legs, which would let heat escape instead of melting solder. I declared this test a failure when the black plastic started melting before the solder did. I have other means to salvage through-hole parts, but I had hoped this would make things easier. Oh well.

Returning to surface-mount components, I wanted to try removing the CPU on this dead Ethernet switch. This would have been difficult with the hot-air gun alone, because most of the heat would be absorbed and quickly dissipated by the black heat sink glued to the chip.

The bottom of the chip is connected to the ground plane of this circuit board, which is a layer of copper occupying nearly the entire circuit board. If I only used hot air gun from above, heat would never get past the glued-on heat sink to this area.

But if I heat from below with the mini hot plate, things heat up enough for the heat sink glue to degrade. Once the heat sink was pulled off, things moved much more quickly.

The mini hot plate sends heat directly into the large heat conducting pad in the middle of the chip, melting the relatively large square of solder in addition to all little pads around chip perimeter. I don’t think I could have done this without the mini hot plate. This test was successful, but we had the advantage of a singled-sided board with no components on the bottom. If there were, then the air gap problem would return. It isn’t a complete answer, but I’m happy to have added the little hot plate to my toolbox.

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