Sticker Brings The Heat

[Carl] is always looking at making heater plates for PCB reflow and other applications. In his latest video, he shows how he is using thin flexible PCBs with adhesive backs as stickers that get hot. You can find gerber files and design files on GitHub.

You might think that this is a pretty simple thing to do with a flex PCB, but it turns out while the PCB might be flexible, the traces aren’t and so the typical long traces you see in a heater won’t allow the sticker to bend, which is a problem if you want to wrap it around, say, a coffee mug.

The answer was to create a pattern where the traces change direction frequently, and that’s what [Carl] did. He also talks about using stiffeners around the edges of the board.

The video shows quite a few tests that indicate the substrate discolor after a long time with high heat. The adhesive also tends to melt in those conditions. So the recommendation is to use them where you need lower temperatures for a long time or higher temperatures for a short duration. Of course, depending on your application, the color change may not matter as long as it doesn’t affect the long-term reliability.

What would you do with a flexible heated sticker? The self-warming mug is a no-brainer. A sticker to put on exposed pipes for a cold day comes to mind. A thin 3D printer bed heater or an irregular-shaped reptile habitat might be useful, too.

As long as you are putting patterns in any way, we wondered about making thermal digits on a sticker like this. It seems like every time we check in on [Carl] he’s heating up something.

17 thoughts on “Sticker Brings The Heat

    1. I think there’s hundreds of products for that purpose already. Mostly textile with velcro and stuff like that.
      Regarding the sticker itself: The idea of course isn’t new. Self-adhesive PEI or silicon heat mats can be bough of many manufacturers. Just search for “self adhesive heating film”…

      Anyway, if you need a custom heating film the above method would of course be king…

    1. No video here either, but the image at the top of the article seems to imply the resistance is 0.7536 ohms.
      Measured with a two-wire connection through alligator clips, no less!
      Never mind the 0.1 milliohm claimed precision, I don’t think I’d have faith in the precision of even that first significant digit (0.1 ohm).

        1. 200 W is a lot of power in 10 cm square. That’s 4x the power density of mine, and mine happily gets to 110 C in less than 10 minutes. 2 W/sq cm will make toast.

          I wonder if it’s more like 5V, 7A. Though that’s not much — about the same power density as another printer of mine that only gets up to 60 C.

          Sad that the info is probably locked up in a video.

  1. I’d be using this for germination pots or wraps. I live in the PNW and love growing peppers and tomatoes, but the warmth needed to grow great peppers far exceeds our *cough cough* Mediterranean climate production – at least for the next ten years, anyway.

    Being able to wrap a heating panel on or around a 5-8 gallon planter in a lightbox with soil sensors would allow me to grow peppers at exactly the right temperature year-round regardless of the weather, and do so using nothing but power from the solar panels that run beautifully in our 45-50 degree winter weather.

    Now just to find the perfect ceramic pot with space for the electronics.

  2. Adhesive engine block and car battery heaters are a lot cheaper per square cm than flex PCB. And available off the shelf in auto parts stores, tractor supplies, and walmarts in close proximity to just about everybody.

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