Mitochondrion Mark 5.0 progress

The power output for the next version of the Mitochondrion glow staff is approaching the level you’d use for an electric bike, hence I’m taking battery management seriously. The current plan is to use a dedicated battery level gauge chip. The Linear LTC2943 looks like it will do the job, except it is 3 mm square, with no legs to solder to, just tiny pads under the chip. It’s designed to be soldering in factories with proper kit, not by a muppet like me with a soldering iron.

So WTH, watch a tutorial, mount my phone as a microscope, flip the chip on its back and deadbug it to a breakout board. How hard could that be?

Really quite hard, it turns out. Got there in the end though.

I know, it doesn’t look great, but it checks out. Everything that should be connected is and everything that shouldn’t be isn’t. I’ll test that the chip is actually working once a few other bits arrive.

4 thoughts on “Mitochondrion Mark 5.0 progress

  1. I don’t know what sort of soldering kit you have. When I have to solder down QFN’s/LLP’s, I put a roughly 1mm long clip of solder on each of the pads, put a dot of solder on the dap that stands higher than the pads, and then put the chip on that, and put the whole works on a hotplate. When the chip stops rocking, the DAP is molten, and it’ll drop down onto the pads. Then, diode-check between each of the pins and the DAP, which should show continuity, and if one is open — oh, important preparatory note, make the pads about 3mm long, way longer than the package would need — I use a Metcal sharp tip, with a nose diameter of about 0.1mm (I’ll find the number, it’s one of the four-digit ones) which is small enough to touch just that one pin. On some LLP’s there is a slight side view of the pins, and that’s way easier, but even if there isn’t, generally I can solder just one pin, typically by putting a bit of solder on the pad and then pushing it along the pad up against the side of the package, (viewed under a scope) at which point it’ll bridge to the pad.
    Huge pain, no doubt, but I’ve put down a couple hundred 40 pin LLP’s this way, with about a 80% first pass success rate, and with the diode drop test, followed by continuity test, I can at least not fry anything.

    1. (with that said, I do love the dead bug approach. For an eight pin it’s definitely easier, faster, and probably more reliable.)

      1. Sadly no hotplate here. In fact, I’m almost thinking I should get around to buying a half-way passable soldering iron, rather than the $18 one I have.

        And yeah, I’m not going to try anything more complicated than an 8 pin with this.

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