soldering mk20 mk22 - power test problem

Werner Almesberger werner at
Mon Aug 31 15:18:18 UTC 2015

Rafael Ignacio Zurita wrote:
> Is it needed all the VSS
> soldered before this kind of test?

It certainly can't hurt. I don't know how they connect internally,
but at least all the VSS on the left side (pins 2, 11, 12) should
be connected to ground. (And connecting pin 23 won't be much of an
effort either :)

> Should I put capacitors first before test?

It can't hurt either. Didn't you have that problem a while ago
already ? I.e., that you didn't have capacitors and the chip
performed erratically.

Also, is your MCU actually powered ? There doesn't seem to be a
direct connection between VOUT33 and VDD*, so I don't know if
you're even in a defined state.

Regarding soldering, the solder will flow towards hot surfaces. So
you don't need to heat up a single pin at a time but you can heat
up several pins at once. Plus, make sure you also heat the pad
under the pin. Only then will you get a proper solder joint.

I usually solder QFNs and such in two passes: the first pass is to
just establish enough solder joints, no matter how untidy, that
the chip stays in place. The second pass is to reflow the areas
where things didn't work out. In the second pass, I can add or
remove solder.

Also make sure your iron is hot enough. If it's just at the point
where solder will melt, it will get too cold as soon as you touch
something. A range of about 280 C to 300 C should be good, but
you'll have to find what works best with your iron and your

Unless you've cranked up the heat far too high, you also don't
have to be in a rush to remove the iron from a solder joint. You
have to keep it there long enough to fully melt the solder and to
fully heat pin and pad. Only then will you get a good solder

Another thing to check is that VOUT33 doesn't accidently make
contact with VREGIN. Also, the regulator may need a minimum
external load of a few uA before it actually can regulate.

- Werner

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