soldering mk20 mk22 - power test problem

Rafael Ignacio Zurita rafaelignacio.zurita at
Mon Aug 31 22:42:39 UTC 2015

On Mon, Aug 31, 2015 at 12:18 PM, Werner Almesberger
<werner at> wrote:
> 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 :)

Still nothing :( I soldered all the VSS on the left side and bottom side.
But, VOUT33 still gives me 5v :( I have checked that there is not
short between pins.
>> 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.

Yes. I had. But it was powering the MCU with 3.3v from nanonote,
without using the internal regulator.

> 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.

No yet. There is not connection between vout33 and vdd.
I wanted to check the vout33 first, before to do those connections.

> 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
> station.
> 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
> joint.

I will save all these tips. Thanks Werner.

> 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.

It does not. At least when checking with tester. ANd I have
put 5v in vregin for a while using two sources in tests:
usb port and using 5v from a pc power supply.

It will be continued ...

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