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Quick question about device.


Daniel Fox 2021/11/18 13:48

I borrowed this unit and on switching it on I was greeted with this screen.  Nanovna saver immediately closes when I try to connect to the device.  Any quick fixes or is it a lost cause?

stevenmclark1 2021/11/18 20:00

Hi Daniel,

I had a similar issue with the NanoVNA v2 Plus4's that I bought recently. I bought 22 for a class and I'm working my way through each beautiful unit!

I found that the assembly house had some trouble with the QFN's in that the solder joint quality was not great.

I was able to fix them by putting some flux around each of the QFN's and just touching the joints with my iron.

As I did this, I could see the solder wick under the pads and make a nice joint. I did *not* have to apply any additional solder; just this local "reflowing" was sufficient.

I did all this under my microscope since I have trouble seeing these little things without magnification.

Oh, I used some "water-soluable" flux and cleaned and dried the boards when I was done with the local reflowing.

I hope that helps!

All the best-
Steve

OwO 2021/11/19 05:41

You can also message the seller for a warranty replacement. All units are tested before shipping, but there is the occasional solder defect that only shows up after shocks from shipping.
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OwO 2021/11/19 06:51

You don't need to reflow the soldering on all of the units, only the one that is broken. Lead free soldering can look dry but that is just the way it looks.

The chips to reflow are U401 and U601.

stevenmclark1 2021/11/19 20:36

Right, but since I need to open the case to install batteries, I will just take a second to do this touch up.

The reason I think this is just a solder profile error (the solder doesn't quite get to liquidus) is that I am two for two on this and they did such a lovely job when they put the paste down. For some folks that don't take the time to run a profile or a test board, QFNs can be "touchy". And I "get it" that it isn't worth X-raying each board since that wouldn't be cost effective. I only insist on X-ray inspection for BGAs and only because I do short runs and I can't afford basically any scrap. Mutter, mutter.... BGAs, mutter...

You are, of course, correct about the visual difference between popular lead-free solders (such as SAC 305) and lead bearing solders (e.g., 63/37), but I think I'm "tuned-in" on this since I converted all our lab classes to lead-free solders and I have been teaching our students to solder with lead free solders for about 6 years. I also explain to the students that are new to building electronics for space, that leaded solders are the way of truth and light because they withstand shock and vibration better and electro-migration isn't a problem we want on a satellite, etc.

I would also make the comment that I'm *not* putting the boards in my reflow oven because I don't want to damage components that won't withstand a reflow cycle. Duh.

I'm not complaining. For me it isn't too bad, kind of a "zen" sort of thing while I'm decompressing from other stuff.

Thanks though! I appreciate your thoughts and kind intent!

All the best-
Steve

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