I've completed assembly of my first QMX kit. The instructions are extremely well thought out, and all went well.
However, during the final inspection prior to applying power, the inspection step 2.31.6 showed a very worrying thing on the buck regulator (you can actually see the same situation in the photo in the instructions):?
The power tab for Q103 extends out past the PCB pad, and actually overhangs the tinned pad for Q104. Although the actual Q104 pin is clear of the overhanging power tab, and I don't measure a short there, the tab and PCB pad are closer together than the thickness of a sheet of printer paper. The tiniest bit of conductive debris will short these points and destroy the unit.?
It's impossible to move the power-tab package, of course. I considered shaving off the edge of the Q104 pad to eliminate the overhang and improve spacing, but that would break continuity with other parts of that trace, so that's also a non-starter. I'm extremely concerned about the possibility of catastrophic failure from this almost-short. (In retrospect, I'm glad I didn't go ahead and wash the PCBs to remove the flux from my through-hole soldering, as that could easily have led to a short.)
The only other remedy I can think of is to apply a drop of thin cyanoacrylate glue to the gap as a conformal coating to isolate the tab from the pad. Does anyone know whether CyA glue is suitable or unsuitable for this application?
Going forward, I recommend adjusting the layout of the buck regulator for the next PCB run for the QMX to eliminate this issue. It has probably destroyed more than one apparently-sound QMX already...
Regards,
Steve
Steve H