Pick'n'place'd wrong

Well, it's been a while since last posting. I'm a bit short on ideas right now but maybe I'll think up something more interesting soon.

Now, on lighter note. Today electronics is typically assembled by large 'pick and place' machines, and they really are fascinating to watch when going at full speed. Sometimes of course accidents happen - components are dropped (although I think modern machines note this and place them again), components placed in wrong way (just slightly skewed, or rotated 90 or 180 degrees so at quick glance you won't notice anything wrong) and end result is non-working (or in worst case, burned) board.

As it happens, sometimes they get through the first inspection. This is why I test every single device I deliver myself before packaging it for delivery (volume isn't that high so it isn't too much strain). Typically defects aren't anything exciting - component missing, bad solder joint or whatnot. But sometimes they get... interesting.

Take your typical SOT23-3 package, pictured here. It has three leads and isn't even symmetrical. It should not even be possible to place it on board wrong, at least in a way that would pass visual inspection.

The device I had on hand failed one certain test, so I started checking the section of the board that might be responsible for the problem. I'll always start with visual inspection with microscope, and when passing by certain component in SOT23-3 package something seemed odd. I couldn't instantly figure out what, exactly it was so I picked the board up and started viewing it from angle. That's when I started to see it...

(No, it wasn't the board or component pictured above; picture here is simulated situation. And unfortunately not very good picture either, sorry about that)

Component was upside-down, leads pointing up from board and thus not even touching the pads. No wonder it didn't work right. I had to laugh for that (which immediately prompted dry "guess he found the problem" from next desk)

How? This specific board was flow-soldered, which means that every component is glued in place with a small dab of glue and then dipped (upside down, hence the glue - otherwise components would fall out) in molten solder which will solder all components. The problem with that technique is that sometimes some leads are left without solder which in real PITA - module passes all tests but then starts acting out several months after delivery when component shifts ever-so-slightly.

Oh, and after flipping the component over it worked perfectly, and for what I know the device is still in use somewhere.