Arfa Daily wrote:
Today, I had a biggish Trace Idiot cross my bench.

Sounds like the result of some kind of chemical assay...

0.3% Dummy
0.1% Fool
Trace Idiot

What I don't understand though, is how this production error can have
occurred in the first place.

I was going to blame a Chinese orphan having a bad day, but their Web
site says "Designed in Great Britain, assembled in the USA". Which is
an interesting division of labor.

However, the board looked like it had undergone flow soldering, and
had normal solder mask over it. But the unsoldered contacts for the
terminations were just naked tinned pads, so how could these have been
prevented from taking solder during the flow soldering process ... ?

Sometimes parts of the boards are taped off before they go through wave
soldering. If you dunked this whole board, some of the holes for the
ribbon cable would probably get filled with solder, which means somebody
would have to clean them out before they could install and hand-solder
the ribbon cable. Putting a piece of tape over the ribbon cable holes
means that they stay solder-free, ready for someone to hand-solder them
(or not, in this case). Another case would be something like a PC
expansion card, where the edge connector "fingers" would get taped off
before soldering.

3M has Kapton tape (5413 among others) that they specifically market for
this application and it's probably available from others as well.

Matt Roberds