Why service print on mass-produced PCB

If a pcb is manufactured totally by machine... and has been designed to be disposable upon failure... then there is no valid reason I can think of for using a silk screen. Are you assuming the pcbs you have looked at were not meant to be repaired?

Hopefully that's because you're trying to save costs? :-) Silkscreens are definitely convenient...

Because your assumption that the boards are all machine assembled is probably wrong. Most PCBs are still touched by human hands for some manually inserted components, *especially* in high-volume markets where labor is cheap compared to the very specialized robots you need for "odd" shaped parts. See:

That being said, I imagine that the reason silkscreens are still so ubiquitous is largely due to convention and determining that -- in high volumes -- the price perhaps still is negligible.

Joerg -- do your products all end up with silkscreens?

---Joel

It could help in quality control - even if actual assembly is automatic, if there is a problem with a resistor placement it would be nice to know it is R234.

The MFE types like to take samples that have been rejected and figure out why, to see what process improvements they can make to improve yield. I'll bet that if you're printing _anything_ on the board there is little or no cost differential to printing the reference designators.

Others suggested why do it at all, and it reminded me of an ad I just saw, for a 'Infinity-ohm' SMT resistor with 2-D barcode, soldered to some extra SMT pads. The purpose was to identify a specific stuffing run (more precise designation than silkscreening on a bare board, and doesn't require a different machine like stick-on labels---plus it's less likely to peel off).

When PC motherboards fail in warranty they go back to the factory... and often come back as "refurbished".

The silkscreen often also has useful stuff, like model number, labels for the various pin headers etc.

Bye. Jasen

There's probably more cost in the addition of the silk layer at layout (necessary for prototype testing) than in the cost of retooling at the fab house plus the cost of printing for runs in many 10s of K.

Once it's on there, why take it off might be another part of the answer.

Cheers

PeteS