Electronics > Beginners

Why do SMT capacitors have no markings?

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wraper:

--- Quote from: tooki on May 12, 2019, 01:16:13 pm ---Why would it not work? You can inkjet print onto essentially any substrate.

--- End quote ---
Printing on ceramic a way that it will survive reflow and washing? Unless it involves additional heat treatment stage, I don't think such marking will last.

T3sl4co1l:
Epoxy or enamel ink would be the way to go.

I wonder also if it's complicated by manufacture variation: are they able to produce values accurately at low reject rate, or is there selection done?  If the latter, marking would have to be done as a final step, which sucks.

Handling also matters.  Caps may be handled loose, in the production or shipping process.  Which side is "up", isn't really obvious after that.  Non-square parts should be easy enough to sort through the handling process, but square parts, dunno.  If this is a key part of the process, it may simply not be worth keeping parts neatly taped and everything.

Whereas resistors are fabbed on ceramic plate, which certainly can't be handled or mounted sideways (at least, not nearly as easily), and they can only be laser trimmed from the same orientation.

Tim

wraper:

--- Quote from: T3sl4co1l on May 12, 2019, 03:17:26 pm ---Epoxy or enamel ink would be the way to go.

--- End quote ---
Which won't fly on already made individual components 30 seconds away from testing and packing. You cannot apply marking before final process stages, but by then it becomes pain in the ass just as I said before. Storing them for curing in particular orientation as they will go into a reel is not trivial.

Ian.M:
They could be printed with a fireable ink (metal oxide pigment + frit) in between tumbling for corner rounding, and the final firing to sinter the terminations.   However that doesn't address Wraper's point about orientation, or T3sl4co1l's point about select on test for possible tolerance binning.  The only remaining practical option that addresses those issues would be  lazer marking immediately before application of the cover tape.  However the industry has had 30 years to get used to unmarked SMD ceramic caps, so bulk customers who would be willing to pay extra for marked caps are IMHO vanishingly rare.

tooki:

--- Quote from: wraper on May 12, 2019, 01:55:00 pm ---
--- Quote from: tooki on May 12, 2019, 01:16:13 pm ---Why would it not work? You can inkjet print onto essentially any substrate.

--- End quote ---
Printing on ceramic a way that it will survive reflow and washing? Unless it involves additional heat treatment stage, I don't think such marking will last.

--- End quote ---
They make solvent-resistant inks. Industrial inkjet is NOT the same as what we have at home! This is what is already used on some Bourns-style trimmers, for example. Remember, pretty much any reasonably thin liquid can be used as ink in a piezo-type inkjet head. This means there are a LOT of ink possibilities. (Like, you know how they make solvent-resistant permanent markers? This is no different!)

Another option is UV-cure lacquer inkjet. I would be surprised if this isn’t already used on electronic components, too. This could easily be done with the caps in their wells in the tape, just before the sealing film is applied. Literally just needs about a foot of space along the line. Bright UV light cures the lacquer literally instantly.

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