Good morning all,
Lately we have run into several situations where it appears the old tried
and true polarity marking conventions for capacitors and diodes no longer
apply on SMT parts. The customary silkscreen "+" to denote the anode end of
the device appears to still be in use. However, the actual part marking
(band, or dot, or chamfered edge or other polarity key) is now showing up on
either the anode or the cathode, depending on how the OEM or supplier
decides to mark the device. It has become necessary to question each
polarized placement of a SMT diode or polarized capacitor when setting up
assembly instructions or programming pick & place profiles.

So, what happened to part marking convention in this regard? I don't believe
any marking changes have taken place in the plated through hole world in
regard to diodes and caps. But suppliers of the SMT versions of these
devices are not necessarily following any marking conventions. They appear
to simply mark the device in the manner they find acceptable, then define
the marking (if you're lucky) in their data sheets. Doesn't help much once
the parts are placed incorrectly and the inspection team thinks they are
placed correctly per the visual part markings that have been a standard over
the years.

Is there any movement afoot to get some industry standardization of SMT part
polarity markings in place? Maybe through SMTA? If so, I'd like to join the
effort to make sure some standardization occurs in this area.

Thanks for your feedback in advance!
Dale Ritzen
Quality Manager
Austin Manufacturing Services

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