Diode Silk Screen Markings

It still happens. In fact, it just happened last night. We had a PCB with plus (+) mark to indicate the polarity of a diode. Unfortunately, that doesn't tell us which way to put the diode. (Read why here).

You just can't always tell. If it's a barrier diode or a zener, the cathode might very well be the positive side. Or, it could be the negative side. An LED will usually have the anode positive, but again, there may be a few scenarios where it's not. The bottom line is that a plus (+) or minus (-) sign doesn't give us enough information to orient the diode.

We prefer that you use the actual diode symbol, or an industry standard anode or cathode indicator. "A" or "C" for anode or cathode can also work. Just make sure you also put the reference designator (D1, D2...) so we know it's not a capacitor.

In the job last night, the build instructions were conflicting so we called and with the help of the designer, figured it all out, but it's always best to do it right the first time. So be clear with your silk screen, the PCB you save may be your own.

Duane Benson
Spider or worm?

Comments

[Billig Webhotell]

Good point. This is the whole point of the diode. If you don't know which way it is supposed to sit, you will screw it up. Strange thing that manufacturers didn't think about this. Thanks for sharing:-)- Ray

[Duane Benson]

Andrew - I just fixed the link. We did some site upgrades recently and apparently moved some things. I'll have to spend some time perusing for more broken links here.

[Andrew]

Just so you know, the link in the article is broken.

[Jack Olson]

Good point, and not addressed often enough!
Here’s some additional information that may help someone interested in the subject:

http://frontdoor.biz/PCBportal/ResolvingComponentPolarityProblems.pdf