How to distinguish the positive and negative poles of SMD ...

Many packages, like some 0603, 0805 and other SMD LEDs, will have a green "T" symbol on the bottom. One horizontal side of the "T" is the positive pole, and the other side is the negative pole. Some SMD LEDs will be marked with a silk screen similar to a triangle symbol, so the bottom side of the triangle is close to the positive pole, and the top corner is close to the negative pole. The lead of the light-emitting diode is generally longer at the anode and shorter at the cathode. Observe the shape of the two lead wires inside the tube from the side, the smaller one is the positive electrode, and the larger one is the negative electrode. Set the multimeter to the “ohm x1” position. When the diode is emitting light, the red test lead is connected to the positive end of the SMDLED, and the black test lead is connected to the negative end of the SMDLED. Because the LED turn-on threshold is about 1.5-1.8V. It is possible that the voltage provided by the digital multimeter cannot start it. So still look at the mark. SMD LEDs have a green dot as the negative electrode and the opposite one as the positive electrode.

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SMD LEDs normally have some kind of marking like the following image from here indicates:

The site states

The CATHODE lead is always the lead to be identified with ALL LEDs, including surface-mount LEDs.

There are definitely manufactures that do NOT follow this scheme like this one from CREE.

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We recently had 300 PCBs manufactured where each had 32 LEDs of those. However, the assembly house placed all LEDs in reverse. The first thing we obviously did was looking at our board layout.

If you assume that always the cathode is indicated, the footprint is correct. However, it is not consistent with the marking of the actual LED that was mounted. The manufacturer probably just looked at the matching markings.

Long story short, the manufacturer checked their production and "admitted" that it was their fault. Actually, we worried that they just "but the marking says otherwise".

This could have ended up in a long discussion about who's fault this was, so:

Is there a standard that defines that the marking actually HAS TO indicate the CATHODE? Has the assembly house to double check something like this?

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