SMD LEDs are small, compact light-emitting diodes that can be mounted directly onto printed circuit boards using surface-mounted technology ( SMT
). SMD LEDs are rectangular or square. As with other SMD components
, the edge lengths are included in the type designation. The specifications are given in tenths of a millimetre.
If the type designation of an SMD-LED is for example 3528, the edge lengths are 3.5 mm x 2.8 mm. The smallest SMD LEDs are 0.4 mm x 0.2 mm, well below 1 mm, while the largest and most powerful SMD LEDs can be 5.6 mm x 5.0 mm or even larger. To ensure that SMD LEDs are not installed incorrectly in production, they have an external marking of the negative electrode. This can be a green color bar, a dot or a notch.