An example, the 219C high-power LED from Nichia, is shown in figure 1. Small variations in the design of high-power LEDs can be found between one manufacturer and another, and even between different product families made by a single manufacturer.
Nevertheless, the basic recipe is almost universally followed. This is because it offers numerous advantages.
- The ceramic substrate is robust and large enough to be easily handled on the production line, and may be assembled on a luminaire’s PCB using a standard surface-mount assembly process.
- The substrate can accommodate a Zener diode to protect the LED against Electro-Static Discharge (ESD), which may be generated when the device is handled in the factory.
- The lens protects the chip and any bonding wires.
- The lens adapts the refractive index so as to maximise light extraction from the die.
- Larger ceramic substrates can accommodate multiple LED chips, providing a higher output from a single package.
OEMs which use high-power LEDs will be aware of certain drawbacks to this type of device. The substrate gives the device a relatively large board footprint – noticeably larger than the footprint of the chip alone. In addition, the lens has a magnification factor which has the effect of making the light source appear bigger than it really is.
Last but not least, the manufacturing cost of the complex package assembly tends to make the unit cost of a high-power LED higher than that of other LED types.