Considerations for high-power LED packaging

For high-power LED packaging, the packaging method and corresponding materials should be selected according to the LED chip. If the LED chip has been flipped, it must be packaged by flipping; if it is a package that integrates multiple chips, it is necessary to consider whether the forward and reverse voltages of each chip are close, as well as the arrangement of the LED chip, the heat sink cooling effect, and the light output efficiency. The staff should perform actual operations based on the original design, make samples for testing, and then analyze them based on the test results. In this way, the best effect can be obtained through repeated experiments, and finally the packaging solution can be determined.

Heat sink material selection

Copper and aluminum are the best heat sink materials from both an economic and manufacturing perspective. However, copper and aluminum contain a lot of alloys, and the thermal conductivity of various alloys (see Table 1) varies greatly. Therefore, when choosing copper or aluminum as a heat sink, it is necessary to look at the specific alloy composition, which is conducive to determining the final heat sink material.

Table 1 Thermal conductivity of copper, aluminum and their alloys

Other materials can also be used as heat sinks, and the effect is also good. For example, silver or a layer of silver plated on copper will have a better thermal conductivity. Thermally conductive ceramics and silicon carbide can also be used as heat sinks, and the effect is also very good.

Since high-power LEDs generate a lot of heat after being powered on, and if the expansion coefficients of the glue and gold wire used for packaging are different, the gold wire will be broken or the solder joint contact resistance will be large during expansion, thus affecting the quality of the light-emitting device. It should be noted that the packaging glue will turn yellow due to excessive temperature, thus reducing the light transmittance and affecting the light output.

In general, when using high-power LEDs, you should consider transferring the heat from the heat sink to other radiators. You should also carefully consider and make necessary calculations (heat dissipation area) for the selection and installation of radiator materials. At present, radiators are generally made of aluminum or copper. There are two issues to note here: First, the bonding material between the heat sink and the radiator should generally be thermally conductive glue. If the surfaces of two objects are in contact, there must be air in the middle, and the thermal conductivity of air is very poor, so there should be a layer of thermally conductive glue between the interfaces to keep them in close contact, so that the thermal conductivity effect will be good. Second, the heat dissipation effect is related to the shape and orientation of the radiator.