The purpose of this application brief is to show a method to determine the maximum permissible power dissipation of the LEDs in a display application, and allow the junction temperature (T_J) to remain below its rated value. Junction refers to the p-n junction within the LED.

In recent years, advancements in the area of optoelectronics due to the deployment of new semiconductor materials in the manufacturing of LEDs have permitted a diversity of color and increased levels of brightness to be achieved. LEDs and LED modules have recently been produced which can be used as a replacement for conventional light devices such as light bulbs and fluorescent lights in many application areas. Backlighting of TFT monitors, for example, was previously accomplished by the use of cold cathode fluorescent lamps (CCFLs). Due to the disadvantages of CCFLs regarding their white balance, spectral distribution and low mechanical strength, new bright light diodes have been considered as a replacement to CCFLs.

SMT Replaces Through Hole Technology.

The use of SMT-TOPLED varies greatly from the use of traditional through hole LEDs. Historically through hole LEDs have been incorporated directly into front panels using the leads as a stand off. Due to the automated nature of SMT assembly, and the size constraints of SMT components and assemblies, SMT-TOPLED applications are different from through hole applications.

What is Surface Mounting? In conventional board assembly technology the component leads are inserted into holes through the PC board and connected to the solder pads by wave soldering on the reverse side (through-hole assembly). In hybrid circuits (thick and thin film circuits) ìchipsî, i.e. Ieadless components, are reflow soldered onto the ceramic or glass substrate in addition to the components already integrated on the substrate. Surface mounting evolved from these two techniques.