Report 2016-12-24 15:04
LED packaging basically provides mechanical, electrical, thermal, and optical supports to LED chips. In frequently used LED packaging processes, the LED die is assembled to the substrate by flip chip bonding, wire bonding or eutectic bonding. In the wire bonding, gold wires are employed to electrically connect the electrodes of the LED die and the substrate to apply a bias across the doped layers, injecting holes and electrons into the active layer where they recombine to produce light. It is challenging to reduce the operational temperature of the LEDs due to the fact the light emitting layer is disposed relatively far away from the package base and the impedance of heat conduction is comparatively high. For this reason, a structure of flip-chip LED package is provided to make the LED chip connect directly with the connecting pins of the positive and the negative electrodes which are located on a bottom surface of the LED for direct bonding to metal pads on a submount. In this manner, there are no top contacts that block the light, thereby conventional metal wire bonding is not needed and the package area can be reduced effectively. The flip-chip bonding has many advantages, including improved thermal heat sinking and reduction of electrode shadowing losses. This means that the reliability of the LED can be enhanced substantially. In terms of packaging technique by flip-chip bonding, chip-scale packaging (CSP) technology has been developed for the purpose of miniaturization.