Forward structure, materials from top to bottom are: P-GaN, luminescent layer, N-GaN, substrate. The light emitted from the active region of the forward structure is emitted through the P-type GaN region and the transparent electrode. The method adopted is to prepare a metal transparent electrode on P-type GaN, so that the current can spread stably and achieve the purpose of uniform light emission.

LED flip chip principle:

Filp chip technology is to use gold wire bonder to make two gold ball solder joints under the P and N poles of the chip as the lead-out mechanism of the electrode, and connect the outside of the chip with the Si backplane with gold wire. The LED chip is flip-chip connected to the silicon substrate through bumps.

The difference between LED front and flip chip is as follows:

1. Different die fixing: the front chip is fixed on the inner point of the reflection cup of the in-line bracket by insulating thermal grease, while the flip chip is mostly connected with the bracket base by silver glue or * * * crystal technology with higher thermal conductivity, and the bracket base itself is usually made of copper with higher thermal conductivity.

2. Different bonding wires: Generally, the driving current and calorific value of the pre-packaged chiplet are relatively small, so a gold wire with a diameter of 0.8 ~ 0.9 mil is welded to the anode and cathode of the bracket respectively. However, the driving current of flip-chip power chip is generally above 350mA, and the chip size is relatively large. Usually, two gold wires of φ 1.0 ~ φ 1.25 mil are welded between the positive and negative electrodes of the chip and the positive and negative electrodes of the bracket respectively.

3. The choice of phosphors is different: the driving current of the front chip is generally around 20mA, while the driving current of the flip chip is generally around 350mA, so their respective calorific values are very different during use. Under the condition of poor heat dissipation treatment, long-term use of phosphor will seriously age and decay, so it is suggested to use silicate phosphor with better high temperature resistance in flip chip packaging process.

4, the choice of colloid is different: the calorific value of small chips is small, so the traditional epoxy resin can meet the needs of packaging; However, the flip-chip power chip has a high calorific value and needs to be encapsulated with silica gel.

5. Different dispensing methods: The traditional way of covering the chip with the whole reflector is usually used in the packaging of the front small chip, while the flat-headed bracket is often used in the packaging process of the flip-chip power chip. Therefore, in order to ensure the uniformity of the whole phosphor coating and improve the luminous efficiency, it is recommended to adopt the conformal coating process.

6. Different casting molding: the front chip is generally filled with epoxy resin and then inserted into the bracket for high temperature curing; Flip-chip power chips need to be filled with silica gel slowly from one of the pores of the lens. The operation should be improved in the filling process to avoid bubbles, cracks and delamination after baking, which will affect the yield.

7. Different heat dissipation design: the front chiplet usually has no additional heat dissipation design; Flip-chip power chips usually need to add a cooling substrate under the bracket, and in special cases, a fan is added behind the cooling substrate to dissipate heat. In the process of welding the bracket to the aluminum substrate? Recommended power