2023-11-06
1. Fixed crystal: The front mounted small chip is fixed with insulating thermal conductive adhesive at the inner point of the reflection cup using a direct plug-in bracket, while the back mounted chip is connected to the bracket base using silver adhesive or eutectic technology with high thermal conductivity. The bracket base is usually made of copper with high thermal conductivity. 2. Welding wire: The front mounted small chip usually has low driving current and relatively low heat, and is welded with positive and negative electrodes φ 0.8~ φ Connect 0.9mil gold wire to the positive and negative poles of the bracket; The driving current of reverse power chips is generally above 350ma, and the chip size is relatively large. To ensure the uniformity and stability of current injection into the chip, the positive and negative electrodes of the chip are welded to the positive and negative electrodes of the bracket φ 1.0~ φ 1.25mil gold wire
3. Fluorescent powder selection: The driving current of the front mounted small chip is generally around 20ma, while the driving current of the back mounted power chip is generally around 350ma. Therefore, there is a significant difference in their respective calorific value during use. At present, the commonly used fluorescent powder in the market is mainly YAG, and the high-temperature resistance of YAG itself is around 127 ℃. After the chip is turned on, the junction temperature (Tj) will be much higher than this temperature. Therefore, in the case of poor heat dissipation treatment, the fluorescent powder will undergo long-term severe aging. Therefore, it is recommended to use silicate phosphors with better high-temperature resistance during the packaging process of reverse mount chips
4. Colloid selection: The front facing small chip has low heat, and traditional epoxy resin can meet packaging needs; The heat of the reverse power chip is high, and it needs to be packaged with silicone adhesive; In order to match the refractive index of the sapphire substrate, it is recommended to choose high refractive index silicone gel (>1.51) to prevent low refractive index from increasing the critical angle of total reflection, so that most of the light is completely reflected in the packaging colloid; At the same time, silicone adhesive has high elasticity, and compared to epoxy resin, its thermal stress is much lower. It can protect chips and wires during use, which is beneficial for improving the reliability of the entire product
5. Glue dispensing: The packaging of front facing small chips usually adopts the traditional method of dot charging the entire reflection cup to cover the chip. In the packaging process of reverse mount power chips, in order to ensure the uniformity of the entire fluorescent powder coating and improve the light output rate, it is recommended to use conformal coating technology
6. Glue injection molding: The positive chip is usually filled with epoxy resin in the particles first, and then the bracket is inserted into the high-temperature curing; The reverse power chip needs to slowly fill the silicon glue from the inlet hole of the lens. During the filling process, the operation should be improved to avoid bubbles and cracks that may affect the yield after baking
7. Heat dissipation design: Front mounted small chips usually do not have additional heat dissipation design; Reverse bonding power chips usually require adding a heat dissipation substrate under the bracket, and in special cases, adding a fan for heat dissipation; During the process of welding the bracket to the aluminum substrate, it is recommended to use a 30W constant temperature soldering iron with a residence time of 3S