1. Chip inspection
Microscopic examination: whether there is mechanical damage on the surface of the material and the lockhill chip size and electrode size is in line with the process requirements whether the electrode pattern is complete.
2. Expanded film
Because the LED chip is still arranged closely after the dicing, the pitch is small (about 0.1 mm), which is not conducive to the operation of the subsequent process. We use a splicing machine to expand the film of the adhesive chip, and the distance between the LED chips is stretched to about 0.6 mm. Manual expansion can also be used, but it can easily cause problems such as chip drop and waste.
3. Dispensing
In the corresponding position of the LED bracket, silver glue or insulating glue. (For GaAs, SiC conductive substrates, red, yellow, and yellow green chips with backside electrodes, silver paste is used. For blue and green LED chips on sapphire insulating substrates, an insulating adhesive is used to fix the chips.)
The difficulty of the process lies in the control of the amount of glue dispensed. There are detailed technical requirements for the height of the colloid and the location of the dispensing. As silver paste and insulating glue have strict requirements in storage and use, silver glue's waking, stirring and using time are all matters that must be paid attention to in the process.
4. Prepare rubber
Contrary to dispensing, the glue is prepared by firstly coating the silver paste on the back electrode of the LED with a stocker, and then mounting the LED with the silver paste on the back to the LED support. The efficiency of stock preparation is much higher than that of dispensing, but not all products are suitable for stock preparation.
5. Manual thorns
The expanded LED chip (prepared or not) is placed on the fixture of the puncture table. The LED pedestal is placed under the fixture and the LED chip is punctured one by one under the microscope to the corresponding position. The advantage of hand-piercing and automatic mounting is that it is easy to replace different chips at any time. It is suitable for products that require multiple chips.
6. Automatic loading
Automatic racking is actually a combination of glue (dispensing) and the installation of the chip in two major steps, first on the LED bracket on the point of silver plastic (insulation glue), and then use a vacuum nozzle to suck the LED chip moving position, and then placed in The corresponding bracket position.
The auto-loading process mainly needs to be familiar with the operation and programming of the equipment, and at the same time, it adjusts the glue and installation accuracy of the equipment. Choose bakelite nozzle as much as possible to prevent damage to the LED chip surface, especially blue and green chips must use bakelite. Because the steel nozzle scratches the current diffusion layer on the chip surface.
7. Sintering
The purpose of sintering is to cure the silver paste. The sintering requires monitoring of the temperature to prevent batch defects. Silver paste sintering temperature is generally controlled at 150 °C, sintering time of 2 hours. According to the actual situation can be adjusted to 170 °C, 1 hour. Insulation glue generally 150 °C, 1 hour.
The silver gel sintering oven must be opened for replacement of the sintered product every 2 hours (or 1 hour) according to the process requirements. Sintering ovens must not be used for other purposes to prevent contamination.
8. Pressure welding
The purpose of pressure welding is to lead the electrode to the LED chip to complete the connection work of the inner and outer leads of the product.
LED pressure welding process gold ball welding and aluminum wire welding two. The figure on the right shows the process of pressure welding of aluminum wire. First press the first point on the LED chip electrode, then pull the aluminum wire to the top of the corresponding bracket, and cut the aluminum wire after pressing the second point. The gold ball welding process burns a ball before pressing the first point, and the rest of the process is similar.
Pressure welding is a key part of LED packaging technology. The main process to be monitored is the shape of gold wire (aluminum wire), the shape of solder joints, and the tensile force. The in-depth study of the pressure welding process involves many issues, such as gold (aluminum) wire material, ultrasonic power, pressure welding pressure, selection of file (steel nozzle), boring knife (steel nozzle) motion trajectory and so on.
9. Dispensing package
LED packaging is mainly a little plastic, potting, molding three. Basically, the difficulty of process control is air bubbles, lack of material, and black spots. The design is mainly for the selection of materials, choose a good combination of epoxy and stent. Manual dispensing packages require high levels of operation (especially for white LEDs). The main difficulty is the control of dispensing volume, as the epoxy thickens during use. White LED dispensing also has the problem of precipitation of phosphors that causes color differences.
10. Plastic encapsulation
The Lamp-LED package is encapsulated. The process of potting is to inject the liquid epoxy into the cavity of the LED mold first, then insert the pressure-welded LED bracket into the oven to allow the epoxy to solidify and then remove the LED from the cavity.