LED production process, the whole process of LED production process!

1. LED chip inspection

Microscopic inspection: whether there is mechanical damage and pitting on the surface of the material (whether the size of the lockhill chip and the size of the electrode meet the process requirements and whether the electrode pattern is complete

2. LED expansion

Since the LED chips are still arranged closely after dicing, the spacing is very small (about 0.1mm), which is not conducive to the operation of the subsequent process. We use a chip expander to expand the film bonding the chip, so that the pitch of the LED chip is stretched to about 0.6mm. Manual expansion can also be used, but it is easy to cause undesirable problems such as chip drop and waste.

3. LED dispensing

Put silver glue or insulating glue on the corresponding position of the LED bracket. (For GaAs and SiC conductive substrates, silver glue is used for red, yellow, and yellow-green chips with back electrodes. For blue and green LED chips with sapphire insulating substrates, insulating glue is used to fix the chips.)

The difficulty of the process lies in the control of the amount of glue dispensed, and there are detailed process requirements for the height of the glue and the position of the glue dispensed.

Since silver glue and insulating glue have strict requirements on storage and use, the wake-up, stirring and use time of silver glue are all matters that must be paid attention to in the process.

4. LED glue preparation

Contrary to glue dispensing, glue preparation is to use a glue preparation machine to first apply silver glue to the electrode on the back of the LED, and then install the LED with silver glue on the back of the LED bracket. The efficiency of glue preparation is much higher than dispensing, but not all products are suitable for glue preparation process.

5. LED manual thorns

Place the expanded LED chip (with or without glue) on the jig of the piercing table, place the LED bracket under the jig, and use a needle to puncture the LED chips to the corresponding position one by one under the microscope. Compared with automatic racking, manual stabbing has an advantage that it is convenient to replace different chips at any time, and is suitable for products that need to install multiple chips.

6. LED automatic loading rack

Automatic mounting is actually a combination of two steps: dipping glue (dispensing glue) and installing chips. First, put silver glue (insulating glue) on the LED bracket, then use a vacuum nozzle to suck up the LED chip and move it, and then place it on the LED bracket. corresponding bracket position. In the process of automatic racking, it is mainly necessary to be familiar with the equipment operation programming, and at the same time to adjust the glue and installation accuracy of the equipment. Bakelite nozzles should be used as much as possible in the selection of nozzles to prevent damage to the surface of LED chips, especially for blue and green chips that must be made of bakelite. Because the steel tip will scratch the current diffusion layer on the surface of the chip.

7. LED sintering

The purpose of sintering is to solidify the silver glue, and the sintering requires temperature monitoring to prevent bad batches. The temperature of silver colloid sintering is generally controlled at 150°C, and the sintering time is 2 hours. According to the actual situation, it can be adjusted to 170°C for 1 hour. Insulating glue is generally 150 ℃, 1 hour.

The silver glue sintering oven must be opened every 2 hours (or 1 hour) to replace the sintered product according to the process requirements, and it must not be opened arbitrarily in the middle. The sintering oven should not be used for other purposes to prevent pollution.

8. LED pressure welding

The purpose of pressure welding is to lead the electrodes to the LED chip and complete the connection of the inner and outer leads of the product.

There are two types of LED bonding processes: gold wire ball bonding and aluminum wire bonding. The picture on the right is the process of aluminum wire pressure welding. First press the first point on the LED chip electrode, then pull the aluminum wire over the corresponding bracket, press the second point and tear off the aluminum wire. In the gold wire ball welding process, a ball is burned before pressing the first point, and the rest of the process is similar.

Pressure welding is a key link in LED packaging technology. The main process needs to be monitored is the shape of the pressure welding gold wire (aluminum wire), the shape of the solder joint, and the tension.

9. LED sealant

There are three main types of packaging for LEDs: gluing, potting, and molding. Basically, the difficulty of process control is air bubbles, lack of material, and black spots. The design is mainly about the selection of materials, and the selection of epoxy and brackets with good combination. (Ordinary LEDs cannot pass the airtightness test)

9.1 LED dispensing:

TOP-LED and Side-LED are suitable for dispensing package. Manual dispensing packaging requires a high level of operation (especially for white LEDs). The main difficulty is the control of the dispensing volume, because epoxy will thicken during use. The dispensing of white LEDs also has the problem of chromatic aberration caused by phosphor precipitation.

9.2 LED potting and encapsulation

The package of Lamp-LED adopts the form of potting. The process of potting is to inject liquid epoxy into the LED molding cavity first, then insert the pressure-welded LED bracket, put it in an oven to let the epoxy cure, and then take the LED out of the cavity to form.

9.3 LED molded package

Put the pressure-welded LED bracket into the mold, close the upper and lower molds with a hydraulic press and vacuumize, put the solid epoxy into the entrance of the glue injection channel and press it into the mold rubber channel with a hydraulic ejector rod for heating, and the epoxy will flow smoothly The glue channel enters each LED molding groove and is cured.

10. LED curing and post-curing

Curing refers to the curing of encapsulated epoxy, and the general epoxy curing condition is 135°C for 1 hour. Molded packaging is generally at 150°C for 4 minutes. Post-curing is to fully cure the epoxy while thermally aging the LED. Post-curing is very important to improve the bond strength of the epoxy to the support (PCB). General conditions are 120°C, 4 hours.

11. LED rib cutting and dicing

Since LEDs are connected together (not single) in production, Lamp packaged LEDs use rib cutting to cut off the ribs of the LED bracket. SMD-LED is on a PCB board and needs a dicing machine to complete the separation work.

12. LED test

Test the photoelectric parameters of LEDs, check the dimensions, and sort LED products according to customer requirements.

13. LED packaging

Finished products are counted and packaged. Ultra-bright LEDs require anti-static packaging.