A. cleaning: cleaning PCB or LED bracket with ultrasonic wave, and drying.

B, mounting: after preparing the silver glue on the bottom electrode of the LED die (wafer), expanding, placing the expanded die (wafer) on the crystal thorn table, mounting the dies one by one on the corresponding pads of the PCB or LED bracket with a crystal thorn pen under a microscope, and then sintering and curing the silver glue.

C, pressure welding: an aluminum wire or a gold wire welder is used as a lead wire for current injection, and the electrode is connected to the LED die. When LED is directly mounted on PCB, aluminum wire welder is generally used. (Gold wire welder is needed to make white top LED)

D, packaging: the LED die and the bonding wire are protected by epoxy resin through dispensing. Dispensing glue on PCB has strict requirements on the shape of cured glue, which is directly related to the brightness of finished backlight. The process will also undertake the task of lighting phosphor (white LED).

E. Welding: If the backlight is SMD-LED or other packaged LED, the LED needs to be welded to the PCB before the assembly process.

F, film cutting: punching various diffusion films and reflective films required by the backlight with a punch.

G. Assembly: According to the requirements of the drawings, manually install various materials of the backlight in the correct position.

H test: check whether the photoelectric parameters and light uniformity of the backlight are good.

G. packaging: the finished products are packaged and put into storage as required.

2. Process flow

Task: Connect the external lead to the electrode of the LED chip to protect the LED chip and improve the light extraction efficiency. The key processes are assembly, pressure welding and packaging.

Process flow and description:

A. Chip detection

Whether there is mechanical damage on the surface of the material, whether the chip size and electrode size of lockhill meet the process requirements, and whether the electrode pattern is complete.

B. Expansion

Because the LED chips are still closely arranged after dicing, the spacing is very small (about 0. 1mm), which is not conducive to the subsequent process operation. We use a film stretcher to expand the film of bonded chips, so as to stretch the spacing between LED chips to about 0.6 mm. Manual expansion is also possible, but it is easy to cause bad problems such as waste of chips.

C. dispensing medicines

Apply silver glue or insulating glue to the corresponding position of LED bracket. (For GaAs and SiC conductive substrates, red, yellow and yellow-green chips with back electrodes are made of silver paste. For blue and green LED chips with sapphire insulating substrate, insulating glue is used to fix the chips. ) The process difficulty lies in the control of dispensing amount, and the height and dispensing position of colloid have detailed process requirements. Because there are strict requirements for the storage and use of silver glue and insulating glue, the proofing, stirring and use time of silver glue are all matters that must be paid attention to in the process.

D. prepare glue

Glue preparation is the opposite of dispensing. Glue-making is to apply silver glue to the electrode on the back of the LED with a glue-making machine, and then install the LED coated with silver glue on the LED bracket. The efficiency of dispensing is much higher than dispensing, but not all products are suitable for dispensing.

E. Hand-punched parts

Put the expanded LED chips (with or without glue) on the fixture of the stabbing table, put the LED bracket under the fixture, and stab the LED chips to the corresponding positions one by one with a needle under the microscope. Compared with automatic mounting, manual punching has an advantage that it is convenient to replace different chips at any time, and it is suitable for products that need to install multiple chips.

F. Automatic shelves

In fact, automatic mounting is a combination of two steps: gluing (gluing) and chip mounting. First, apply silver glue (insulating glue) on the LED bracket, then suck up and move the LED chip with a vacuum nozzle, and then put it in the corresponding bracket position. In the process of automatic mounting, it is mainly necessary to be familiar with the equipment operation programming, and at the same time, to adjust the gluing and installation accuracy of the equipment. In the selection of suction nozzle, try to use bakelite suction nozzle to prevent damage to the surface of LED chip, especially blue-green chip. Because the steel nozzle will scratch the current diffusion layer on the chip surface.

G. sintering

The purpose of sintering is to solidify the silver paste, and the sintering needs to monitor the temperature to prevent batch defects. The sintering temperature of silver paste is generally controlled at 65438 050℃ and the sintering time is 2 hours. It can be adjusted to 170℃ and 1 hour according to the actual situation. Insulation glue is generally 150℃ 1 hour. The silver glue sintering furnace must be opened every 2 hours (or 1 hour) according to the process requirements to replace the sintered products, and it is not allowed to be opened at will. The sintering furnace shall not be used for other purposes to prevent pollution.

H. crimping

The purpose of pressure welding is to lead the electrode to the LED chip and complete the connection of the internal and external leads of the product. There are two bonding processes for LED: gold wire ball bonding and aluminum wire bonding. Aluminum wire bonding process: first press the first point on the electrode of the LED chip, then pull the aluminum wire above the corresponding bracket, and then press the second point to break the aluminum wire. The gold wire ball welding process is to burn a ball first and then press the first point, and other processes are similar. Bonding is a key link in LED packaging process, and the main process to be monitored is the arch wire shape, solder joint shape and tension of bonding gold wire (aluminum wire). The in-depth study of pressure welding technology involves many problems, such as gold (aluminum) wire material, ultrasonic power, pressure of pressure welding, selection of cleaver (steel nozzle), motion trajectory of cleaver (steel nozzle) and so on.

A, dispensing packaging LED packaging

There are three kinds of LED packaging: dispensing, potting and plastic packaging. Basically, the difficulties in process control are bubbles, lack of materials and black spots. The design is mainly about the selection of materials, and the combination of epoxy and bracket is selected. (Generally, LED can't pass the air tightness test) Top LED and side LED are suitable for dispensing package. Manual dispensing packaging requires a high level of operation (especially white LED), and the main difficulty is to control the amount of dispensing, because epoxy will thicken during use. The dispensing of white LED still has the problem of color difference caused by phosphor precipitation.

J. encapsulating LED lamps.

The LED lamp is encapsulated by potting. The process of potting is to inject liquid epoxy resin into the LED molding cavity, then insert the pressure welded LED bracket, put it in the oven to cure the epoxy resin, and then take the LED out of the molding cavity for molding.

K. Forming and packaging

Molding and packaging: 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 resin into the rubber channel of the mold with a hydraulic ejector pin, heat it at the entrance of the rubber channel, and the epoxy resin enters each LED molding groove along the rubber channel for curing.

Length curing and post curing

Curing refers to the curing of encapsulated epoxy resin. Generally, the curing conditions of epoxy are 135℃ and 1 hour. Molding and packaging are generally carried out at 150℃ for 4 minutes.

Post-curing is to completely cure epoxy resin and thermally age LED. Post curing is very important to improve the bonding strength between epoxy resin and PCB. The general condition is 120℃ for 4 hours.

Meter (short for meter)) rib cutting and scoring

Because the LEDs are connected together (not single) in production, the LEDs in the lamp package adopt the method of rib cutting to cut off the ribs of the LED bracket. SMD-LED is on PCB, and it needs dicing machine to complete the separation.

test

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

O. packaging

And packaging the finished product. Ultra-bright LEDs need anti-static packaging.

3. The source of technology

(1) dispensing, the difficulty lies in the control of dispensing quantity, and Huazhong University of Science and Technology is adopted to dispense glue from top to side.

(2) Packaging: internationally accepted packaging forms: lamp LED, top LED, side LED, patch LED, high-power LED, etc.

(3) The remaining technologies are independently developed by the company.

4. Flowchart of 4.LED white light source production process (production equipment)