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Twelve Steps in the manufacturing process of LED chips


Upstream chip technology has always been the bottleneck of domestic LED, and most of the core technologies are mastered abroad. The following is an introduction to the chip manufacturing process:

1. LED chip inspection

Microscopic inspection: whether there is mechanical damage on the surface of the material, whether the chip size of pockmarks and pits and whether the electrode size meet the process requirements, and whether the electrode pattern is complete

2.LED enlargement

As the LED chips are still arranged close after scribing (about 0.1mm), it is not conducive to the operation of the subsequent process. Using the expander to expand the film of the bonding chip, the spacing of the LED chip is stretched to about 0.6mm. It can also be expanded by hand, but it is easy to cause bad problems such as chip dropping and waste.

3.LED dispensing

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

The difficulty of the process lies in the control of dispensing amount. There are detailed process requirements in the gel height and dispensing position. Due to the strict requirements for storage and use of silver glue and insulating glue, the wake-up, mixing and use time of silver glue must be paid attention to.

4.LED preparation

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

5. Led manual stabbing

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

6. LED automatic mounting

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

7.LED sintering

The purpose of sintering is to solidify the silver glue. Sintering requires monitoring the temperature to prevent poor batch properties. The sintering temperature of silver glue is generally controlled at 150 ℃, and the sintering time is 2 hours. According to the actual situation, it can be adjusted to 170 ℃ for one hour. Insulating glue is generally 150 ℃ for 1 hour.

The silver glue sintering oven must be opened every 2 hours (or 1 hour) according to the process requirements to replace the sintered products, and shall not be opened at will in the middle. Sintering oven shall not be used for other purposes to prevent pollution.

8.LED pressure welding

The purpose of pressure welding is to lead the electrode to the LED chip and complete the connection of internal and external leads of the product.

There are two kinds of pressing welding processes for LED: gold wire ball welding and aluminum wire pressing welding. The process of aluminum wire press welding is to press the first point on the LED chip electrode, then pull the aluminum wire to the corresponding bracket, press the second point, and then tear the aluminum wire. In the process of wire ball welding, a ball is burned before pressing the first point, and the other processes are similar.

Pressure welding is the key link in LED packaging technology. In the process, the shape of the arch wire, the shape of the solder joint and the tensile force of the pressure welding gold wire (aluminum wire) need to be monitored.

9.LED sealing

There are three kinds of LED packaging: dispensing, potting and molding. Basically, the difficulties of process control are bubble, material shortage and black spot. In the design, it is mainly about the selection of materials and the selection of epoxy resin and bracket with good combination. (general led cannot pass air tightness test)

Led dispensing top led and side LED are suitable for dispensing package. Manual dispensing package requires a high level of operation (especially white LED), the main difficulty is to control the dispensing amount, because the epoxy will thicken in the use process. There is also the problem of light color difference caused by the deposition of phosphor in the dispensing of white LED.

Led glue filling package lamp LED package is in the form of filling. The filling and sealing process is to inject liquid epoxy into the LED molding cavity first, then insert the pressed and welded LED bracket, put it into the oven to allow the epoxy to solidify, and then take the led out of the cavity for molding.

Led molding package puts the pressed and welded LED bracket into the mold, closes the upper and lower two molds with hydraulic press and vacuumizes them, puts the solid epoxy into the entrance of the injection channel, heats it with hydraulic ejector and presses it into the mold channel, and then the epoxy enters each LED molding slot along the channel and solidifies.

10. LED curing and post curing

Curing refers to the curing of encapsulated epoxy. Generally, the curing condition of epoxy is 135 ℃ for 1 hour. Generally, the molding temperature is 150 ℃ for 4 minutes. The purpose of post curing is to allow the epoxy to fully cure and to heat age the LED at the same time. Post curing is very important to improve the bonding strength between epoxy and PCB. The general condition is 120 ℃, 4 hours.

11. Led rib cutting and scribing

Because LED is connected (not single) in production, lamp package LED adopts cutting rib to cut off the connecting rib of LED bracket. Smd-led is on a PCB, which needs a scriber to complete the separation.

12.LED test

Test the LED photoelectric parameters, check the overall dimensions, and sort the LED products according to the customer's requirements.

Yiwu Fuwei e-commerce firm (IACS Co., Limited) is a very professional Led manufacturer who produces high quality outdoor led light. Our popular products are solar led lights, UFO lights, underwater lights and so on. If you have any question about the led product, please feel free to contact us.