Knowledge of LED packaging technology is essential

The packaging technology of LED lamps and lanterns. LED is a high-tech stuff. In this circle, there are many so-called trade secrets.These things directly determine whether the enterprise can have central competitiveness, here today to publish the LED industry packaging technology knowledge, I hope to give you some help.

Production technology

1. Production:

A) cleaning: use ultrasonic wave to clean PCB or LED stands and dry them.

B) mounting: after the silver glue is prepared on the electrode at the bottom of the led core (large wafer), the expanded core (large wafer) is placed on the stinger crystal platform. Under the microscope, the core is installed one by one on the corresponding solder pad of PCB or led bracket, and then sintered to solidify the silver glue.

C) pressure welding: the electrode is connected to the LED core by aluminum wire or gold wire welding machine to serve as the lead for current injection.LED installed directly on PCB, usually aluminum wire welding machine.(gold wire welding machine is needed to make white light top-led)

D) encapsulation: the LED core and welding line are protected with epoxy through the point glue.On the PCB board, there are strict requirements on the shape of solidified colloids, which is directly related to the output brightness of backlight products.The process will also take on the task of lighting phosphor (white LED).

E) welding: if the backlight is smd-led or other sealed LED, the LED shall be welded to the PCB board before the assembly process.

F) film cutting: all kinds of diffusion film and reflective film required by back light source cutting with punch die.

G) assembly: according to the requirements of the drawing, manually install various materials of backlight to the correct position.

H) test: check the photoelectric parameters of backlight and the uniformity of the outgoing light.

2. Packaging: the finished products are packed and stored as required.

Ii. Packaging technology

1. LED encapsulation task

It is to connect external lead to the electrode of the LED chip, protect the LED chip and improve the efficiency of light removal.Key processes are mounting, pressure welding, packaging.

2. LED packaging form

LED packaging can be said to be multifarious, mainly according to different applications to use the corresponding shape size, heat countermeasures and light effect.Led can be classified into Lamp led, top-led, side-led, smd-led, high-power-led, etc.

3. LED packaging process

A) chip test

Microscopy:

1. Whether there is mechanical damage to the material surface and pockmark pit (lockhill);

2. Whether the chip size and electrode size meet the process requirements;

3. Whether the electrode pattern is complete.

B) expanding slice

Since the LED chip is still arranged with small close spacing (about 0.1mm) after chip cutting, it is not conducive to the operation of the latter process.The film of the bonding chip is expanded by using the expanding machine. The spacing of the LED chip is stretched to about 0.6mm. Manual expansion can also be adopted, but it is easy to cause undesirable problems such as chip drop and waste.

C) dispensing

Silver or insulating glue is applied at the corresponding position of the led holder.

(for GaAs and SiC conductive substrates, red, yellow and green chips with back electrodes are adopted with silver glue.For blue and green led chips with sapphire insulating substrate, insulating glue is used to fix the chip.The difficulty of the process lies in the control of the amount of the dispensing.Because of the strict requirements for the storage and use of silver glue and insulating glue, the awakening of silver glue, stirring and use time are all matters needing attention in the process.

D) prepare glue

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

E) hand-made sashimi

The expanded LED chip (with or without glue) is placed on the clamp of the splint table. The LED bracket is placed under the fixture, and the LED chip is pricked one by one by the needle under the microscope.Compared with automatic mounting, manual splicing has the advantage of changing different chips at any time, and it is suitable for products that need to install multiple chips.

F) automatic mounting

The automatic mounting rack is actually a combination of two steps of gluing (dotting) and mounting the chip. First, the led holder is touched with silver glue (insulating glue), and then the led chip is sucked up and moved with a vacuum suction nozzle, and then placed on the corresponding bracket position.

In the process of automatic mounting, you should be familiar with the equipment operation and programming, and adjust the equipment‘s sticking and installation accuracy.The selection of the suction nozzle should be made of bakelite to prevent damage to the surface of the led chip, especially the blue and green chips which must be made of bakelite.The nozzles scratch the current diffusion layer on the surface of the chip.

G) sintering

The purpose of sintering is to solidify the silver glue. The sintering requires monitoring the temperature to prevent the bad batch property.

Silver glue sintered at 150 ℃, the temperature of the general control sintering for 2 hours.According to the actual situation can be adjusted to 170 ℃, 1 hour.Insulated generally 150 ℃, 1 hour.The ag-gel sintering oven shall be opened and replaced at 2 hours (or 1 hour) according to the technological requirements, and shall not be opened at will.Sintered oven can not be used for other purposes to prevent pollution.

H) pressure welding

The purpose of pressure welding is to lead the electrode to the led chip and to connect the inner and outer leads of the product.LED pressure welding process has two kinds of metal ball welding and aluminum wire welding.The picture on the right shows the process of aluminum wire welding. First, press the first point on the LED chip electrode, then pull the aluminum wire above the corresponding support, press the second point, and then tear the aluminum wire.Gold wire ball welding process before pressing the first point to burn a ball, other processes similar.

Pressure welding is a key part in LED packaging technology. The main process needs to be monitored is the shape of the arch wire, welding spot and tensile force of the metal wire (aluminum wire).The in-depth study of pressure welding process involves many problems, such as gold (aluminum) wire materials, ultrasonic power, pressure welding pressure, selection of wedge (steel tip), motion track of wedge (steel tip) and so on.(the picture below is the micro picture of the welding spot pressed by two different cleavers under the same conditions. There are differences in microstructure between the two, which affect the product quality.)We will not recap here.

　　I) dot glue packaging

LED packaging mainly a bit of glue, sealing, moulding three.Basically, the difficulty of process control is air bubble, lack of materials and black spots.The main design is the selection of materials, choice of a good combination of epoxy and bracket.(common LED cannot pass the air tightness test) TOP-LED and Side-LED as shown in the figure on the right can be used for dispensing.Manual dispensing packaging requires a high level of operation (especially white LED), and the main difficulty is to control the amount of dispensing, as the epoxy will thicken during use.White LED point glue also has the problem of color difference caused by phosphor precipitation.

J) filling and sealing

Lamp-led packaging adopts the form of filling and sealing.The filling and sealing process starts by injecting liquid epoxy into the led mold cavity, and then insert the pressed welded led bracket, put it into the oven and let the epoxy solidify, and then take the led out of the mold cavity and shape it.

K) moulded packaging

The pressed welded led supports were put into the mold, the upper and lower molds were clamped and vacuumed by hydraulic press, and the solid epoxy was put into the mold resin duct by hydraulic jacking bar at the entrance of the glue canal for heating, and the epoxy went into each led molding groove and solidified.

L) curing and post-curing

Curing is refers to the encapsulation of epoxy curing, general epoxy curing condition at 135 ℃, 1 hour.Moulded packaging is in commonly 150 ℃, 4 minutes.

M) after curing

The post-curing is designed to allow the epoxy to fully solidify while heat aging the led.Post-curing is very important for improving the adhesive strength of epoxy and PCB.General conditions of 120 ℃, 4 hours.

N) slitting and cutting

Since the led is connected together (not single) in production, Lamp encapsulates led by cutting rib to cut off the joint of led bracket.Smd-led is on a PCB board, which needs the scriber to complete the separation work.

O) test

Test the led‘s photoelectric parameters, check its shape and size, and sort the led products according to customer requirements.

P) packaging

Packing the finished product.Super bright LED needs anti-static packaging.