What Is the LED Assembly Process?

What is the LED PCB assembly process

LED lights are the fourth band of energy. LEDs have special effects such as energy saving and environmental protection, making them the first choice for lighting in daily life. The LED assembly and production process have long been very mature, except that the LED light chip needs to be made in a special factory, and other materials are not troublesome to obtain. LED assembly and production costs are relatively low. Let’s understand the LED assembly process together and see how our daily lighting tools are assembled step by step.

LED light chip detection

LED light chip inspection is the first link in LED assembly, and it is also a very important link. If the light of the chip is abnormal, the LED light will emit abnormally or even not bright. If there is a problem with the light of the LED light chip, there is no objection to the subsequent work. Mainly check whether the electrode of the LED chip is intact, test with a universal meter to see whether various parameters meet the design requirements, whether the electrode pattern is complete, and whether the surface of the entire chip is flat.

LED chip distance expansion

After the chip is inspected, the chip distance should be expanded. In order to better carry out the subsequent LED assembly work, it is very necessary to stretch the distance between the LED chips. After the LED chips are cut, the pitch is about 0.1mm, and a film expander is needed to expand the distance between the chips to about 0.6mm. This task can also be done manually, but the manual efficiency is low, the error is large, and the cost is high. Basically, it is completed with a film expander.

LED chip dispensing

When opening the silver glue or insulating glue, keep stirring the silver glue or insulating glue. Pay attention to the mixing time, not too long. The cost of silver glue and insulating glue is flammable, and there are strict standards for use and storage. Place the finished glue dots on the corresponding position of the LED bracket. The location of the glue and the amount of glue have strict process requirements, and those that do not meet the requirements must be reworked. Different materials use different glues. Blue and green LED chips to use sapphire insulating substrates, and insulating glue is used to fix the chips. Red, yellow, and yellow-green chips use SiC and GaAs conductive substrates. There are back electrodes, and silver glue is used to fix the chip.

Glue on the back of the LED chip

Different from the glue dispensing, the glue on the back of the LED is to apply the silver glue prepared in advance on the electrode on the back of the LED, and the glue preparation machine is the main tool of this process. Install the glued LED on the bracket. Not all products require this process. This step is also more efficient in the LED assembly process, and the comparative process requirements are not high.

Manual installation of LED chips

Place the processed LED chip on the workbench, and place the LED bracket at the lower position, with a microscope on the workbench. Observe the structure of the LED bracket with a microscope, and install the chips one by one to the corresponding position. Manual installation can install relatively complex products and can install multiple chips on a bracket, but the efficiency is lower than that of automatic installation, and the success rate is relatively low.

Automatic mounting frame for LED chips

The automatic chip installation can directly complete the two steps of glue dispensing and installation. First, the prepared glue is dotted on the LED bracket, and then the chip is sucked up and moved, and then the chip is installed on the LED bracket. Try not to use metal nozzles for the suction nozzle. The surface of the LED chip is very fragile, especially the blue-chip and the green chip. The metal suction nozzle is easy to scratch the chip and damage the current diffusion layer on the surface of the chip. The automatic installation rack operation requires familiarity with the operation programming of the equipment, and there are certain requirements on the installation accuracy and dispensing in the process.

LED sintering

After the glue is dotted, the glue needs to be sintered to make it fixed. The sintering temperature and time of silver glue and insulating glue are different. These need to be adjusted according to the actual situation. Silver glue generally needs to be sintered at a temperature of 150°C for two hours, and sometimes it can be sintered at a temperature of 170°C for 1 hour. Insulating adhesive curing is relatively simple, generally sintering at a temperature of 150 ℃ for one hour. In order to ensure the quality of the product, the oven should not be opened at will, nor should it be used for other purposes.

LED pressure welding

There are two types of pressure welding, one is gold wire ball bonding, and the other is aluminum wire bonding. Aluminum wire bonding uses aluminum wire to connect the electrode to the chip. The operation process is to press the aluminum wire between the wires on the electrode, and then the other end of the aluminum wire is pulled at the corresponding position of the LED bracket and the aluminum wire is broken. The process of gold wire ball bonding is similar to that of aluminum wire bonding, that is, the wire burns a ball at the position of the solder joint, and then connects the aluminum wire to the two metal balls. Pressure bonding connects the inner and outer leads of the chip and connects the electrodes to the chip. Pressure welding is a key part of LED assembly, and there are process requirements for the tension of the pressure welding aluminum wire and the solder joints.

LED package

The LED packaging methods used for different LED products are different, some are suitable for dispensing, some are suitable for potting, and some are suitable for molding. During the packaging process, this accumulation problem will occur for a long time, such as bubbles in the packaging, incomplete packaging materials, and black lights on the packaging.

Dispensing and packaging are mostly done by machines, and manual operations are too demanding and difficult to complete. The packaging material tends to thicken during use, all the dispensing speeds should be fast, and the dispensing volume should be appropriate. LEDs containing phosphors have higher requirements for dispensing, and the precipitation of phosphors will have a difference in a light color.

Glue encapsulation is to inject the glue material into the LED molding cavity, then insert the LED bracket, then dry, and finally, take out the molded LED product

Molded packaging is to put the LED bracket into a vacuum mold, use a hydraulic rod to push the solid packaging material into the mold and cure, and finally take out the LED product.

Curing and post-curing

Curing and post-curing are to strengthen the package and strengthen the connection strength of the epoxy to the PCB. The curing time of the compression mold package is relatively short, and it is completed in 4 minutes at a temperature of 150°C. It takes a relatively long time for potting and dispensing, and it needs to be baked at 135℃ for one hour.

LED segmentation

When LEDs are produced, they are not produced individually but are produced in batches. This leads to many LED brackets that are connected together and need to be divided into individual pieces. Different LED products use different technologies, and the Lamp package directly cuts off the LED bracket connection. SMD-LED is a large piece attached to the PCB board, and it is best to use a dicing machine to separate the LED.

LED classification

The photoelectric parameters and the LED with the same shape are classified and distributed according to the needs of customers.

LED packaging

Packing the cost of LED requires anti-static treatment.

LED assembly is not a complex project, but the whole process requires high technology, a link can directly affect the quality of LED. MOKOLight LED PCB assembly technology industry-leading, can quickly produce a variety of customers need LED lights

Written by ——
Adelyn Ward
Adelyn Ward
Master of Science; professional electronic engineer with over 7 years of experience in electronic design and engineering projects; proven expertise of LED manufacturing processes, capable of communicating intricate ideas to a broad range of audiences. Reach Me Now>>
Adelyn Ward
Adelyn Ward
Master of Science; professional electronic engineer with over 7 years of experience in electronic design and engineering projects; proven expertise of LED manufacturing processes, capable of communicating intricate ideas to a broad range of audiences. Reach Me Now>>
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