LED package manufacturing process and related precautions

1. We can divide the specific manufacturing process of the LED package into the following steps:

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1. Cleaning step: Ultrasonic cleaning of the PCB or LED holder and drying.

2. Mounting step: After the silver electrode at the bottom of the LED die is filled with silver glue, the expansion is performed, and the expanded die is placed on the thorn crystal table, and the dies are mounted on the PCB or the LED one by one under the microscope with a stylus. On the corresponding pads, sintering is then performed to cure the silver paste.

3. Pressure welding step: The electrode is connected to the LED die by an aluminum wire or gold wire welding machine for the current injection lead. The LED is directly mounted on the PCB, and an aluminum wire welder is generally used.

4. Packaging step: protect the LED die and bonding wire with epoxy by dispensing. Dispensing on the PCB, there are strict requirements on the shape of the gel after curing, which is directly related to the brightness of the backlight product. This process will also take on the task of phosphors.

5. Soldering step: If the backlight is an SMD-LED or other packaged LED, the LED needs to be soldered to the PCB before the assembly process.

6. Film cutting step: various diffusion films, reflective films, etc. required for backlighting are punched by a punch.

7. Assembly steps: According to the drawings, the various materials of the backlight are manually installed in the correct position.

8. Test procedure: Check whether the photoelectric parameters of the backlight and the uniformity of light output are good.

9. Packing step: Pack the finished product as required and put it into storage.

2. The following is a specific flow chart of the LED lamp bead package:

Every detail in the production process of LED lamp bead package must be strictly controlled. The following detailed explanation of the above flow chart is detailed:

1, the first is the LED chip inspection

(1) Microscopic examination: Whether there is mechanical damage and pitting on the surface of the material, whether the size and size of the LED chip electrode meet the process requirements; whether the electrode pattern is complete

2, the expansion machine expands its film

Since the LED chips are still closely spaced after the dicing, the operation is not conducive to the operation of the post process. We use a film expander to expand the film of the bonded chip. The distance between the LED chips is stretched to about 0.6 mm. It can also be manually expanded, but it is easy to cause problems such as chip falling waste.

3, dispensing

Place silver glue or insulating glue on the corresponding position of the LED bracket. The difficulty of the process lies in the control of the amount of glue, and there are detailed technical requirements in the height of the glue and the position of the glue. Since silver glue and insulating glue have strict requirements in 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, ready glue

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

5, hand-piercing

The expanded LED chip is placed on the jig of the lancet table, the LED bracket is placed under the clamp, and the LED chips are punctured one by one under the microscope with the needle. Hand-made thorns have an advantage over automatic loading, making it easy to replace different chips at any time, for products that require multiple chips.

6, automatic loading

In the automatic loading, the two steps are combined with the glue and the chip. First, the silver glue is placed on the LED bracket, and then the vacuum chip is used to suck the LED chip to the moving position, and then placed in the corresponding bracket position. In the process of automatic loading, the equipment should be familiar with the operation and programming of the equipment, and at the same time adjust the glue and installation accuracy of the equipment. In the selection of the nozzle, the bakelite nozzle should be used as much as possible to prevent damage to the surface of the LED chip. In particular, the blue and green chips must be made of bakelite. Because the steel nozzle will scratch the current diffusion layer on the surface of the chip.

7. Sintering

The purpose of sintering is to cure the silver paste, and the sintering requires monitoring of the temperature to prevent batch defects. The temperature at which the silver paste is sintered 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. The insulating glue is generally 150 ° C for 1 hour.

The silver-glue sintering oven must be opened and replaced with a sintered product within 2 hours according to the process requirements, and the middle shall not be opened at will. Sintering ovens must not be used for other purposes to prevent contamination.

8, pressure welding

The purpose of the pressure welding is to lead the electrode to the LED chip to complete the connection of the inner and outer leads of the product. There are two kinds of LED pressure welding processes: gold wire ball bonding and aluminum wire pressure welding. The picture on the right is the process of aluminum wire bonding. First, press the first point on the electrode of the LED chip, then pull the aluminum wire over the corresponding bracket, and press the second point to tear the aluminum wire. The gold wire ball bonding process burns the ball before the first point, and the rest of the process is similar. Pressure welding is a key link in LED packaging technology. The main need to monitor the process is the shape of the welded gold wire arch, the shape of the solder joints, and the tensile force. In-depth study of the pressure welding process involves a variety of issues, such as gold wire materials, ultrasonic power, pressure welding pressure, file selection, boring motion track and so on.

9, dispensing package

LED packaging is mainly a little glued, potted, molded. Basically, the difficulty of process control is bubbles, lack of materials, and black spots. The design is mainly for the selection of materials, and the combination of good epoxy and brackets is selected. In general, TOP-LED and Side-LED are suitable for dispensing. Manual dispensing has high requirements on the level of operation. The main difficulty is the control of the amount of dispensing, because the epoxy will thicken during use. The dispensing of white LEDs also has the problem of phosphor precipitation leading to chromatic aberration of light.

10, glue packaging

The lamp-LED package is in the form of a potting. The potting process is to first inject liquid epoxy into the LED molding cavity, then insert the pressure-bonded LED bracket into the oven to cure the epoxy, and then remove the LED from the cavity to form.

11, molded package

The pressure-welded LED bracket is placed in the mold, and the upper and lower molds are clamped by a hydraulic machine and vacuumed, and the solid epoxy is placed in the inlet of the injection molding pipe and pressed into the mold rubber channel by the hydraulic ejector. The glue lane enters each LED forming groove and solidifies.

12, curing and post curing

Curing refers to the curing of the encapsulating epoxy, which is typically cured at 135 ° C for 1 hour. The molded package is typically at 150 ° C for 4 minutes.

13, post curing

Post-cure is to allow the epoxy to fully cure while thermally aging the LED. Post-cure is important to increase the bond strength of the epoxy to the stent. The general conditions are 120 ° C for 4 hours.

14, cutting and dicing

Since the LEDs are connected together in production, the Lamp packaged LED uses a rib to cut the ribs of the LED holder. SMD-LED is on a PCB board and requires a dicing machine to complete the separation.

15, testing

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

16, packaging

The finished product is counted and packaged. Among them, super bright LEDs require anti-static packaging.

The above series of manufacturing steps of LED lamp beads to lamps are very clear, and anything is not so simple, we need to do it ourselves, because the production of LED lamp beads is a very delicate work, it requires no static electricity in the external environment. Otherwise, the gold line will be destroyed. The final factory inspection is also important. Here is a brief introduction to how to do static protection in LED package production from the following aspects:

Electrostatic protection: LED is a semiconductor device, which is sensitive to static electricity. Especially for white, green, blue and purple LEDs, it is necessary to prevent static electricity generation and eliminate static electricity.

1. There are three main types of static electricity:

(1) Frictional electrification: In daily life, any two objects of different materials are separated and contacted to generate static electricity, and the most common method of generating static electricity is to generate electricity by friction. The better the material's edge, the easier it is to rub the electricity. In addition, the separation of any two different substances can also generate static electricity after contact.

(2) Inductive electrification: For conductive materials, because electrons can move freely on its surface, such as placing it in an electric field, due to the same-sex repellent, the opposite sex attracts, and the positive and negative ions are transferred on the surface. It will generate a charge.

(3) Conduction: For conductive materials, charge transfer occurs due to the free movement of electrons on its surface, such as contact with a charged object.

2, the harm of static electricity to LED:

Special attention should be paid to the fact that static electricity also poses a great hazard to the LED package itself.

(1) The LED is partially injured due to the heat generated by the instantaneous electric field or current, which means that the leakage current increases rapidly and still works, but the brightness is lowered (the white light will change color) and the life is impaired.

(2) Because the electric field or current destroys the edge layer of the LED, the device cannot work (complete destruction), and it is a dead light, which is neither bright.

3. Elimination measures:

All employees who are in direct contact with the LED (production, testing, packaging, etc.) must take measures to prevent and eliminate static electricity.

Mainly: (1) The workbench is an anti-static workbench, and the production machine is well grounded.

(2) The workshop shall be equipped with an anti-static floor and grounded.

(3) The operator wears an anti-static suit with an anti-static wrist strap, gloves or an ankle ring.

(4) The packaging is made of antistatic material.

(5) Apply an ion fan and solder the soldering iron to make grounding measures.

The above information is just a brief introduction to the LED packaging process and precautions. I hope I can help you. (Global Hardware Network)

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