The Production Process Of LED Lamp Beads
- Cleaning: Use ultrasonic to clean the PCB or LED bracket and dry it.
- Mounting: After the bottom electrode of the LED die (large wafer) is prepared with silver glue, expand it, place the expanded die (large wafer) on the thorn crystal table, and use a thorn crystal pen to place the die under the microscope. One by one is mounted on the corresponding pads of the PCB or LED bracket, and then sintered to cure the silver glue.
- Pressure welding: Use an aluminum wire or gold wire bonder to connect the electrode to the LED die to serve as a lead for current injection. If the LED is directly mounted on the PCB, an aluminum wire welding machine is generally used. (The production of white light TOP-LED requires a gold wire bonder)
- Encapsulation: Protect the LED die and bonding wires with epoxy by dispensing. Dispensing glue on the PCB board has strict requirements on the shape of the colloid after curing, which is directly related to the brightness of the finished backlight source. This process will also take on the task of point phosphors (white LEDs).
- Soldering: If the backlight source is SMD-LED or other packaged LEDs, the LEDs need to be soldered to the PCB before the assembly process.
- Cutting film: Die-cut various diffusion films, reflective films, etc. required for the backlight with a punch.
- Assembly: According to the requirements of the drawings, manually install the various materials of the backlight in the correct positions.
- Test: Check whether the photoelectric parameters of the backlight and the uniformity of light output are good.
- Packaging: The finished products are packaged and stored as required.
The Packaging Process Of LED Lamp Beads
The Task Of LED Packaging
The external lead is connected to the electrode of the LED chip, while protecting the LED chip and improving the light extraction efficiency. The key processes are rack mounting, pressure welding and packaging.
LED Package Form
LED packaging forms can be said to be varied, and the corresponding external dimensions, heat dissipation measures and light output effects are mainly adopted according to different applications. LEDs are classified into lamp LED, top led, side LED, SMD LED, high power LED and so on.
The Process Flow Of LED Packaging
- To expand the crystal, open the densely arranged wafers to facilitate crystal consolidation.
- For crystal fixing, point conductive / non-conductive glue on the bottom of the support (the conductivity depends on whether the wafer is an up-down PN junction or a left-right PN junction) and then put the wafer into the support.
- Short baking, so that the wafer does not move when the glue solidifies the bonding wire.
- Solder wire, use gold wire to connect the wafer and the support.
- Pre test, preliminary test whether it can be lit.
- Glue the chip and the bracket with glue.
- Bake for a long time to let the glue solidify.
- Post test, test whether it can be lit and whether the electrical parameters meet the standard.
- Light and color separation, to separate products whose color and voltage are roughly the same.
- LED Packaging.
The Process Description Of Packaging
Microscopic inspection: whether there is mechanical damage on the surface of the material, whether the chip size and electrode size of the pockmill meet the process requirements, and whether the electrode pattern is complete.
Since the LED chips are still arranged closely after dicing, the spacing is very small (about 0.1mm), which is not conducive to the operation of the subsequent process. We use the expanding machine to expand the film of the adhesive chip, and the spacing of the LED chips is stretched to about 0.6mm. Manual expansion can also be adopted, but it is easy to cause undesirable problems such as chip dropping and waste.
Apply silver glue or insulating glue on the corresponding positions of the LED bracket. (for GaAs and SiC conductive substrates, silver glue is used for red, yellow and yellow green chips with back electrodes. For blue and green LED chips with sapphire insulating substrates, insulating glue is used to fix the chips.) The difficulty of the process lies in the control of the dispensing amount. There are detailed process requirements for the height of the colloid and the dispensing position. Since there are strict requirements for the storage and use of silver glue and insulating glue, the awakening, stirring and use time of silver glue are all matters that must be paid attention to in the process.
In contrast to dispensing, the glue preparation machine is used to apply silver glue on the back electrode of the LED, and then install the LED with silver glue 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.
Place the expanded LED chips (with or without glue preparation) on the jig of the stabbing table, put the LED bracket under the jig, and stab the LED chips to the corresponding positions 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, and it is suitable for products that need to install multiple chips
6.Automatic Rack Mounting
In fact, the automatic rack mounting is a combination of two steps: gluing (dispensing) and chip mounting. First, put silver glue (insulating glue) on the LED bracket, then use the vacuum nozzle to suck the LED chip to the moving position, and then place it on the corresponding bracket position. In the process of automatic rack mounting, it is mainly necessary to be familiar with the equipment operation programming, and adjust the glue adhesion and installation accuracy of the equipment. In the selection of suction nozzles, try to use bakelite suction nozzles to prevent damage to the surface of LED chips, especially the blue and green chips must use bakelite. Because the steel nozzle will scratch the current diffusion layer on the chip surface.
The purpose of sintering is to solidify the silver glue. The sintering requires monitoring the temperature to prevent bad batch. The sintering temperature of silver glue is generally controlled at 150 ℃, and the sintering time is 2 hours. It can be adjusted to 170 ℃ for 1 hour according to the actual situation. The insulating adhesive 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. Sintering oven shall not be used for other purposes to prevent pollution.
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. We will not repeat here.
LED packaging mainly includes dispensing, potting and molding. Basically, the difficulties of process control are bubbles, excessive lack of materials and black spots. The design is mainly about the selection of materials and the selection of epoxy and support with good combination. (general LEDs cannot pass the air tightness test) there is also a problem of light color difference caused by phosphor precipitation in the dispensing of white LEDs.
10.Glue Filling And Sealing
Lamp LED is encapsulated in the form of potting. The filling process is to first inject liquid epoxy into the LED molding cavity, then insert the pressure welded LED bracket, put it into the oven to cure the epoxy, and then take the led out of the mold cavity to form.
Put the pressure welded LED support into the mold, close the upper and lower molds with a hydraulic press and vacuum them, put the solid epoxy into the inlet of the injection channel, heat it and press it into the mold rubber channel with a hydraulic ejector rod, and the epoxy enters each LED molding groove along the rubber channel and solidifies.
12.Curing And Post Curing
Curing refers to the curing of encapsulated epoxy. Generally, the curing condition of epoxy is 135 ℃ for 1 hour. The molding package is generally at 150 ° C for 4 minutes.
Post curing is to fully cure the epoxy and heat aging the LED. Post curing is very important to improve the adhesive strength between epoxy and PCB. The general condition is 120 ℃ for 6 hours.
14.Cutting And Slicing
Since the LEDs are connected together (not single) in production, the lamp package LED adopts cutting ribs to cut the connecting ribs of the LED bracket. Smd-led is on a PCB board and requires a dicing machine to complete the separation work.
Test the photoelectric parameters of LED, check the overall dimensions, and sort LED products according to customer requirements.
Count and pack the finished products. Super bright LED needs anti-static packaging.