LED packaging technology is currently developing in the direction of high luminous efficiency, high reliability, high heat dissipation and thinning. The main highlights are ceramic substrate packaging, flip chip technology, phosphor coating technology, and metal wire bonding technology. The steps of LED packaging can be divided into twelve steps.
1, dispensing
Place silver glue or insulating glue on the corresponding position of the LED bracket. (For GaAs, SiC conductive substrates, red, yellow, and yellow-green chips with back electrodes, silver paste is used. For blue and green LED chips of sapphire insulated substrates, insulating paste is used to fix the chips.)
2, automatic loading
The automatic loading is actually a combination of two steps of glue (dispensing) and mounting the chip. 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 in the 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.
3. 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-glued sintering oven must be opened and replaced with a sintered product within 2 hours (or 1 hour) according to the process requirements, and should not be opened at will. Sintering ovens must not be used for other purposes to prevent contamination.
4, 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. Pressure welding is a key link in LED packaging technology. The main requirements of the process are the pressure welding of gold wire (aluminum wire) arch shape, solder joint shape, and tensile force.
In-depth research on the pressure welding process involves many problems, such as gold (aluminum) wire material, ultrasonic power, pressure welding pressure, boring tool (steel nozzle) selection, boring tool (steel mouth) trajectory and so on.
5, 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. (General LEDs cannot pass the air tightness test.) TOP-LED and Side-LED as shown on the right are suitable for dispensing. Manual dispensing requires a high level of operation (especially white LEDs). The main difficulty is the control of the amount of dispensing, as the epoxy thickens during use. The dispensing of white LEDs also has the problem of phosphor precipitation leading to chromatic aberration of light.
6, potting package
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.
7, 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.
8, 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.
9, 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 support (PCB). The general conditions are 120 ° C for 4 hours.
10, cutting and dicing
Since the LEDs are connected together in a production process (not a single one), 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.
11, test
Test the photoelectric parameters of the LED, verify the external dimensions, and sort the LED products according to customer requirements.
12, packaging
The finished product is counted and packaged, and the blue/white/green super bright LED needs anti-static packaging.
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