one. LED production process
1. Process:
a) Cleaning: Ultrasonic cleaning of the PCB or LED holder and drying.
b) Mounting: After the silver electrode is placed on the bottom electrode of the LED die (large wafer), the expansion is performed, and the expanded die (large wafer) is placed on the thorn crystal table, and the die is punched under the microscope with a stylus. One by one is mounted on the corresponding pad of the PCB or LED holder, and then sintered to cure the silver paste.
c) Pressure welding: The electrode is connected to the LED die by an aluminum wire or gold wire welder for current injection. The LED is directly mounted on the PCB, and an aluminum wire welder is generally used. (Making a white light TOP-LED requires a gold wire welder)
d) Packaging: The LED die and bonding wires are protected 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 a point phosphor (white LED).
e) Soldering: If the backlight is an SMD-LED or other packaged LED, the LED needs to be soldered to the PCB before the assembly process.
f) Film cutting: Various diffusion films, reflective films, etc. required for backlighting are punched by a punch.
g) Assembly: Manually install the various materials of the backlight in the correct position according to the drawings.
h) Test: Check whether the photoelectric parameters of the backlight and the uniformity of light output are good.
i) Packaging: The finished product is packaged and put into storage as required.
two. Packaging process
(1). The task of LED packaging
The external lead is connected to the electrode of the LED chip, and the LED chip is protected, and the light extraction efficiency is improved. The key processes are mounting, pressure welding and packaging.
(2). LED package form
LED package form can be said to be varied, mainly according to different applications, the corresponding size, heat dissipation measures and light-emitting effects. LEDs are classified into Lamp-LED, TOP-LED, Side-LED, SMD-LED, High-Power-LED, etc. in package form.
(3). LED packaging process
(4). Package process description
Chip inspection
Microscopic examination:
Whether there is mechanical damage on the surface of the material and pitting
Whether the chip size and electrode size meet the process requirements
Is the electrode pattern intact?
2. Expansion
Since the LED chip is still arranged with a small close spacing (about 0.1 mm) after dicing, it is not conducive to the operation of the post process. We use a film expander to expand the film of the bonded chip, and 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.
(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.)
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. Preparation 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 (with or without glue) is placed on the jig of the lancet table, and the LED holder is placed under the clamp, and the LED chips are punctured one by one under the microscope with a 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
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.
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