First, the production process
1. Production:
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 pressed with a stylus under the microscope. 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.
2. Packing: Pack the finished product as required and put it into storage.
Second, the packaging process
1. The task of LED packaging is to connect the external leads to the electrodes of the LED chip , while protecting the LED chip, and to improve the efficiency of light extraction. The key processes are mounting, pressure welding and packaging.
2. LED package form The LED package form can be said to be varied, mainly according to different application occasions, the corresponding size, heat dissipation countermeasures and light-emitting effect. Led is classified into Lamp-LED, TOP-LED, Side-LED, SMD-LED, High-Power-LED, etc. according to the package form.
3. LED packaging process flow
a) Chip inspection
Microscopic examination: 1. Whether there is mechanical damage on the surface of the material and the lockhill;
2. Whether the chip size and electrode size meet the process requirements;
3. Whether the electrode pattern is complete.
b) 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.
c) dispensing
Silver glue or insulating glue is placed at 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 with sapphire insulating 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.
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