The development of blue LED products has opened up the application of full-color LED kanbans in display panels. Due to the light-emitting characteristics of LEDs, LEDs have the advantages of small size, low power consumption, long life, and collision resistance. With production technology, Improvement of equipment, product price acceleration and rationalization, and then expand the application areas of the LED industry, such as the indicator lights of home appliances, car lights, traffic signs and outdoor large billboards. The successful development of white LEDs will become an alternative to indoor lighting and backlights for mobile phone panels, making the LED industry a broader market in the future.
Photoresist, also known as photoresist, is a photosensitive material used in many industrial processes. Like lithography, a patterned coating can be engraved on the surface of the material.
There are two types of photoresist, positive photoresist and negative photoresist.
The forward photoresist is a kind of photoresist, and the portion which is irradiated to the light is dissolved in the photoresist developing solution, and the portion which is not irradiated with light is not dissolved in the photoresist developing solution.
The negative photoresist is a kind of photoresist, and the portion which is irradiated to the light is not dissolved in the photoresist developing solution, and the portion which is not irradiated with light is dissolved in the photoresist developing solution.
Positive-type photoresists and negative-type photoresists are mainly used in the metal electrode evaporation Lift-off process for LED chip manufacturing. Since the metal materials used for LED electrodes are not easy to make circuit patterns by etching, they are pulled up. (Lift-off) lithography process, obtaining an overhang photoresist pattern, so that the metal will not be continuously deposited on the photoresist during the evaporation process, and the photoresist will be used without the metal. The photoresist portion of the cloth cover is pulled up to complete the pattern of the metal electrode.
In the optical exposure mode, the upper layer of the photoresist receives higher energy than the lower layer, so that most of the positive photoresist is imaged as narrow and wide, and cannot be exposed by one exposure. That is, the pattern of Overhang is obtained, and the image of the negative photoresist is exactly opposite to the image of the positive photoresist, so the negative photoresist is the best choice for the lift-off process.
For example, ENPI200 photoresist is mainly a chemically amplified negative photoresist mainly composed of phenolic resin (Novolak) and photoacid. Because phenolic resin is soluble in alkaline aqueous solution, compared with rubber type (Rubber type). The negative photoresist has the advantage of being environmentally friendly. The photoresist imaging principle is that the acid is generated in the exposed block due to the acid acid receiving energy, and the high temperature after exposure and exposure causes the phenolic resin and the cross-linking agent to generate a cross-linking cross-linking reaction to leave a pattern. The high-resolution lift-off photoresist EPI622 requires a special process to shrink the Overhang photoresist line to less than 1 μm, which is suitable for high-brightness LED thin line width processes.
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