The liquid photoresist undergoes a cross-linking polymerization reaction after being irradiated with UV light (300-400 nm), and the part exposed to the light forms a film and hardens without being affected by the developer. The commonly used exposure lamps are high-brightness, medium-pressure mercury lamps or metal halide mercury lamps. The lamp tube is 6000W, the exposure amount is 100-300mj/cm2, and the density measurement adopts a 21-level optical density table (Stouffer21) to determine the best exposure parameters, usually 6-8 levels. Liquid photoresist does not have strict requirements on the use of parallel light for exposure, but its photosensitive speed is not as fast as that of dry film, so a high-efficiency exposure machine (Drawer) should be used.
The photopolymerization reaction depends on the light intensity and exposure time of the lamp. The light intensity of the lamp is related to the excitation voltage and the use time of the lamp tube. Therefore, in order to ensure sufficient light energy for the photopolymerization reaction, it must be controlled by a light energy integrator. Its working principle is to ensure that when the light intensity changes during the exposure process, the exposure time can be automatically adjusted to maintain the total exposure energy unchanged, and the exposure time 25 to 50 seconds.
Factors that affect exposure time: (1) The closer the distance of the light, the shorter the exposure time. (2) The thicker the liquid photoresist, the longer the exposure time. (3) The higher the air humidity, the longer the exposure time. (4) The higher the pre-baking temperature, the shorter the exposure time.
When the exposure is excessive, it is easy to form astigmatic refraction, the line width is reduced, and it is difficult to develop. When the exposure is insufficient, the development is prone to defects such as pinholes, hairs, and falling off, and the corrosion resistance and electroplating resistance are reduced. Therefore, choosing the best exposure parameters is an important condition to control the development effect.
The quality of the negative film directly affects the exposure quality. Therefore, the graphic line of the negative film should be clear, and there should be no dizziness, virtual edge and other phenomena. It is required to have no pinholes, trachoma, and good stability. The negative film requires high black and white contrast: the optical density of silver salt film (Density) DMAX ≥ 3.5, DMIN ≤ 0.15; the optical density of diazonium film DMAX ≥ 1.2, DMIN ≤ 0.1.
Generally speaking, after the film is made, it is transferred from one process (factory) to another process (factory), or stored for a period of time, before entering the yellow light room. After experiencing different environments, the dimensional stability of the film is difficult to guarantee. In my opinion, the negatives should be directly entered into the yellow light room, and if more than 80 plates are produced for each negative, they should be discarded. This can avoid the micro-deformation of the pattern, especially the micro-hole technology should pay more attention to this.
Precautions for Exposure Process Operation:
(1) It is essential for the exposure machine to vacuumize the drying box, and the vacuum degree is ≥90%. Only by vacuuming the negative film and the workpiece closely, the image can be guaranteed without distortion and the accuracy can be improved.
(2) During the exposure operation, if there is a sticky production film, it may be caused by insufficient pre-baking or too strong vacuum in the drying box. The pre-baking temperature and time should be adjusted in time or the vacuuming of the drying box should be checked.
(3) After the exposure is stopped, the PCB board should be taken out immediately, otherwise, the residual light in the lamp will cause excess glue after development.
(4) The working conditions must be met: dust-free yellow light operating room, cleanliness of 10,000 to 100,000 grades, and air-conditioning facilities. The exposure machine should have a cooling exhaust system.
(5) During exposure, the film surface of the negative film must be facing down, so…
(A final have been posted above, please let me know if you would like me to continue)
The photopolymerization reaction depends on the light intensity and exposure time of the lamp. The light intensity of the lamp is related to the excitation voltage and the use time of the lamp tube. Therefore, in order to ensure sufficient light energy for the photopolymerization reaction, it must be controlled by a light energy integrator. Its working principle is to ensure that when the light intensity changes during the exposure process, the exposure time can be automatically adjusted to maintain the total exposure energy unchanged, and the exposure time 25 to 50 seconds.
Factors that affect exposure time: (1) The closer the distance of the light, the shorter the exposure time. (2) The thicker the liquid photoresist, the longer the exposure time. (3) The higher the air humidity, the longer the exposure time. (4) The higher the pre-baking temperature, the shorter the exposure time.
When the exposure is excessive, it is easy to form astigmatic refraction, the line width is reduced, and it is difficult to develop. When the exposure is insufficient, the development is prone to defects such as pinholes, hairs, and falling off, and the corrosion resistance and electroplating resistance are reduced. Therefore, choosing the best exposure parameters is an important condition to control the development effect.
The quality of the negative film directly affects the exposure quality. Therefore, the graphic line of the negative film should be clear, and there should be no dizziness, virtual edge and other phenomena. It is required to have no pinholes, trachoma, and good stability. The negative film requires high black and white contrast: the optical density of silver salt film (Density) DMAX ≥ 3.5, DMIN ≤ 0.15; the optical density of diazonium film DMAX ≥ 1.2, DMIN ≤ 0.1.
Generally speaking, after the film is made, it is transferred from one process (factory) to another process (factory), or stored for a period of time, before entering the yellow light room. After experiencing different environments, the dimensional stability of the film is difficult to guarantee. In my opinion, the negatives should be directly entered into the yellow light room, and if more than 80 plates are produced for each negative, they should be discarded. This can avoid the micro-deformation of the pattern, especially the micro-hole technology should pay more attention to this.
Precautions for Exposure Process Operation:
(1) It is essential for the exposure machine to vacuumize the drying box, and the vacuum degree is ≥90%. Only by vacuuming the negative film and the workpiece closely, the image can be guaranteed without distortion and the accuracy can be improved.
(2) During the exposure operation, if there is a sticky production film, it may be caused by insufficient pre-baking or too strong vacuum in the drying box. The pre-baking temperature and time should be adjusted in time or the vacuuming of the drying box should be checked.
(3) After the exposure is stopped, the PCB board should be taken out immediately, otherwise, the residual light in the lamp will cause excess glue after development.
(4) The working conditions must be met: dust-free yellow light operating room, cleanliness of 10,000 to 100,000 grades, and air-conditioning facilities. The exposure machine should have a cooling exhaust system.
(5) During exposure, the film surface of the negative film must be facing down, so…
(A final have been posted above, please let me know if you would like me to continue)
