DSR-2200NC solder mask ink process control III
2018-06-15 03:01:44
3.2.6 Exposure
The pre-baked substrate can be exposed by standing to cool to room temperature. The exposure should be completed within 24 hours after pre-baking, otherwise it will cause difficulty in development. The exposure is classified into contact exposure type and non-contact exposure type. At present, most of the exposure exposure type on the market represents the development direction of solder mask processing technology.
The exposure was performed with a silver salt backsheet or a diazo sheet as a mask on a vacuum exposure machine with a cooling system. Exposure machine power can not be too small, generally 5kW ~ 8kW. The exposure light source can use a halogen lamp with a light emission wavelength of 310 nm to 420 nm to facilitate the absorption of the photosensitive ink. DSR-2200NC solder resist ink exposure energy requirements in the 400mj/cm2 ~ 600mj/cm2, if the film is thick, the exposure time should be appropriately extended to make full exposure.
Exposure is a critical step in solder mask processing and largely determines the quality of solder mask processing. The most direct reflection of the lack of exposure energy is that during development, the solder mask is eroded and the surface loses its luster. In severe cases, the surface of the solder mask even appears as a "crack crack," resulting in scrap. The indirect reflection is that the physical properties of the solder mask, such as solvent resistance, acid and alkali resistance, and thermal shock resistance, are degraded, and the service life cannot be guaranteed. In addition, the exposure clip should reach a certain degree of vacuum when exposed, so that the mask close to the board surface, but the vacuum can not be too large, otherwise it will cause the film and the surface of the film adhesion. This is also one of the reasons why the surface of the solder mask is "cloudy." Exposure clamp temperature should be controlled below 40°C. If the cooling system does not meet the requirements, the continuous exposure time cannot be too long. After a period of time should be intermittent for half an hour, such as the exposure clip temperature naturally reduced to room temperature before exposure. In this way, although the processing cycle is extended, the processing quality can be guaranteed. The exposed substrate is allowed to stand for at least 10 minutes to completely cure the cross-linking. However, the exposed substrate must be developed within 12 h, otherwise it will cause development difficulties.
3.2.7 Development
Development should be performed on the developing machine. When developing, several parameters such as developer concentration, temperature, developing speed, and spray pressure should be controlled. Usually choose the concentration of the developer solution is 1.0% ~ 1.2% Na2CO3 solution; temperature control at 25 °C ~ 35 °C; development speed at about 1m/min, time control within 90s; spray pressure of 2kg/cm2. The developer should be changed frequently according to the number of developing substrates to ensure the activity of the developer. After development, rinse thoroughly with water to remove residual developer and film from the plate and metallized holes. Otherwise it will lead to the next process hot air leveling, the pads and holes can not blow on the tin and lead.
3.2.8 Curing
Curing is the last step of solder mask processing, and the process is relatively simple. Simply place the developed substrate in a hot air circulation oven at 150°C±5°C for 35 minutes to 60 minutes. However, it is better to control the curing temperature and curing time, otherwise it will reduce its physical properties.
4 Conclusion
The liquid photosensitive thermosetting solder mask ink processing technology has been widely used in the printed circuit industry and is inseparable from its process characteristics. In this paper, in combination with actual production, each step of this process (screen printing type) is discussed in detail, and the quality control method for each step is described. In addition to strictly controlling the above-mentioned key steps, we must also strengthen the protection of solder masks in hot air leveling, profile processing, packaging and transportation and other aspects to ensure the quality of finished printed circuit board solder masks.
Aerospace Technology Group 771 Research Branch
The pre-baked substrate can be exposed by standing to cool to room temperature. The exposure should be completed within 24 hours after pre-baking, otherwise it will cause difficulty in development. The exposure is classified into contact exposure type and non-contact exposure type. At present, most of the exposure exposure type on the market represents the development direction of solder mask processing technology.
The exposure was performed with a silver salt backsheet or a diazo sheet as a mask on a vacuum exposure machine with a cooling system. Exposure machine power can not be too small, generally 5kW ~ 8kW. The exposure light source can use a halogen lamp with a light emission wavelength of 310 nm to 420 nm to facilitate the absorption of the photosensitive ink. DSR-2200NC solder resist ink exposure energy requirements in the 400mj/cm2 ~ 600mj/cm2, if the film is thick, the exposure time should be appropriately extended to make full exposure.
Exposure is a critical step in solder mask processing and largely determines the quality of solder mask processing. The most direct reflection of the lack of exposure energy is that during development, the solder mask is eroded and the surface loses its luster. In severe cases, the surface of the solder mask even appears as a "crack crack," resulting in scrap. The indirect reflection is that the physical properties of the solder mask, such as solvent resistance, acid and alkali resistance, and thermal shock resistance, are degraded, and the service life cannot be guaranteed. In addition, the exposure clip should reach a certain degree of vacuum when exposed, so that the mask close to the board surface, but the vacuum can not be too large, otherwise it will cause the film and the surface of the film adhesion. This is also one of the reasons why the surface of the solder mask is "cloudy." Exposure clamp temperature should be controlled below 40°C. If the cooling system does not meet the requirements, the continuous exposure time cannot be too long. After a period of time should be intermittent for half an hour, such as the exposure clip temperature naturally reduced to room temperature before exposure. In this way, although the processing cycle is extended, the processing quality can be guaranteed. The exposed substrate is allowed to stand for at least 10 minutes to completely cure the cross-linking. However, the exposed substrate must be developed within 12 h, otherwise it will cause development difficulties.
3.2.7 Development
Development should be performed on the developing machine. When developing, several parameters such as developer concentration, temperature, developing speed, and spray pressure should be controlled. Usually choose the concentration of the developer solution is 1.0% ~ 1.2% Na2CO3 solution; temperature control at 25 °C ~ 35 °C; development speed at about 1m/min, time control within 90s; spray pressure of 2kg/cm2. The developer should be changed frequently according to the number of developing substrates to ensure the activity of the developer. After development, rinse thoroughly with water to remove residual developer and film from the plate and metallized holes. Otherwise it will lead to the next process hot air leveling, the pads and holes can not blow on the tin and lead.
3.2.8 Curing
Curing is the last step of solder mask processing, and the process is relatively simple. Simply place the developed substrate in a hot air circulation oven at 150°C±5°C for 35 minutes to 60 minutes. However, it is better to control the curing temperature and curing time, otherwise it will reduce its physical properties.
4 Conclusion
The liquid photosensitive thermosetting solder mask ink processing technology has been widely used in the printed circuit industry and is inseparable from its process characteristics. In this paper, in combination with actual production, each step of this process (screen printing type) is discussed in detail, and the quality control method for each step is described. In addition to strictly controlling the above-mentioned key steps, we must also strengthen the protection of solder masks in hot air leveling, profile processing, packaging and transportation and other aspects to ensure the quality of finished printed circuit board solder masks.
Aerospace Technology Group 771 Research Branch
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