The second solder mask process in the PCB board production process is developing.
The developing operation is generally carried out in the developing machine, and the developing parameters such as the temperature of the developing solution, the conveying speed, and the spray pressure are well controlled to obtain a better developing effect.
The development is to remove the solder mask on the pad with a developing solution for the shading part. The developing solution is 1% anhydrous sodium carbonate, and the liquid temperature is usually between 30 and 35 degrees Celsius. Before the formal development, the temperature of the developing machine should be raised to make the solution reach a predetermined temperature, so as to achieve the best development effect.
The developing machine is divided into three parts:
The first stage is the spray, which mainly uses high-pressure injection of anhydrous sodium carbonate to dissolve the unexposed solder resist.
The second stage is the water washing stage. The first is to use a high-pressure pump to wash the residual solution with water, and then enter the circulating water to wash it thoroughly.
The third stage is drying. There is an air machine before and after the drying section, which mainly uses hot air to dry the board. If the temperature of the drying stage is higher, the board can be dried.
The correct development time is determined by the development point, which must be kept at a constant percentage of the total length of the development section. If the development point is too close to the exit of the development section, the unexposed solder mask will not be fully developed. It will cause the residue of the unexposed solder resist layer to remain on the board surface. If the display point is too close to the entrance of the developing section, the exposed solder resist layer may be etched due to long-term contact with the developer. It becomes hairy and loses its luster. Usually the display point is controlled within 40%-60% of the total length of the developing section.
In addition, it should be noted that it is easy to scratch the board during development. The usual solution is to put on the board when the operator wears gloves, handle the board gently, and the size of the printed board is different, so try to put together the same size as possible. When placing the board, keep a certain distance between the board and the board to prevent the board from being crowded during transmission and causing “jamming” and other phenomena. After showing the film, place the printed board on the wooden bracket.
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