In addition to the green paint function to avoid oxidation and welding short circuit, what impact? How to improve the PCB board wet film and text on both sides of the color difference? How to make the copper surface is not oxidized?
The main function of green paint is anti-oxidation and anti-welding. In addition, because it is also a dielectric material, it will still have a certain influence on the impedance. Board color differences are difficult to solve, especially when the copper area on the board is different. Because of the difference in color, often comes from the state of color reflection on the surface of the circuit board. If there is a large difference in copper area, there is no way to change the state of reality. Chromatic aberration will certainly exist. Therefore, the problem of color difference should focus on whether there should be discoloration of inks, copper surfaces, and plates that should not have occurred. Other problems should not be important quality issues. Of course, some people simply use dark ink, which can hide the ugly. As for the copper surface oxidation, the surface should be dry and maintained after drying prior to painting. In particular, it must not be stacked before the circuit board is actually dried. Because this kind of stack will make the residual hot water gas unable to be eliminated, it will soon affect the oxidation of the copper surface.
In general, the method of making solder masks will be pre-baked after unilateral coating of ink, followed by second-side coating. If the drying time is not long, the color of the copper surface will not change much. But more or less, the surface color will be a bit deeper. This problem, if used with existing processes, seems difficult to avoid. Therefore, some manufacturers will work on both sides of the circuit board, first apply one side of the coating, pre-baking, exposure, development, hardening, and then perform a pre-treatment, so that the other side of the copper also shows fresh copper, and then make a whole Process. Although this practice can improve the copper surface color problem, it has a negative impact on dimensional control, exposure alignment, plate surface smoothness, and processing costs. Therefore, it is not practical.
At present, many circuit board manufacturers begin to use spray-stop paint spray treatment, which can reduce the color difference risk of two baking. As for the problems that cannot be overcome in practice, it is recommended to discuss practical functional issues with the customer. As long as there is no problem with the function, the color difference should not be the main consideration for quality. Of course, the board can not be like a big face, so that customers will lose the quality of confidence, it is not possible, the above for your reference.