Calculation Formula of Screen Printing Thickness of PCB Soldering Resistance Ink
The thickness of the wet film is calculated by the following formula:
hw＝[hs- (S + hs)]+P％
In the formula, hw is the wet film thickness; Hs is the screen thickness; S is the filled area; P is the solid content of the ink.
Take 100 mesh screen as an example:
Wire mesh thickness: 60 μ m； Opening area: 30%; Solid content of ink: 50%.
Thickness of wet film=[60 - (60 × 70％)] × 50％=9 μ m
When the wet film is used for corrosion resistance, the film thickness is generally required to be 15-20 μ m； When used for anti electroplating, the film thickness is generally required to be 20-30 μ m。 Therefore, when the wet film is used for corrosion resistance, it should be printed twice with a thickness of 18 μ M, meeting the corrosion resistance requirements; When it is used for anti electroplating, it shall be printed for 3 times, and the thickness is 27 μ M, meeting the requirements for the thickness of anti electric coating. When the wet film is too thick, it is easy to have shortcomings such as insufficient exposure, poor imaging, poor corrosion resistance, etc. It will be etched by liquid medicine during electroplating, resulting in film stripping, and has high pressure sensitivity. It is easy to have film sticking when pasting the negative film; When the film is too thin, it is easy to cause overexposure, poor electroplating insulation, film stripping and electroplating metal on the film. In addition, when the film is overexposure, the film removal speed is also slow.