Cover photosensitive solder resist ink on the board surface with circuit pattern，The ink protects the circuit from oxidation and allows the customer to avoid soldering of the pads and unwanted wires during soldering (preventing soldering).
2.Main materials involved in the Inner layer
1)Copper Clad Laminate( CCL) with circuit patterns
2)solder mask ink
3)screen printing Stencil
1)The purpose of the ash pretreatment line : Clean the board surface by mechanical brushing and chemical cleaning, and roughen the copper surface with volcanic ash to increase the bonding force between the ink and the board surface.
2)The purpose of screen printing machine : Covering the ink onto the board through screen printing Stencil
3)The purpose of pre-baking : Initially curing the ink covered on the board surface, facilitating CCD exposure, avoiding ink staining of film and CCD equipment
4)The purpose of CCD Exposure : hardening the surface ink (polymerization) by strong light irradiation, avoiding the ink from sticking to the film and transferring the circuit pattern on the film to the CCL
5)The purpose of developing : Remove the ink that needs to be soldered to make the pad exposed
6)After baking : to harden the ink on the board thoroughly
1)The minimum soldering bridge can achieve 3.5 mil
2)The alignment accuracy of the pad Opening can achieve 0.8 mil
3)The minimum BGA Opening can achieve 8 mil
4)Hole plugging ability : 0.2 mm-0.65 mm; fullness of Hole plugging ＞85%
5)Maximum screen printing ability : Can screen 8 oz copper surface
6)Maximum ink thickness can be produced to: 50 um.