The circuit graphics on PCB board are completed by PCB manufacturers using exposure imaging and development etching technology. Both PCB multi-layer board and flexible circuit board need exposure imaging and development technology when making circuit graphics. The following is a detailed introduction of the processing characteristics and principles of the two processes.
(1) exposure. Due to the thickness of the dielectric layer on the substrate of coated PCB PCB, the PCB should be exposed by a higher rate exposure machine, such as a lamp with a 7 kw metal halide (such as tungsten lamp) and an exposure machine with parallel (or reflected quasi-parallel light). The light quantity on the surface of the drying insulating medium layer should be between 200 and 250, and the exposure time can be adjusted by the light ladder gauge test or the conditions provided by the supplier. Generally, a larger exposure amount and a shorter exposure time should be adopted. For the use of low-power exposure machine, due to the low light energy, resulting in a long exposure time, light refraction, diffraction, etc., which is adverse to the manufacture of fine detail distance or high density interconnect through hole.
Development and cleaning. Development and cleaning conditions and liquid photosensitive resistance welding ink and conditions are much the same. Attention should be paid to the change in the concentration and temperature of sodium carbonate in the developer, often adjust the development time (or transfer speed) or adjust the solution, which is related to the PCB graphics development on the problem of whether completely dry.
Curing (thermal curing and UV curing). After exposure and development, the PCB circuit board is basically cured by the photochemical (cross-link) action of the exposure, but it is mostly incomplete. Add the water that develops, clean to wait to absorb, want to finish through heating so. On the one hand can remove water and solvent, on the other hand, mainly to further complete and deepen the curing. But heat curing is mostly done by conducting heat. Therefore, its curing is carried out or completed gradually from the surface to the interior, so it presents a gradient curing degree state. However, due to the characteristics of UV light penetration of substances, but also due to the strong absorption of epoxy resin UV light characteristics, so there is a strong light cross chain reaction, so that the curing completely and completely out of the organic solvent substances. Therefore, the insulating dielectric layer used as a laminate must be fully cured and completely drained of water and solvents in order to meet the requirements of Tg(glass fiber temperature) and dielectric constant. So in the curing most of the use of thermal curing after UV curing these two steps, to complete curing
Note that curing should be strictly controlled. The control time should be set according to the experiment and test. If the PCB board is overcured or undercured, it will lead to deterioration of product performance and change of roughness (drawing). This will bring great quality hidden trouble to the following electroplating process. Through a long – term practical experience, such as through the circuit board manufacturers in the exposure and development process will have strict technical parameters control.