What is the flow of screen printing process

In the printed circuit process, we commonly screen printing process flow for: substrate pre-treatment → screen printing → pre-bake → exposure → development → baking → etching or plating → de-filming, the next step by the Ru Sheng to take you into the PCB factory to feel the screen printing process flow in the PCB industry

PCB industry Ru Sheng.

Substrate preparation

For example, the substrate pretreatment methods described in the section on dry film can be applied to liquid photoresist, but the focus is different from dry film. Addressing surface cleanliness and surface roughness are the main substrate pretreatment issues.

Liquid resist is usually a polymer with acrylates as the basic component. It bonds to copper via free-moving unpolymerized acrylic genes. To ensure this bonding, the copper surface must be fresh, unoxidized, and in a free state without bonding. Excellent adhesion can then be obtained by proper roughening and increasing the surface area. Dry films have a good viscosity and a high degree of cross-linking, with few movable chemically bonded free genes, and the predominant way to accomplish the adhesion process is through mechanical bonding. Therefore, liquid resists emphasize surface cleanliness, while dry film resists emphasize the microscopic roughness of the copper foil surface.

The PCB industry is like pith.

Screen Printing

Screen Printing coating should be carried out in the range of 5-7 mm larger than the effective area of each side of the printed circuit board, rather than in the entire plate coating, in order to facilitate the firmness of the plate positioning during the exposure, because if the plate positioning tape affixed to the film layer, the viscosity will be greatly reduced after repeated use, and in the process of exposure to vacuum is likely to result in the production of the board offset. Especially in the production of images within the multilayer board, this offset is not easy to find, but when the surface layer of the production of images and etching, can be seen, but at this time can not be remedied, the product can only be scrapped. After screen printing, the cardboard must be placed on a shelf, and there must be a certain distance between the cardboard to ensure that the next baking dry evenly and thoroughly.

PCB industry such as pith.

Pre-bake

Different types of liquid-induced resist have different requirements for pre-bake temperature and time. They can be determined by accessing specifications and specific production practices. Generally, 75-80 degrees Celsius for 10-15 minutes on the first side of both sides and 15-20 minutes on the second side (oven). Pre-baking can also be done after screen printing on both sides. When using the oven, the oven must be controlled by blast and thermostat to make the temperature more uniform on all parts. When the oven reaches the set temperature, the pre-drying time should be calculated.

Because the pre-baking temperature can cause a lot of damage to the product. If the prebake temperature is too high or too long, it will be difficult to develop and remove the film. However, if the prebake temperature is too low or too short, the backing plate will stick to the resist coating during exposure and will be easily damaged when the backing plate is removed. After prebaking, the board should be removed from the oven immediately. After air cooling or natural cooling, it can enter the next process.

PCB industry such as pith.

Exposure

Since the hardness of the film layer after pre-baking is less than 1h, special attention should be paid to avoid scratches during exposure alignment. Although the wet film has a wider exposure range, it is better to use high exposure in order to improve the corrosion resistance and plating resistance of the film layer. Its sensitivity is much slower than that of dry film, so a high-power exposure machine should be used. Because of its high sensitivity, like dry film, never operate under fluorescent light. When overexposed, the positive-phase negative plate is prone to image scattering refraction, resulting in a reduction in line width, and in severe cases, no shadow is revealed; on the contrary, the negative-phase negative plate forms a scattering expansion, the line width increases, and a residual film is left behind when developing. When the exposure is not enough, after the development of the film appeared on the pinhole, film hair and shedding, resistance to etching and plating is reduced.

PCB industry such as pith.

development

Use 1% anhydrous sodium carbonate solution, temperature 30 + 2c, spray pressure 1.5 ~ 2.0kg/cm?, development time 40 + 10s. imaging point control in 1/3 to 1/2. When the wet film into the hole, the development time should be extended. Too high temperature and concentration of developer and too long developing time will destroy the surface hardness and chemical resistance of the film, and too low concentration and temperature will affect the developing speed. Therefore, the concentration, temperature and development time should be controlled within the appropriate range.

PCB industry such as pith.

Baking

In order to give the film excellent resistance to etchants and plating, the film should be cured after development. Baking conditions are 100 degrees Celsius for 1 to 2 minutes. The hardness of the film after baking can be up to 2 h.

De-filming

The use of a 4-8% sodium hydroxide solution at a temperature of 50-60 degrees Celsius and a spray pressure of 2-3 kg/cm_ can be effective in improving the removal speed, temperature ratio and concentration.

The above substrate pre-treatment → screen printing → pre-baking → exposure → development → baking → etching or plating → to film you have understood it, for more help or to add the message board below to leave a message to contact!