In the printed circuit process, our common screen printing process is: substrate pretreatment → screen printing → pre-baking → exposure → development → baking → etching or electroplating → film removal. Next, Ru Sheng takes everyone into the PCB factory to experience the screen printing process in PCB industry.

The PCB industry is Ru Sheng.

preparation before the substrate

for example, the substrate pretreatment method described in the dry film section can be applied to liquid photoresist, but the emphasis is different from the dry film. Solving the problems of surface cleanliness and surface roughness is the main problem of matrix pretreatment.

liquid resists are usually polymers with acrylate as the basic component. It binds to copper through a freely moving unpolymerized acrylic acid gene. In order to ensure this bonding, the copper surface must be fresh, oxidation-free, and in a free state without bonding. Then excellent adhesion can be obtained by proper coarsening and increasing surface area. Dry film has good viscosity and high degree of crosslinking, and there are few movable chemical bonds and free genes. The most important way is to complete the adhesion process through mechanical bonding. Therefore, the liquid resist emphasizes the cleanliness of the surface, while the dry film resist emphasizes the micro-roughness of the copper foil surface.

PCB industry is like sheng.

screen printing

screen printing coating should be carried out within the range of 5-7 mm larger than the effective area of each side of the printed circuit board, rather than in the whole plate coating, so as to facilitate the firmness of plate positioning during exposure, because if the plate positioning tape is attached to the film layer, the viscosity will be greatly reduced after repeated use, and it is easy to cause deviation of the production plate during exposure and vacuum pumping. Especially in the production of images in multilayer boards, this deviation is not easy to find, but it can be seen when the surface layer is produced and etched, but it can't be remedied at this time, and the product can only be scrapped. After screen printing, the cardboard must be placed on the shelf with a certain distance from the cardboard to ensure uniform and thorough drying in the next baking.

PCB industry is like sheng.

prebaking

different types of liquid resists have different requirements on prebaking temperature and time. They can be determined by accessing specifications and specific production practices. Generally speaking, the first side of the two sides is 75-8 degrees Celsius for 1-15 minutes, and the second side is 15-2 minutes (oven). It can also be pre-baked after double-sided screen printing. When using the oven, the oven must be controlled by air blast and constant temperature to make the temperature of each part more uniform. When the oven reaches the set temperature, the pre-drying time should be calculated.

because the pre-baking temperature will cause great damage to the product. If the pre-baking temperature is too high or too long, it is difficult to develop and remove the film. However, if the pre-baking temperature is too low or too short, the master will stick to the resist coating during exposure, and it will be easily damaged when the master is removed. After pre-baking, the cardboard should be removed from the oven immediately. After air cooling or natural cooling, it can enter the next process.

PCB industry is like sheng.

exposure

since the hardness of the pre-baked film is less than 1h, special attention should be paid to avoid scratches during exposure alignment. Although the exposure range of wet film is wide, in order to improve the corrosion resistance and electroplating resistance of the film, it is best to use high exposure. Its photosensitive speed 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, do not operate under fluorescent lamp. When the exposure is over-exposed, the positive negative plate is easy to produce astigmatism refraction, which leads to the reduction of line width, and in serious cases, it can not show the shadow; On the contrary, the negative phase master forms astigmatism, increases line width, and leaves residual film during development. When the exposure is insufficient, pinholes, film fuzz and peeling will appear on the developed film, and the corrosion resistance and electroplating will be reduced.

PCB industry is like sheng.

Developing

Using 1% anhydrous sodium carbonate solution, the temperature is 3+2c, and the spraying pressure is 1.5~2.kg/cm? , development time 4+1s. The imaging point is controlled at 1/3 to 1/2. When the wet film enters the hole, the development time should be extended. If the temperature and concentration of the developer are too high and the development time is too long, the surface hardness and chemical resistance of the film will be destroyed, and if the concentration and temperature are too low, the development speed will be affected. Therefore, the concentration, temperature and development time should be controlled in an appropriate range.

PCB industry is like sheng.

baking

in order to make the film have excellent resist and electroplating ability, the film should be cured after development. The baking condition is 1 degrees Celsius for 1 to 2 minutes. The hardness of the film can reach 2 hours after baking.

membrane removal

4-8% sodium hydroxide solution, temperature of 5-6℃ and spray pressure of 2-3kg/cm_, can effectively improve the removal speed, temperature ratio and concentration.

Have you understood the above substrate pretreatment → screen printing → pre-baking → exposure → development → baking → etching or electroplating → film removal? If you need more help or supplement, please leave a message below the message board! PCB industry such as Sheng answers for you.