PCB Fabrication

PCB solder mask process

by:A-TECH      2021-03-31
The PCB we see in daily life is basically composed of solder mask, silk screen layer, copper wire and other parts. Generally speaking, we call the part of the printed circuit board that needs to be painted as solder mask; solder mask The layer uses a negative output, so after the shape of the solder mask is mapped to the board, it is not the green solder mask, but the copper skin is exposed. The role of the solder mask in controlling the reflow soldering process is very important. In the FPC printed board, the solar solder mask process is a printed board with solder mask after screen printing. Cover the pads on the printed board with a photo master so that it will not be irradiated by ultraviolet light during exposure, and the solder resist protection layer is more firmly attached to the printed board surface after ultraviolet light, and the pads are not exposed to UV Light irradiation can expose the copper pads so that lead and tin can be applied during hot air leveling. Today, I want to focus on the process of solder mask. 1. Pre-bake The purpose of pre-bake is to evaporate the solvent contained in the ink and make the solder mask non-sticky. For different inks, the temperature and time of pre-bake are different. If the pre-bake temperature is too high or the drying time is too long, it will cause poor development and reduce the resolution; if the pre-bake time is too short or the temperature is too low, the film will stick during exposure, and the solder mask will be exposed to sodium carbonate solution during development. Corrosion, causing the surface to lose luster or the solder mask to swell and fall off. 2. Exposure Exposure is the key to the entire process. If overexposure, due to light scattering, the solder resist film on the edge of the pattern or line reacts with light (mainly the photosensitive polymer contained in the solder resist reacts with light), resulting in a residual film, which reduces the resolution and causes the development of The pattern becomes smaller and the lines become thinner; if the exposure is insufficient, the result is contrary to the above situation, the developed pattern becomes larger and the lines become thicker. This situation can be reflected by the test: if the exposure time is long, the measured line width is a negative tolerance; if the exposure time is short, the measured line width is a positive tolerance. In the actual process, a 'light energy integrator' can be used to determine the best exposure time. 3. Ink viscosity adjustment The viscosity of liquid photosensitive solder resist ink is mainly controlled by the ratio of hardener to main agent and the amount of diluent added. If the amount of hardener added is not enough, an imbalance of ink characteristics may occur. The above is the PCB solder mask process that the PCB editor briefly talked about. I hope it can help everyone. PCB always insists on superb technical force, sophisticated production equipment, perfect testing methods, and product quality higher than industry standards. , Warm and thoughtful service, won the praise and welcome of global merchants and users.
Custom message
Chat Online 编辑模式下无法使用
Chat Online inputting...
Please hold on and we will get back to you soon