Harm of chloride ion to PCB and its treatment---from Shenzhen Vip Circuit Co.,Ltd
Generally people only know that chlorine can be sterilized, in tap water and swimming pool are usually used. Chlorine bleach can also make our clothes white and bright, but the daily life and electronic products are not the same. PCB producers should be concerned about the following things: the PCB assembly, the presence of chloride ions will cause leakage, erosion and metal ionization. Chlorine is a very non-metallic active substance. If there is enough chloride on the assembly board, the ionic electrode potential formed by the combination of chlorine and moisture in the moisture can cause corrosion and metal ionization.
There are many potential sources of chloride ions in the process of PCB production. Under normal circumstances, it is difficult to find all the sources of chloride ions. Often this situation includes hot air leveling (HASL) in the flux, the operator's skin sweat and cleaning with tap water and so on.
The chloride ion content is affected by the chemical composition of the flux. Due to the natural properties of rosin, the use of high-quality solid rosin in the assembly process as flux (such as active flux or mild active flux), then the chloride ion content is relatively high. Resin-based or rosin-based water-soluble fluxes and no-clean fluxes are opposite in this respect. Therefore, the content of water-soluble or no-clean flux chloride ions used in the final assembly process is low.
The chloride ion content is affected by the material quality of the PCB. The material of the PCB sheet (including its insulating substrate and attached metal) determines the permissible chloride ion content during assembly. Ceramic substrate, or other material formed on the refractory material, such as aluminum, is more sensitive to the presence of chloride ions than organic substrates such as epoxy glass cloth substrates. This is partly due to the extent to which the surface integrated distribution has reached the microscopic range. For the surface metal layer, the nickel / gold surface itself is much cleaner than the lead / tin surface.