Protect HDI Circuit Boards
It’s no secret that circuit boards are sensitive to environmental contamination like dust, dirt, and moisture. Even if the PCB’s enclosure protects it from direct contact with these contaminants, they can still enter the device through gaps and crevices. Consequently, it’s imperative to take precautionary measures to keep the board from being exposed to these contaminants. One method involves coating the board in waterproof material, which is a good solution for any environment with heavy rain or high humidity.
Another method is ensuring that the base materials of the PCB are properly handled and stored before lamination. This includes avoiding exposing the cores and prepregs to a higher-than-normal temperature, since heat has a dehydrating effect on the layers. It’s also a common practice among some PCB fabricators to bake the prepregs and cores prior to lamination, which helps prevent moisture pockets or blisters from forming on the finished product. However, this process is largely unnecessary if the boards are being shipped or stored in a regulated, dehumidified storage cabinet/cabinet.
The hdi circuit boards PCB fabrication process itself can also have a significant impact on how susceptible to moisture a board is. It’s important for the PCB fabricator to use a temperature-controlled, dehumidified work environment and to regulate the air system with desiccant packs. Then, the boards should be packaged and shipped with a layer of silica gel and in an ESD safe moisture barrier bag to reduce their exposure to moisture.
How to Protect HDI Circuit Boards From Moisture
During the assembly and soldering process, it’s also critical to take measures to minimize the amount of moisture in the air. This can be done by assembling in a clean and well-ventilated room with an ESD-safe floor mat and by using a humidity indicator card to monitor the level of moisture in the air. It’s also a good idea to preheat the oven before placing the bare circuit board inside, which will force out any embedded traces of moisture.
Once the circuit board is finished, it’s a good idea to use a lint-free cloth and household non-phosphate cleaner to wipe down the surface and remove any visible grime. After rinsing, blot the surface with a clean, lint-free cloth and dry it before placing components on it.
In addition to these measures, the manufacturer of a hdi circuit board should also consider waterproofing it for any environments with extreme conditions. There are several options for this, including para-xylylene and fluoropolymer, both of which have excellent moisture resistance properties. These are generally applied to the topside of the board, but can be used on both sides if needed. When applying the waterproofing material, it’s a good idea to visually examine the board to ensure complete and uniform coverage. This can be done with a microscope or other magnifying tool.
