pcb circuit board handle exposure to UV radiation
Printed circuit boards (PCBs) are crucial components in every electronic device we use. But how do these tiny pieces of metal and glass handle their exposure to UV radiation? UV lasers, which are comprised of wavelengths shorter than visible light, exhibit excellent absorption rates for PCB materials such as resin and copper. In addition, the lower temperatures generated by UV lasers work well with temperature-sensitive substrate materials such as polyimide.
pcb circuit board production uses a multi-step process that requires the creation of multiple layers. This is because the smallest parts on a board must be easily accessible for hand soldering to occur. The first layer is the base material or substrate. This is followed by a copper layer, which can either be foil or full-on copper coating. This layer carries electrical signals from one side to the other of the board, much like the nervous system carries messages between the brain and muscles.
To protect the copper layer, a photoresist is used. This is a light-sensitive coating that allows for the selective removal of copper. Once the desired portions of the board have been coated with photoresist, they are exposed to a blast of UV light. The UV light hardens the areas that are meant to remain as pathways, while exposing the areas of the copper that will be etched away later. The resulting patterns can be printed onto a zinc plate, allowing the manufacturer to make more of the same board.
How do pcb circuit board handle exposure to UV radiation?
After the inner and outer layers have been properly coated, they are aligned using a machine that creates registration holes in each film. Once the layers are lined up, they receive another coating of photoresist. This time, the coating is negative acting, utilizing an ink that is black in color and prevents UV light from reaching areas of the copper that are not intended to be pathways.
Once the desired pattern is printed on the plate, it’s a good idea to wash it off with an alkaline solution that will remove any remaining photoresist. The plate is then ready for imaging, which involves a UV beam that’s absorbed by the exposed portions of the photoresist. This triggers chemical reactions that etch away the unwanted copper.
Once the unwanted copper is removed, the PCB can be plated with tin to provide protection against corrosion. The last step is to apply the solder mask, which covers the signal traces and leaves pads to solder to. This process is often done in a solder pot, which contains a small amount of molten solder that the technician can quickly dip the board into. This will ensure that the solder joints are strong and durable. Despite these protective measures, there are still a number of ways that a PCB can be damaged throughout the manufacturing process. This can result in busted solder joints or cracked components, both of which will likely cause the board to be discarded. However, modern UV systems work straight from the CAD data to process the boards, dramatically reducing the risks of damage.
