Photoresist dry film is a crucial component in the fabrication of printed circuit boards (PCBs). The process involves applying a thin layer of photoresist on top of a copper-clad board and exposing it to ultraviolet (UV) light through a photomask, which selectively hardens the photoresist in certain areas. The unhardened photoresist is then washed away, leaving behind a patterned resist layer that protects the underlying copper during the etching process. However, commercially available photoresist dry films can be expensive and hazardous to handle, prompting many DIY enthusiasts to explore alternative and safer methods.
One such method involves using a combination of benzophenone and polyvinyl acetate (PVA) to create a photoresist dry film that is both safe and high-resolution. Benzophenone is a photo-initiator that is commonly used in the photopolymerization of resins, while PVA is a water-soluble polymer that is widely available and relatively inexpensive.
Compared to other photoinitiators such as diazo salts, benzophenone is less toxic, not friction sensitive and does not produce harmful byproducts when exposed to UV light. It is also less sensitive to temperature and can be used at room temperature without the need for additional heating.
Here are the steps to create your own photoresist dry film using benzophenone and PVA:
- PVA (polyvinyl acetate) glue
- Clear plastic sheet (such as acetate)
- Black inkjet printer
- Glass plate
- Flat object (such as a book or a weight)
- UV light source
- Mix benzophenone with ethanol in a ratio of 1:1.
- Pour a small amount of PVA glue into a container, and then add the benzophenone/ethanol mixture to the container. Mix the solution thoroughly until it becomes a smooth and homogeneous liquid.
- Print your PCB design onto the clear plastic sheet using a black inkjet printer. Be sure to print a mirrored image of the design so that it is correctly oriented when transferred to the board.
- Place the printed plastic sheet onto the glass plate, and then pour a small amount of the PVA/benzophenone mixture onto the plastic sheet.
- Use the flat object to spread the mixture evenly over the entire surface of the plastic sheet.
- Allow the mixture to dry completely. This may take several hours.
- Once the mixture is dry, carefully peel the plastic sheet away from the dried film. You should now have a sheet of photoresist dry film that is ready to be applied to your copper-clad board.
- Place the photoresist dry film onto the board with the dried side facing down onto the copper.
- Apply pressure to the film using the flat object to ensure good contact with the board.
- Expose the board to UV light through the printed plastic sheet for the required amount of time (usually a few minutes).
- Remove the plastic sheet from the board, and then develop the board using an appropriate chemical solution.
Note: This method is just one of many ways to make your own photoresist dry film, and it may require some experimentation to get the right mixture and exposure times for your specific needs. Additionally, handling chemicals and UV light requires caution and safety measures, so be sure to follow proper safety procedures.
This DIY method of creating photoresist dry film using benzophenone and PVA is relatively easy and safe to handle. Moreover, the use of a water-soluble polymer such as PVA makes it easy to clean up the excess photoresist and avoid any hazardous waste disposal. The resulting resist layer is also high-resolution, making it suitable for fine-pitch surface-mount components.
In conclusion, DIY enthusiasts can create their own photoresist dry film using benzophenone and PVA, thereby avoiding the high cost and potential hazards of commercial alternatives. The process is relatively simple and easy to handle, making it accessible to hobbyists and professionals alike.