Final answer:
In photoetching, all areas covered by light-sensitive enamel that are not protected by the circuit template are exposed. The exposed photoresist hardens, and then a developer removes the unexposed portions, followed by an etching process to remove unprotected material, forming the circuit pattern.
Step-by-step explanation:
When a printed circuit is manufactured by the photoetching process, the portions of the plastic or phenolic sheet that are actually photographically exposed are all areas covered by light-sensitive enamel not covered by the circuit template. During this process, a photoresist or light-sensitive enamel is applied to the entire surface of the circuit board material.
The circuit template, which shields certain areas of the photoresist, is then applied. This template is typically a negative of the circuit pattern, meaning that it covers all areas that should not be etched away. The board is then exposed to light, and the areas not covered by the template polymerize and become resistant to the etching solution.
Subsequently, the board is treated with a developer that washes away the unexposed photoresist, followed by an etching solution. The etching solution removes the unprotected copper, but the polymerized photoresist protects the desired circuit pattern. This process relies on the photoconductor properties, similar to those used in devices like an ink jet printer and xerography processes. Here, light exposure changes the conductivity of certain materials, such as selenium, which are used to create images on a conducting aluminum drum by selectively neutralizing positive charges in the areas exposed to light.