So first, we need to make two layers of circuits of the middle core. After the copper clad plate is cleaned, a layer of photosensitive film will be covered on the surface. This film will solidify when exposed to light, forming a protective film on the copper foil of the copper clad laminate.

Insert the two-layer PCB layout film and double-layer copper clad laminate, and finally insert the upper layer PCB layout film to ensure that the upper and lower layers of PCB layout film are stacked accurately.

The photosensitive machine uses a UV lamp to illuminate the photosensitive film on the copper foil. The photosensitive film is solidified under the transparent film, and there is no solidified photosensitive film under the opaque film. The copper foil covered under the cured photosensitive film is the required PCB layout circuit, which is equivalent to the role of laser printer ink for manual PCB circuit boards. In the paper PCB layout of the laser printer in the last issue, the copper foil to be retained is covered under the black ink foundation make-up. At this stage, the copper foil covered by black film will be corroded, while the transparent film will be preserved due to the curing of the photosensitive film.

Then clean the uncured photosensitive film with lye, and the required copper foil lines will be covered by the solidified photosensitive film.

Inner core plate etching

Then use strong alkali, such as NaOH, to etch the unwanted copper foil.

Tear off the cured photosensitive film to expose the copper foil for PCB layout.

Core plate drilling and inspection

The core board has been made successfully. Then make alignment holes on the core plate to facilitate alignment with other raw materials.

Once the core board is pressed together with PCB of other layers, it cannot be modified, so inspection is very important. The machine will automatically compare with the PCB layout drawing to check the errors.

The first two layers of PCB have been fabricated.