6 Layer PCB Manufacturing

A 6-layer PCB is manufactured by laminating PCB layers on the PCB core. Once the circuit is etched on the PCB core and the third and fourth layers are done, the second and fifth layers are laminated on the core under high temperatures and high pressures. Then the circuit is etched on the second and fifth layers. And the top and bottom layers are also laminated on the 4-layer board and the circuit is etched. And the solder mask is spayed on the top and bottom layers and the surface finish is processed on the PCB pads.

You may ask, how about drilling on the 6-layer PCB, and how is the circuit etched on the copper layer?

Two circuit etching methods can be the PCB layers. Choosing which methods depends on whether the layer requires to be drilled with HDI vias. The two circuit etching methods are:

Positive plane etching - the etching liquid is lye, and this method is used on PCB layers that don't require HDI via drilling. Its process - the UV light casts the circuit pattern on the copper layer that has been printed with a UV-sensitive film. The film on copper under the circuit pattern shadow is still liquid, and the film on unwanted copper hardens. Then the liquid film is washed away. And then tin is plated on the exposed copper as a protective layer. Next, the dry film is peeled off. Finally, the exposed unwanted copper is etched away with lye, and only copper in the circuit pattern remains.
Negative plane etching - the etching liquid is acid, and this method is used on PCB layers that require HDI via drilling. Its process is - the UV light casts the circuit pattern shadow on the copper layer that has been printed with the other type of UV-sensitive film. The film on copper under the circuit pattern shadow hardens, and the film on unwanted copper is still liquid. Then the liquid film is washed away. And the exposed unwanted copper is etched away with acid. Finally, the dry film is peed off, and only copper in the circuit pattern remains.
For the PCB core, both circuit etching methods can be used; for the top and bottom layer, only positive plane etching can be used.

If PCB holes of the 6-layer PCB are only PTH holes, the PCB board is mechanically drilled after lamination, and then the PTH holes are electroplated with copper for circuit layer connection.

For the 6-layer HDI PCBs, the top layer, bottom layer, second layer, fifth layer are laser-drilled and electroplated before lamination. The PCB core is plated-through laser-drilled and electroplated before lamination.