Electronic – 8-layer Stackup: 3 cores vs 4 cores

pcbpcb-designpcb-fabrication

For a new project I am looking to use 8 layers and I am currently figuring out the layer stack I want to use. As for usage, I will most likely go with:

  1. Top
  2. GND Plane 1
  3. Signal 1
  4. Power plane 1
  5. Power Plane 2
  6. Signal 2
  7. GND Plane 2
  8. Bottom

And for an overall thickness of ~1.6mm (because the PCB will be plugged into a connector directly) I was thinking about using four 200um cores and three ~180um prepregs.

However, I just checked the layer stackup proposal on multi-circuit-boards. Unlike me, they did not use 4 cores and 3 prepregs, but 3 cores and 4 prepregs, with electroplated copper on the outer layers.

What are the advantages/disadvantages when using 3 or 4 cores?

Best Answer

This is due to how PCBs are built. Inner layers are etched in pairs to copper that is pre-laminated to both sides of a core. Outer layers are bare copper sheets that are etched when the whole PCB is already laminated. Thus 8 layer boards almost always have 3 cores and 4 prepreg layers because there are three pairs of inner layers. You can find videos in youtube etc that explain how multilayer PCBs are manufactured.

Related Topic