Multilayer Builds

This section describes the different materials available for multilayer circuit boards and the basic guidelines governing stacking possibilities.

Basic guidelines

A multilayer circuit board is made up of 3 groups of materials:

Cores: sheet of dielectric material covered with copper on both sides.

Prepreg: sheet of dielectric material pre-impregnated with resin to join the different layers of a multilayer circuit board.

Copper sheets: sheet of copper with a uniform, controlled thickness, used for the external layers of a multilayer circuit board.

Basic structures:

Basic 4-layer stack-up

Basic 6-layer stack-up

Given the wide variety of materials available, it is possible to design boards with different thicknesses and electrical specifications. Nevertheless, in order to avoid any possible difficulties in the manufacturing process or mechanical distortions in the circuit board, it is important to follow the guidelines below:

Create symmetrical builds

Do not stack more than 2 prepegs in a row

Use the same thickness of copper on symmetrical layers. Cu top=Cu bottom // Cu int.1=Cu int.2

Materials available

Cores

* Except in 0.35mm and 0.5mm, the core dielectric must be the nominal minus the corresponding microns for each side.
Nominal Thickness*	18/18µ	35/35µ	70/70µ
0.35mm	✘	✔	✘
0.50mm	✔	✔	✘
0.80mm	✔	✔	✔
1.0mm	✔	✔	✘
1.2mm	✔	✔	✘
1.6mm	✔	✔	✔
2.0mm	✔	✔	✔
2.4mm	✔	✔	✔

Prepreg

Reference	Nominal Thickness
1080	0.065mm
2116	0.105mm
7628	0.175mm

Copper sheets

Copper nominal thickness	18µ	35µ	70µ