What is the board thickness?

What is the board thickness?

The board thickness is the thickness (in mm) of the measured base material, including copper foil on top and bottom. So the board thickness does not represent the final thickness of the PCB as for that we need to add plating, solder mask, etc…
As with all manufacturing processes the Finished PCB Thickness is influenced by various factors and thus there is a tolerance applied to the final thickness.The process of manufacturing a PCB starts with the Base Materials (e.g. FR4) and are available in various thicknesses.The thicknesses available are nominal values and do not include the copper foil, basically just the laminate (resin and glass fiber weave).These base materia ls also have a manufacturing tolerance applied to the nominal thickness.This thickness tolerance is defined by the manufacturer in their data sheets.For example, the typical thickness tolerance for FR4 is ±10% of the nominal value.So a base material of 1.00mm may actually be somewhere between 0.90mm to 1.10mm thick (excluding copper).

Influences on Single and Double Sided PCB’s
For single and double sided PCB’s controlling the final thickness is less complicated, it’s mainly just the base material tolerance to take in to account.
Influences on Multilayer PCB’s
For multilayers there are many for factors influence the final thickness of the PCB these are:
1.Base Materials Tolerances.
2.Prepregs Tolerances (similar to base material tolerances).
3.Type of Buildup (number of cores, prepregs etc.).
4.The Lamination Process (Bonding of the layers).
5.Pressure and Heat Control.
6.Resin content of the Prepreg.
7.Flow characteristics.
8.Copper Layout (Balance/Distribution)
9.More copper in one area will increase the PCB thickness in that area).