The Guinness book of records reports that the most layers in a Multilayer PCB is 129 (to date 2017). It was created in Japan in 2012 for use in electronic devices, such as computers and cell phones.
3 Steps to Decide the Number of Layers in Multilayer PCBs:
With PCB design tools, some basic parameters should be calculated first including grid number, network density, average pin density, operation frequency etc.
In terms of the number of layers in multilayer PCBs, some other elements have also to be taken into account, including reliability, signal operating speed, PCB manufacturing cost and lead time.
The number of layers in multilayer PCBs can be decided based on pin density and number of signal layers. The following table is the empirical reference in terms of the determination of the number of layers in multilayer PCBs.