Finally, your favorite PCB layout tool may not support four-layer boards. Eagle’s free version is limited to two layers, as is Fritzing.

The PCB now takes on additional responsibilities by incorporating fine-pitch redistribution layers (RDL) through advanced HDI ...

That left very little room for traces on the 2-mm-wide arms, so the PCBs had to have four layers, which raised eyebrows at the PCB house when [Sasa] submitted the design.

Nevertheless, PCB thickness has been limited to 7.6 mm due to various constraints, and 108 layers was the maximum limit with conventional technology.

Trends, opportunities, and forecast for the global standard multilayers in the global PCB market from 2017 to 2028 by product type (layer 3-6, layer 8-10, and layer 10+), end use industry ...