Our cookbook of PCB recipes includes an assortment of odd layer PCBs.
About 8% of PCB boards we are asked to produce are comprised of an odd number of layers. But unless you have a specific requirement, it is usually best to design a multilayer board with an even number of layers. Reducing an even layered board by one layer may seem like a cost-saving move, but from a PCB perspective it is not. It may actually increase the cost as well as lead-time and leave you with a warped PCB board which may not meet your expectations. Let's look at the issues in detail.