In some case it might be useful to place PTH on the board edge. For instance when you want to solder two PCB onto each other in a 90° angle or when soldering the PCB to a metal casing.
This techniques requires extra steps in production e.g. an extra pass in the drilling department after direct metallization and dry film imaging of the outer layers.
This introduces an extra cost and extra attention of our data preparation department. Therefore it is needed to indicate this in the order details.
See our design guidelines.