It is recommended that Mechanical 1 & 2 layer is used for specifying non-plated and plated slots respectively. If slots are indicated on Mechanical 1 & 2 layers it then gives the PCB manufacturer options on how to create the slot. Slots can be created by direct routing of the slot. This could result in an additional process if the slot is to be plated as the PCB Manufacturer would have to drill, rout, process and then rout again. Slots less than 1.2mm in width result in higher process costs due to reduced stack heights i.e. reduced to 1 panel – this is also true for drilling.