Castellated/Edge-plated PCBs: Comments on Mechanical/Electrical contact reliability
Complexity Levels (or Class levels) 
There are several factors that contribute to the complexity of a castellated hole. The main critical design attributes are: 


Hole size
Number of holes per board
Single hole or multiple hole designs
Surface finish 


Recommendations and comments 
When castellated features are required, it is best to use the following general rules when at all possible 


Use the largest hole size possible
Use the largest Outerlayer pad possible, both top and bottom sides 
If possible, place Innerlayer pads to anchor the hole barrel. This will also help reduce burring during the castellation process. 
If the castellation is not used for a mechanical connection (i.e. insertion of a connector device), allow additional dimensional tolerance for the castellation opening if possible.



courtesy of Hitech