Glass fiber reinforced substrate drill and method of forming through holes in glass fiber reinforced substrate

A method of forming through holes in a glass fiber reinforced substrate, comprising:

• providing a drill comprising a drill body having a cutting edge part on a front end side of the drill body, and a neck part on a base end side of the drill body such that the cutting edge part has a larger diameter than the neck part and that the drill body has a step formed between the cutting edge part and the neck part;
• and
• drilling a through hole in a glass fiber reinforced substrate using the drill,
• wherein the drill body has a single continuous chip evacuation groove, and the single continuous chip evacuation groove formed in the drill body has a main groove and a secondary groove such that the main groove has an L-shaped cross section and is extending from a front end of the cutting edge part over the step to the neck part and that the secondary groove has a U-shaped cross section and a smaller groove width and a smaller groove depth than the main groove and is extending along the main groove from the front end of the cutting edge part over the step to the neck part and merging into the main groove at the neck part.