Small Hole Drilling

Back taper drills, back taper drills with cylindrical tips and spade type drills were the three types available in the past for drilling multilayer boards in the diameter range of 0·8 to 1·1 mm. With packaging developments, drilling of smaller diameters, such as 0·4 mm, became necessary and care had to be taken to avoid drill breakage. The effects of board thickness, drill diameter and feed on drill breakage are analysed, followed by discussion of parameters affecting drilling accuracy and drill run‐out. The paper then deals with the effect of drill design on drill breakage, resin smear, nailheading and hole wall roughness. Results obtained using one back taper reference drill and seven other different spade type drill designs are analysed.