One of the main technological criteria affecting the quality of drilling the holes is the correct geometry of a cutting tool and the amount of its wear. The determination of the “critical” amount of a drill wear is possible only through the indirect way, in particular by the presence of the copper foil burrs at the tool output from the printed circuit board, since with the up-to-date degree of integration of micro-assemblies, the main part of the processed holes has the diameter of about 0.6-0.8 mm, and it is quite challenging to determine the tool wear without special equipment, and in conditions of mass production it is almost impossible.
A number of industrial experiments with the hard-alloy drills of standard sharpening geometry of various amount of wear was carried out in order to assess the influence of the cutting tool geometry and the amount of wear on the drilling process. To assess the quality of the processed holes, the chip size (Lch), the micro-roughness of the holes (Ra) and the size of the copper foil burrs at the output of the workpieces (Hb) were additionally measured with a specialized precision tool. In total, 1500 holes were drilled at each previously determined operating mode.
The “critical” value of the tool blunting, the maximum allowable values of Lch,Ra and Hbwere practically defined in the course of work. On the basis of the conducted experiments, the threshold values of the axial feed speeds for the work of the “worn out” and “blunted” tool were defined. In addition, the general recommendations were formulated for the operator when drilling the foiled fiberglass and eliminating mass defects at printed circuit board manufacture.
