Abstract: The appearance of stresses when remelting printed circuit boards should be avoided. The remelting process of the tin-lead layers ensues in a pressure vessel at elevated ambient gas pressure. The quantity of heat required for the remaining can be supplied on the basis of known methods (infrared irradiation, oil, etc.) or by heating the compressed gas itself. As needed, the compressed gas can be designed as a protective atmosphere. Printed circuit boards of any and all types can be remelted by this process.

Abstract: A method and apparatus for locating terminal points on an internal conductive layer on an internal board section of a multi-layer printed circuit board assembly. Conductive locating patterns are arranged on the internal board section which are preferably fabricated by the same fabrication technique as for the conductive layer. An electrical probe such as a metal drill is then employed to locate the conductive pattern relative to a reference point. Such information is then used for drilling holes through the internal terminal points.

Abstract: A hard metal drill is disclosed for drilling contact holes in multi-legend printed circuit boards formed of synthetic resin. The drill has a diameter of not more than 1.5 mm. and has main and secondary cutting edges and spiral-shaped flutes lying opposite the drill longitudinal axis. At least one of these edges has a different angle or a different legend with respect to a corresponding other edge. The amount of difference of the two cutting angles or lengths to be compared is selected such that a gap between the drill and an edge of the drill hole is at least 20 .mu.m and not more than 50 .mu.m. In order to produce such holes more readily, the two spiral-shaped flutes have different depths.

Abstract: A method is disclosed for producing accretion-free holes with a diameter of less than 1.5 mm in circuit boards made of plastic. A hard metal drill is employed having a cylindrical chucking shank and a fluted twist section. A central axis of the twist section of the drill is moved eccentrically in relation to a central axis of rotation and therefore to a central axis of the drilled hole while drilling such that a widening of the hole occurs which is at least 20/.mu.m but not more than 50/.mu.m.