From the manufacture of printed circuit boards the use of photolithographic methods is known, in order to produce a desired conductor pattern on an insulating support material. When producing soldered bumps on copper pads a triple photoresist film is applied and subsequently the holes over the copper pads are opened by exposure and development. After filling the holes by means of a solder paste and subsequent heating or reflow, soldered bumps are formed on the copper pads. The remaining resist material is then removed.
The disadvantage of this prior art method is that it is not possible to produce soldered bumps which are higher than the resist film, because the solder volume in the opening above the copper pad cannot be raised. In addition, it is not possible to reliably produce in this way diameters smaller than 100 .mu.m, because the resolution of a triple laminated resist with an approximate height of 80 .mu.m is no longer adequate for such small structures. Another problem is represented by the minimum diameter of the solder globules in the paste, because in the case of smaller diameters the microholes can no longer be filled in an optimum manner.
Therefore the problem of the invention is to produce large-volume solder bumps, which have a diameter smaller than 100 .mu.m and following the reflow process are higher than the mask used.
According to the invention this problem is solved by the features of the main claim. Further advantageous developments form the subject matter of the subclaims.