The present invention relates to method of manufacturing a printed wiring board perfectly free from any possibility of solder bridging that often takes place with the hitherto known printing wiring board.
Prior to entering description of the present invention, a typical conventional printed wiring board will be briefly described with reference to FIG. 1. As illustrated in FIG. 1, the conventional printed wiring board is provided with a solder resist thin layer 1 which is coated all over the insulator base board exclusive a land 2 of a printed circuit to be soldered, the coating being effected in the regular printed method. The said solder resist thin layer 1 has a substantially constant thickness but is thinner than the land 2, that is, the conductive foil. This causes a stepped portion 2a to appear between the upper face of the land 2 and the solder resist thin layer 1 on the side wall of the said land 2, resulting in an exposed part of conductive metallic foil. Thus, particularly in case of very crowded land area such as integrated circuit where a large number of land is arranged, solder bridging often occurs between the exposed metallic surfaces during soldering operation, resulting in wrong wiring. Moreover it is pointed out as another drawback with the conventional printed wiring board that solder is insufficiently deposited on the land, because the solder resist thin layer is flat in the vicinity of the land and situated lower than the same.
To eliminate the aforesaid drawbacks with the conventional printed wiring board, the inventors carried out extensive research and development works and found out that they could resolve the problems with them by providing a raised portion of solder resist ink around the land or at the area between the lands to be soldered.
USPTO Backgrounds
USPTO Backgrounds