PURPOSE: To shorten a heating time at soldering and to restrain a bus bar from rising in temperature so as to protect an insulating substrate against warpage by a method wherein the soldering part between a circuit pattern and the bus bar is made irreducibly minimum in area.

CONSTITUTION: A wiring board of this design is composed of bus bars 1 which are formed of good conductor metal such as copper or the like in pattern and a large current flows through, an insulating substrate 2 such as a glass fabric base epoxy region board, copper patterns 4 formed on the insulating substrate 2 through etching or the like, soldering parts 5 where the bus bars 1 are soldered to the copper patterns 4, and holes 5 through which locking screws are inserted. The area of the soldering part 5 is set to the irreducible minimum (for instance, 20mm or below in length, equal to width of bus bar or below in width). Even if the whole insulating substrate 2 is heated at soldering as in the case of a reflow soldering method, the insulating substrate 2 can be protected against warpage and a secure electrical connection can be realized, as the soldering part 5 is set as small in area as possible and the insulating substrate 2 is fastened by bolts using the locking holes 6 after soldering when the wiring is connected to a power module or the like.