PURPOSE: To form multiple conductor layers in square shape for enabling bumps in high density to be formed by a method wherein the multiple conductor layers formed on the rear surface or one plane of an insulating substrate are cut-in lengthwise and crosswise reaching the insulating substrate in the proper groove width and pitch.

CONSTITUTION: Both surfaces of a ceramic substrate 2a are ground down while a wiring pattern is formed by thin film on the main surface whereon IC chips are mounted. A mixed paste of Mo and Mn is screen-printed on the surface of the ceramic substrate 2a so as to form metalized layers (conductor layers) 2b by baking the mixed paste in reducing atmosphere. Next, the rear surface of the substrate 2a is cut-in lengthwise and crosswise by a cutting machine 3 having a diamond cutter. The respective residual metallized layers 2b in square shape are formed into bumps 1 by cutting-in the rear surface of the substrate 2a lengthwise and crosswise. Through these procedures, the bumps 1 can be formed in higher density than that of conventional process by setting up the thickness of the diamond cutter as well as the cutting-in pitch at smaller value.