| 摘要 |
PROBLEM TO BE SOLVED: To form a multilayer circuit board having extremely highly reliable via holes with high productivity by connecting conductor circuit layers to each other after the bottom sections of small holes for forming the via holes are etched and the carbon concentrations on the bottoms of the holes are made lower than a specific value. SOLUTION: After a conductor circuit layer 2 is provided on a substrate 1, another conductor circuit layer 4 is formed on the layer 2 through an insulating layer 3. Then holes are formed into the outermost conductor circuit layer 4 by partially etching off the layer 4 at prescribed positions and the insulating layer 3 exposed in the holes is removed with a laser beam. Therefore, small holes for electrical connection can be formed with high dimensional accuracy without giving any damage to the peripheral sections of the holes. After the holes are bored, the depths of the holes are increased to >=3μm by etching the holes with an aqueous solution of ferric chloride, cupric chloride, etc., so that the carbon concentrations on the bottoms of the holes may become <=6×10<-8> g/mm<2> . Then the conductor circuit layers 4 and 2 are electrically connected to each other by forming via holes 5 by plating the holes with solder or copper. |
