To provide a method for preparing CAM data for an electronic circuit board in which the CAD data of a line conductor or a surface conductor can be converted appropriately and efficiently into the CAM data consisting of the plating widow of the exposure mask for pattern plating.
The extension ratio η of the line width when the pattern data of a line conductor is converted into the pattern data of a plating window through CAD/CAM conversion is set higher for a region where the line conductors are distributed coarsely. In the region of a conductor layer where the line conductors are formed densely and the region where the line conductors are formed relatively coarsely, the etching margin is not identical even if the line width is identical, and the region where the line conductors are formed coarsely has a trend of having a larger etching margin. When the extension ratio η of the line width is set larger for the region where the line conductors are distributed coarsely, occurrence of deficient line width due to overetching can be prevented effectively in a line conductor having a small line width.
YOKOI KENJI
OHASHI HATSUO
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