Method of manufacturing a printed circuit board

A method of manufacturing a printed circuit board comprising the steps of:

• providing a substrate having a first surface and a second surface being in a different plane than said first surface, said first and second surfaces having a conductive layer thereon, said conductive layer having a photoresist layer thereon;
• placing a single planar photomask adjacent to and spaced above said photoresist layer and being substantially parallel to respective planes containing said first and second surfaces, said photomask being formed with an opaque mask pattern and a light-transmissive pattern;
• radiating a parallel light beam through said photomask to said photoresist layer to provide an exposed pattern of an intended width "L" on said photoresist layer corresponding to said light-transmissive pattern;
• removing said exposed pattern of said photoresist layer to leave a patterned area of said conductive layer not covered by said photoresist layer;
• and
• forming a circuit pattern on said conductive layer on said substrate in accordance with said patterned area of said conductive layer;
• said method being characterized in that:
• (1) said light-transmissive pattern is configured so as to satisfy the following relationships:
• when D=0, W/L=1,
• when D>0, W/L<1,
• wherein "W" is a width of said light-transmissive pattern for forming said exposed pattern of said intended width "L", and "D" is a distance between said light-transmissive pattern and said photoresist layer;
• (2) said planar photomask comprises a first photomask portion having a first size ratio "W1/L1", which is disposed such that it is spaced from said photoresist layer on said first surface by a distance D1 in which D1 is .gtoreq.0, and at least one second photomask portion having a second size ratio "W2/L2", which is disposed such that it is spaced from said photoresist layer on said second surface by a distance D2 in which D2 is >0 and in which D2 is >D1, wherein "L1" is a first intended width of said exposed pattern to be formed on said photoresist layer on said first surface, "W1" is a first width of said light-transmissive pattern of said first photomask portion used to form said exposed pattern having said first intended width "L1", "L2" is a second intended width of said exposed pattern-to be formed on said photoresist layer on said second surface, "W2" is a second width of said light-transmissive pattern of said second photomask portion used to form said exposed pattern having said second intended width "L2", and said first size ratio is greater than said second size ratio;
• (3) said planar photomask is disposed such that said light beam is radiated to said photoresist layer on said first surface though said light-transmissive pattern of said first photomask portion and to said photoresist layer on said second surface through said light-transmissive pattern of said second photomask portion.