Process for the production of printed circuit boards with extremely dense wiring using a metal-clad laminate

A process for the production of a plurality of multilayered printed circuit boards with extremely dense wiring comprising the steps of

• providing an elongated strip of a thin insulating material;
• producing a series of metal clad laminates along the strip, each laminate having a portion of the strip as an insulating layer and first and second electrically conductive layers bonded to opposite surfaces thereof and having a total thickness of less than 500 .mu.m;
• in a first photochemical processing, forming a plurality of through-holes in the first and second electrically conductive layers of each laminate;
• with plasma etching, selectively forming openings through the insulating layer at selected locations of the through-holes in the conductive layers;
• plating through the through-holes in the insulating layer to form electrically conductive passages electrically interconnecting the first and second conductive layers;
• and
• in a second photochemical processing step, forming high-density wiring patterns concurrently in the first and second electrically conductive layers.

A printed circuit board comprising

• a first, flexible metal clad laminate having a first insulating layer and first and second electrically conductive layers bonded to opposite surfaces of said insulating layer and having a total thickness of less than 500 .mu.m;
• a plurality of through-holes in said first and second electrically conductive layers;
• a plurality of openings through said insulating layer at selected locations of said through-holes in said conductive layers;
• electrically conductive material extending through said through-holes in said insulating layer electrically interconnecting said first and second conductive layers;
• high-density wiring patterns formed in said first and second electrically conductive layers;
• a second, flexible laminate comprising a second insulating layer and a third electrically conductive layer bonded to one surface of said second insulating layer and having a thickness of less than 500 .mu.m;
• a plurality of through-holes in said third electrically conductive layer;
• a plurality of openings through said second insulating layer at selected locations of said through-holes in said third conductive layer;
• electrically conductive material extending through said through-holes in said second insulating layer electrically connecting said third conductive layer with an opposite surface of said second insulating layer;
• and
• means bonding said opposite surface of said second insulating layer to one of said first and second electrically conductive layers so that said electrically conductive material extending through said second insulating layer is in electrical contact with said one of said first and second electrically conductive layers.