Process of preparing copper foil for use in fine geometry circuit boards

Abstract

Process of preparing copper foil for use in fine geometry circuit boards in which spaced apart islands are formed in the copper foil, with the islands being smaller in dimension than crystals in the foil so that most of the islands are single crystals, and the islands are grown out until they meet one another to form a continuous foil having a columnar structure that etches preferentially along the intersections of the islands in directions perpendicular to the surface of the foil thus formed.

1 . A process of preparing copper foil for use in fine geometry circuit boards, comprising the steps of: forming spaced apart islands in the copper foil, with the islands being smaller in dimension than crystals in the foil so that most of the islands are single crystals, and growing the islands out until they meet one another to form a continuous foil having a columnar structure that etches preferentially along the intersections of the islands in directions perpendicular to the surface of the foil thus formed. 
   
   
       2 . The process of  claim 1  wherein the islands are also grown in height to the final thickness of the foil, and the islands do not finish growing out to meet one another before the final thickness of the foil is reached. 
   
   
       3 . The process of  claim 1  wherein growing of the islands is terminated before the islands have grown completely together at the surface of the foil, leaving indentations in the top surface above the intersections of the islands which further promote etching perpendicular to the top surface of the foil.