Etching process for accurately making small holes in thick materials

Claim 1

A process for making etched openings in a continuous sheet of material whereby the etched openings have a minimum dimension which is less than the thickness of the continuous sheet of material; forming an etchant resist pattern on opposite sides of a continuous sheet of material having a thickness T, a first etchant resist pattern defining an opening larger than the thickness of the material and a second etchant resist pattern on the opposite side defining an opening having a dimension which is less than 40% of the thickness T of said material; placing so as to face downward the first side of the continuous sheet of material having etchant resist defining an opening which is larger than the thickness of said material; applying a removable etchant resist shield over said material and the first etchant resist pattern which defines an opening having a dimension which is less than 40% of the thickness T of said material to completely cover said material and said etchant resist pattern to thereby prevent etchant from attacking said material while the opposite side of said material is being etched; first spray etching only on the first side of said material having etchant resist defining an opening which is larger than the thickness T of said material by spraying etchant from below said material until the depth of the etch on the first side of said material produces a region which has a thickness on the order of the minimum dimension of the final opening; removing the etchant resist shield; and then simultaneously etching the material from the first and second side of said material to simultaneously remove material from said first and said second sides of said material to thereby produce an opening in said material which has a mimimum dimension which is less than 40% of the thickness T of said material.