Metal stencils and process for making them

Claim 1

A PROCESS FOR FORMING A MASK ADAPTED TO HAVE VERY NARROW INDICIA ETCHED THEREIN, COMPRISING THE STEPS OF (A) FORMING AN ASSEMBLY OF SHEETS CONSISTING OF (1) A FIRST, RELATIVELY THIN, SHEET OF AN ETCHABLE MATERIAL, (2) A SECOND, RELATIVELY THICK, SHEET OF AN ETCHABLE MATERIAL, AND (3) A CONTINUOUS BONDING LAYER BETWEEN THE UNITING SAID FIRST AND SECOND SHEETS; (B) AFFIXING A FIRST RESIST TO THE UNBONDED SURFACE OF SAID FIRST SHEET, AND A SECOND RESIST TO THE UNBONDED SURFACE OF SAID SECOND SHEET; (C) REMOVING FROM EACH OF SAID RESISTS THE AREAS CORRESPONDING TO THE INDICIA TO BE ETCHED, THEREBY EXPOSING, AT SAID AREAS, THE UNBONDED SURFACES OF EACH OF SAID FIRST AND SECOND SHEETS, SAID AREAS BEING IN REGISTRY; (D) ETCHING SAID FIRST SHEET WITH AN ETCHANT THEREFOR, AT THE EXPOSED AREAS IN SAID FIRST RESIST, THEREBY TO ETCH THROUGH AND EXPOSE SAID BONDING LAYER TO PROVIDE A SHARP, DIMENSIONALLY CORRECT PATTERN OF THE DESIRED SIZE AND SHAPE FOR PROVIDING INDICIA THROUGH SAID MASK WHEN POSITIONED AGAINST AN OBJECT TO BE MARKED, THE ETCHING OF SAID FIRST SHEET BEING WITHOUT ANY SIGNIFICANT UNDERCUTTING; (E) ETCHING SAID SECOND SHEET WITH AN ETCHANT THEREFOR, AT THE EXPOSED AREAS IN SAID SECOND RESIST, THEREBY TO ETCH THRUGH TO AND EXPOSE SAID BONDING LAYER, WHILE PERMITTING UNDERCUTTING OF SAID SHEET, SAID SHEET BE OF SUFFICIENT THICKNESS THAT SAID UNDERCUTTING CAN TAKE PLACE DURING SKETCHING, AND TO PROVIDE SUPPORTING STRENGTH FOR SAID MASK; SAID ETCHANTS BEING INEFFECTIVE TO ATTACK SAID BONDING LAYER; AND (F) THEREAFTER REMOVING SID BONDING LAYER WHERE SO EXPOSED BY SAID ETCHANTS WITHOUT ANY SIGNIFICANT UNDERCUTTING OF SAID BONDING LAYER, THEREBY TO FORM SAID MASK.