Preparation of Actual-Size Printed Wiring Layouts

Difficulties encountered in maintaining accurate registraion between layers of multilayer printed wiring cards has resulted in a method of preparing artwork actual size instead of by the usual enlarged artwork-photoreduction procedure. Fundamental to the approach is the fact that precise placement of lands, or pads, is more important than exact positioning of etched conductors: Accurate (±0.001 in) land location is assured by jig-boring land-size holes in sheet metal (Invar) and contact printing the hole pattern (lands) onto a glass photographic plate. Conductor paths are added using narrow (0.016 in min) black crepe printed-wiring layout tape. Presstype transfer letters and numbers are added as required for titles or identification. Final artwork is formed by proJection-printing the composite artwork onto another photographic plate using collimated light. Laboratory use of the technique has been successful in eliminating registration difficulties with 8 in x 15 in multilayer printed-wired cards.