Burns, Doane, Swecker & Mathis
Method for drilling reference holes in multi-layer printed wiring board assembly
 A method for drilling reference holes in a multi-layer printed wiring board assembly, in which drilling position marks provided on inner-layer circuit board in the assembly are roughly detected through each of two outer-layer boards of the assembly, a spot-facing is made with respect to the outer-layer boards at roughly detected points of the marks, and thereafter the marks are precisely detected at the faced spots. Positions for drilling the reference holes can be thereby determined at the spots precisely in close proximity to the internally provided drilling position marks, to allow the drilling performed very accurately in simpler and economical manner. 
Matsushita Electric Works, Ltd.
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Toshinori Shinji
Fujii Okamoto