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US 4,781,495 AGranted
Dry lubricant drilling of thru-holes in printed circuit boards
AssigneeLubra Sheet Corp.
InventorsWilliam R. Hatch, John W. Foster
Life of this patent
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AssigneeLubra Sheet Corp.
InventorsWilliam R. Hatch, John W. Foster
Estimating the term…
Thru-holes are drilled in a printed circuit board panel having alternating dielectric layers and electrically conductive layers. A water soluble dry film lubricant sheet is placed adjacent an electrically conductive outer layer of the panel prior to drilling thru-holes through the panel with a rotary drill. The drill surface is lubricated while forming a clean thru-hole from contact between the drill and the lubricant. The dry film lubricant generally may comprise a water soluble lubricant hardened to a solid or semi-solid dry film-form and impregnated in a carrier such as a porous paper sheet. In one embodiment, the dry film lubricant includes a water soluble lubricant such as dipropylene glycol, a non-ionic surfactant, and a wax-like hardener. Following drilling of the thru-holes, the dry film lubricant sheet is removed, and the thru-holes can be rinsed in an aqueous alkaline solution. The thru-holes are then plated with an electrically conductive metal for forming electrical contacts between the metalized thru-holes and the electrically conductive layers of the panel. The dry film lubricant extends drill life and produces a clean thru-hole that prevents epoxy smear and avoids the prior art use of harsh chemical treatment following drilling to otherwise remove dielectric smear or fibers that might extend into the thru-hole and disrupt the continuity of the later-formed electrical contact.
In a process for drilling printed circuit boards in a dry state which includes drilling a thru-hole in a printed circuit board panel having a dielectric layer made from a material which can be smeared onto other portions of the circuit board panel by the drilling tool and thereby interfere with subsequent electrical performance of the finished circuit board, an improvement for reducing dielectric smear comprising the steps of:
In a process for drilling printed circuit boards in a dry state which includes drilling a thru-hole in a printed circuit board panel having an electrically conductive layer adjacent a dielectric layer, the improvement comprising placing a water soluble and substantially dry lubricating film in solid film form adjacent one of said layers, and operating a rotary drill to drill in a dry state through the circuit board panel, including drilling through the lubricating film and at least through the dielectric layer of the panel to form a thru-hole in the panel, the lubricating film being formed in a film thickness sufficient to lubricate the drill tool surface with lubricating material transferred from the lubricating film to the drill tool surface while forming a clean thru-hole in the panel, the lubricating film having as its components a water soluble hardener component and a water soluble lubricant combined to form said water soluble substantially dry solid lubricating film.
A process for drilling a thru-hole in a printed circuit board panel having a dielectric layer made from a material which can be smeared onto other portions of the circuit board panel by the drilling tool and thereby interfere with electrical performance of the circuit board, the method comprising the steps of:
Dependencies are inferred from the claim text.