Cutting by use of rotating axially moving tool – Processes – Bit detachable
Patent
1993-09-15
1995-07-25
Bishop, Steven C.
Cutting by use of rotating axially moving tool
Processes
Bit detachable
B23B 3500, B23B 5106
Patent
active
054356717
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of drilling holes in printed circuit boards and to an entry or backing board adapted for use in such a method.
It is well known that in drilling printed circuit boards it is usual to use dummy boards on either side or both sides of the board or boards to be drilled. These dummy boards are sometimes referred to as backing and entry boards. A backing, or back-up, board is disclosed in U.S. Pat. No. 3,700,341, comprising a laminate of aluminum foil firmly bonded to Masonite, a fibrous board. A laminated entry board is disclosed in U.S. Pat. No. 4,311,419. When many boards are being drilled they are usually made up in stacks consisting of an entry board on top of the printed circuit board material. There are a number of reasons for this-one of these is to reduce burring, another to prevent damage to the top laminate in the stack and another to improve drilling accuracy. At the bottom of the stack there is usually another board called the back-up board which is there for a number of reasons, one of which being to prevent the drills drilling into the base tooling plate of the drilling machine, and another being to prevent burring of the printed circuit board material. Various materials are used for the dummy boards, but the most common dummy boards are composite boards consisting of a metal cladding on one or both sides of a softer, often organic, sheet of material. The metal is rigidly and permanently bonded to the substrate or substrate by means of a permanent adhesive such as an epoxy resin.
Large quantities of these cladded boards are in use and the difficulty of their disposal is a matter for concern. The metal component makes it difficult to dispose of the used boards and the strong adhesion of the metal makes it difficult to reclaim same economically. Strong adhesion has been considered to be important for the rigidity of the board and for its resistance to the torsion of the drill bit. There is thus an environmental problem as well as an economic problem through the failure to recycle the dummy boards.
The invention overcomes this problem by providing a composite entry or backing board for use adjacent a printed circuit board during drilling therethrough, in which the adjacent faces of two laminar components of the entry board are joined such that there is no relative slip during transportation, cutting and positioning, and such that they are separable by peeling them apart after use.
Preferably, the two laminar components are a substrate, which may be fibrous board or paper, and a metal or metal alloy foil or sheet; typical thickness ranges being respectively 0.1-4 mm and 0.02-1 mm. The substrate thickness is preferably at least 0.020 mm, preferably at least 0.20 mm, and in many cases at least 0.5 mm, and the foil or sheet is preferably at least 0.04 mm thick. The laminar components are preferably joined by an intermediate layer or a low-strength, preferably permanent tack, adhesive; alternatively, a similar result may be achieved using an intermediate double-sided adhesive tape. The adhesive materials in each case should preferably be coupled less strongly to the metal or metal alloy component, where one is used, than to the other laminar component, so that it may more readily be recycled.
Alternatively, the laminar components may be joined by keying together their opposed surfaces, by for example roughening or texturing one or both surfaces and pressing them together. Thus the laminar components are joined face to face without any intermediate adhesive.
The join between the laminar components need not extend over their whole area, but may take effect in strips or spots or other partial areas, provided there is sufficient regidity for the intended application.
Another problem associated with the drilling of printed circuit boards has been the effect of the board material on the drill bit. Circuit boards commonly contain much epoxy resin. During the drilling operation the resin becomes firmly bonded to the margins and flutes of the drills. This increases the power requ
REFERENCES:
patent: 3414084 (1968-12-01), Bues et al.
patent: 3700341 (1972-10-01), Block
patent: 4311419 (1982-01-01), Block
patent: 4781495 (1988-11-01), Hatch et al.
Bishop Steven C.
Holders Technology PLC
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