Backup material for small bore drilling

Abstract

A backup material for small bore drilling in hard crystalline materials, such as multilayer circuit boards containing polyimide/glass, polyimide kevlar or modified epoxy BT/glass, includes at least one layer of hard crystalline material. Standard LCOA material with an additional layer selected from the group comprising polyimides, fluorocarbons and high temperature polycarbonates has proven successful.

Description

This invention relates to a backup or substrate for drilling small holes in polyimide and modified epoxy materials.

Multilayer printed circuit boards are typically constructed of an insulative layer separating conductive layers, such as copper. Standard multilayer boards, having 2 to 20 layers, range in thickness from 0.015 to about 0.125 inches each. Heretofore, it was possible to successfully drill holes down to about 0.006 inches in diameter in printed circuit boards constructed of epoxy glass using backup materials such as LCOA, a material commercially available from Laminating Company of America of Escondido, Calif. However, more recently printed circuit boards have been constructed of polyimide/glass, polyimide/kevlar and modified epoxy BT/glass materials. These particular materials are hard crystallinehard crystalline hard structures. Particularly, the material has proven useful in connection with drilling materials constructed of polyimide glass, polyimide-kevlar and modified epoxy BT-glass material. In addition, although polyimide material is disclosed as being the preferred material to adhered by acrylics to LCOA back-up material, it has also been found that flurocarbons, such as Teflon, and high temperature polycarbonates are also useful in place of polyimide materials.

This invention is not to be limited by the embodiment shown in the drawing and described in the description, which is given by way of example and not of limitation, but only in accordance with the scope of the appended claims.

Claims

1. In a backup sheet for backing a work sheet during a small bore drilling process, said work sheet containing at least one layer of hard crystalline hard material selected from the group comprising polyimide/glass, polyimide/kevlar and modified epoxy BT/glass, said backup sheet having a core, the improvement comprising an additional layer of hard crystalline hard material selected from the group comprising polyimides, fluorocarbons and high temperature polycarbonates fixed to opposite sides of said core.

2. A backup sheet according to claim 1 wherein said additional layer consists of a layer of polyimide of the order of about 0.002 inches thick fixed to said core with a layer of acrylic adhesive of the order of 0.001 inches thick.

3. A backup sheet for backing a work sheet during a small bore drilling process, said work sheet containing at least one layer of hard crystalline hard material, said backup sheet comprising a core constructed of a compressed organic material and a binder, said organic material being selected from the group comprising wood chips and sawdust, said core having opposite planar surfaces; a first aluminum layer adhered to one of said planar surfaces of said core and a second aluminum layer adhered to the other of said planar surfaces of said core; and a first layer of hard crystalline hard material adhered to said first aluminum layer and a second layer of hard crystalline hard material adhered to said second aluminum layer, said first and second layers of hard crystalline hard material being selected from the group comprising polyimides, fluorocarbons and high temperature polycarbonates.

4. A backup sheet according to claim 3 wherein said first and second layers of hard crystalline hard materials each consist of a layer of polyimide of the order of about 0.002 inches thick and are adhered to the respective first and second aluminum layers with a layer of acrylic adhesive of the order of about 0.001 inches thick.