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Filling Holes in Printed Circuit Boards

IP.com Disclosure Number: IPCOM000090968D
Original Publication Date: 1969-Sep-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Mendola, SS: AUTHOR

Abstract

Microscopic plated through-holes in a multilayer printed circuit board are filled with epoxy using an ordinary laminating or vacuum fixture. Successive stages of the process are shown in drawings A...D. Composite multilayer substrate structure 1 is combined, drawing A, in a sandwich-like assembly with backing sheet 2, fronting mask 3, and thin epoxy sheet 4. The small diameter through-holes such as 5, e.g., .0135 inches in diameter, in structure 1 are concentrically registered with slightly larger holes 6, e.g., .016 inch diameters, in mask 3. This and sheet 2 are spray-coated with or otherwise provided with surface coverings of polytetrafluoroethylene. In drawing B, the assembly is subjected to heat at 340 degrees F and pressure of 250 psi in a vacuum laminating fixture.

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Filling Holes in Printed Circuit Boards

Microscopic plated through-holes in a multilayer printed circuit board are filled with epoxy using an ordinary laminating or vacuum fixture. Successive stages of the process are shown in drawings A...D. Composite multilayer substrate structure 1 is combined, drawing A, in a sandwich-like assembly with backing sheet 2, fronting mask 3, and thin epoxy sheet 4. The small diameter through-holes such as 5, e.g., .0135 inches in diameter, in structure 1 are concentrically registered with slightly larger holes 6, e.g., .016 inch diameters, in mask 3. This and sheet 2 are spray-coated with or otherwise provided with surface coverings of polytetrafluoroethylene. In drawing B, the assembly is subjected to heat at 340 degrees F and pressure of 250 psi in a vacuum laminating fixture. This causes the epoxy in sheet 4 to extrude compactly into holes 5 and 6. Filler plugs 7, formed by the extruded epoxy, are separated from the now thinner main body of remaining epoxy by peeling away mask 3 and sheet 2, drawing C. Soaking in a mild solvent enhances mask removal and reusability. Light sanding, drawing D, with #400 and #600 grit fine sandpaper leaves plugs 7 flush with the exterior surfaces of structure 1. The plugs are compact and void-free.

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