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Low Dielectric Printed Circuit

IP.com Disclosure Number: IPCOM000095627D
Original Publication Date: 1964-Apr-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Haddad, MM: AUTHOR

Abstract

This is a printed circuit board which exhibits a low and uniform dielectric constant.

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Low Dielectric Printed Circuit

This is a printed circuit board which exhibits a low and uniform dielectric constant.

In high speed circuitry, printed circuit boards must exhibit low dielectrics to reduce interline capacities, if high signal propagation rates are to be sustained. Certain types of polyolefins have low dielectrics in the vicinity of 2-2.3 and are suitable for such circuit applications. These are, e.g., linear polyethylene, or co- polymers of polyethylene propylene, polyethylene butylene, propylene, cross- linked polyethylene, or co-polymers of polyethylene propylene, polyethylene butylene.

To further reduce the dielectric constant of these materials, beads of aerated glass or puffed silica are added. The air which is trapped by these additives results in an overall dielectric reduction of the materials. This technique, however, causes problems when through holes are drilled and plated. The puffed silica, while trapping air in the board, also gives rise to fissures and cracks within the board. Thus, when the through hole plating is applied, copper tends to run into the fissure and creates undesirable dielectric-variations.

To overcome this problem, silica hollowspheres, a product of Emerson Cummings Corp., Canton, Mass., are added in lieu of puffed silica. As shown in the lower drawing, when through hole 10 is drilled, it exposes the interior of some of the hollowspheres, e.g., 12 and 14. But when the through hole is plated, the copper plate 16 is pr...