摘要：
Dielectric materials having low dielectric constant are provided, the materials comprising fabrics impregnated with theremosetting resins, at least a portion of the fibers in the fabrics being fluorocarbon fibers. Also provided is a method of manufacture of these dielectric materials. The dielectric materials are useful in the fabrication of multilayer printed circuit boards.
技术功效语段：
[0015]The invention also provides a process for making the dielectric material comprising: (a) treating fluorocarbon fibers to render them wettable by an uncured thermosetting resin, the fibers being held under longitudinal tension during such treatment, thereby preventing longitudinal shrinkage of the fibers during treatment, (b) weaving the fabric containing at least a portion of the treated fluorocarbon fibers, (c) impregnating the fabric with an uncured thermosetting resin, and (d) heating and drying the resin-impregnated-fabric to cure the resin to at least the semi-cured, B-stage state. Alternatively the process for making the dielectric material may comprise the steps of: (a) treating a fabric containing at least a portion of fluorocarbon fibers to render the fluorocarbon fibers wettable by an uncured thermosetting resin, the fabric being restrained from shrinkage during such treatment or, alternatively, the fabric being allowed to shrink during treatment and stretched to nearly its original dimensions after treatment, (b) impregnating the fabric with an uncured thermosetting resin, and (c) heating and drying the resin-impregnated-fabric to cure the resin to at least the semi-cured, B-stage state. The process may include the step of calendering the fabric to reduce its thickness. The treatment to make the fluorocarbon fibers wettable may include applying an alkali naphthanate solution to the fluorocarbon fibers or fabric. The process may include napping the fluorocarbon fibers to improve wettability and adhesion between fibers and resin.
权利要求：
1. A dielectric material comprising a fabric having fibers and interstices between said fibers, in which at least a portion of the fibers in said fabric are fluorocarbon fibers which have been treated to make the fluorocarbon fibers wettable by an uncured thermosetting resin, the fabric being impregnated within said interstices between said fibers with a thermosetting resin cured to at least the semi-cured, B-stage state, the dielectric constant of said dielectric material being less than 3.5.
2. A dielectric material according to claim 1 characterised in that it has a dielectric constant less than 3.0.
3. A dielectric material according to claim 1 or claim 2 characterised in that the thermosetting resin is cured to the fully-cured, C-stage state.
4. A dielectric material according to claim 3 characterised by an electrically conductive foil bonded to at least one surface of the impregnated fabric.
5. A dielectric material according to claim 3 or claim 4 characterised in that the impregnated fabric is in sheet form having an electrically conductive foil bonded to one side thereof.
6. A dielectric material according to claim 5 characterised in that the impregnated fabric has electrically conductive foil bonded to both sides thereof.
7. A dielectric material according to any one of claims 4 to 6 characterised in that said foil is copper foil.
8. A dielectric material according to claim 3 in the form of a laminated composite structure characterised by it comprising two or more sheets of the impregnated fabric and having an electrically conductive foil bonded to at least one side of at least one of said sheets.
9. A dielectric material according to claim 1 in the form of a laminated composite structure characterised by one or more sheets of the impregnated fabric in which the thermosetting resin is cured to the fully-cured, C-stage state, and one or more sheets of the impregnated fabric in which the thermosetting resin is cured to the semi-cured, B-stage state, wherein, wherever a layer of material in said C-stage state contacts another layer, said other layer is of material in said B-stage state.
10. A dielectric material according to claim 1 in the form of a laminated composite structure characterised by one or more sheets of the impregnated fabric in which the thermosetting resin is cured to the fully-cured, C-stage state, and having an electrically conductive foil bonded to at least one side of at least one of said sheets, and one or more sheets of the impregnated fabric in which the thermosetting resin is cured to the semi-cured, B-stage state, wherein, wherever a layer of material in said C-stage state contacts another layer, and wherever an electrically conductive foil contacts another layer, said other layer is of material in said B-stage state.
11. A dielectric material according to any one of claims 8 to 10 characterised by at least one additional layer which is a layer of epoxy/fiberglass, fluorocarbon/fiberglass, polyimide/fiberg- lass, epoxy/polyaramide fiber, epoxy/quartz fiber or polyimide/quartz fiber composites.
12. A dielectric material according to any preceding claim characterised in that said thermosetting resin is an epoxy, polyimide, polyamide, polyester, phenolic or acrylic thermosetting resin.
13. A dielectric material according to any preceding claim characterised in that all said fibers in said fabric other than fluorocarbon fibers are fiberglass fibers or polyaramide fibers or quartz fibers.
14. A dielectric material according to any preceding claim characterised in that said fabric is a woven fabric or a non-woven felt or mat.
15. A dielectric material according to any preceding claim characterised in that said fluorocarbon fibers are drawn, non-porous, sintered PTFE fibers, or expanded, porous PTFE fibers, and said fluorocarbon fibers contain a dielectric insulator material or other material as a filler.
16. A dielectric material according to claim 15 characterised in that said filler is electrically conductive or semi-conductive, and is a metal, a metal oxide, carbon, ceramic or glass.
17. A process for making the dielectric material of claim 1 characterised by: (a) treating fluorocarbon fibers to render them wettable by an uncured thermosetting resin, the fibers being held under longitudinal tension during such treatment, thereby preventing longitudinal shrinkage of said fibers during treatment. (b) weaving said fabric containing at least a portion of said treated fluorocarbon fibers, (c) impregnating said fabric with an uncured thermosetting resin, and (d) heating and drying said resin-impregnated-fabric to cure said resin to at least the semi-cured, B-stage state.
18. A process for making the dielectric material of claim 1, characterised by: (a) treating a fabric containing at least a portion of fluorocarbon fibers to render said fluorocarbon fibers wettable by an uncured thermosetting resin, (b) impregnating said fabric with an uncured thermosetting resin, and (c) heating and drying said resin-impregnated-fabric to cure said resin to at least the semi-cured, B-stage state.
19. A process according to claim 17 or claim 18 characterised by the step of calendering said fabric to reduce its thickness.
20. A process according to claim 17 or claim 18 characterised in that said treating includes applying an alkali naphthanate solution to said fluorocarbon fibers or fabric.
21. A process according to claim 20 characterised by napping the fluorocarbon fibers to improve wettability and adhesion between said fibers and resin.
22. A process according to claim 17 or claim 18 characterised in that said fibers or fabric are bleached subsequent to treating them to make them wettable.
23. A process according to claim 22 characterised by the use of an oxidizing agent to bleach the fibers or fabric.
24. A process according to claim 23 characterised in that the fibers or fabric are bleached by heating to a temperature in the range of about 500°F to about 675°F (260°C to 357°C).
25. A process according to claim 18 characterised in that said fabric is held in longitudinal and transverse tension during said treatment, thereby preventing shrinkage of said fabric in the longitudinal and transverse directions during treatment.
26. A process according to claim 18 characterised in that said fabric is unrestrained during said treatment and is allowed to shrink, following which the fabric is stretched to approximately its original dimensions prior to said treatment.