Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Utility Patent
1999-10-15
2001-01-02
Lam, Cathy F. (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S297400, C428S297700, C428S298100, C428S458000, C428S901000, C428S174000, C428S208000, C428S208000, C428S442000, C428S208000, C428S378000
Utility Patent
active
06168855
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to polyolefin composites for use as a base material in printed circuit boards (PCBs), antennas and the like, to a base material including the composite and further to electronic modules, such as PCBs, antennas and the like, including the base material. More particularly, the present invention relates to an ultrahigh molecular weight polyethylene (UHMWPE) composite for use as a dielectric in PCBs, antennas and the like. The composites of the present invention are characterized by low dielectric constant and dissipation factor and therefore enable transmission of high frequency electromagnetic signals with short signal transmission delay times, and possess desired mechanical properties, such as rigidity and/or flexibility.
A base material for the production of PCBs, antennas and the like, includes a single or a plurality of dielectric layers and electroconductive layers glued, bonded or otherwise intimately attached to one another. The dielectric layer(s) provide the required mechanical and dielectric properties to support the functionality of the electroconductive layer(s) in the final product (PCB, antenna and the like).
If high frequency electromagnetic signals with short signal transmission delay times are to be transmitted via the electroconductive layer in the final product, the dielectric layer should be provided with a combination of low dielectric constant (&egr;) and low dissipation factor (tan &dgr;).
Additional properties of the dielectric layer preferably include superior mechanical properties, excellent environmental resistance, which is important because tan &dgr; is very sensitive to water tracks that may be present in the dielectric layer, and good adhesion performances to facilitate effective bonding between the dielectric and electroconductive layers.
It is also desirable to achieve a base material in which the thermal expansion coefficient is comparable to that of the conducting or semiconducting material attached to it.
Dielectric materials presently used to support high frequency electromagnetic signals in PCBs, antennas and the like are polytetrafluorene (PTFE) [&egr;=2.2; tan &dgr;=0.0002], quartz fibers [&egr;=3.78, tan &dgr;=0.0002] and ceramics with low dielectric constant and dissipation factor.
Some of these materials also exist as foam substrates showing even lower dielectric constants.
Different techniques of attaching these materials to an electroconductive layer are also known.
For further detail the reader is referred to U.S. Pat. Nos. 4,772,507; 4,775,911; and 5,141,800, which describe the use of PTFE as a base material for PCBs.
The production, properties and present use of ultra high molecular weight polyethylene (UHMWPE) substrates (e.g., fibers, matrix resin) are described in IL 115229; PCT/IL96/00095 and in a review published in the proceedings of the International SAMPE Symposium (Feb. 9-12, 1992) on pages 1406-1420. These references are hereby incorporated by reference as if fully set forth herein.
UHMWPE has a low dielectric constant and a low dissipation factor [&egr;=2.2; tan &dgr;=0.0002] and possesses good mechanical properties, and may therefore support transmission of electromagnetic signals at high frequencies with short signal transmission delay times.
Although the use of conventional, low molecular weight foamed polyethylene [&egr;=1.3, tan &dgr;=0.001] in microwave circuit modules was described (U.S. Pat. No. 4,937,585), the prior art fails to teach the use of UHMWPE composite as a base material for PCBs and antennas.
There is thus a widely recognized need for, and it would be highly advantageous to have, an ultrahigh molecular weight polyethylene composite for use in a base material for the production of printed circuit boards or antennas, a base material including the composite and electronic modules, such as PCBs, antennas and the like, including the base material, all enjoy the electrical and physical properties of the ultrahigh molecular weight polyethylene composite as further detailed below.
SUMMARY OF THE INVENTION
According to the present invention there are provided an ultrahigh molecular weight polyethylene composite for use in a base material for printed circuit board, antenna and the like, a base material including the composite and electronic modules including the base material.
As used herein in the specification and claims section below, the phrase “ultrahigh molecular weight” refers to an average molecular weight of above 500,000, preferably between 500,000 and 10,000,000, more preferably between 1,000,000 and 8,000,000, most preferably between 2,000,000 and 5,000,000. “Regular” or “common” polyolefins refer to an average molecular weight of below 1,000,000 and usually below 500,000.
As used herein in the specification and claims section below, the phrase “polyolefin” or “polyolefin polymer” refers to polyolefins produced from one or more species of olefin monomers as well as polyolefin copolymers produced from polyolefin and non-polyolefin monomers.
As used herein in the specification and claims section below, the word “oriented” refers to the alignment/direction of individual molecules and/or crystallites from which fibers, whiskers, monofilaments, and the like are formed; “ordered” refers to the orientation of groups of such particles (fibers, whiskers, etc.) on the macroscopic level.
An exception to the above is the term “oriented reinforcement component”, a commonly-used term, which, as used herein in the specification and claims section below, refers to a material such as fibers, whiskers, monofilaments, and the like, possessing an oriented molecular and/or crystallite structure.
As used herein in the specification and claims section below, the word “region” refers to a continuous segment of a space (volume) or surface.
According to further features in preferred embodiments of the invention described below, the base material comprising at least one dielectric layer including an ultrahigh molecular weight polyethylene composite and at least one electroconductive layer including an electroconductive material, the dielectric and electroconductive layers being intimately bonded to one another.
According to still further features in the described preferred embodiments the composite includes ultrahigh molecular weight polyethylene fibers, the fibers are held together.
According to still further features in the described preferred embodiments the composite further includes an ultrahigh molecular weight polyethylene matrix for effecting holding the fibers together.
According to still further features in the described preferred embodiments the ultrahigh molecular weight polyethylene fibers are in a form selected from the group consisting of a network of randomly arranged fibers, a unidirectional layer of fibers and a layer of fibers cloth.
According to still further features in the described preferred embodiments the fibers are held together via self bonding.
According to still further features in the described preferred embodiments the matrix is formed from a substance selected from the group consisting of an ultrahigh molecular weight polyethylene powder, an ultrahigh molecular weight polyethylene gel, an ultrahigh molecular weight polyethylene mat, and via recrystallization of partly dissolved ultrahigh molecular weight polyethylene fibers of the composite.
According to still further features in the described preferred embodiments the electroconductive material is selected from the group consisting of a copper foil, a silver foil, a gold foil and an electroconductive polymer sheet.
According to still further features in the described preferred embodiments, a surface of each of the dielectric layers, the surface facing one of the conductive layers, includes exposed free ends of broken ultrahigh molecular weight polyethylene fibrils. This is preferably effected by abrasion treatment applied to the surface.
According to still further features in the d
Cohen Yachin
Rein Dmitry
Vaykhansky Lev
Friedman Mark M.
Lam Cathy F.
Polyeitan Composites Ltd.
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