(12) United States Patent
`Mohamed et al.
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US00644 7886Bl
`US 6,447,886 Bl
`Sep.10,2002
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54) BASE MATERIAL FOR A PRINTED CIRCUIT
`BOARD FORMED FROM A THREE(cid:173)
`DIMENSIONAL WOVEN FIBER STRUCTURE
`
`(75)
`
`Inventors: Mansour H. Mohamed, Raleigh; R.
`Bradley Lienhart, Cary; Pu Gu, Apex,
`all of NC (US)
`
`(73) Assignee: 3Tex, Inc., Cary, NC (US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/528,621
`
`(22) Filed:
`
`Mar. 20, 2000
`
`(51)
`(52)
`
`(58)
`
`(56)
`
`Int. Cl? . ... ... .. ... ... ... ... .. ... ... ... ... ... .. ... ... ... . B32B 3/00
`U.S. Cl. ....................... 428/209; 442/205; 174/255;
`428/901
`Field of Search ................................. 442/203, 205;
`428/209, 901; 174/255, 258
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`* 2/1988 Hirokawa ................... 428/225
`* 10/1990 Becker et a!.
`.............. 428/113
`2/1992 Mohamed et a!.
`12/1993 Middelman
`11/1995 Mohamed et a!.
`* 5/1996 Van Skyhawk et a!.
`
`.... 428/251
`
`4,725,485 A
`4,966,801 A
`5,085,252 A
`5,269,863 A
`5,465,760 A
`5,520,999 A
`
`5,637,375 A * 6/1997 Hohman ..................... 428/113
`5,670,250 A * 9/1997 Sanville, Jr. et a!.
`....... 428/323
`5,807,793 A
`9/1998 Scari et a!.
`
`OTHER PUBLICATIONS
`
`Clyde F. Coombs, Jr., "Base Materials," Printed Circuits
`Handbook, 4th ed., McGraw-Hill (New York), pp. 8.1-8.31,
`(1988), (No Month).
`* cited by examiner
`
`Primary Examiner-Cathy Lam
`(74) Attorney, Agent, or Firm-Jenkins & Wilson, P.A.
`
`(57)
`
`ABSTRACT
`
`A base material for a printed circuit board, and a printed
`circuit board constructed therefrom. The base material is
`formed from a three-dimensional orthogonally woven fabric
`having a crimp-free fiber architecture in the x-y plane and an
`integrated multi-layer structure. The base material com(cid:173)
`prises a first system of straight first fibers extending along a
`first direction in a first plane, a second system of straight
`second fibers extending along a second direction in a second
`plane parallel to the first plane, and a third system of third
`fibers extending along a third direction through the first and
`second systems and binding the first and second fibers
`thereof. A filler material coats a portion of the first, second
`and third systems. The printed circuit board comprises the
`base material and one or more conductive layers attached to
`surfaces of the base material.
`
`17 Claims, 7 Drawing Sheets
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`.24A
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`20
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`FIG. 1
`Prior Art
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`FIG. 2
`Prior Art
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`FIG. 3
`Prior Art
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`2
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`Sheet 3 of 7
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`FIG. 4A
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`FIG. 4B
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`FIG. 5
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`Sheet 7 of 7
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`1
`BASE MATERIAL FOR A PRINTED CIRCUIT
`BOARD FORMED FROM A THREE(cid:173)
`DIMENSIONAL WOVEN FIBER STRUCTURE
`
`TECHNICAL FIELD
`
`The present invention is generally directed to printed
`circuit boards and, more particularly, to printed circuit
`boards exhibiting improved structural properties through the
`provision of a base material or substrate that is formed from
`an integrated, three-dimensional woven fiber structure.
`
`BACKGROUND ART
`
`Printed circuit boards, or PCBs, are typically provided in
`the form of copper-clad laminates consisting of three prin(cid:173)
`cipal components: a base or reinforcing material; a resin
`system or matrix; and copper foil. Commonly employed
`base materials include paper, glass matte, woven glass cloth,
`quartz, and aramid material. In the typical process for
`manufacturing the laminated PCB, the base material is
`impregnated or coated with a resin. The resin is then
`polymerized in a treater or coater to a state suitable for
`storage and final pressing. The base material is treated by
`passing it through a dip pan containing the resin, and
`subsequently passing the impregnated base material through
`a set of metering rollers, such as squeeze rollers, and in turn
`through a drying oven to cure or semi-cure the resin. The
`oven is of the air-circulating or infrared type, in which most
`of the volatile compounds such as solvents residing in the
`resin are driven off. The resulting product is often referred
`to as a prepreg. Rigorous process control is exercised during
`treating in order to monitor the ratio of resin to base material,
`the final thickness of the prepreg, and the degree of resin
`polymerization. Once the prepreg has been prepared, the
`copper foil is applied to one or two sides of the prepreg,
`typically by the process of electrodeposition.
`Important criteria in the production of printed circuit
`boards include prevention of delamination, punchability and
`machinability (especially drillability), uniformity of dielec(cid:173)
`tric strength, tensile strength and modulus, surface flatness,
`dimensional stability, and measling and blistering (often
`caused by entrapped moisture resulting from poor drill hole
`quality). Dimensional stability in the lengthwise and cross(cid:173)
`wise dimensions x, y is a function of the laminate reinforce(cid:173)
`ment (e.g., glass or paper), while vertical or thickness
`expansion in the z-direction is generally a function of the
`resin system or matrix. Some prior approaches to improving
`these properties have been concerned with improving the
`process of manufacturing the PCB as generally described
`above, while other approaches have focused on improving
`the structure of the base material itself.
`The base material for PCBs has in the past been con(cid:173)
`structed from a multi-layer composite laminate. Laminates
`most widely used include materials designated FR-2, CEM-
`1, CEM-3, FR-4, FR-5, and GI. FR-2 laminates comprise 55
`multiple plies of paper that have been impregnated with a
`flame-retardant phenolic resin. FR-3 laminates comprise
`multiple plies of paper that have been impregnated with an
`epoxy-resin binder. CEM-1 is a composite having a paper
`core impregnated with epoxy resin. Its two planar surfaces
`are covered by woven glass cloth impregnated with the same
`type of resin. CEM-3 is a composite having an epoxy
`resin-impregnated non-woven fiberglass core with epoxy
`resin-impregnated woven glass cloth surface sheets. FR-4
`laminates, perhaps the most widely used material in the PCB
`industry, include multiple plies of epoxy resin-impregnated
`woven glass cloth. FR-5 (military-type GH) laminates
`
`5
`
`2
`include multiple plies of woven glass cloth impregnated
`with mostly polyfunctional epoxy resin. GI laminates
`include multiple plies of woven glass cloth impregnated
`with a polyimide resin.
`Woven laminates typically consist of several layers of
`two-dimensional plain weave fabric that have been impreg(cid:173)
`nated with a resin system. One example of a layer of
`two-dimensional plain weave is illustrated in cross-section
`in FIG. 1. The fabric is produced in a "one-up, one-down"
`10 weaving process, wherein one set of fibers 1 disposed in the
`0° (x-, warp or lengthwise) direction is interlaced with
`another set of fibers 2 disposed in the 90° (y-, weft, fill or
`crosswise) direction. Because of the interlaced
`configuration, all of the fibers contained in this type of fabric
`15 are necessarily crimped. It is known by those skilled in the
`art that the crimped structure significantly reduces the
`mechanical properties of the resulting fabric, such as the
`tensile strength and modulus. In addition, it is known that
`such fabric has an undesirably low dimensional stability
`20 since the crimped fibers are prone to stretching. Moreover,
`multi-layered composites formed from layers of two(cid:173)
`dimensional fabric weaves are prone to delamination. Still
`further, in the manufacture of PCBs, the waved cross(cid:173)
`sectional profile of crimped yarns creates a significant risk of
`25 deflection of the drill bit during drilling operations.
`Accordingly, it has become apparent in the industry that a
`better performing fabric is needed in the manufacture of the
`base material of a PCB. This need is especially significant in
`view of the fact that the density and complexity of the
`30 architecture of the modern PCB is increasing.
`Thus far, most approaches for producing an improved
`base material to adequately satisfy the requirements of
`modern PCB manufacture have focused on improving the
`structure of two-dimensional fabrics. One such approach has
`35 been to reduce the degree or extent of crimping and thereby
`improve the surface roughness, waviness, and evenness or
`flatness of the fabric. This has purportedly been accom(cid:173)
`plished by interlacing the crosswise yarns 2 of a textile
`fabric in its lengthwise direction with a lena interwoven
`40 binding comprising glass yarns 3, as illustrated in FIG. 2. A
`PCB is then produced from the resulting two-dimensional
`fabric base layer by conventional means, i.e., the fabric is
`treated with resin and a copper layer is placed on the surface
`of the top-most layer of the impregnated fabric. An example
`45 of this approach is disclosed in U.S. Pat. No. 5,807,793 to
`Scari et al. It can be seen, however, from FIG. 2 that all
`crosswise yarns 2 nevertheless remain interlaced with all
`lengthwise yarns 1 and, by necessity, all lengthwise yarns 1
`remain interlaced with all crosswise yarns 2. Moreover, the
`50 pairs of lena interwoven yarns 3 are by definition interlaced
`with crosswise yarns 2. The resulting fabric is thus still
`characterized by crimped yarns and, in connection with the
`manufacture of PCBs, is subject to all of the deleterious
`effects attending crimped, two-dimensional designs.
`Another approach is proposed in U.S. Pat. No. 5,269,863
`to Middelman, which discloses a process wherein two(cid:173)
`dimensional fiber laminates are provided in an entirely
`non-woven format. Referring to FIG. 3, double layers of
`crosswise threads 2 are laid in parallel relation and stretched
`60 under tension onto single and/or double layers of lengthwise
`threads 1, also laid in parallel relation and stretched under
`tension. All layers are thus formed without any interweaving
`or binding among the threads 1 and 2. The threads 1 and 2
`utilized in this process are of an untwisted type such as
`65 E-glass filaments. Subsequently, the laminate is fed to a
`metering unit which impregnates the laminate with an epoxy
`resin and then to an infrared pre heater to initiate curing. The
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`impregnated laminate is then fed to a double belt press. As
`the laminate enters the double belt press, upper and lower
`copper foils 4A, 4B are respectively unwound from rollers
`onto upper and lower surfaces of the laminate. The com(cid:173)
`posite laminate of filament layers and copper foils is passed
`through the double belt press under elevated pressure and
`temperature, and its continuous length is apportioned into
`discrete PCBs by a cutting device. It should be apparent that
`while the base material thus produced contains essentially
`crimp-free fibers, structural integrity is nonetheless compro-
`mised by the fact that the fibers are non-woven and hence
`bound only by the metered resin.
`A critical deficiency in prior art base materials such as
`those just described and illustrated in FIGS. 1-3, as well as
`related two-dimensional designs, is that their structural 15
`properties depend on the resin matrix to an unacceptable
`degree. That is, the resin matrix essentially serves as the
`primary structural component for the base material, while
`the fiber systems serve in merely in a reinforcing capacity.
`Closely related to this problem is the fact that these prior art 20
`base materials are laminates. Consequently, the resin matrix
`is also burdened with the task of binding several layers of
`two-dimensional fabric together and retaining the overall
`structural integrity of the PCB. As a result of these problems,
`base materials manufactured in the form of composite 25
`laminates, even those whose two-dimensional fabric layers
`are crimp-free as in FIG. 3, are quite prone to delamination.
`Structural failure of the base material can thus occur at many
`stages, such as during curing, drilling, or even during
`operations performed by others after the manufacture of the 30
`PCB has been completed. In addition, lamination is a labor
`intensive, expensive, and time consuming process.
`Accordingly, there exists a long-felt need to provide a
`PCB having a base material that is not prone to delamination
`and that at the same time has improved properties relating to 35
`strength and drillability. To this end, applicants have found
`that the base material for a PCB can be constructed from a
`woven fabric having an integrated three-dimensional fiber
`structure with crimp-free fibers. Such a three-dimensional
`fiber structure can be formed in an essentially one-step
`process that is relatively inexpensive and non-labor inten(cid:173)
`sive.
`The resulting novel base material eliminates the risk of
`delamination and improves dimensional stability in all three
`dimensions, because its integrated three-dimensional
`structure, even if multi-layered, is not a laminate in the
`conventional sense since its fibers are bound together or
`interlocked in three dimensions. In the present invention,
`therefore, the fibers themselves are the true primary struc(cid:173)
`tural components of the base material, albeit a material such
`as resin can be added if desired in order to fill voids on the
`surface of the three-dimensional fabric and any interstices
`between the fibers within the core volume of the fabric. In
`addition, all fibers in at least the x-y plane of the novel base
`material are straight (i.e., crimp-free) so that the properties 55
`important to PCBs, e.g. drillability, dimensional stability,
`flatness, etc., are vastly improved.
`Three-dimensional woven fabrics have been developed in
`the textile industry. In general, such a fabric has been formed
`by arranging warp yarns in multiple layers that define sheds 60
`therebetween. A plurality of needles containing doubled
`filling or weft yarns are simultaneously inserted a uniform
`distance into the warp sheds from one side thereof. The
`filling yarns are held on the opposite side of the warp sheds
`by a catch yarn which passes through the loops of the 65
`doubled weft or filling yarns and thus forms the fabric
`selvedge. The weft needles are then returned to their original
`
`4
`position at one side of the warp yarn sheds after inserting the
`doubled filling yarns, and a reed is urged forwardly to
`beat-up and pack the yarns into a tight structure at the fell of
`the fabric. Next, a layer of vertical yarns is inserted into the
`fell of the three-dimensional fabric, and the reed is returned
`to its original remote position so that the entire weaving
`cycle may be repeated.
`An innovative and improved method for weaving a vari(cid:173)
`able cross-section three-dimensional fabric of the same
`general construction as the woven fabric described herein(cid:173)
`above defining a non-variable cross-section is disclosed in
`U.S. Pat. No. 5,085,252 to Mohamed et al. To applicants'
`knowledge, however, a base material for a printed circuit
`board having an integrated three-dimensional fiber structure,
`or a PCB constructed therefrom, has not heretofore been
`developed.
`
`DISCLOSURE OF THE INVENTION
`
`Accordingly, a three-dimensional orthogonal fabric hav(cid:173)
`ing a crimp-free fiber architecture in the x-y plane and an
`integrated multi-layer structure is provided. In one embodi(cid:173)
`ment according to the present invention, a base material for
`use in a printed circuit board is formed from a three(cid:173)
`dimensional woven fabric. A first system of straight first
`fibers extends along a first direction in a first plane. A second
`system of straight second fibers extends along a second
`direction perpendicular to the first system in a second plane
`parallel to the first plane. A third system of third fibers
`extends along a third direction through the first and second
`systems and binds the first and second fibers thereof. A filler
`material coats at least a portion of the first, second and third
`systems.
`One or more of the fiber systems can be constructed of
`different materials, such that the fabric has a hybrid struc(cid:173)
`ture. Also, it is preferable that a plurality of corresponding
`first and second systems forming multiple layers are
`provided, all of which are bound by the third system.
`In another embodiment according to the present
`40 invention, a printed circuit board comprises a base material
`formed from three-dimensional woven fabric having a
`crimp-free fiber architecture. The base material includes a
`first system of straight first fibers extending along a first
`direction in a first plane, a second system of straight second
`45 fibers extending along a second direction perpendicular to
`the first system in a second plane parallel to the first plane,
`and a third system of third fibers extending along a third
`direction through the first and second systems and binding
`the first and second fibers thereof. A first layer of conductive
`50 material is attached to a first surface of the base material.
`Preferably, several layers including first and second systems
`are provided in the base material, and a filler material such
`as epoxy resin is added to coat at least a portion of the fibers
`of the first, second and third systems.
`In yet another embodiment according to the present
`invention, a method is provided for manufacturing a printed
`circuit board. A base material is formed from three(cid:173)
`dimensional woven fabric having a crimp-free fiber archi(cid:173)
`tecture in the x-y plane. The base material includes a first
`system of straight first fibers extending along a first direction
`in a first plane, a second system of straight second fibers
`extending along a second direction perpendicular to the first
`system in a second plane parallel to the first plane, and a
`third system of third fibers extending along a third direction
`through the first and second systems and binding the first and
`second fibers thereof. A first layer of conductive material is
`attached to a first surface of the base material. Preferably, the
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`base material is formed from a plurality of first and second
`systems defining multiple layers that are integrated by the
`third system, and a filler material is added to at least a
`portion of the first, second and third systems.
`It is therefore an object of the present invention to provide 5
`a base material for use in the manufacture of a printed circuit
`board, wherein the base material is formed from a three(cid:173)
`dimensional orthogonal fabric having a crimp-free fiber
`architecture in the x-y plane and an integrated multi-layer
`structure.
`It is another object of the present invention to provide a
`base material for a printed circuit board having improved
`properties such as drillability, dimensional stability, tensile
`strength and modulus and prevention against delamination,
`thereby representing a significant advance over composite 15
`laminates and other two-dimensional structures heretofore
`employed.
`It is a further object of the present invention to provide a
`printed circuit board and method for manufacturing the
`same, which employs a base material having the aforemen(cid:173)
`tioned advantageous structure and properties.
`Some of the objects of the invention having been stated
`hereinabove, other objects will become evident as the
`description proceeds when taken in connection with the
`accompanying drawings as best described hereinbelow.
`
`10
`
`6
`The first and second systems cooperate to define a layer
`L of fabric, which layer Lis disposed along a plane referred
`• • • Ln can be
`to as the in-plane. One or more layers L0
`constructed in accordance with the present invention. Each
`layer L can be defined as including one system of x-fibers X
`and one system of y-fibers Y, except for the outermost
`surface layers where only y-fibers Yare present. The actual
`number of layers L will depend upon the desired thickness
`of the finished base material for the PCB.
`A third system includes a plurality of z-fibers Z running
`in parallel relation through the planes of x-fibers X and
`y-fibers Y, such that z-fibers Z can be said to interconnect or
`bind the first and second systems and, in the case of a
`multiple-layered fabric, to interconnect or bind all layers L
`forming fabric 10. Preferably, z-fibers Z generally extend
`along the Cartesian z-axis such that z-fibers Z are mutually
`orthogonal to both x-fibers X and y-fibers Y or, stated
`differently, the third system is preferably disposed in an
`out-plane that is perpendicular to the in-plane defined by the
`20 first and second systems. Alternatively, or in addition to the
`orthogonal z-fibers Z, fabric 10 can include fibers running
`along a bias direction, or a direction angled with respect to
`the Cartesian axes. It is further preferable that z-fibers Z
`consist of one or more fibers which extend through the first
`25 and second systems in one direction along the z-axis and
`reverse direction in a repeated manner around curved sec(cid:173)
`tions 14 at the edge of fabric 10.
`Many different types of materials can be used for x-fibers
`X, y-fibers Y, and z-fibers Z. These materials include, but are
`30 not limited to, organic fibrous material such as cotton, linen,
`wool, nylon, polyester, and polypropylene and the like; and
`inorganic fibrous materials such as glass fiber, carbon fiber,
`metallic fiber, asbestos and the like. The fibers can be either
`twisted, zero-twisted, or a combination of both. In addition,
`35 fabric 10 can be provided as a hybrid structure containing
`different types of fibers in one or more of the fiber systems.
`For example, x-fibers X could be E-glass, y-fibers Y could
`be an aramid, and z-fibers Z could be copper filament.
`Preferably, the total fiber volume fraction, i.e., the percent
`by volume, of fabric 10 ranges from approximately 0.3 to
`approximately 0.6 and, more preferably, from 0.35 to 0.55.
`This can be tailored in each of the x-, y- and z-directions in
`order to adjust the properties of the overall three-
`45 dimensional structure of fabric 10. Additionally, each of the
`fibers forming fabric 10 preferably has a diameter in the
`range from approximately 5 to approximately 13 microns.
`Also, the linear density of the fibers is preferably within the
`range of approximately 10 to approximately 275 TEX.
`FIG. 5 illustrates an embodiment of a PCB generally
`designated 20 according to the present invention. PCB 20
`includes a base material 22 comprising three-dimensional
`woven fabric 10, and one or more conductive layers 24A,
`24B for which base material 22 serves as a supporting
`55 substrate. Conductive layer or layers 24A, 24B can be
`constructed from copper foil. Conductive layers 24A, 24B
`can be applied and adhered to base material 22 by a number
`of known methods, such as a subtractive process, an additive
`process or a combination thereof. PCB 20 can also include
`60 a filler material, or a binder material such as epoxy resin, in
`order to fill in voids 26 and further improve the surface
`flatness of fabric 10.
`A number of advantages result from the provision of
`fabric 10 to form base material 22 of PCB 20. Importantly,
`all x-fibers X and y-fibers Y making up fabric 10 are
`completely straight and thus not crimped, the exception
`being those fibers looped at the outer surfaces of fabric 10.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a cross-sectional view of a two-dimensional
`fabric known in the prior art;
`FIG. 2 is a cross-sectional view of another two(cid:173)
`dimensional fabric known in the prior art;
`FIG. 3 is a cross-sectional view of yet another two(cid:173)
`dimensional fabric known in the prior art;
`FIG. 4A is a perspective view of a volumetric section of
`a three-dimensional woven fabric used in a base material for
`a printed circuit board according to the present invention;
`FIG. 4B is a top plan view of the fabric of FIG. 4A;
`FIG. 4C is a side elevation view of the fabric of FIG. 4A; 40
`FIG. 5 is a sectional side view of a printed circuit board
`according to the present invention; and
`FIG. 6 is a schematic view of a process used in the
`manufacture of the base material for a printed circuit board
`according to the present invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`Referring to FIGS. 4A-4C, a volumetric section of a
`three-dimensional woven fabric according to the present 50
`invention is shown and generally designated 10. Fabric 10
`includes at least three primary systems of fibers. In the
`preferred embodiment, a first system includes a plurality of
`x-fibers (or warp fibers) X running straight and in a spaced
`parallel relation along the x-axis. A second system includes
`a plurality of y-fibers (or fill or weft fibers) Y running
`straight and in a spaced parallel relation along the y-axis.
`Preferably, y-fibers Y are actually one or more single,
`continuous fibers that are extended in one direction along the
`y-axis across the plane defined by the first system ofx-fibers,
`and then made to reverse direction in a repeated manner
`around loops or curved sections 12 at the fold of fabric 10
`so as to extend across the plane of the first system in the
`opposite direction. It is also preferable that x-fibers X and
`y-fibers Y, and thus the first and second systems, be disposed 65
`in a mutually orthogonal relation, such that the x- andy-axes
`are defined as in a Cartesian coordinate system.
`
`11 of 12
`
`

`
`US 6,447,886 Bl
`
`7
`It can be seen that within the three-dimensional core of
`fabric 10, z-fibers Z are substantially straight. It can also be
`seen that curved sections, 12 and 14 are quite straight in and
`of themselves, and thus do not significantly reduce the
`overall flatness of the outer surfaces. Also important is the 5
`fact that the strength and structural integrity of fabric 10,
`owing to its three-dimensional interlocking architecture,
`eliminates the risk of delamination of one or more layers L.
`By comparison, the failure of the resin matrix in prior art
`base materials significantly increases such risk. In addition, 10
`the size present on the fibers of fabric 10 is directly com(cid:173)
`patible with resin systems commonly used in the production
`of PCBs. As a further advantage, fabric 10 can be woven
`without the need for additional sizing, resulting in signifi(cid:173)
`cant cost savings and simplification of the manufacturing 15
`process due to the elimination of the manufacturing steps of
`size application, finishing, and removal.
`The process by which fabric 10 is formed will now
`generally be described with reference to the schematic
`shown in FIG. 6. Lengthwise or x-fibers X are drawn under 20
`tension from an x-fiber feeding device 32 such as a set of
`warp beams (as shown) or a creel (not shown), between
`heddles 34 of harnesses 36, and through a beat-up reed 38,
`thereby forming systems of x-fibers X which are in hori(cid:173)
`zontal and vertical alignment. Crosswise or y-fibers Y (not 25
`shown) are inserted between the systems of x-fibers X using
`fill insertion rapiers 42. Preferably, ally-fibers Yare inserted
`simultaneously in order to guarantee their straightness
`within the core of finished fabric 10 and to increase pro(cid:173)
`ductivity. Beat-up reed 38 is actuated to apply force on 30
`y-fibers Y as fabric 10 is being formed, thereby packing
`x-fibers X and y-fibers Y into a tight structure. It will be
`understood that other devices, such as a conventional sel(cid:173)
`vedge hold device 44 (for preventing the selvedge or edge on
`either side of the fabric from unraveling) and fill hold device 35
`46 (for tensioning of y-fibers Y), are preferably employed in
`known manner during the forming of fabric 10.
`Z-fibers Z are drawn under tension from a z-fiber feeding
`device 48 such a creel with bobbins (as shown) or one or
`more beams (not shown), and inserted through the layers
`formed by the systems of x-fibers X andy-fibers Yunder the
`control of harnesses 36 with cross-moving heddles 34 and
`beat-up reed 38. Take-up roll 52 is used to advance fabric 10
`forwardly. One specific and exemplary process and appara(cid:173)
`tus that can be utilized to form a preform such as fabric 10
`is described in detail in U.S. Pat. No. 5,085,252 to Mohamed
`et al., which applicants incorporate herein by reference.
`It thus can be seen that applicants have provided a printed
`circuit board and base material therefor having an improved
`three-dimensional, straight-fiber architecture and exhibiting
`improved properties such as drillability, dimensional
`stability, strength modulus and prevention against
`delamination, thereby representing a significant advance
`over composite laminates and other two-dimensional struc(cid:173)
`tures heretofore employed.
`It will be understood that various details of the invention
`may be changed without departing from the scope of the
`invention. Furthermore, the foregoing description is for the
`purpose of illustration only, and not for the purpose of 60
`limitation-the invention being defined by the claims.
`What is claimed is:
`1. A printed circuit board comprising:
`(a) a base material formed from a three-dimensional
`woven fabric having a crimp-free fiber architecture in
`
`8
`an x-y plane and including a first system of straight first
`fibers extending along a first direction in a first plane,
`a second system of straight second fibers extending
`along a second direction in a second plane parallel to
`the first plane, and a third system of third fibers
`extending along a third direction through the first and
`second systems and binding the first and second fibers
`thereof; and
`(b) a first layer of conductive material attached to a first
`surface of the base material.
`2. The printed circuit board according to claim 1 wherein
`the base material has a multiple layered structure including
`a plurality of first and second systems, the first and second
`systems cooperatively defining a plurality of fabric layers,
`each fabric layer disposed in parallel relation to the other
`fabric layers and including one of the first systems and a
`corresponding one of the second systems, wherein the third
`system binds the plurality of layers.
`3. The printed circuit board according to claim 1 further
`comprising a second layer of conductive material attached to
`a second surface of the base material.
`4. The printed circuit board according to claim 1 wherein
`the first layer of conductive material is constructed from
`copper.
`5. The printed circuit board according to claim 1 further
`comprising a filler material coating at least a portion of the
`first, second and third systems of the base material.
`6. The printed circuit board according to claim 1 wherein
`the first fibers extend along a direction orthogonal to the
`direction of the second fibers.
`7. The printed circuit board according to claim 6 wherein
`the third fibers extend along a direction orthogonal to the
`respective directions of the first and second fibers.
`8. The printed circuit board according to claim 1 wherein
`the third fibers extend along a