MXPA97002059A - Preimpregnado material unidirectionally oriented of thin thread and laminar unit for printed wiring board prepared from mi - Google Patents

Abstract

The invention relates to a basic material for manufacturing a PWB sheet unit, which is a pre-impregnated thin-film material UD comprising a layer of thin sheet of conductive metal bonded to a layer made of unidirectionally oriented parallel reinforcing fibers, having a diameter below 30æm, impregnated with matrix resin not fully consolidated, the pre-impregnated thin-film material UD can be used to manufacture cross-laminated PWB laminate units US, stacking and pressing them together, and between other UD layers, which can be already pre-impregnated layers that are not in the form of thin sheet, or mixed layers UD not fluid

Description

PREIMPREGNADO MATERIAL UNIDIRECTIONALLY ORIENTED OF THIN THREAD AND LAMINAR UNIT FOR PRINTED WIRING BOARD PREPARED FROM IT.

The present invention pertains to a basic material for manufacturing a PWB laminate unit comprising at least one layer of parallel, unidirectionally oriented (UD) reinforcing fibers, impregnated with matrix resin not yet fully consolidated, i.e., a prepreg layer YOU. The invention also pertains to laminar units for use in printed wiring boards (PUBs) prepared from said pre-impregnated layer UD. From US Pat. No. 4,814,945 a predetermined UD material for making PWBs is known. This description refers to a laminar unit of PUIt comprising a matrix resin reinforced with parallel aramid fibers. The laminar unit is made of layers of unidirectional aramid tape stacked one on top of the other crosswise. The aramid ribbon is formed by exposing a single layer of parallel aramid fibers to form fiber strips, coating the fiber strips with resin, and heating them until they cure or stage "B". A problem that arises easily when producing cross-fold laminar units UD is disorientation of the UD layers. It is necessary to retain adequate guidance to obtain a laminar unit that has sufficient planarity, which is a property of particular importance for a laminar unit of PUB. Particularly, if a still fluid matrix resin is used, for example, material from stage "B", there is a substantial risk of disorientation occurring, since, because of the flow occurring during the lamination, it can not be adequately controlled. the tension and therefore the orientation of the layers UD. It is still desired to produce UD reinforced cross-crease laminate units based on prepreg. The manufacture of laminar units based on prepreg (usually pre-impregnated woven glass fabric) is common in the field of PUB laminates and it may be advantageous to be able to use resin systems and proven viability lamination technology in this field . Of course, by virtue of the structure of the woven fabric, customary pre-dressed materials are less prone to disorientation problems. However, the replacement of the woven fabric structure by a UD crossover structure leads to considerable advantages such as improved surface area quality, a comparatively low linear coefficient of thermal expansion (TCE) in the x and y directions, With the option of incorporating a high fiber content, and a favorable dimensional stability, in this respect, the UD cross-folded sheet units are pre-eminently suitable as a substrate for PWB. Of course, this only holds if these laminar units can be manufactured by a method that allows to retain the proper orientation. Several such methods are known in the art, for example EP 478 051, UO 92/22191, and US 4,943,334. None of these is based on lamination of pre-impregnated materials, while the present invention is directed to providing cross-folded sheet units UD on the basis of UD prepregs. A problem associated with UD fiber orientation is handled in DE 3542295. It pertains to photographic sealing materials based on a substrate layer of oriented fibers contained in a matrix resin. It is disclosed that by applying a plate of a synthetic sheet that shrinks with heat on the substrate layer, position deviations of the parallel fibers during their shaping under pressure can be suppressed. The use of a thin sheet that shrinks with heat causes the UD prepreg to bend slightly in the direction of the fiber. Although this may be convenient in the case of a sealing material, in a PWB laminate unit it must be completely avoided. Another problem that can occur when using UD prepregs, especially if thin laminar units are to be used, is that it is difficult to handle a single cap.; a UD fibers impregnated with resin that is still fluid (even if the resin is solid at the handling temperature). This problem is increased by the fact that the UD layers have a tendency to deform in the longitudinal direction. This is due to the lack of resistance of the UD layer in the direction perpendicular to that of the fibers. A further problem is found when the fully unconsolidated matrix resin is a thermally curable resin. Unlike a thermoplastic resin, such a thermoset resin has not yet fully consolidated, it does not yet have its final properties; that is, all the mechanical properties are still inferior. This leads to an additional problem in handling the prepreg, since it can be easily damaged. It should be noted that another prior art in which pre-impregnated materials UD is used belongs to the manufacture of round shaped articles such as golf clubs. In this way, 3P-Hei-4-329-132, teaches a hybrid prepreg article for use in the same. The hybrid prepreg comprises two different types of parallel fibers, essentially thick ones having a diameter of 30 to 500 μm and thin ones of 5 to 30 μm, and a metal layer of thickness of 5-100 μm. For PUBs that must meet modern requirements, it is important that any reinforcing fibers are filaments having a diameter below 30 μm, and preferably from 3 to 15 μm, since thicker fibers are prohibitive for hole punching and to obtain a convenient surface flatness. It is particularly with thin prepregs, which have thin reinforcing fibers, that the handling problems occur. Another prior art is JP-Hei-6-008, 240. It teaches mixed structural bodies, the outermost layer of which has been covered with a metal or metal-composite film. Although the mixed body core can be reinforced with unidirectional parallel wires, the outer layers are reinforced with glass fabric. The description is directed to configured round articles such as golf clubs or antennas. The Japanese Patent Application No. 201699/185 discloses a heat-sensitive electrical protection material comprising a thin sheet of metal, a layer of heat-bondable resin formed thereon, and a multitude of reinforcing wires parallel to the resin layer. The conductor wires, which have a diameter of 0.03 to 0.5 mm, are spaced apart from 10 to 15 crn. It is disclosed that if the thin metal sheet is prevented from wrinkling, the protective material must be wound together with a cushioning material, for example a sheet of polyurethane foam. Additional background techniques on PWB laminar units include EP 0 372 505. This essentially describes a thermoplastic laminar unit reinforced with fiber. The fiber reinforcement can be in any form. The thermoplastic sheet unit is provided with a thin sheet of metal when it is in the molten state. It is generally a high temperature thermoplastic, which is solid at room temperature. The laminar body described is not of the basic material type to produce PUBs that the invention intends, and serves as a laminar unit of PUB itself. Therefore, the laminar unit manufactured according to EP 372 505 is a laminar unit having the final properties of a PUB substrate. The invention is essentially directed to UD prepregs which can be used to make PUBE, but are not suitable as laminar units for PUB by themselves. Being thin and having fiber reinforcement in one direction, you will have the proper properties in that direction only. Therefore, it is difficult to handle, and easily deforms. As indicated above, this problem is even more apparent when using a thermally curable resin not fully consolidated. Now, the invention seeks to provide a pre-impregnated layer UD that allows subsequent handling and treatment without incurring problems such as those inded above, and is of a type essentially suitable for manufacturing a laminar-unit of PUB. Furthermore, the invention seeks to provide a UD prepreg layer in which it is possible to employ a thermally curable resin such as the resin not fully consolidated without suffering from the additional problems associated therewith. For this purpose, the invention provides a basic material for producing a PUB sheet unit comprising a UD prepreg layer of the type inded above, wherein the reinforcing fibers have a diameter below 30 μm, and a thin film layer of conductive metal, such as thin copper foil, the thin foil layer of conductive metal is bonded to the prepreg UD layer. The thin film layer of conductive metal makes a UD prepreg have sufficient strength perpendicular to the direction of the fibers to avoid deformation during handling. If the thin sheet is laminated onto the prepreg UD before it is cut to size, the problem of handling a thin copper sheet is also solved. As inded above, the invention pertains to a basic material for manufacturing a laminar unit for PUB. This basic material comprises a layered structure, the two consecutive layers joined together are a layer of a thin sheet of metal, such as copper foil, and a layer of parallel fibers, unidirectionally oriented, impregnated with matrix resin not completely consolidated. The term "pre-impregnated" is well known in the art and generally indes a reinforcing material impregnated with resin and (serai) cured. Usually it is still in a slimy stage. The term "matrix material not fully consolidated" indes that the resin can still be further cured. In the case of a soil-hardened resin, it generally refers to the matrix resin which is in step B. The different stages of matrix material (matrix resins) are usually identified in the technique co or the steps "A", " B ", and" C ", stage A indes non-solidified resin (ie, in the case of a terrnofraced resin: the uncured stage) stage B generally indes partial solidifion (in the case of a thermoset resin: the reaction it has advanced to the formation of longer chains, but not complete network formation), and stage C indes a solidified (cured) stage. The terms stage A, stage B, stage C are known to the person of experience in the subject and do not require further elucidation herein. The thin-film prepreg materials of the invention can be laminated with other pre-impregnated layers or with layers of a consolidated material. Of course, it is entirely possible that these other layers comprise a woven fabric reinforcement, but if the advantages of UD reinforcement are desired in their entirety, the other layers must also have UD parallel fibers, that is, they must have pre-impregnated layers UD or layers. mixed UD consolidated (non-fluid), as described in UO 92/22191. The current normal basic materials for printed wiring boards are generally manufactured in accordance with the procedure described for example in C.F. Coornbs, Jr.'s Printed Circuits Handbook (tcGraw-Hill), which includes the following steps: Woven glass fibers are impregnated with an epoxy resin solution in MEK. The solvent is then evaporated and the resin partially cured in a so-called stage B. The resulting prepreg is cut to the desired length and stacked between two thin sheets of copper. This package is cured under high temperature pressure in a press in daylight. The copper-coated laminar unit on both sides thus manufactured is then formed on a wiring board printed by engraving. The laminar units of PUB on the basis of the prepreg material UD according to the invention can be manufactured essentially analogously. Of course, the preparation of pre-impregnated basic material UD deviates from the process of impregnation and curing of a woven fabric. UD prepreg can conveniently be prepared by coating a thin sheet of copper with matrix resin to form a thin-film resin layer, heating the thin-film resin layer to ensure that the resin is sufficiently fluid for impregnation to occur of filaments, and apply parallel filaments on the resin to form a layer of reinforced resin UD in thin film. The impregnation can also be carried out inversely, for example by applying the parallel filaments on a layer of resin not necessarily fluid, and then heating the resin so as to make it sufficiently fluid for impregnation to occur. Depending on the type of resin used, the thin-film reinforced resin layer UD is then heated or subjected to actinic radiation to effect partial curing of the resin (for example in step B) or cooled so that the resin solidifies (e.g. with a thermoplastic resin that is solid at room temperature). Surprisingly, the resulting pre-impregnated thin film material UD is easier to handle than the uncoated copper thin sheet, and the corresponding UD prepreg material which is not in the form of a thin sheet. The pre-impregnated thin-film material is cut to length and is ready to be stacked and laminated with other UD layers that are not thin-film. The UD layers that are not thin-film form the inner sheets and are sandwiched between two thin-film UD prepregs (with the thin Cu-sheet layers on the outer surfaces). In this respect, the invention also pertains to a method of manufacturing a PUB sheet unit where several layers comprising unidirectionally oriented parallel reinforcing fibers contained in a resin matrix are stacked and pressed. In this method, the layers forming the outer surfaces of the sheet unit are formed from a prepreg material UD in the thin sheet comprising a thin sheet layer of conductive metal bonded to a prepreg layer UD, the conductive metal sheet is on the outside of the laminar unit. In one embodiment, the layers forming the inner sheets of the web unit PUB and the prepregs comprise unidirectionally oriented parallel reinforcing fibers impregnated with matrix resin not fully consolidated, ie prepreg UD not in the form of a thin sheet. In another embodiment, the layers forming the inner sheets of the laminar unit are formed of non-fluid mixed UD layers or non-fluid cross-fold laminar units. The term "non-fluid mixed body UD" is used to indicate a mixed material comprising unidirectionally oriented reinforcing fibers encased in a matrix material that has been solidified (consolidated) to such an extent that it does not become fluid again during the remainder of the term. manufacturing procedure. In general, this means that during storage and treatment, the non-flowing mixed body UD is under such conditions of pressure and temperature that it is below its softening point (ie below apparent Tg or Tg), or solidified in a stage in which flow no longer occurs. For convenience of storage and treatment, it is preferred to have reached stage C for the solidification of the non-fluid mixed UD body, or for those resins used which comprise rigid molecular chains, in which under regular storage and treatment conditions, a non-fluid state in a stage still called stage B. However, notably when the pressing in the rolling zone is carried out under isobaric conditions, material can also be used in stage A. In the embodiments where the internal sheets are formed of mixed bodies UD non-fluid, these sheets can be prepared in accordance with UO 92/22191. It is also possible to stack and laminate UD prepreg materials in thin film according to the invention using intermediate substrates such as described in UO 91/22192 which may or may not be covered with adhesive. As is known, the cross-fold layered units UD are preferably balanced and symmetrical. The term "balanced" indicates equal properties in perpendicular directions (ie, an equal number of filaments in the x and y directions) the term "symmetrical" indicates mirror image symmetry over the thickness of the laminar unit, i.e., the laminar unit is symmetric in the middle of itself: >tria, which runs through the center of the laminar unit and is parallel to the outer surfaces of the laminar unit, is either the boundary between two UD layers, or an imaginary plane that runs through a UD layer, depending of the number and order of layers UD on the thickness of the laminar unit. A main disadvantage of said balanced and symmetric laminar unit in flat medium provided with reinforced layers UD applied in a cross-shaped manner consists of iso-orphism of its properties in the x and y directions (ie, the two fiber directions perpendicular to each other). Particular preference is given to the composite sheet unit such that the reinforced layers UD are oriented as specified in one of the following models, remaining at 0o and 90o for directions of orthogonal orientation and the relative thicknesses of the layers indicated repeating the orientation given where it is necessary: 0 ° / 90o90o / 0 ° 0 ° / 90o90o / Do0o / g0o90o / 0o. In general, for use in PUBs, the reinforced layers UD in the laminar unit according to the invention have a thickness in the scale of 6 to 800 μm, preferably of approximately 12.5 to 400 μm. The outer layers of the cross-folded sheet unit are formed by a pre-impregnated material UD in the thin sheet according to the present invention, i.e., a layered structure having a layer of thin sheet metal (e.g. Cu) and a UD layer (for example, 0o). In the previous example, in which the inner UD layers have a double thickness compared to the outer UD layers, the inner layers can be made of a UD prepreg. Of course, in that case there is the aforementioned danger of disorientation, but the double thickness UD layers do not display the same handling problems as a UD layer of only one thickness (whose problem is solved according to the invention by applying thin film of metal). In this embodiment, it is preferred that the lamination be carried out in an isobaric press, in order to avoid a driving force for the flow. Preferably, however, the inner layers are the non-fluid mixed UD layers identified above in accordance with UO 92/22191. As is clear from the foregoing, it is preferred that the stacking of the UD layers which are not in thin sheet form sandwiched between two thin-film UD prepregs (with thin Cu-sheet layers on the outer surfaces) is such that Reinforced UD layers are oriented as specified in one of the previous models, ie Cu0 ° / 90o90o / 0 ° Cu, or Cu0o / 90o90o / 0o0o / 90o90o / 0 ° Cu. The lamination can be carried out in a daylight press, an autoclave, a vacuum press, a double-band press, or in any other suitable apparatus. The laminar units of PUB made on the basis of the thin-film prepreg UD according to the present invention are suitable for use in multilayer PUBs (MLBs), for example as described in UO 92/22192. The materials used to carry out the present invention are not especially critical. Preferably, use is made of the materials mentioned below. The matrix material is a thermoplastic or a thermoset polymer, preferably thermosetting resins. The use of an epoxy resin based on matrix material is preferred, but other resins are also useful in principle. Examples include cyanate esters, unsaturated polyester resins (UD), vinyl ester resins, acrylate resins, BT epoxy resin, bisrnaleimide resin (BMI), polynide (PI), phenol resins, triazines, polyurethanes, silicone resin , biscitracone resin (BCI). Alternatively, combinations of said resins can be used and it is also possible to mix the aforementioned resins with certain suitable thermoplastics, such as PPO, PES, PSU, and PEI, among others. Interpenetrating polymer networks (IPNs) may also be suitable. It is advantageous to incorporate compounds in the matrix material to make them resistant to flame, such compounds containing phosphorus or halogen (particularly bromine). A particular matrix material which is preferred for its favorable flow and cure properties comprises approximately 100 parts by weight of Epikote R828 EL, approximately 73 parts by weight of Epikote R5050, and approximately 4 parts by weight of a complex of boron tri-fluoride and monoethylamine . Although the preferred reinforcing material consists of filament yarns, non-continuous fibers may also be employed. According to the invention, the reinforcing threads are preferably selected from the following group of materials: glass, for example E glass, A glass, C glass, D glass, AR glass, R glass, SI glass, and S2 glass, and different Ceramic materials, such as alumina and silicon carbide. Also suitable for use are polymer-based fibers, particularly so-called liquid crystalline polymers, such as terephthalamide T for phenylene (PPDT), polybenzobisoxazole (PBO), polybenzobisthiazole (PBT), and polybenzoirnidazole (PBI), such as fibers based on polyethylene naphthalate (PEN), polyethylene terephthalate (PET), and polyphenylene sulfide (PPS). The fibers (filaments) should have a diameter below 30 μm, e.g., 20 μm. Typical diameters in particular vary from 3 to 15 μ, and preferably are from 5 to 13 μ. In general, the fiber content in the matrix is about 10-90 X by volume, preferably in the range of 40 to 70% by volume. A fiber volume fraction of about 50% by volume is highly satisfactory. Unlike reinforced woven fabric laminar units, the mixed laminar units manufactured using the method according to the invention are also suitable for use in a flexible laminar unit or panel and in rigid-flexible laminar units. When used in a flexible panel, woven fabrics undergo cracking at the warp and weave joints, due to the fact that fibers oriented in the direction of flexure are interwoven with fibers perpendicular to the direction of flexure.; this adverse effect increases with the high concentration of fiber in these joints, which leads to cracking to a relatively low degree of flexion. These cracks cause a high concentration of stress in conductive lines present in the flexible laminar unit, and consequently a high risk of cracking, which leads to circuit breakage. In a flexible laminar unit (or in the flexible portion of a rigid-flexible laminar unit), the orientation of the outer UD layers is preferably parallel to the desired direction of bending. In addition, the UD crossfold laminar units present are highly suitable for use as support material in devices with different integrated circuits provided therein (ultichip modules). This is due notably to the favorable TCEe, which are mainly the result of the high fraction of fiber volume that can be obtained when using cross-folding laminar units and can be close to the TCE of electronic components (chipe) used in conjunction with PUBs, more particularly flLBs. Such components may be provided on the top of an MLB (chip on board) or may be included in a substrate such as an intermediate substrate in accordance with UO 92/22192 (chip on board). The fabrication of laminar units made on the basis of the thin-film UD prepreg of the present invention is further illustrated in the schematic drawings. Figure 1 shows a pre-impregnated thin film UD material (1) according to the invention. It is indicated in the figure, which shows cross sections in the x and y direction of thin sheet of copper (2), which is applied on a UD prepreg layer (3) made of unidirectionally oriented parallel reinforcing fibers (4) impregnated with non-matrix resin. fully consolidated (5). Figure 2 shows a non-fluid mixed body UD (6) according to WO 92/22191. In the figure, two elaborated layers of UD fibers (7) impregnated with non-fluid matrix resin (8) are indicated (cross sections x and y). Figure 3 shows a PWB Cu0 ° / 90o90o / 0 ° Cu laminar unit made by stacking and laminating the non-fluid mixed body UD (6) with two pre-impregnated UD thin-film materials (1).

Claims (7)

NOVELTY OF THE INVENTION CLAIMS

1. - A basic material (1) for manufacturing a laminar unit of PUB comprising a pre-impregnated layer UD (3) made of parallel reinforcing fibers, oriented unidirectionally (4) impregnated with matrix resin not fully consolidated (5), characterized in that the basic material (1) is a thin-film UD prepreg material comprising a layer of a thin sheet of conductive metal (2) bonded to the prepreg layer UD (3); the reinforcing fibers (4) in the prepreg layer UD (3) have a diameter below 30μm.

2. A basic material (1) for manufacturing a laminar unit of PWB according to claim 1, characterized in that the thin metal sheet (2) is a thin sheet of copper having a thickness below l? Μrn.

3. A basic material (1) for manufacturing a laminar unit of PWB according to claim 1 or 2, characterized in that the matrix resin (5) is a thermally curable resin.

4. A method of manufacturing a pre-impregnated layer UD (3) wherein the unbonded filaments in the form of a woven fabric are parallel, in a single direction, characterized in that the parallel filaments (4) are impregnated with a resin of fluid matrix (5) attached to, and supported by, a thin sheet layer of conductive metal (2).

5. A laminar unit of PUB having layers of a thin sheet of conductive metal (2) on the external surfaces, the laminar unit is made of a plurality of layers UD, each layer UD comprises a resin matrix (5) reinforced with parallel fibers oriented unidirectionally (4), the UD layers are arranged crosswise, and the laminar unit has a plane of symmetry parallel to the external surfaces, characterized in that the thin sheet of conductive metal (2) and the adjacent outer UD layers (3) are formed of a thin-film UD prepreg (1) according to any of claims 1-3.

6. A method for manufacturing a PUB laminate unit in which several pre-impregnated layers are stacked and pressed, the pre-impregnated layers comprise unidirectionally oriented parallel reinforcing fibers impregnated with non-fully consolidated matrix resin, characterized in that the pre-impregnated layers (3 ) forming the outer surfaces of the laminar unit are formed of a pre-impregnated thin-film material UD (1) comprising a layer of a thin sheet of conductive metal (2) bonded to a prepreg layer UD (3), the thin sheet Conductor metal (2) is on the outer side of the laminar unit.

7. - A method for manufacturing a laminar unit of PUB characterized in that several layers comprising parallel reinforcement fibers, unidirectionally oriented in a resin matrix, are stacked and pressed, characterized in that the layers forming the inner laminae of the laminar unit are formed of UD non-fluid mixed layers (6), and the layers forming the outer surfaces of the laminar unit are formed of a pre-impregnated thin-film material UD (1) comprising a layer of a thin sheet of conductive metal (2) bonded to it. a layer (3) comprising parallel reinforcing fibers oriented unidirectionally (4) impregnated with matrix resin not fully consolidated (5), the thin sheet of conductive metal (2) is on the outer side of the laminar unit.