Glass-cloth epoxy sheet and method and apparatus for manufacturing the same

Abstract: A glass-cloth epoxy sheet is manufactured by impregnating a varnish, which is prepared by dissolving a curing epoxy resin composition into a solvent, into glass cloth and curing the varnish. If a thickness X of the glass-cloth epoxy sheet ranges from 20 to 75 µm, the content of the glass cloth is set within the range of 0.4X + 25 (wt%) to 70 (wt%). If the thickness X of the epoxy sheet ranges between 75 and 200 µm, the content of the glass cloth is set at 55 (wt%) to 70 (wt%). With this content of the glass cloth, a glass-cloth epoxy sheet with good punching characteristics can be obtained. In a method of manufacturing a glass-cloth epoxy sheet excellent in smoothness, fuzz properties, and flexibility, glass cloth is pulled up vertically from an impregnating tank containing a varnish. The varnish is kept out of contact with anything while being cured.

Description: The present invention relates to a glass-cloth epoxy sheet usable as a flexible printed circuit or a carrier tape for mounting LSIs or the like, and a method and an apparatus for manufacturing this glass-cloth epoxy sheet. The present invention more particularly relates to a glass-cloth epoxy sheet excellent in various characteristics, such as punching characteristics, evenness in thickness, surface smoothness, homogeneity, adhesive properties of an adhesive, soldering heat resistance, and flexibility, and a method of manufacturing this glass-cloth epoxy sheet. A flexible printed circuit using a glass-cloth epoxy sheet is generally manufactured as follows. That is, after an adhesive is coated on a glass-cloth epoxy sheet, holes serving as device holes or through holes are formed by punching or the like. Thereafter, a copper foil is laminated on the sheet by using a heat press or a heat roll and etched to form a predetermined circuit pattern. In the punching of holes in the above manufacturing process, if the interface between glass cloth and an epoxy resin peels off or fibers of the glass cloth come out from the epoxy sheet, a gap is formed in that portion. When an etching solution penetrates into such a gap, a portion that is originally not to be etched is also etched, and this may break the circuit. This problem arises similarly when voids exist in the glass-cloth epoxy sheet and produce a portion which is inhomogeneous in quality. If, on the other hand, the glass-cloth epoxy sheet has a portion with an uneven thickness or a surface defective portion such as glass fuzz, a circuit pattern in that portion breaks after etching. Of these problems, peeling of the interface between the glass cloth and the epoxy resin and coming out of the glass cloth fibers occurring in the punching of holes are generally prevented by improving the adhesive power of the interface between the glass cloth and the epoxy resin by: a. performing a surface treatment for glass-cloth fibers; or b. impregnating an epoxy resin composition into the glass cloth for a sufficiently long time period by, e.g., performing the impregnating step twice. As for unevenness in thickness and mixing of voids, after a varnish of a curing epoxy resin composition is impregnated into the glass cloth, a semi-cured B-stage glass-cloth epoxy sheet having a sticky surface is cut into a predetermined size and heated under pressure by using a heat press or the like, thereby obtaining an even thickness and removing voids. In this manner, glass-cloth epoxy cut sheets for flexible printed circuits are manufactured (one by one), thereby preventing unevenness in thickness and mixing of voids. As circuit design has advanced and has become sophisticated recently, however, a demand has increasingly arisen not only for an improvement in punching characteristics but for a continuous glass-cloth epoxy sheet which makes continuous formation of circuits feasible. No satisfactory punching characteristics, however, can be obtained by the conventional techniques described above. In addition, the above conventional techniques cannot manufacture a continuous glass-cloth epoxy sheet because evenness in thickness and prevention of mixing of voids are realized by the use of a heat press. SUMMARY OF THE INVENTION It is the first object of the present invention to provide a glass-cloth epoxy sheet with good punching characteristics. It is the second object of the present invention to provide a method capable of continuously manufacturing a glass-cloth epoxy sheet excellent in, e.g., evenness in thickness, surface smoothness, and homogeneity in quality. These objects are attained by the method of claim 1. To improve these objects of the present invention, the present inventors have made extensive studies and found the following. That is, in a glass-cloth epoxy sheet manufactured by the above method with good punching characteristics can be obtained by setting the content of the glass cloth to 0.4X + 25 wt% to 70 wt% for a thickness X of the glass-cloth epoxy sheet ranging between 20 and 75 µm. In addition, a glass-cloth epoxy sheet with good punching characteristics can be obtained by setting the content of the glass cloth to 55 wt% to 70 wt% for a thickness of the glass-cloth epoxy sheet ranging between 75 and 200 µm. According to the manufacturing method of the present invention, on the other hand, after a varnish is impregnated continuously into glass cloth in an impregnating tank, this glass cloth is pulled up vertically in a free state from the impregnating tank. Subsequently, the varnish is cured without bringing the surface of the glass cloth impregnated with the varnish into contact with anything. This makes it possible to continuously manufacture a glass-cloth epoxy sheet with a high evenness in thickness and a high homogeneity in quality. Furthermore, the glass-cloth epoxy sheet with 20 to 200 µm in thickness is manufactured by using a varnish with a viscosity of 3 to 50 cp in accordance with the above manufacturing method, provides a glass-cloth epoxy sheet having both a high flexibility and a high surface smoothness. Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing a glass-cloth epoxy sheet according to the embodiment of the present invention; Fig. 2 is a block diagram showing the arrangement of an apparatus for manufacturing the glass-cloth epoxy sheet shown in Fig. 1; and Fig. 3 is a table showing the comparison between glass-cloth epoxy sheets according to samples of the present invention and general glass-cloth epoxy sheets. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The embodiment of the present invention will be described below with reference to the accompanying drawings. Fig. 1 is a sectional view showing a glass-cloth epoxy sheet according to this embodiment. In Fig. 1, surface unevenness is emphasized for convenience sake. Referring to Fig. 1, this glass-cloth epoxy sheet is generally denoted by reference numeral 100. Reference numeral 1010 denotes warps of glass cloth; 1011, wefts of the glass cloth; 102, epoxy resin portions formed by impregnating a varnish, which is prepared by dissolving a curing epoxy resin composition into a solvent, into glass cloth 101 and curing the varnish; and 103, the thickness of the glass-cloth epoxy sheet. (1) Curing epoxy resin composition The curing epoxy resin composition for impregnating glass cloth used in this embodiment is prepared by dissolving a mixture of an epoxy resin and an epoxy hardener into a solvent. (Epoxy resin) Examples of the epoxy resin used in this embodiment are a tetraglycidylether epoxy resin, a bisphenol A epoxy resin, a bisphenol F epoxy resin, a novolak epoxy resin, an alicyclic epoxy resin, a glycidylester epoxy resin, a glycidylamine epoxy resin, a heterocyclic epoxy resin, and an urethane-modified epoxy resin. These resins can be used either singly or in the form of a mixture of two or more types of them. (Epoxy hardener) Examples of the epoxy hardener used in this embodiment are an amine-based hardener, a polyaminoamide-based hardener, acids and acid anhydrides, dicyandiamide, a basic active hydrogen compound such as organic acid dihydrazide, imidazoles, amineimides, Lewis acid, Brönsted acid salts, and a phenolic resin. These hardeners can be used either singly or in the form of a mixture of two or more types of them. (Solvent) Examples of the solvent used in this embodiment are acetone, methylethylketone, toluene, methylcellosolve, and dimethylformamide. These solvents can be used either singly or in the form of a mixture of two or more types of them. (2) Viscosity of varnish The varnish used in this embodiment is prepared by dissolving the above-mentioned epoxy resin composition into one or a mixture of two or more types of the solvents described above. The viscosity of the varnish is adjusted by changing the solvent ratio. If the viscosity of the varnish is less than 3 cp, the varnish flows easily to make it impossible to control the impregnation quantity of the varnish into the glass cloth. If the viscosity of the varnish exceeds 50 cp, on the other hand, the flowability of the varnish lowers, and so the varnish sags unevenly on the surface of the glass cloth. Consequently, the thickness of the resultant glass-cloth epoxy sheet becomes uneven. The viscosity of the varnish, therefore, must be 3 to 50 cp, more preferably 5 to 30 cp. Note that the measurement of the viscosity in examples to be described later was performed by using an E viscometer. (3) Thickness (103) of glass-cloth epoxy sheet If the thickness of the glass-cloth epoxy sheet 100 is less than 20 µm, the glass-cloth epoxy sheet is stretched or broken in the step of coating an adhesive in order to mount LSI chips or the like or in the subsequent step of laminating a copper foil by using a heat roll or the like. If, on the other hand, the thickness of the glass-cloth epoxy sheet exceeds 200 µm, the flexibility of the glass-cloth epoxy sheet is impaired to make continuous coating of an adhesive difficult. The thickness of the glass-cloth epoxy sheet is therefore 20 to 200 µm, and preferably 30 to 150 µm. (4) Content of glass cloth 101 If a content of the glass cloth is less than 0.4X + 25 wt% for a thickness X of the glass-cloth epoxy sheet 100 ranging between 20 and 75 µm or if the content is less than 55 wt% for the thickness X ranging between 75 and 200 µm, stiffness decreases and the linear expansion coefficient increases, making it impossible to obtain performance required as a flexible printed circuit. If, on the other hand, the content of the glass cloth exceeds 70 wt%, the amount of the epoxy resin with respect to the glass cloth decreases, resulting in an insufficient adhesion between the glass cloth and the epoxy resin. This causes peeling between the glass cloth and the epoxy resin during punching of holes, whitening the peripheral portions of the holes. (5) Method of manufacturing glass-cloth epoxy sheet 100 First, a varnish is impregnated into continuous glass cloth. The impregnation of the varnish is preferably performed by arranging a plurality of rolls in an impregnating tank and impregnating the varnish into the glass cloth with the glass cloth in contact with the rolls. This is so because bringing the glass cloth into contact with the rolls squeezes out voids from the glass cloth to allow formation of a homogeneous glass-cloth epoxy sheet containing no voids. Subsequently, the glass cloth impregnated with the varnish is continuously pulled up vertically in a free state at a constant rate such that the liquid surface of the varnish in the impregnating tank does not ripple. If the liquid surface of the varnish in the impregnating tank ripples, the thickness of the glass-cloth epoxy sheet becomes uneven in the longitudinal direction of the sheet. If the glass-cloth epoxy sheet is not pulled up vertically, the thickness of the glass-cloth epoxy sheet becomes uneven in both the widthwise and longitudinal directions of the sheet. Curing of the glass-cloth epoxy sheet thus pulled up, i.e., curing of the varnish is performed in a free state in which the surface of the sheet is brought into contact with nothing but hot air. Curing means herein a cured state in which the surface of the glass-cloth epoxy sheet is not damaged even if it is brought into contact with rolls or the like and the weave pattern of the glass cloth does not deform even upon application of an external force within an elastic deformation limit to the sheet. Solvent drying and curing are performed at, for example, normal temperature to 200°C for one to 60 minutes. In situations where the degree of curing needs to be further increased, additional processing, such as curing at 60 to 200°C for 10 minutes to 72 hours may be performed. The cured glass-cloth epoxy sheet is continuously wound up into the form of a roll. The following two points are important in the manufacturing method of this embodiment. 1) Pulling up the glass-cloth epoxy sheet vertically from the impregnating tank. If the glass-cloth epoxy sheet is pulled up obliquely, the varnish sags toward the lower surface to cause a difference in the varnish quantity between the upper and lower surfaces. 2) Bringing nothing into contact with the surface of the glass-cloth epoxy sheet before the varnish is cured. To control the impregnation quantity of the varnish into glass cloth, it is common practice to perform a method of bringing, e.g., a blade or a coil-wound bar into contact with one or both of the surfaces of a glass-cloth epoxy sheet immediately after the sheet is pulled up from an impregnating tank. In this method, excess varnish sags downward unevenly from the coil-wound bar or the like. This produces portions where the varnish sags and portions where it does not or causes differences in the amount of sagged varnish between portions where the varnish sags. Various conditions, e.g., evaporation of the solvent, slightly change depending on these differences, and this degrades evenness in thickness of the glass-cloth epoxy sheet in the widthwise and longitudinal directions of the sheet. In addition, bringing the coil-wound bar or the like into contact with the glass-cloth epoxy sheet gives damages to the glass cloth, causing breaking of some fibers of the glass cloth or loosening of the fibers into the form of a loop, resulting in glass fuzz. This glass fuzz impairs the surface smoothness of the glass-cloth epoxy sheet after the varnish is cured. Likewise, if the glass-cloth epoxy sheet is brought into contact with the roll before the varnish is cured, the varnish is wiped by the contact pressure, degrading the surface smoothness of the sheet. (6) Description of manufacturing apparatus Fig. 2 shows a manufacturing apparatus of this embodiment to which the manufacturing method as described above is applied. Referring to Fig. 2, 1,500 m of 1,050-mm wide, 80-µm thick glass cloth 10, for example, is wound on a sheet roll 1. This manufacturing apparatus includes rolls for controlling the running direction of the glass cloth, i.e., a delivery guide roll 2, first to third impregnating rolls 41 to 43, first and second oven rolls 51 and 52, and a wind-up guide roll 6. The diameter of the first to third impregnating rolls 41 to 43 is set to be smaller than those of the other rolls in order to prevent mixing of voids during impregnation of the varnish. More specifically, the diameter of the first to third impregnating rolls 41 to 43 is set at about 50 to 80 mm, and the diameters of the other rolls are set at about 100 to 200 mm. A push bar 3 is made of a material, such as brass, having good sliding properties with respect to glass cloth and is provided between the first roll 2 and the first impregnating roll 41. This push bar 3 slightly pushes the glass cloth 10 outward to thereby discourage formation of wrinkles of the glass cloth 10. The tip of the push bar 3 is rounded so as not to damage the glass cloth 10. An impregnating tank 4 is of a three-roll type having the first to third impregnating rolls 41 to 43 in order to suppress mixing of voids during impregnation of the varnish. The impregnating tank 4 contains a predetermined amount of a varnish 44 whose viscosity is adjusted in accordance with a glass-cloth epoxy sheet to be manufactured. A liquid level sensor 403 detects the liquid level of the varnish in the impregnating tank 4 and sends a detection signal to a varnish supply control unit 401. On the basis of this detection signal, the varnish supply control unit 401 controls the quantity of the varnish to be supplied to the impregnating tank by a varnish supply unit 402, thereby maintaining the liquid level of the varnish constant. The varnish supply control unit 401 also controls the temperature of a heater 405 in accordance with the temperature of the varnish 44 detected by a temperature sensor 404, maintaining the temperature of the varnish 44 constant to thereby hold its viscosity at a constant value. A drying oven 5 cures the varnish 44 impregnated into the glass cloth 10 by blowing hot air. The drying oven 5 has six drying chambers 511 to 516 whose temperatures can be set independently of one another. Although the temperatures of the individual drying chambers are determined properly in accordance with the distance and the velocity the glass cloth 10 moves in the oven, they are set such that the varnish is cured at the time the glass cloth 10 touches the first oven roll 51 at the latest. Note that the temperature of each drying chamber is controlled by a temperature control unit 501. The positions of the first oven roll 51 and the third impregnating roll 43 are set such that the glass cloth 10 impregnated with the varnish 44 is pulled up in a direction perpendicular to the liquid surface of the varnish 44. After the glass cloth 10 passes by the first oven roll 51, the fourth to sixth drying chambers 514 to 516 may be used to further cured the varnish as needed. A far-infrared heater 7 has a structure in which, for example, a heater is incorporated into earthenware and is arranged at a distance of 40 to 50 cm from the glass cloth 10 with its surface temperature set at approximately 500°C. The far-infrared heater 7 is used when the running velocity of the glass cloth 10 is high or when the degree of curing needs to be further increased. The temperature of the far-infrared heater 7 is controlled by a temperature control unit 701. An epoxy sheet roll 8 winds up the glass-cloth epoxy sheet in which the varnish is cured completely. A wind-up motor 801 drives the epoxy sheet roll 8. A velocity control unit 802 controls the conveyance velocity of the glass cloth 10 in this apparatus by adjusting the speed of the wind-up motor 801. Braking means (not shown) is also provided at, for example, the axis of the sheet roll 1 to prevent wrinkles of the glass cloth 10 and keep its tension constant. If necessary, driving units may be provided for the individual rolls (2, 41 to 43, 51, 52, and 6) shown in Fig. 2 to assist conveyance of the glass cloth 10. It is also possible to provide driving rolls in addition to those shown in Fig. 2, thereby assisting conveyance of the glass cloth 10. Note that if a driving roll is additionally arranged between the impregnating roll 43 and the first oven roll 51, it is required that the varnish be cured before it contacts the additional driving roll. (7) Comparison between samples Comparison between samples (ten types) according to this embodiment and comparative samples (five types) falling outside the range of the embodiment will be described. <Samples 1 - 6> Samples 1 to 6 were formed from the following materials under the following conditions by using the apparatus shown in Fig. 2. 1) Epoxy resin composition The epoxy resins, the epoxy hardeners, and the solvents used and their mixing ratios were as follows. (Epoxy resin) Tetraglycidylether epoxy resin 30 parts by weight ("EPICOAT 1031S" available from Yuka Shell Epoxy K.K.: epoxy equivalent weight 195) Bisphenol epoxy resin 40 parts by weight ("EPICOAT 1001" available from Yuka Shell Epoxy K.K.: epoxy equivalent weight 460) Halogenated novolak epoxy resin 30 parts by weight ("BUREN" available from NIPPON KAYAKU CO., LTD.: bromine content 36 wt%, epoxy equivalent weight 285) (Epoxy hardener) Dicyandiamide 5 parts by weight Imidazole-based hardener 0.5 parts by weight ("IB2MZ" available from Shikoku Chemicals Corp.) (Solvent) Solvent mixture of methylethylketone/methylcellosolve = 3/1 (weight ratio) 2) Viscosity By adjusting the amount of the solvent mixture, varnishes with viscosities of 5, 10, 15, 20, 25, and 30 cp were prepared for samples 1 to 6, respectively. 3) Conditions (common to samples 1 to 6) Varnish temperature 30°C Glass cloth density 60 warps/25 mm 64 wefts/25 mm Glass cloth thickness 80 µm Glass cloth dimensions width 1,040 mm length 500 m Glass cloth running velocity 3 m/min Drying oven stroke 20 m Drying oven temperature 1st chamber 130°C 2nd to 6th chambers 170°C Far-infrared heater used Fig. 3 shows the evaluation results of samples 1 to 6 manufactured under the above conditions. <Samples 7 & 8> Only the conditions below were changed among the conditions for samples 1 to 6. Varnish the same as samples 3 and 4 (15 cp and 20 cp) Glass cloth density 60 warps/25 mm 52 wefts/25 mm Glass cloth thickness 25 µm Glass-cloth epoxy sheets of samples 7 and 8 were manufactured under the same conditions as for samples 1 to 6 except for the above conditions. The evaluation results of samples 7 and 8 are shown in Fig. 3. <Sample 9> Varnish the same as sample 3 (15 cp) Glass cloth density 42 warps/25 mm 32 wefts/25 mm Glass cloth thickness 180 µm Glass cloth dimensions width 1,050 mm length 500 m A glass-cloth epoxy sheet of sample 9 was manufactured under the same conditions as for samples 1 to 6 except for the above conditions. The evaluation results of sample 9 are shown in Fig. 3. <Sample 10> A glass-cloth epoxy sheet was manufactured under the same conditions as for sample 9 except that a varnish with a viscosity of 130 cp was prepared by using the epoxy resin composition and the solvent mixture used in the formation of samples 1 to 6. The evaluation results of sample 10 are shown in Fig. 3. <Comparative samples 1 & 2> Varnishes with viscosities of 1 and 70 cp were prepared by using the epoxy resin composition and the solvent mixture used in samples 1 to 6. A glass-cloth epoxy sheet was manufactured under the same conditions as for samples 1 to 6 except for the viscosities of the varnishes. The evaluation results are shown in Fig. 3. In each of comparative samples 1 and 2, the viscosity of the varnish fell outside the range of 3 to 50 cp, and so unevenness in thickness was large and smoothness was poor. In addition, since the glass cloth content also fell outside the range of 55 to 70 wt%, punching characteristics were poor. <Comparative sample 3> In the manufacturing apparatus shown in Fig. 2, in order to adjust the content of the varnish, two bars 10 mm in diameter each formed by closely winding an SUS wire with a diameter of 0.5 mm around a core 9 mm in diameter were provided at staggered positions at a distance of 50 cm from the liquid surface of the varnish 44. The varnish was impregnated into the glass cloth 10 by using the same materials (varnish viscosity 30 cp) as those of sample 6 under the same conditions, and both the surfaces of the glass cloth 10 were wiped by the above bars such that the thickness after the impregnation was 85 µm. Thereafter, the glass cloth 10 thus impregnated was cured under the same conditions as for samples 1 to 6, manufacturing a glass-cloth epoxy sheet (comparative sample 3). The evaluation results of comparative sample 3 are shown in Fig. 3. Comparative sample 3 had a high flexibility and good punching characteristics because the thickness was 85 µm and the glass cloth content was 63 wt%. Since, however, the glass cloth was brought into contact with the bars after being impregnated with the varnish and before the varnish was cured, evenness in thickness, surface smoothness, and fuzz properties were poor. <Comparative sample 4> Varnish the same as sample 3 (15 cp) Glass cloth density 32 warps/25 mm 25 wefts/25 mm Glass cloth thickness 280 µm Glass cloth dimensions width 1,040 mm length 100 m A glass-cloth epoxy sheet was manufactured under the same conditions as for samples 1 to 6 except for the above conditions. The evaluation results of comparative sample 4 are shown in Fig. 3. Comparative sample 4 had nearly good characteristics because the conditions except for the average thickness fell within the range of the embodiment. However, the flexibility of the sheet was poor because of its large thickness. <Comparative sample 5> A varnish with a viscosity of 55 cp was prepared by using the epoxy resin composition and the solvent mixture used in samples 1 to 6. Varnish temperature 30°C Glass cloth density 60 warps/25 mm 58 wefts/25 mm Glass cloth thickness 100 µm Glass cloth dimensions width 1,040 mm length 600 m Glass cloth running velocity 1 m/min Drying oven stroke 20 m Drying oven temperature 1st chamber 130°C 2nd to 6th chambers 155°C Far-infrared heater used The evaluation results of comparative sample 5 are shown in Fig. 3. The glass cloth content, the manufacturing method, and the average thickness of comparative sample 5 fell within the range of this embodiment, so the punching characteristics, the fuzz properties, and the flexibility of comparative sample 5 were good. Since, however, the varnish viscosity was 55 cp, evenness in thickness and smoothness were poor. The measurements and the evaluations shown in Fig. 3 were performed as follows. <Evaluation of evenness in thickness> The thickness of each epoxy sheet manufactured was measured in the widthwise direction at an interval of 20 mm, and a thickness variation was calculated by the following equation: thickness variation (%) = {(maximum thickness) - (minimum thickness)}/{(average thickness x 2) x 100} x 100 The present inventors determined that if the thickness variation was within ±10%, evenness in thickness was satisfactory (indicated by o (circle) in Fig. 3) as a condition for coating an adhesive evenly onto a glass-cloth epoxy sheet. <Glass cloth content> A square glass-cloth epoxy sheet of 200 mm side was burned in a crucible, and the glass cloth content was calculated by dividing the weight of the burned sheet by the weight of the original sheet. That is, glass cloth content (wt%) = (weight of burned 200-mm squared glass-cloth epoxy sheet)/(weight of 200-mm squared glass-cloth epoxy sheet) x 100 <Punching characteristics (punching of holes 1 mm in diameter)> Holes 1 mm in diameter were punched in each epoxy sheet at an interval of 20 mm in the widthwise direction by using a punch consisting of super hard steel. It was determined that an epoxy sheet in which the peripheral portion of at least one hole was whitened was unsatisfactory. That is, o (satisfactory): no whitening of 0.2 mm or more was found around any hole x (unsatisfactory): whitening of 0.2 mm or more was found around at least one hole <Smoothness> Three arbitrary portions each 100 mm long in the longitudinal direction were selected from each epoxy sheet manufactured, and undulations in these portions were measured by using a contact continuous thickness meter. It was determined that undulations within ±3 µm were satisfactory. <Fuzz properties> It was determined that an epoxy sheet in which one or less fuzz portion was found per m 2 by visual observation was good. <Flexibility> Each epoxy sheet was wound on a circular pipe 30 mm in diameter and checked by visual observation, and it was determined that the sheet was good if no cracks were found. An epoxy sheet found to be satisfactory in the evenness in thickness, punching characteristics, smoothness, fuzz properties, and flexibility described above can be used as a printed circuit for mounting LSI chips and the like without causing any problems. As is apparent from the comparison results (Fig. 3) between the individual samples, the present invention can provide a glass-cloth epoxy sheet excellent in punching characteristics, evenness in thickness, smoothness, fuzz properties, and flexibility and a method of manufacturing this glass-cloth epoxy sheet. In addition, according to the manufacturing method of the present invention, a varnish is impregnated into a glass-cloth sheet and then cured while being kept out of contact with other members. Therefore, the resultant glass epoxy sheet maintains a necessary smoothness. Yet, microscopically, as shown in Fig. 1, fine undulations resulting form undulations of glass cloth are produced on the surface of the sheet. The glass-cloth epoxy sheet of the present invention therefore exhibits good adhesion properties when it is bonded to other members. Since the thickness of an epoxy resin layer formed on glass cloth is even, the degree of exposure of the glass cloth is also even when sandblasting is performed. As a result, a glass-cloth epoxy sheet sandblasted evenly can be obtained. Furthermore, if glass cloth is cured in a clamped state by using a heat press or the like, the glass cloth is cured with strain produced in it. This may cause changes in dimensions of the resultant glass-cloth epoxy sheet during storage or use of the sheet. In the present invention, however, glass cloth is cured with no pressure applied to it, so a glass-cloth epoxy sheet which does not cause any significant dimensional changes can be obtained. Note that the present invention achieves its effect particularly in the manufacture of a continuous glass-cloth epoxy sheet, but the invention is also applicable to the manufacture of glass-cloth epoxy cut sheets.

Claims: A method of manufacturing a glass-cloth epoxy sheet, comprising: supplying a sheet of glass cloth into an impregnating tank containing varnish prepared by dissolving a curable epoxy resin composition in a solvent, thereby impregnating the resin into the sheet material; pulling the sheet material up vertically in a free state from said impregnating tank; followed by curing the resin impregnated into the sheet material pulled from the tank, wherein the sheet material is kept vertical and the surfaces of the sheet material are kept out of contact with anything at least during execution of said curing step, wherein the viscosity of the varnish contained in said impregnating tank is 3 to 50 cp, and the thickness of the glass-cloth epoxy sheet after curing is 20 to 200 µm. A method according to claim 1, wherein the sheet of glass cloth is supplied continuously. The method of claim 2, wherein glass cloth is supplied from a roll. The method of claim 2 or 3, further comprising applying tension to the sheet material before the impregnation step to prevent formation of wrinkles in the sheet material. The method of claim 2, 3 or 4 further comprising continuously winding up the glass-cloth epoxy sheet, in which the impregnated varnish is cured by the curing step, into the form of a roll. The method accprding to any preceding claim, wherein the cured state of the resin after the curing step is at least a state in which the surface of the resin impregnated into the sheet material is not damaged even if it is brought into contact with a roll. The method according to any preceding claim, wherein the cured state of the resin achieved by the curing step is at least a state in which a weave pattern of the glass cloth does not deform even upon application of an external force within an elastic deformation limit of the sheet material. The method according to any preceding claim, wherein the sheet material is brought into contact with one or a plurality of rolls provided in said impregnating tank. The method according to any preceding claim, wherein a pulling rate of the sheet material is at a rate at which the varnish contained in said impregnating tank does not ripple. An apparatus for manufacturing a glass-cloth epoxy sheet, comprising: impregnating means for supplying a sheet material of glass cloth into an impregnating tank containing a varnish prepared by dissolving a curable epoxy resin composition into a solvent, thereby impregnating the resin into the sheet material; pulling means for pulling up the sheet material vertically in a free state from said impregnating tank; and curing means for curing the resin impregnated into the sheet material pulled by said pulling means, wherein said curing means keeps the sheet material vertical and the surfaces of the sheet material out of contact with anything, and wherein the viscosity of the varnish contained in said impregnating tank is 3 to 50 cp, and the thickness of the glass-cloth epoxy sheet after curing is 20 to 200 µm. An apparatus for manufacturing a glass-cloth epoxy sheet, comprising: supply means for continuously supplying a sheet material of glass cloth; impregnating means for dipping the sheet material into an impregnating tank containing a varnish prepared by dissolving a curable epoxy resin composition into a solvent, thereby impregnating the resin into the sheet material; pulling means for contiuously pulling up the sheet material vertically in a free state from said impregnating tank and curing means for curing the resin impregnated into the sheet material pulled by said pulling means, wherein said curing means keeps the sheet material vertical and the surfaces of the sheet material out of contact with anything, and wherein the viscosity of the varnish contained in said impregnating tank is 3 to 50 cp, and the thickness of the glass-cloth epoxy sheet after curing is 20 to 200 µm. The apparatus according to claim 11, wherein said supply means continuously supplies a continuous sheet material of glass cloth from a sheet roll. The apparatus according to claim 11 or 12, further comprising: means for preventing formation of wrinkles in the sheet material by applying a proper tension to the sheet material supplied by said supply means before impregnation is executed by said impregnating means. The apparatus according to claim 10,11, 12 or 13, further comprising: winding means for continuously winding up the cured glass-cloth epoxy sheet into the form of a roll. The apparatus according to any of claims 10 to 14, wherein the cured state of the resin achieved by said curing means is at least a state in which the surface of the resin impregnated into the sheet material is not damaged even if it is brought into contact with a roll. The apparatus according to any of claims 10 to 15, wherein the cured state of the resin achieved by said curing means is at least a state in which a weave pattern of the glass cloth does not deform even upon application of an external force within an elastic deformation limit to the sheet material. The apparatus according to any of claims 10 to 16, further comprising one or a plurality of rolls in said impregnating tank, which are contacted by the sheet material. A glass-cloth epoxy sheet obtainable according to the methods of claims 1-9; wherein the thickness of said glass-cloth epoxy sheet has a value X ranging between 20 µm and 75 µm and wherein the percentage by weight of glass cloth in said glass-cloth epoxy sheet is 0.4X + 25 to 70. A glass-cloth epoxy sheet obtainable according to the methods of claims 1-9; wherein the thickness of said glass-cloth epoxy sheet has a value ranging between 75 µm and 200 µm and wherein the percentage by weight of glass cloth in said glass-cloth epoxy sheet is 55 to 70. A method for manufacturing resin impregnated glass-cloth, which comprises: providing an impregnation station at which the cloth is impregnated with resin liquid; and causing the cloth to travel from the impregnation station to a curing station at which it at least partially cured and alters to a state where the surface of the resin liquid impregnated cloth is resistant to damage from contact with a roll, wherein the cloth is arranged to travel vertically and freely between the impregnation and curing stations and the at least partial curing operation is performed on the freely vertically travelling cloth, and wherein the viscosity of the varnish contained in said impregnating tank is 3 to 50 cp, and the thickness of the glass-cloth epoxy sheet after curing is 20 to 200 µm. A method according to claim 20, wherein the curing is by heat. A method according to claim 21, wherein the curing is by means other than heat.

Inventors: HAMANO SHUJI, HIGUCHI SADAO, ITO AKIYOSHI, KADA MASUMI, NEMOTO YOSUI, OKUYAMA KATSUMI, HAMANO, SHUJI, HIGUCHI, SADAO, ITO, AKIYOSHI, KADA, MASUMI, NEMOTO, YOSUI, OKUYAMA, KATSUMI, Hamano, Shuji, c/o Yokkaichi Sogo Kenkyusho, Higuchi, Sadao, c/o Yokkaichi Jigyosho, Ito, Akiyoshi, c/o Yokkaichi Jigyosho, Kada, Masumi, c/o Yokkaichi Sogo Kenkyusho, Nemoto, Yosui, c/o Tsukuba Sogo Kenkyusho, Okuyama, Katsumi, c/o Yokkaichi Sogo Kenkyusho
Applicants: MITSUBISHI CHEM CORP, MITSUBISHI CHEMICAL CORPORATION
Application year: 1993
Main classification: C08J5
IPC codes: H05K1, B29B11, B29B15, B29C70, H05K3, C08J5