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  Glass cloth and film substrate using itUSPTO Application #: 20060035552Title: Glass cloth and film substrate using it Abstract: Glass cloth which is formed of a warp yarn and a weft yarn of the same glass yarn, wherein a ratio of warp yarn width to weft yarn width is not less than 0.80 and not more than 1.20 and a ratio of an elongation rate in a length direction when a load in a range of 25 N to 100 N per 25 mm width of the glass cloth is added in a warp yarn direction, to an elongation rate in a width direction when said load is added in a weft yarn direction is not less than 0.80 and not more than 1.20. (end of abstract) Agent: Finnegan, Henderson, Farabow, Garrett & Dunner LLP - Washington, DC, US Inventors: Yoshinobu Fujimura, Yasuyuki Kimura USPTO Applicaton #: 20060035552 - Class: 442208000 (USPTO) Related Patent Categories: Fabric (woven, Knitted, Or Nonwoven Textile Or Cloth, Etc.), Woven Fabric (i.e., Woven Strand Or Strip Material), Woven Fabric Is Characterized By A Particular Or Differential Weave Other Than Fabric In Which The Strand Denier Or Warp/weft Pick Count Is Specified, Warp Differs From Weft The Patent Description & Claims data below is from USPTO Patent Application 20060035552. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to glass cloth for use in a printed circuit board in the electronics/electric field and also relates to a film substrate using the glass cloth as a flexible substrate. BACKGROUND ART [0002] Recent applications of glass cloth used in a printed circuit board have widened to the development of package applications. Many packages have a square shaped XY plane and a substrate called an interposer used in this package is required to have no anisotropy in the XY directions. [0003] For these packages, generally, a polyimide film based substrate or a substrate impregnated with a matrix resin and glass cloth as a reinforcing material is used. In view of the requirements for such an application, such as high rigidity, high dimensional stability, low thermal expansion, and the like, the use of a film substrate using glass cloth has been increasing. However, anisotropy in the XY directions of the film substrate, expressed by structural differences between the warp yarn direction and the weft yarn direction derived from the glass cloth, has now become a problem. At the same time, because of a requirement for a thinner package, a thinner interposer itself is needed and thus the thickness of the glass cloth used is required to be as thin as 50 .mu.m to 20 .mu.m. [0004] For such a thin glass cloth, those with a reduced clearance rate by narrowing yarn distance by a fiber-opening treatment have been proposed in JP-A-5-286055, JP-A-8-18179, JP-A-11-114956 and JP-A-2002-38367. [0005] However, the invention described in JP-A-5-286055 aims at the suppression of the dimensional change rate in a multilayer plate molding and in the Examples thereof, a multilayered plate composed of a 6 layered prepreg is described, but there is no description of a one-layer film substrate. [0006] Also the invention described in JP-A-8-18179 aims at the improvement of the heat resistance in soldering and there is no description on the effects of anisotropy in the XY directions. [0007] The invention described in JP-A-11-114956 also aims at the prevention of pore generation in a resin during prepreg preparation and there is no description on the effects of anisotropy in the XY directions. [0008] Furthermore, in the invention described in JP-A-2002-38367, there is a description that suggests a reduction of anisotropy in the XY directions by increasing the opening rate in the XY directions. However, sufficient reduction of anisotropy in the XY directions could not be attained, as shown by the difference between the opening rate of the warp yarn and the opening rate of the weft yarn in the Examples described in Table 1 or 4. As is also clear from the description on the dimensional change rate between the width and the length directions in the Examples described in Table 1 or Table 2, there is no description of a one-layered film substrate, although a multi-layered plate composed of a 4 layered pregreg is described. DISCLOSURE OF THE INVENTION [0009] It is an object of the present invention to provide glass cloth for use in a thin printed circuit board that is superior in isotropy, dimensional stability and mechanical characteristics and a film substrate using said glass cloth. [0010] The present inventors have extensively studied a way to solve the above-described problems and found that anisotropy in the XY directions of a film substrate using said glass cloth is dramatically improved by making the warp yarn and the weft yarn of the glass cloth of the same glass yarn and by making the cross-sectional shape and the waviness of said warp yarn and weft yarn the same. They also found that a film substrate using said glass cloth has superior isotropy and is thin, similar to a film composed of a resin only, by optimization of the average diameter and the number of filaments forming the yarn used, and have thus completed the present invention. [0011] That is the present invention includes the following aspects. [0012] 1. Glass cloth which is composed of a warp yarn and a weft yarn of the same glass yarn, wherein a ratio of warp yarn width to weft yarn width is not less than 0.80 and not more than 1.20 and a ratio of an elongation rate in a length direction when a load in a range of 25 N to 100 N per 25 mm width of the glass cloth is added in a warp yarn direction, to an elongation rate in a width direction when said load is added in a waft yarn direction is not less than 0.80 and not more than 1.20. [0013] 2. Glass cloth according to the above aspect 1, which is obtained by a flattening processing under a tension exerted on the glass cloth of not more than 49 N/m per 1 m width of the glass cloth. [0014] 3. Glass cloth according to the above aspect 1 or 2, wherein a thickness of the glass cloth is not less than 10 .mu.m and not more than 50 .mu.m. [0015] 4. Glass cloth according to any one of the above aspects 1 to 3, wherein an average diameter of filaments of the glass yarn forming the glass cloth is not less than 3.0 .mu.m and less than 6.0 .mu.m and the number of filaments of the glass yarn is not less than 50 and not more than 204. [0016] 5. A film substrate composed of one sheet of glass cloth according to any one of the above aspects 1 to 4 and a matrix resin. BRIEF DESCRIPTION OF THE DRAWING [0017] FIG. 1 is a graph showing measurement results of an elongation ratio under load in a width direction and an elongation ratio in a length direction of 2116 type glass cloth as an example of a glass cloth woven by conventional technology. BEST MODE FOR CARRYING OUT THE INVENTION [0018] In general, glass cloth is produced under tension in the length direction as a long object. Therefore, even if it is woven by using the same glass yarn as the warp yarn and the weft yarn, the cross-sectional shape of the warp yarn and the weft yarn are generally different and their waviness state is also different. The term "the same glass yarn" means in this context, yarn having the same kind of glass such as E-glass, the same average diameter and the same number of filaments forming a strand, and the same number of strands forming the yarn. Generally, the waviness of a warp yarn under a tension load tends to be less than the waviness of a weft yarn. However, when a high density is required so that the clearance between adjacent warp yarns is substantially zero, the waviness of the warp yarn may be larger. [0019] Therefore, it is considered that the anisotropy of a film substrate using said glass cloth can be reduced by making the cross-sectional shape of the warp yarn and the weft yarn the same and by making the waviness state of each yarn the same, in addition to using the same glass yarn as the warp yarn and the weft yarn forming the glass cloth. [0020] The term "cross-sectional shape" means in this context the width and the thickness of the yarn forming the glass cloth and can be measured by observing, using an electron microscope, the cross-section of said yarn obtained by embedding said yarn in an epoxy resin, followed by a cutting out by machining. When the same glass yarn is used, yarn thickness is reduced by increasing the yarn width by fabrication and the like, and therefore, in regard to anisotropy in the XY directions, yarn width can represent the cross-sectional shape. To reduce the anisotropy of a film substrate using glass cloth, the ratio of warp yarn width to weft yarn width, forming said glass cloth, is not less than 0.80 and not more than 1.20, and preferably is not less than 0.90 and not more than 1.10. [0021] Glass cloth has a woven fabric structure, and therefore it has the characteristic of elongating in one direction in a XY plane under tension. The elongation correlates to the waviness of the yarn. That is, a larger waviness amount provides a higher elongation under tension. It is known that under only one directional tension, the waviness of a yarn in a crossing direction to said direction also has an influence on the elongation under tension in said direction (crimp shift) and thus the waviness of the yarns forming the glass cloth has large effects on the elongation under tension. Therefore, the waviness state of whole glass cloth can be evaluated by the elongation rate in the length direction and the elongation rate in the width direction under tension. [0022] In the present invention, said elongation rate under tension is evaluated by using the method described in JIS R3420, "A general method for glass fiber, item 7.4 Tensile strength". In said JIS specified method, a load at break is determined as follows: A test piece, having a width of 30 mm and a length of about 250 mm, is sampled from a woven fabric in a warp yarn direction and a weft yarn direction and two chucks with a width of 25 mm are set at about 150 mm distance apart to be subjected to an elongation of about 200 mm/min by holding said test piece at the two chuck parts. [0023] In the present invention, however, to improve measurement accuracy in a load range before break, the elongation rate was determined by increasing the rate of the distance between the chuck parts under load (100.times.(distance under load-distance under no load)/distance under no load), under the same conditions as in the JIS specified method, except that the elongation speed was set to be 10 mm/min and a test piece with width of 35 mm and length of 185 mm was used and the distance between the chucks was set to be 75 mm. FIG. 1 shows the measurement results of the elongation rate in each direction of a conventional glass cloth called 2116 type glass cloth, as an example of the results measured by increasing the load per 25 mm chuck width, from 5 N to 100 N. Because this 2116 type glass cloth has a larger waviness in the weft yarn than the warp yarn to which tension is loaded during weaving, the elongation rate is larger in the width direction than in the length direction. [0024] It was clarified by a study of the present inventors that the use of elongation rate as a waviness state index was not suitable, because a large mesh bend was generated in the glass cloth under load condition per 25 mm of more than 100 N, although break did not occur. It was also clarified that in a low load range, the ratio of the elongation rate in the length direction to the elongation rate in the width direction was not constant. However, in a load per 25 mm in a range from 25 to 100 N, it was nearly constant. Therefore, the elongation rate was determined to be measured under load per 25 mm width of glass cloth in a range from 25 to 100 N. Based on a study by the present inventors, to reduce the anisotropy of a film substrate using glass cloth, the ratio of the elongation rate in the length direction under load in the length direction to the elongation rate in the width direction under load in the width direction, in a load range of from 25 N to 100 N per 25 mm, is preferably not less than 0.80 and not more than 1.20, more preferably not less than 0.90 and not more than 1.10 and further preferably not less than 0.95 and not more than 1.05. Continue reading... Full patent description for Glass cloth and film substrate using it Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Glass cloth and film substrate using it patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. 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