Title:
Glass cloth wiring substrate
Kind Code:
A1


Abstract:
According to the present invention, variations in characteristic impedance and transmission loss of a signal wiring in a glass cloth wiring substrate can be reduced. There is provided a glass cloth wiring substrate in which signal wirings, plural glass cloth layers, and conductor faces are laminated, and spaces between the signal wirings, the plural glass cloth layers, and the conductor faces are impregnated with resin, wherein the glass cloth layers are formed by weaving bundles of glass fibers in a lattice shape, and the adjacent glass cloth layers are laminated on each other while rotating the warp-weft directions of the glass fibers by a predetermined angle with respect to each other. It is preferable that the rotation angle of the warp-weft directions of the glass fibers of the adjacent glass cloth layers falls within a range from 30 to 60 degrees.



Inventors:
Ogihara, Masao (Hadano, JP)
Nakajima, Kazunori (Sagamihara, JP)
Application Number:
12/005592
Publication Date:
07/24/2008
Filing Date:
12/26/2007
Assignee:
Hitachi, Ltd. (Tokyo, JP)
Primary Class:
International Classes:
D03D13/00
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Primary Examiner:
CHOI, PETER Y
Attorney, Agent or Firm:
Kilpatrick Townsend & Stockton LLP - West Coast (Atlanta, GA, US)
Claims:
What is claimed is:

1. A glass cloth wiring substrate in which signal wirings, a plurality of glass cloth layers, and conductor faces are laminated, and spaces between the signal wirings, the plurality of glass cloth layers, and the conductor faces are impregnated with resin, wherein the glass cloth layers are formed by weaving bundles of glass fibers in a lattice shape, and the adjacent glass cloth layers are laminated on each other while rotating the warp-weft directions of the glass fibers by a predetermined angle with respect to each other.

2. The glass cloth wiring substrate according to claim 1, wherein the glass cloth layers are arranged on both sides of the signal wirings, and are sandwiched by the conductor faces from outside.

3. The glass cloth wiring substrate according to claim 1, wherein the glass cloth layers are arranged on one side of the signal wirings, and the conductor face is arranged on a side opposed to the signal wirings of the glass cloth layers.

4. The glass cloth wiring substrate according to claim 1, wherein the width of each signal wiring is smaller than that of each bundle of the glass fibers configuring the glass cloth layers.

5. The glass cloth wiring substrate according to claim 1, wherein the rotation angle of the warp-weft directions of the glass fibers of the adjacent glass cloth layers falls within a range from 30 to 60 degrees.

Description:

CLAIM OF PRIORITY

The present application claims priority from Japanese application serial no. JP2007-000700, filed on Jan. 5, 2007, the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a glass cloth wiring substrate used in electronic devices, and particularly to a glass cloth wiring substrate in which variations in characteristic impedance and transmission loss of signal wirings can be reduced.

(2) Description of the Related Art

With a recent increased trend towards high performance, sophisticated functions, high density, and downsizing of electronic devices, characteristics suitable for transmission of a high-speed signal as well as high density of signal wirings are required for a wiring substrate used in electronic devices. In order to realize high density of the signal wirings, it is necessary to reduce a conductor width and a conductor thickness of each signal wiring and a thickness of an insulation layer, and at the same time, it is necessary to use a material having characteristics suitable for high density and miniaturization even for a material configuring the insulation layer. For a material of the wiring substrate, there is used a glass cloth substrate material in which a glass cloth is impregnated with resin in order to improve warpage, dimensional stability, workability, and mechanical strength of the wiring substrate. However, in order to realize high density and miniaturization of the signal wirings, it is necessary to optimize mechanical characteristics of the glass cloth.

For example, Japanese Unexamined Patent Application Publication No. 2004-124324 discloses that dimensions of a warp width and a gap between warps of a glass cloth or dimensions of a weft width and a gap between wefts of the glass cloth are optimized by using very thin glass fibers, each having a width of several μm, as a glass cloth material suitable for high density and miniaturization of a wiring substrate, thus realizing a glass cloth that is excellent in resin impregnation, surface smoothness, and hole drilling.

Further, Japanese Unexamined Patent Application Publication No. 2002-158442 discloses that in order to improve reliability by eliminating dimensional changes caused by thermal expansion and contraction, warpage, and torsion of a multilayered printed circuit board, respective prepregs to be laminated on a circuit board are disposed on each other so that the fiber directions of fiber materials of the prepregs are different from each other.

Further, Japanese Unexamined Patent Application Publication No. Hei 8-321679 discloses that when plural inner-layer substrates and prepregs are alternately laminated, the fiber direction of the inner-layer substrates intersect with that of the prepregs by a different angle (about 45 degrees) for arrangement.

Meanwhile, Japanese Unexamined Patent Application Publication No. Sho 63-86495 discloses a wiring substrate, which is not a glass cloth substrate, in consideration of transmission of a high-speed signal. In Japanese Unexamined Patent Application Publication No. Sho 63-86495, patterns, each having a constant cycle, are provided on upper and lower conductor faces by which a signal wiring is sandwiched through an insulation layer, and the patterns on the upper and lower conductor faces are formed while shifting the patterns by half the cycle from each other, thus equalizing distributions of wiring capacities and reducing a fluctuation amount of characteristic impedance.

SUMMARY OF THE INVENTION

A material used for a wiring substrate, such as glass epoxy resin, is made of a material obtained by solidifying a glass cloth with resin such as epoxy. The glass cloths are woven in a lattice shape in a wiring substrate while directing at right angles formed by X-Y axes on a substrate face. The dimension of one bundle of the glass cloths is as large as about several 10 to 100 μm, which is larger than a conductor width of a signal wiring that is as large as several 10 μm. Thus, there is a problem that a difference in density between the glass cloths causes variations in characteristic impedance and transmission loss.

Specifically, in the case where the width of the signal wiring is smaller than that of a warp and a weft of the glass cloth, effective relative permittivity and dielectric loss tangent of an insulation layer differ when the signal wiring passes through warp and weft portions and resin portions of the glass cloth. Thus, characteristic impedance and transmission loss of the signal wiring vary. The characteristic variations in this case include two problems: characteristic variations resulting from a positional relation between each signal wiring and the glass cloth; and periodic fluctuation in characteristic impedance depending on a position on one signal wiring.

For example, by obliquely arranging the direction of the signal wiring with respect to those of the warp and weft of the glass cloth by 45 degrees, it can be expected that contributions of relative permittivity and dielectric loss tangent affecting the characteristics of the signal wiring are averaged. However, the oblique arrangement can not solve the problem of the periodic fluctuation in characteristic impedance on one signal wiring.

The configurations of the wiring substrates described in Japanese Unexamined Patent Application Publication No. 2004-124324, Japanese Unexamined Patent Application Publication No. 2002-158442, and Japanese Unexamined Patent Application Publication No. Hei 8-321679 aim at stabilization of mechanical characteristics, such as warpage, torsion, and dimensional changes caused by heat applied to the wiring substrate, and do not consider stabilization of electric characteristics such as transmission of a high-speed signal. In addition, a positional relation between the signal wiring and the glass cloth is not particularly specified in Japanese Unexamined Patent Application Publication No. 2004-124324, Japanese Unexamined Patent Application Publication No. 2002-158442, and Japanese Unexamined Patent Application Publication No. Hei 8-321679.

In the technique disclosed in the Japanese Unexamined Patent Application Publication No. Sho 63-86495, transmission of a high speed-signal of a wiring substrate is considered. If it is assumed that the technique disclosed in Japanese Unexamined Patent Application Publication No. Sho 63-86495 is applied to a glass cloth wiring substrate, a pattern having a constant cycle is provided on a conductor face that is a return circuit of a high-speed signal current and serves as power feeding. Such a configuration increases impedance on power feeding routes, resulting in anticipation of a new problem that power-supply noise is increased.

An object of the present invention is to solve the above-described problems and to provide a glass cloth wiring substrate in which variations in characteristic impedance and transmission loss of a signal wiring is reduced.

According to the present invention, there is provided a glass cloth wiring substrate in which signal wirings, plural glass cloth layers, and conductor faces are laminated, and spaces between the signal wirings, the plural glass cloth layers, and the conductor faces are impregnated with resin, wherein the glass cloth layers are formed by weaving bundles of glass fibers in a lattice shape, and the adjacent glass cloth layers are laminated on each other while rotating the warp-weft directions of the glass fibers by a predetermined angle with respect to each other. It is preferable that the rotation angle of the warp-weft directions of the glass fibers of the adjacent glass cloth layers falls within a range from 30 to 60 degrees.

According to the present invention, variations in characteristic impedance and transmission loss in a glass cloth wiring substrate can be reduced and transmission characteristics of a high-speed signal can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view showing a structure of a glass cloth wiring substrate according to a first embodiment of the present invention;

FIG. 2 is a transparent view showing an inner structure of the glass cloth wiring substrate in FIG. 1;

FIG. 3 is transparent view showing an inner structure of a glass cloth wiring substrate according to a second embodiment of the present invention;

FIG. 4 is a perspective view showing a structure of a glass cloth wiring substrate according to a third embodiment of the present invention;

FIG. 5 is a perspective view showing a structure of a glass cloth wiring substrate according to a fourth embodiment of the present invention;

FIG. 6 is a perspective view showing a structure of a conventional glass cloth wiring substrate, as a comparative example;

FIG. 7 shows a cross sectional view of the wiring substrate of FIG. 6 in the X direction;

FIG. 8 shows a cross sectional view of the wiring substrate of FIG. 6 in which positions of signal wirings are shifted;

FIG. 9 shows a transparent view of the wiring substrate in each of FIG. 7 and FIG. 8; and

FIGS. 10A and 10B are diagrams, each showing electric characteristics of the glass cloth wiring substrates according to the embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinafter, embodiments of the present invention will be concretely described by using the drawings.

First Embodiment

FIG. 1 is a perspective view showing a structure of a glass cloth wiring substrate according to a first embodiment of the present invention. In FIG. 1, the reference numerals 110 and 111 denote conductor faces, each serving as a return circuit of a high-speed signal current, 100 and 101 denote signal wirings, and 120 and 121 denote two-layered glass cloths. The signal wirings 100 and 101 are sandwiched between the two-layered glass cloths 120 and 121, and spaces (gaps) sandwiched between the conductor faces 110 and 111 are filled with resin 130. The fiber directions of the upper glass cloth 120 are different from those of the lower glass cloth 121, and warp-weft directions U-V of the lower glass cloth 121 are rotated by 45 degrees with respect to warp-weft directions X-Y of the upper glass cloth 120. Each glass cloth is formed in such a manner that glass fibers, each having a width of several μm, are bundled so as to have a width of about 100 μm and the bundles are woven in a lattice shape.

FIG. 2 is a transparent view showing an inner structure of the glass cloth wiring substrate in FIG. 1. In FIG. 2, the conductor faces 110 and 111 are omitted, and an arrangement example of the two-layered glass cloths 120 and 121 and signal wirings 102 and 103 is shown. The upper glass cloth 120 is laminated on the lower glass cloth 121 while rotating both of the warp-weft directions by 45 degrees. The signal wirings 102 and 103 are arranged in parallel to the warp direction (Y direction) of the upper glass cloth 120. There is exemplified a case in which when the signal wiring 103 corresponds to the position of one of the warps, the signal wiring 102 is arranged at an intermediate position of the adjacent warp. Since the upper glass cloth 120 and the lower glass cloth 121 are arranged while rotating both of the warp-weft directions by 45 degrees, frequency of appearance of the glass cloths and the resin 130 closer to the signal wirings 102 and 103 is equalized by the two-layered glass cloths 120 and 121.

As a result, variations in characteristic impedance and transmission loss of the signal wirings caused by difference in relative positions of the signal wirings in a planar direction (for example, difference in positions in the X direction as shown by the signal wirings 102 and 103) and by difference in positions of the signal wirings in the Y direction can be reduced.

Second Embodiment

FIG. 3 is a transparent view showing an inner structure of a glass cloth wiring substrate according to a second embodiment of the present invention. In this case, the upper glass cloth 120 in the first embodiment is laminated on a lower glass cloth 121′ while rotating the warp-weft directions of the lower glass cloth 121′ by 30 degrees (or 60 degrees) with respect to those of the upper glass cloth 120. There is exemplified a case in which when a signal wiring 105 corresponds to the position of one of the warps of the upper glass cloth 120, a signal wiring 104 is arranged at an intermediate position of the adjacent warp.

Also in this case, frequency of appearance of the upper glass cloth 120, the lower glass cloth 121′ and the resin 130 closer to the signal wirings 104 and 105 is equalized. As a result, variations in characteristic impedance and transmission loss of the signal wirings can be reduced.

Third Embodiment

FIG. 4 is a perspective view showing a structure of a glass cloth wiring substrate according to a third embodiment of the present invention. The same elements as those in FIG. 1 are given the same reference numerals, and the explanations thereof are omitted. In the third embodiment, the reference numerals 120 to 123 denote four-layered glass cloths, and the glass cloth wiring substrate is configured in the lamination order of, from the conductor face 110 side, two layers of upper glass cloths 122 and 120, the signal wirings 100 and 101 and two layers of lower glass cloths 121 and 123. The warp and weft directions of the adjacent glass cloths 122, 120, 121 and 123 are rotated by 45 degrees with respect to each other.

As a result, frequency of appearance of the glass cloths and the resin 130 closer to the signal wirings 100 and 101 is further equalized by the four-layered glass cloths 122, 120, 121 and 123. As a result, variations in characteristic impedance and transmission loss of the signal wirings caused by difference in relative positions of the signal wirings in a planar direction and by difference in positions of the signal wirings can be reduced.

Fourth Embodiment

FIG. 5 is a perspective view showing a structure of a glass cloth wiring substrate according to a fourth embodiment of the present invention. The same elements as those in FIG. 1 are given the same reference numerals, and the explanations thereof are omitted. In the fourth embodiment, the glass cloth wiring substrate has a structure in which the two-layered glass cloths 121 and 123 are arranged only on one side (the lower side in this case) of the signal wirings 100 and 101. The reference numeral 111 denotes a conductor face serving as a return circuit of a high-speed signal current, the two-layered glass cloths 123 and 121 and the signal wirings 100 and 101 are laminated thereon, and spaces between the signal wirings 100 and 101 and the conductor face 111 are filled with the resin 130. Also in the embodiment, the warp-weft directions of the glass cloth 121 are rotated by 45 degrees with respect to those of the glass cloth 123.

As a result, frequency of appearance of the glass cloths and the resin 130 closer to the signal wirings 100 and 101 is equalized by the two-layered glass cloths 121 and 123. Although the embodiment has a structure in which the glass cloths are present only on one side of the signal wirings, variations in characteristic impedance and transmission loss of the signal wirings caused by difference in relative positions of the signal wirings in a planar direction and by difference in positions of the signal wirings can be reduced.

Comparative Example

FIG. 6 is a perspective view showing a structure of a conventional glass cloth wiring substrate, as a comparative example. The reference numerals 210 and 211 denote conductor faces, 200 and 201 denote signal wirings, and 220 and 221 denote two-layered glass cloths. The signal wirings 200 and 201 are sandwiched between the two-layered glass cloths 220 and 221. In a conventional structure, the upper glass cloth 220 is laminated on the lower glass cloth 221 in such a manner that the warp-weft directions X-Y of the upper glass cloth 220 are identical to the warp-weft directions U-V of the lower glass cloth 221. In such a structure, there is a problem that characteristic impedance and transmission loss of the signal wirings vary due to difference in relative positions of the signal wirings in a planar direction and difference in positions of the signal wirings, the reason of which will be described below with reference to FIGS. 7 and 8.

FIG. 7 shows a cross sectional view of the wiring substrate of FIG. 6 in the X direction (U direction). The warps of the upper glass cloth 220 in the vicinity of the signal wirings 200 and 201 are denoted by the reference numeral 330, and crossing positions of the wefts are denoted by the reference numeral 331. Then, attention is paid to whether or not the positions of the signal wirings 200 and 201 are closer to the warps or wefts of the glass cloth. FIG. 7 is a case in which the positions of the signal wirings 200 and 201 in the X direction are closer to the warps 330 of the upper glass cloth 220. The wefts are orthogonal to the signal wirings 200 and 201 and alternately closer thereto along the Y direction, and distances from the signal wirings 200 and 201 to the positions of the wefts in the X direction are constant. The same relation is also established for distances between the warps and wefts of the lower glass cloth 221 and the signal wirings 200 and 201.

In the case of the configuration as in FIG. 7, the signal wirings 200 and 201 are closely opposed to the warps 330 of the upper glass cloth 220 and the lower glass cloth 221, and thus electric characteristics of the signal wirings are largely affected by the glass cloths. Specifically, the values of characteristic impedance and transmission loss of the signal wirings are obtained by being largely affected by effective relative permittivity and dielectric loss tangent of the glass cloths.

FIG. 8 shows a cross sectional view of the wiring substrate of FIG. 6 in the X direction (U direction) in which the signal wirings 202 and 203 are shifted for arrangement. FIG. 8 is a case in which the positions of the signal wirings 202 and 203 in the X direction are apart from the warps 330 of the upper glass cloth 220, and are closer to the crossing positions 331 of the wefts.

In the case of the configuration as in FIG. 8, the signal wirings 202 and 203 are closely opposed to the crossing positions 331 of the wefts of the upper glass cloth 220 and the lower glass cloth 221, and thus electric characteristics of the signal wirings are affected by not only the glass cloths but also the resin. As a result, a mean value of characteristic impedance and transmission loss of the signal wirings is obtained by being affected by electric characteristics of both of the glass cloths and the resin.

Further, FIG. 9 shows a transparent view of the wiring substrate in each of FIG. 7 and FIG. 8. The signal wiring 200 (201) is located at a wiring position in the case of FIG. 7, and the signal wiring 202 (203) is located at a wiring position in the case of FIG. 8. The warp 330 of the glass cloth is always closely opposed to the signal wiring 200 along the wiring direction (Y direction). Accordingly, characteristic impedance of the signal wiring 200 does not vary depending on a position on the signal wiring. On the other hand, the wefts 331 of the glass cloth and the resin 130 are repeatedly closely-opposed to the signal wiring 202 along the wiring direction (Y direction). In such a case, electric characteristics of the signal wiring are alternately and periodically affected by the glass cloths and the resin along the signal wiring, and the characteristic impedance of the signal wiring periodically varies depending on a position on the signal wiring. As a result, the resonance phenomenon occurs, and it is not preferable from the viewpoint of transmission of a high-speed signal.

FIGS. 10A and 10B are diagrams, each showing electric characteristics of the glass cloth wiring substrates according to the above-described embodiments. In this case, there are shown the characteristic impedance along the signal wirings of the wiring substrates in the first and second embodiments and the comparative example. FIG. 10A is the case of the first embodiment (FIG. 2, the rotation angle is 45 degrees), and FIG. 10B is the case of the second embodiment (FIG. 3, the rotation angle is 30 degrees), and the results are shown with the comparative example.

In FIG. 10A, a curve line 900 denotes a characteristic of the signal wiring 202 in the comparative example (FIG. 9). A curve line 920 denotes a characteristic of the signal wiring 102 in the first embodiment (FIG. 2). A curve line 930 denotes a characteristic of the signal wiring 103. The characteristic of the signal wiring 103 is identical to that of the signal wiring 200 in the comparative example (FIG. 9). As shown in the diagram, according to the first embodiment, variations in characteristic impedance based on difference in positions in the X direction as shown by the signal wirings 102 and 103 can be reduced. Further, even in the case where the signal wiring is located while being alternately opposed to the glass cloths and the resin as in the case of the signal wiring 102, fluctuation in characteristic impedance caused by difference in positions of the signal wiring in the Y direction can be reduced.

Further, in FIG. 10B, a curve line 940 denotes a characteristic of the signal wiring 104 in the second embodiment (FIG. 3), and a curve line 950 denotes a characteristic of the signal wiring 105. As shown in the diagram, even in the case where the rotation angle is 30 degrees, variations in characteristic impedance based on difference in positions in the X direction as shown by the signal wirings 104 and 105 can be reduced. Further, even in the case where the signal wiring is located while being alternately opposed to the glass cloths and the resin as in the case of the signal wiring 104, fluctuation in characteristic impedance caused by difference in positions of the signal wiring in the Y direction can be reduced.

In any one of the cases, each of the glass cloth wiring substrates according to the embodiments is more suitable for transmission of a high-speed signal because of less fluctuation in characteristic impedance along the signal wiring. The curve lines 930 and 950 have offsets with respect to the design center. However, since variations in characteristic impedance along the signal wiring are reduced, each of the glass cloth wiring substrates according to the embodiments is more suitable for transmission of a high-speed signal.

In the respective embodiments, the number of layers of the glass cloths is two or four, but the number is not limited thereto. The layers may be arbitrary multilayers. In addition, the glass cloths may be arranged on both sides or one side of the signal wirings. When arranging the glass cloths, it is preferable that the adjacent glass cloths are laminated on each other while rotating the warp-weft directions with respect to each other, and the rotation angle falls within a range from 30 to 60 degrees.

According to the present invention, improvements of waveform distortion, waveform variations, and frequency limit of a high-speed signal which are challenges along with an increase in density of a wiring substrate can be made. Application of the glass cloth wiring substrate according the present invention contributes to high performance and downsizing of electronic devices, such as computers, communication devices, and medical devices.

While we have shown and described several embodiments in accordance with our invention, it should be understood that disclosed embodiments are susceptible of changes and modifications without departing from the scope of the invention. Therefore, we do not intend to be bound by the details shown and described herein but intend to cover all such changes and modifications that fall within the ambit of the appended claims.