Printed wiring board, information processing apparatus, and method of manufacturing the printed wiring board

Disclosed is a printed wiring board comprising an insulating layer having a rectangular flat shape and provided with fibers in the layer, the direction of the fiber in the layer being almost parallel to any side of the rectangle, a reference potential layer disposed on one surface side of the insulating layer, a plurality of wiring patterns for signal transmission disposed on the other surface side of the insulating layer so as to have nearly similar angles respectively with respect to the direction of the fiber in the insulating layer, and a pad portion to mount a semiconductor device, disposed on the other surface side of the insulating layer to conduct the plurality of wiring patterns.

CROSS-REFERENCE TO THE INVENTION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2004-287091, filed on Sep. 30, 2004; the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a printed wiring board, an information processing apparatus provided with this printed wiring board, and a method of manufacturing the printed wiring board.

2. Description of the Related Art

In recent years, printed wiring boards to mount densely integrated semiconductor devices such as hybrid ICs, MCMs (Multi Chip Modules), and the like have been made denser using a greater number of layers or finer patterns and have greatly contributed to the reduction in size and weight of electronic equipment as densely packed circuit boards in electronic parts.

In such a printed wiring board designed to be so dense, in order to ensure connection reliability, a technology to restrain cracking or the like in the wiring pattern due to stress or the like added from outside by a structure in which the excurrent direction of prepreg fiber (direction of fiber) used as an insulating layer is slanted, for instance, by 45 degrees with respect to a side of the substrate body, is proposed (for instance, Patent Document 1).

[Patent Document 1] Japanese translated application of PCT International Application (P2002-501676=JP-A 2003-535743=WO 01/094134 A)

However, in the case of the printed wiring board described in the above-document, since a rectangular shape of the printed wiring board needs to be cut down and hauled out from a parent material being an insulating layer in a state having an angle with respect to the direction of fiber, much of the parent material is left as scrap, which poses a problem in terms of manufacturing costs.

On the other hand, when a printed wiring board which obtains an insulating layer from prepreg and the like is used as a controlling board which requires high speed data transmission, the following problem becomes apparent: the transmission characteristics of the signals carried by wiring patterns deteriorate in a printed wiring board having a ground layer and a plurality of wiring patterns for signal transmission positioned facing to the ground layer while sandwiching a fiber-containing insulating layer.

Concretely, a wiring pattern wired right above the fibers along the direction of fiber in the insulating layer and a wiring pattern wired at a position away from right above the fibers differ in capacitance created between their respective ground layers (thickness direction of the substrate). Accordingly, impedance in the extending direction of the wiring pattern (transmitting direction of signal) differs between the former wiring pattern and the latter wiring pattern, which creates differences in signal transmission speed or signal noise. These phenomena become more apparent as the signal transmission speed increases.

SUMMARY

It is an object of the present invention to provide a printed wiring board, an information processing apparatus, and a method of manufacturing the printed wiring board, which can keep manufacturing costs low and realize stable transmission of signals.

The printed wiring board relating to the present invention comprises: an insulating layer having a rectangular flat shape and provided with fibers in the layer, a direction of the fiber in the layer being almost parallel to any side of the rectangle; a reference potential layer disposed on one surface side of the insulating layer; a plurality of wiring patterns for signal transmission disposed on another surface side of the insulating layer so as to have nearly similar crossing angles respectively with respect to the direction of the fiber in the insulating layer; and a pad portion to mount a semiconductor device, disposed on the other surface side of the insulating layer to conduct the plurality of wiring patterns.

A method of manufacturing a printed wiring board relating to the present invention comprises: cutting down an insulating layer provided with fiber in the layer in a rectangular shape such that any side thereof is almost parallel to a direction of the fiber; and patterning a conductive layer provided on one surface of the insulating layer into a plurality of patterns having nearly similar angles respectively with respect to the direction of the fiber in the insulating layer.

According to the present invention, it is possible to provide a printed wiring board, an information processing apparatus, and a method of manufacturing the printed wiring board, which can keep manufacturing costs low, and realize stable transmission of signals.

DETAILED DESCRIPTION

EXPLANATION OF EMBODIMENTS

Embodiments of the present invention will be described with reference to the drawings, but these drawings are presented only for the illustrative purpose and in no respect are intended to limit the present invention.

Embodiments to implement the present invention will be explained based on the drawings as follows.

First Embodiment

FIG. 1is a plan view schematically showing a state that a semiconductor package is mounted on a printed wiring board according to a first embodiment of the present invention, andFIG. 2is a sectional view of the printed wiring board shown inFIG. 1(the semiconductor package is not shown). Here, in order to make the internal formation of this printed wiring board clear,FIG. 1illustrates its structure in perspective.

As shown inFIGS. 1 and 2, the printed wiring board1is a multi-layered substrate having a plurality of conductive layers, and is composed of a substrate body2having a rectangular appearance. The substrate body2of the printed wiring board1includes insulating layers3and4, a ground (GND) layer5which is an example as a reference potential layer, a plurality of wiring patterns6and7for signal transmission, and a plurality of pad sections10to solder-mount rectangular semiconductor packages8and9on the substrate body2.

The above-described insulating layer3is formed by hardening prepreg. The fiber components (fiber cluster)3aand3bcontained in the layer run almost parallel to any one of side portions (edge faces)2a,2b,2cand2dof the substrate body2(in a plane of the substrate body2). An example of the above-described prepreg is a sheet-like substance made of carbon fiber, glass fiber or aramid fiber, etc. impregnated with thermosetting resin (epoxy resin, for instance) before hardening. The insulating layer3made of this prepreg has a bi-directional fiber in which the fiber components3aand3bin the layer intersect respectively in a grid pattern. In other words, the insulating layer3has portions both thin and thick in density in a plane of the substrate.

The ground layer5is layered to cover one entire surface (a bottom surface of the insulating layer3inFIG. 2) of the insulating layer3, as shown inFIG. 2. In the present embodiment, the ground layer5is shown as an example of the reference potential layer, but the reference potential layer is not limited to the ground layer5. An voltage supply source layer can also be used so long as it is a conductive layer covering at least a region facing the wiring patterns6and7via the insulating layer3.

The wiring patterns6and7for signal transmission are respectively disposed at positions facing the ground layer5across the insulating layer3as shown inFIG. 2. The wiring patterns6and7are wired having nearly similar angles (obliquely-crossing angles) with respect to the directions of the fiber components3aand3bin the insulating layer3respectively, as shown inFIG. 1. In detail, the wiring patterns6and7are wired having nearly 45 degrees respectively with respect to the directions of the fiber components3aand3b. In addition, the wiring patterns6and7are wired on one surface layer of the printed wiring board1(substrate body2), and the surface is covered with a solder resist11.

The plurality of pad portions10to mount the semiconductor packages8and9are provided on the surface layer (the uppermost surface inFIG. 2) of the printed wiring board1, and are connected to respective end portions of the wiring patterns6and7, as shown inFIG. 1. The semiconductor packages8and9mounted on the pad portions10via solder bumps are installed on the printed wiring board (PWB)1such that their own sides8aand9aare positioned 45 degrees to the sides2a,2b,2cand2dof the substrate body2so as to correspond with the 45° setting angle of the wiring patterns6and7. Thus, a printed circuit board (PCB) is structured.

When the above-described printed wiring board1is manufactured, the insulating layer3is cut down from a parent material in a rectangular shape so that any sides thereof are almost parallel to the directions of the fiber components3aand3bin the insulating layer3first. Then, the ground layer5is provided on one surface side of the insulating layer3on this substrate, and the wiring patterns6and7are formed on the other surface side facing the ground layer5via the insulating layer3so as to have angles of 45 degrees respectively with respect to the directions of the fiber components3aand3bin the insulating layer3. At this time, the pad portions10for the rectangular semiconductor packages8and9mounted at an angle of 45 degrees with respect to the sides of the insulating layer3can be formed so as to correspond with formation angles of the wiring patterns6and7. The printed wiring board1can be obtained in this manner. It should be noted that the cutting of the insulating layer3and the formation of the ground layer5and the wiring patterns6and7can be reversed in order.

Next, a structure of the printed wiring board1of this embodiment to realize stable transmission of signals while keeping the manufacturing costs inexpensive will be explained in detail based onFIGS. 3 to 6, in addition toFIGS. 1 and 2. Here,FIG. 3shows a sectional view showing a state in that a wiring pattern is disposed right above a fiber component in an insulating layer, andFIG. 4is a sectional view showing a state in that a wiring pattern is disposed away from right above a fiber component in an insulating layer.FIG. 5is a plan view showing a printed wiring board in which a plurality of wiring patterns for signal transmission are respectively wired in parallel with the direction of fibers in the insulating layer, andFIG. 6is a plan view showing a printed wiring board in which the direction of fibers in an insulating layer is set to 45 degrees with respect to a side of a substrate body.

Between a wiring pattern13wired right above a fiber component12ain an insulating layer12as shown inFIG. 3, and a wiring pattern14wired in a position avoiding right above the fiber component12ain the insulating layer12as shown inFIG. 4, capacitance formed between a ground layer15and the respective wiring patterns13and14differs from each other. In this case, between the wiring pattern13and the wiring pattern14, impedance differs from each other in the directions along which these patterns extend, in other words, in the direction of signal transmission, and difference in signal transmission speed, or signal noise can be generated. Accordingly, as shown inFIG. 5, a printed wiring board16in which the wiring patterns13and14for signal transmission are wired in parallel with the directions of the fiber components12aand12bin the insulating layer12respectively may worsen signal transmission characteristics.

The respective wiring patterns6and7for signal transmission facing the ground layer5via the insulating layer3are designed to be disposed on the printed wiring board1of the present embodiment respectively, crossing the fibers in the insulating layer3almost equally (from the slanting direction of 45 degrees) as shown inFIG. 1. Accordingly, it becomes possible to make the capacitance generated between the ground layer5and the respective wiring patterns6and7uniform. Thereby, it becomes possible to align impedance in the direction along which the wiring patterns6and7extend, so that stable transmission of signals can be realized. Since the wiring patterns6and7are wired at angles of 45 degrees respectively with respect to the direction of the fiber components3aand3bin the insulating layer3as described above, the printed wiring board1of the present embodiment is serviceable not only when fiber components in the insulating layer are one directional fibers but also when as the insulating layer3in the present embodiment, the fiber components in the insulating layer are bi-directional ones respectively intersecting at right angles in a grid pattern. In other words, respective wiring patterns for signal transmission can be equally crossed from a slanting direction of 45 degrees for any of fiber clusters disposed longitudinally and latitudinally in the insulating layer respectively.

Even with a printed wiring board21, in a case of forming it as shown inFIG. 6, in other words, when the fiber direction in an insulating layer17is tilted at 45 degrees with respect to side portions17a,17b,17cand17dof a substrate body17, and the side portions17aand17cof the substrate body17are disposed in parallel with respective wiring patterns19and20, it is expected that the same effect as that realized by the printed wiring board1of the present embodiment can be obtained. However, in the case of the printed wiring board21, since it is required that a rectangular shape of the substrate body17be cut down from a parent material in a slanted state at 45 degrees, much of the parent material is left as scrap, which pose a problem in manufacturing costs.

On the other hand, the printed wiring board1of the present embodiment does not require a rectangular shape of the printed wiring board1to be cut down with an inclination with respect to the parent material, and does not leave much scrap of the parent material after the cutting. Accordingly, the rectangular shape of the printed wiring board can effectively be cut out from the parent material side, which results in lower manufacturing costs. Thus, the printed wiring board1according to the present embodiment can keep the manufacturing costs inexpensive, and at the same time, can stabilize data transmission.

The printed wiring board1of the present embodiment can be structured on the assumption of applying, for example, PCI Express which is a bus standard for PCI-SIG. The PCI Express performs data transmission serially using a one-way exclusive bus for ascending and descending as one unit, and its basic communication speed is 2.5 Gbps. In addition to this, since the PCI Express can use plural pieces of buses tied up in a bundle, it is possible to realize a communication speed of 80 Gbps by using, for example, 32 lanes in a bundle. Here, the printed wiring board1of the present embodiment structured so as to align the impedance in an extending direction (in the direction of signal transmission) of the wiring patterns6and7effectively works when a high speed data transmission in a GHz band such as the PCI Express is required.

Second Embodiment

A second embodiment of the present invention will be explained based onFIG. 7next. Here,FIG. 7is a sectional view showing a printed wiring board of the second embodiment. A printed wiring board31according to this embodiment is a modification of the structure of the printed wiring board1explained in the first embodiment in a peripheral structure of a pad portion on the surface layer of the substrate body.

That is, this printed wiring board31is provided with a plurality of via holes34, inside which a conductive substance33is filled, as vertical conductive sections right under pad portions35. Thereby, the conductive substance33electrically connects to the pad portions35. On the pad portions35; the semiconductor package8(or9) is mounted via solder bumps36. The via hole34may be a non-feed through via hole connecting between a middle conductive layer inside the substrate and a conductive layer on the surface layer, or it may be a full feed through via hole (through hole) extending though the entire substrate.

In the printed wiring board31according to the present embodiment thus structured, since a conductive substance is filled in each of the via holes34, and the pad portions35for mounting the semiconductor packages8and9are disposed right above the via holes34, the vertical conductive sections made of the conductive substance are not affected by the impedance due to the fiber component in the insulating layer, and shows excellent signal transmission characteristics.

The present invention has been concretely explained according to various embodiments, but the present invention is not limited to these embodiments, and it is possible to variously modify it without deviating from its outline. For instance, it may be a printed wiring board43on which a V-shaped wiring pattern41(or42) is formed of two parts having different slantly-crossing angles with respect to the direction of the fiber direction with each other as shown inFIG. 8. It may also be a printed wiring board47provided with a wiring pattern45(or46) formed of two parts having different slantingly-crossing angles with respect to the fiber direction with each other, and a part without slant crossings as shown inFIG. 9. In this case, it is possible to mount the semiconductor packages8and9in parallel with the sides of the substrate body. It should be noted that, when the printed wiring board47is adopted, in order to restrain the above-described effect of the impedance, it is desirable to make the length of wiring without a part crossed slantingly with the fiber direction as short as possible. By applying the printed wiring boards43,47and the like shown inFIG. 8andFIG. 9, a degree of freedom in a layout of parts to be mounted or wirings can be increased.

In the embodiments described above, the insulating layer3having bi-directional fiber components in which the fiber components in the layer intersect at right angles respectively in a grid pattern is shown as an example, but instead of this, an insulating layer in which the fiber components is, for instance, a mono-directional one can also be formed as a printed wiring board. In that event, wiring may be performed by intersecting the wiring pattern at right angles to a monodirectional fiber direction. Although there is no specific description about the number of wiring layers in the above-described embodiments, needless to say, even a multi-layered printed wiring board having four or eight wiring layers may be adopted.

Further, as shown inFIG. 10, it is possible to form an information processing apparatus designed to have a stable data transmission performance inside the apparatus by installing the printed wiring board1or31explained in the first and second embodiments as examples.

It is to be understood that the present invention is not intended to be limited to the specific modes which are described here using the drawings, and that all changes which come within the meaning and range of equivalency of the following claims are intended to be embraced therein.