Patent ID: 12245364

DESCRIPTION OF EMBODIMENT

One embodiment of a wiring board and an electronic device disclosed in the present application will be described in detail below with reference to the drawings. The present invention is not limited by the embodiment below.

FIG.1is a diagram illustrating an external appearance of an electronic device100according to one embodiment. The electronic device100illustrated in FIG.1is, for example, a wearable device that is wearable on a human body, and can be wound around an arm or a leg by being bent in a longitudinal direction, for example. The electronic device100is constructed by mounting an electronic component on a wiring board that is configured with a flexible substrate. Specifically, the wiring board includes mounting units110and connecting units120, and electronic components115are mounted on the mounting units110.

The mounting units110are regions that are spread in a planar manner so as to have predetermined areas and that have surfaces on which the electronic components115are mountable. In the example illustrated inFIG.1, the wiring board includes the plurality of mounting units110, and the mounting units110are connected to one another by the connecting units120.

The electronic components115include, for example, a semiconductor device, a chip part (a chip condenser, a chip resistor, a chip inductor, or the like), a crystal oscillator, and the like. The electronic components115are mounted on the mounting units110and electrically connected to a conductor layer of the wiring board (to be described later).

The connecting units120connect the mounting units110and are formed in a bendable manner. Specifically, the connecting units120connect the adjacent mounting units110and bend such that the mounting units110approach each other, so that the entire electronic device100bends in a longitudinal direction. In other words, the wiring board includes at least the two mounting units110and the connecting unit120that connects the two mounting units110, and the wiring board bends in a direction in which the mounting units110are connected by a straight line.

FIG.2is a cross-sectional view of the wiring board cut along a line I-I inFIG.1. As illustrated inFIG.2, the wiring board is a multilayer substrate in which insulating layers and conductor layers are laminated. Specifically, the wiring board includes insulating layers211to215, conductor layers221to224, and conductor layers231to234.

The insulating layers211to214are formed by using, for example, flexible insulating resin, such as epoxy resin or polyimide resin, and thicknesses of the insulating layers211to214may be set to, for example, about 20 to 45 micrometers (μm).

The conductor layers221to224are conductor layers that are formed on the mounting units110, and formed on upper surfaces of the insulating layers211to214, respectively. The conductor layers221to224include wiring patterns for transmitting electrical signals, and ground patterns connected to a ground power supply (not illustrated). The wiring patterns of the different conductor layers221to224are electrically connected by vias241and242that penetrate through the insulating layers211to214. Further, the ground patterns of the conductor layers221to224are spread in a planar manner, and cover upper surfaces of the insulating layers211to214in a planar manner. The conductor layers221to224are formed by using, for example, copper or a copper alloy, and thicknesses of the conductor layers221to224may be set to, for example, about 10 to 20 μm.

The conductor layers231to234are conductor layers that are formed on the connecting units120, and formed on upper surfaces of the insulating layers211to214, respectively. The conductor layers231to234include wiring patterns for transmitting electrical signals, and ground patterns connected to a ground power supply (not illustrated). In the connecting units120, the wiring patterns of the different conductor layers231to234are not connected by a via, but the wiring patterns of the conductor layers231to234are electrically connected to wiring patterns of the conductor layers221to224in the adjacent mounting units110. Further, in the connecting units120, the ground patterns of the conductor layers231to234do not completely cover the upper surfaces of the insulating layers211to214, but are formed in shapes with intervals. Shapes of the ground patterns of the conductor layers231to234will be described in detail later. The conductor layers231to234are formed by using, for example, copper or a copper alloy, and thicknesses of the conductor layers231to234may be set to, for example, about 10 to 20 μm.

The insulating layer215is a solder resist layer, and is formed by using flexible insulating resin, such as phenolic resin or polyimide resin, for example. The insulating layer215may be formed by using the same insulating resin as the insulating layers211to214, and a thickness of the insulating layer215may be set to, for example, about 15 to 35 μm.

The insulating layer211is a layer that forms a lowermost layer of the wiring board, and the conductor layer221and the conductor layer231are formed on an upper surface thereof. The conductor layer221and the conductor layer231are formed on the upper surface of the insulating layer211by, for example, the subtractive method or the semi-additive method. The conductor layer231is mainly configured with a ground pattern, and formed in a certain shape that exposes the upper surface of the insulating layer211so as to maintain the bendability of the connecting unit120.

The insulating layer212is a layer that covers the conductor layer221and the conductor layer231, and the conductor layer222and the conductor layer232are formed on an upper surface thereof. The conductor layer222and the conductor layer232are formed on the upper surface of the insulating layer212by, for example, the subtractive method or the semi-additive method. The conductor layer232is mainly configured with a ground pattern, and formed in a certain shape that exposes the upper surface of the insulating layer212so as to maintain the bendability of the connecting unit120.

The insulating layer213is a layer that covers the conductor layer222and the conductor layer232, and the conductor layer223and the conductor layer233are formed on an upper surface thereof. The conductor layer223and the conductor layer233are formed on the upper surface of the insulating layer213by, for example, the subtractive method or the semi-additive method. A wiring pattern of the conductor layer223is electrically connected to, for example, a wiring pattern of the conductor layer222via the via241. Specifically, the via241penetrate through the insulating layer213and connects the wiring patterns of the different layers. The conductor layer233is mainly configured with a ground pattern, and formed in a certain shape that exposes the upper surface of the insulating layer213so as to maintain the bendability of the connecting unit120.

The insulating layer214is a layer that covers the conductor layer223and the conductor layer233, and the conductor layer224and the conductor layer234are formed on an upper surface thereof. The conductor layer224and the conductor layer234are formed on the upper surface of the insulating layer214by, for example, the subtractive method or the semi-additive method. A wiring pattern of the conductor layer224is electrically connected to, for example, a wiring pattern of the conductor layer223via the via242. Specifically, the via242penetrates through the insulating layer214and connects the wiring patterns of the different layers. The conductor layer234is mainly configured with a ground pattern, and formed in a certain shape that exposes the upper surface of the insulating layer214so as to maintain the bendability of the connecting unit120.

The insulating layer215covers the conductor layer224and the conductor layer234. In the mounting unit110, an opening portion251is formed in a part of the insulating layer215and exposes the upper surface of the conductor layer224. It is possible to electrically connect a terminal of the electronic component115to the conductor layer224that is exposed from the opening portion251.

Shapes of the ground patterns of the conductor layers231to234in the connecting unit120will be described below with reference toFIG.3AtoFIG.5.FIG.3Ais a plan view illustrating the shape of the conductor layer231that is formed on the upper surface of the insulating layer211in the connecting unit120. InFIG.3A, a left-right direction corresponds to the longitudinal direction of the electronic device100and serve as a bending direction of the connecting unit120.

As illustrated inFIG.3A, the ground pattern of the conductor layer231has a certain shape in which a plurality of unit patterns310are connected in plan view. Meanwhile, the plan view is a viewpoint at which the surface of the insulating layer211on which the conductor layer231is formed is viewed from a vertical direction. As illustrated inFIG.3B, each of the unit patterns310has a certain shape in which center portions of a U-shaped pattern311and an inverted U-shaped pattern312that are arranged such that respective opening sides are located away from each other are connected by a straight line pattern313. The bending direction of the connecting unit120is perpendicular to the straight line pattern313included in the unit pattern310. Here, “perpendicular” indicates not only a state in which the bending direction of the wiring board and the straight line pattern313cross each other at a right angle, but also a state in which the bending direction of the wiring board and the straight line pattern313cross each other at an angle in a predetermine range including the right angle.

In the ground pattern of the conductor layer231, one end311aof a U-shaped pattern311of a first unit pattern310is connected to one end312bof an inverted U-shaped pattern312of a second unit pattern310that is located in the upper left, and one end311bof the U-shaped pattern311of the first unit pattern310is connected to one end312aof an inverted U-shaped pattern312of a third unit pattern310that is located in the upper right. Similarly, one end312aof an inverted U-shaped pattern312of the first unit pattern310is connected to one end311bof a U-shaped pattern311of a fourth unit pattern310that is located in the lower left, and one end312bof the inverted U-shaped pattern312of the first unit pattern310is connected to one end311aof a U-shaped pattern311of a fifth unit pattern310that is located in the lower right.

In this manner, by adopting the shape in which the unit patterns310are connected, the ground pattern of the conductor layer231has a certain shape in which a conductor pattern that extends in a top-bottom direction perpendicular to the bending direction alternately includes a portion that protrudes to the right and a portion that protrudes to the left. Further, the portion that protrudes to the right in the conductor pattern extending in the top-bottom direction is connected to a portion that protrudes to the left in a conductor pattern that is located adjacently on the right side, and the portion that protrudes to the left in the conductor pattern extending in the top-bottom direction is connected to a portion that protrudes to the right in a conductor pattern that is located adjacently on the left side.

Furthermore, in the conductor layer231, the insulating layer211is exposed from vertically long cross-shaped regions surrounded by the ground pattern. By providing the regions in which the insulating layer211is exposed, it is possible to ensure the bendability of the connecting unit120due to the flexibility of the insulating resin. Moreover, a region in which the insulating layer211is exposed is divided into small regions that are surrounded by the ground pattern, so that it is possible to maintain a constant thickness of the insulating layer212that covers the conductor layer231for each of the small regions. Furthermore, in this shape, a relatively large number of conductor patterns are arranged in the vicinity of the straight line pattern313of the unit pattern310, so that it is possible to increase the remaining copper rate that is a ratio of an area that is covered by the conductor layer231in the upper surface of the insulating layer211. As a result, it is possible to prevent variation in a substrate thickness of the wiring board, and it is possible to improve positional accuracy of the wiring pattern. In other words, it is possible to maintain the bendability and ensure dimensional stability.

Here, as illustrated inFIG.4, a width L1of the conductor pattern that forms the ground pattern of the conductor layer231may be set to, for example, about 25 to 100 μm. Further, a width L2of a narrow portion of the vertically long cross-shaped region in which the insulating layer211is exposed may be set to, for example, about 50 to 150 μm. Furthermore, a width L3of a wide portion of the vertically long cross-shaped region in which the insulating layer211is exposed may be set to, for example, about 100 to 350 μm. A height L4of the vertically long cross-shaped region in which the insulating layer211is exposed may be set to, for example, about 500 to 700 μm.

Meanwhile, in the connecting unit120, only the ground pattern is formed in the conductor layer231, but wiring patterns for transmitting electrical signals between the adjacent mounting units110may be formed in the conductor layers231to234. Specifically, as illustrated inFIG.5for example, a wiring pattern235is formed on the conductor layer232that is formed on the upper surface of the insulating layer212, in addition to the same ground pattern as the ground pattern of the conductor layer231as described above.

The wiring pattern235transmits an electrical signal between the adjacent mounting units110. Specifically, the wiring pattern235connects the conductor layers222of the two mounting units110that are connected to each other by the connecting unit120, and an electrical signal is transmitted between the conductor layers222of the adjacent mounting units110. In the conductor layer232, a ground pattern is formed in a region in which the wiring pattern235is not formed, similarly to the conductor layer231. The ground pattern may be connected to the ground patterns of the conductor layers222of the adjacent mounting units110.

A ground pattern is formed on each of the entire conductor layers231to234of the connecting unit120in the same manner as the conductor layer231as described above, or a wiring pattern is formed in a part of each of the conductor layers231to234on an as-needed basis in the same manner as the conductor layer232. It is preferable to form the wiring patterns in the conductor layers232and233except for the conductor layer231that is the lowermost layer and the conductor layer234that is the uppermost layer.

The bendability of the ground pattern according to one embodiment will be described below by using a specific example.

As described above, the ground pattern in each of the conductor layers231to234of the connecting unit120according to the present embodiment has a certain shape in which the unit patterns310are connected. Each of the unit patterns310has a certain shape in which the center portions of the U-shaped pattern311and the inverted U-shaped pattern312that are arranged such that the respective opening sides are located away from each other are connected by the straight line pattern313.

In contrast, as illustrated inFIG.6Afor example, it may be possible to form a ground pattern that has a certain shape in which H-shaped unit patterns320are connected.FIG.6Billustrates verification results that are obtained by a bendability analysis tool with respect to the ground pattern in which the unit patterns310according to the present embodiment are connected, and the ground pattern in which the unit patterns320are connected as illustrated inFIG.6A.

InFIG.6B, the remaining copper rate is set to the same value of 44.6% for the case in which the unit patterns310are adopted and the case in which the unit patterns320are adopted. Even if the remaining copper rate is the same as described above, in the case in which the unit patterns310are adopted, the bending modulus is 352 megapascal (MPa), which is smaller than the bending modulus of 407 MPa in the case in which the unit patterns320are adopted. At the same time, a reaction force and a maximum stress value are reduced in the case in which the unit patterns310are adopted, as compared to the case in which the unit patterns320are adopted.

This indicates that, when the unit patterns310are adopted, it is possible to bend the connecting unit120with a reduced force and it is possible to ensure good bendability of the connecting unit120according to the present embodiment.

FIGS.7A and7Bare diagrams illustrating a specific example of stress distributions of the unit patterns310and320. Specifically,FIG.7Aillustrates the stress distribution of the unit pattern310, andFIG.7Billustrates the stress distribution of the unit pattern320. InFIGS.7A and7B, darker portions represent higher stress.

As illustrated inFIGS.7A and7B, in the unit pattern320, the stress is concentrated in a center portion in the H-shape, whereas the stress is relatively distributed without being concentrated in the straight line pattern313in the unit pattern310. This may occur because if the unit pattern310is pulled in the left-right direction when being bent in the bending direction, the U-shaped pattern311and the inverted U-shaped pattern312are relatively easily stretched in the left-right direction, so that the stress is distributed.

In this manner, the stress at the time of bending is distributed due to the shape of the unit pattern310, so that if the ground pattern of the connecting unit120is formed into the shape in which the unit patterns310are connected, it is possible to ensure the preferable bendability of the connecting unit120.

As described above, according to the present embodiment, in the conductor layer that is formed on the upper surface of the insulating layer of the multilayer wiring board, the ground pattern in which the plurality of unit patterns are connected is formed. Further, each of the unit patterns has a certain shape in which the U-shaped pattern and the inverted U-shaped pattern are arranged such that the respective opening sides are located away from each other and the center portions of the U-shaped pattern and the inverted U-shaped pattern are connected by the straight line pattern. Therefore, even if a ratio of the area that is covered by the conductor layer in the upper surface of the insulating layer is increased, it is possible to distribute the stress that is applied to each of the unit patterns when the wiring board bends, so that it is possible to maintain the flexibility and ensure the dimensional stability.

Meanwhile, in one embodiment as described above, the four-layer wiring board including the insulating layers211to214, the conductor layers221to224, and the conductor layers231to234is described as an example, but the number of layers of the wiring board is not limited to this example. As long as the wiring board has a configuration in which the conductor layer is laminated on the insulating layer, it is possible to maintain the bendability of the wiring board and ensure the dimensional stability regardless of the number of the layers by forming the conductor pattern into a certain shape in which the unit patterns310are connected.

According to one embodiment of the wiring board and the electronic device disclosed in the present application, it is possible to maintain the bendability and ensure the dimensional stability.

All examples and conditional language recited herein are intended for pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment of the present invention has been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.