Board joint structure

A first board includes a first insulating substrate including a first main surface, a first electrode pad, and a first resist film. The first electrode pad is a conductor pattern provided on the first main surface. The first resist film is provided on the first main surface and is located closer to the first electrode pad than any conductor provided on the first main surface. The first resist film is spaced away from the first electrode pad with a gap provided between the first resist film and the first electrode pad. The first resist film is thicker than the first electrode pad.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a board joint structure that is joined by application of heat and pressure using a hot bar.

2. Description of the Related Art

A conventional structure where a board such as a cable is joined to a mount board is known (WO 2016/088592 A).

The board is heated and pressed against the mount board by a hot bar or the like to be joined to the mount board with solder. In particular, when a board having flexibility is joined by reflow soldering or the like, the board easily deforms at the time of being mounted. Therefore, it is suitable for the board to be joined to the mount board by a hot bar or the like.

However, when the board is joined to the mount board by the above-described method, solder (hereinafter, referred to as a conductive joint material) may be scattered from a joint section during application of heat and pressure (at the time of joining). Alternatively, the conductive joint material may be wet-spread over an unnecessary portion. These may lead to a short circuit at the joint section or changes in electrical characteristics of the board and the mount board.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide board joint structures that are each able to significantly reduce or prevent a change in characteristics due to scattering or wet-spreading of a conductive joint material at the time of joining the board, even when a board is joined to a mount board or the like by a hot bar or the like.

A board joint structure according to a preferred embodiment of the present invention includes a board, and a mounting board, in which the board includes a first insulating substrate including a first main surface, a first electrode pad provided on the first main surface, and a first resist film provided on the first main surface and located closer to the first electrode pad than any conductor provided on the first main surface. The first resist film is spaced away from the first electrode pad with a gap provided between the first resist film and the first electrode pad and is thicker than the first electrode pad. The mounting board includes a second insulating substrate including a second main surface, and a second electrode pad provided on the second main surface. The first main surface faces the second main surface with the first resist film interposed between the first main surface and the second main surface, and the first electrode pad and the second electrode pad are joined together with a conductive joint material.

During application of heat and pressure by a hot bar (at the time of joining the board to the mounting board), the first resist film defines and functions as a bank to significantly reduce or prevent scattering or excessive wet-spreading of the conductive joint material from a joint section between the first electrode pad and the second electrode pad. Therefore, a change in characteristics due to scattering or excessive wet-spreading of the conductive joint material during application of heat and pressure is able to be significantly reduced or prevented.

Further, since the first resist film located closer to the first electrode pad than any conductor provided on the first main surface is thicker than the first electrode pad, application of excessive pressure to the joint section between the first electrode pad and the second electrode pad during application of heat and pressure by the hot bar is able to be significantly reduced or prevented. This in turn further significantly reduces or prevents scattering or excessive wet-spreading of the conductive joint material from the above-described joint section during application of heat and pressure.

The mounting board preferably includes a second resist film provided on the second main surface and located closer to the second electrode pad than any conductor provided on the second main surface. Further, the second resist film is preferably spaced away from the second electrode pad with a gap provided between the second resist film and the second electrode pad and thicker than the second electrode pad. Further, the first main surface preferably faces the second main surface with the first resist film and the second resist film interposed between the first main surface and the second main surface. Accordingly, scattering or excessive wet-spreading of the conductive joint material from the above-described joint section is able to be further reduced or prevented during application of heat and pressure.

The first insulating substrate is preferably flexible. Accordingly, even when the board comes into contact with the mounting board to which the board is mounted during application of heat and pressure by the hot bar, the first insulating substrate is able to be deformed (for example, to define or function as a shock absorber) to significantly reduce or prevent damage to the board.

The second insulating substrate is preferably flexible. Accordingly, even when the board comes into contact with the mounting board during application of heat and pressure by the hot bar, the second insulating substrate is able to be deformed (for example, to define or function as a shock absorber) to significantly reduce or prevent damage to the board or the mounting board. Further, since both the first insulating substrate and the second insulating substrate are flexible, the above-described advantageous features and effects are further improved.

According to preferred embodiments of to the present invention, boards are provided that are able to be significantly reduce or prevent a change in characteristics due to scattering or wet-spreading of the conductive joint material even when the board is joined to a mount board or the like by a hot bar or the like.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a plurality of preferred embodiments for carrying out the present invention will be described with reference to the drawings and some specific examples. In the drawings, the same portions are denoted by the same reference numerals. Although the preferred embodiments will be described separately, for the sake of convenience, in consideration of easy explanation or understanding of the gist, some components shown in different preferred embodiments may be replaced or combined. In second and subsequent preferred embodiments, no description will be provided of points common to a first preferred embodiment, and only differences will be described. In particular, no description will be provided of the same advantageous features and effects of the same or similar components or elements one by one for each preferred embodiment.

First Preferred Embodiment

FIG. 1Ais an external perspective view of a first board101according to a first preferred embodiment of the present invention, andFIG. 1Bis a plan view of the first board101.FIG. 2is a cross-sectional view of the first board101. InFIGS. 1A and 1B, a first electrode pad P11is shown in the form of a dot pattern for easy understanding of the structure.

The first board101includes a first insulating substrate10, the first electrode pad P11, a first resist film1, and the like. Note that the first board101includes elements or components (a conductor, a component, or the like, for example) in addition to those described above, but the components or elements are not shown.

The first insulating substrate10is a cuboid or substantially cuboid insulating element and includes main surfaces S1, S2on opposite sides of the first insulating substrate10. Specifically, the first insulating substrate10is, for example, a resin flat plate primarily including a resin material (thermoplastic resin, for example) and having flexibility. The first insulating substrate10is a flat plate preferably primarily including, for example, a liquid crystal polymer (LCP) or polyetheretherketone (PEEK).

In the first preferred embodiment, the main surface S1of the first insulating substrate10corresponds to a “first main surface”.

The first electrode pad P11is a rectangular or substantially rectangular conductor pattern provided on the main surface S1. The first electrode pad P11is preferably a conductor pattern made of, for example, a Cu foil.

The first resist film1is a protective film provided all or substantially all over the main surface S1and located closer to the first electrode pad P11than any conductor provided on the main surface S1. The first resist film1includes an opening CP at a position corresponding to the first electrode pad P11. Therefore, providing the first resist film1on the main surface S1exposes the first electrode pad P11. As shown inFIGS. 1A, 1B, and 2, the first resist film1is spaced away from the first electrode pad P11with a gap provided between the first resist film1and the first electrode pad P11. That is, the first resist film1has a clearance resist structure with respect to the first electrode pad P11.

The first resist film1is a solder resist film preferably made of a thermosetting resin, for example, an epoxy resin (EP). The first resist film1includes, for example, a thermosetting resin applied to the main surface S1and then cured. Further, the first resist film1may be a coverlay film made of, for example, polyimide (PI) or polyethylene terephthalate (PET). Such a first resist film1may include, for example, a patterned film applied to the main surface S1, or may include a film applied to the main surface S1and then patterned. In the present specification, “close to the first electrode pad” means that the first resist film is located closer to the first electrode pad than any of the conductors provided on the main surface S1is. That is, a case where the shortest distance between the first resist film and the first electrode pad is smaller than the shortest distance between any of all the conductors provided on the main surface S1and the first electrode pad is referred to as “the first resist film is “close to the first electrode pad””.

As shown inFIG. 1B, the first resist film1surrounds an entire or substantially an entire circumference of the first electrode pad P11in plan view of the main surface S1(when viewed along a Z-axis). Further, as shown inFIG. 2, a thickness (H1: thickness along the Z-axis orthogonal or substantially orthogonal to the main surface S1) of the first resist film1is larger than a thickness (H2) of the first electrode pad P11(H1>H2).

Next, a description will be provided of the board joint structure of the first preferred embodiment with reference to the drawings.FIG. 3is a cross-sectional view of a main portion of an electronic device301according to the first preferred embodiment.

The electronic device301includes the first board101, the second board201, and the like. The first board101is mounted on the second board201. Note that a board other than the first board101, an electronic component, and the like are mounted on the second board201, but they are not shown.

The second board201includes a second insulating substrate20, second electrode pads P21, P22, P23, a conductor41, and the like. Note that the second board201includes components or elements (a conductor, a component, and the like, for example) in addition to those described above, but the components or elements are not shown. The second board201is a cuboid or substantially cuboid printed wiring board, for example, a glass/epoxy board.

In the first preferred embodiment, the second board201corresponds to a “mounting board”.

The second insulating substrate20is a cuboid or substantially cuboid insulating element and has a main surface PS1. The second electrode pads P21, P22, P23are rectangular or substantially rectangular conductor patterns provided on the main surface PS1. The conductor41is a conductor pattern provided in the second insulating substrate20. The second electrode pads P21, P22, P23and the conductor41are each preferably a conductor pattern made of, for example, a Cu foil.

In the first preferred embodiment, the main surface PS1of the second insulating substrate20corresponds to a “second main surface”.

As shown inFIG. 3, the main surface S1(first main surface) of the first board101faces the main surface PS1(second main surface) of the second board201with the first resist film1interposed between the main surface S1and the main surface PS1. The first electrode pad P11of the first board101and the second electrode pad P21of the second board201are joined together with a conductive joint material5. The conductive joint material5is preferably, for example, solder.

The first board101is joined to the second board201by, for example, a joining process described below.FIGS. 4A and 4Bare cross-sectional views of the first board101and the second board201according to the first preferred embodiment, sequentially showing the process of joining the first board101and the second board201.

First, as shown inFIG. 4A, the first board101and the second board201are prepared. Then, a conductive paste5P is applied (or printed) to a surface of the second electrode pad P21of the second board201. The conductive paste5P is preferably, for example, a solder paste.

Next, the first board101is held by suction by a hot bar3and then provided (placed) on the second board201. Specifically, the first board101is provided on the second board201to cause the first electrode pad P11of the first board101and the second electrode pad P21of the second board201to face each other. At this time, the main surface S1(first main surface) of the first insulating substrate10faces the main surface PS1(second main surface) of the second board201with the first resist film1interposed between the main surface S1and the main surface PS1.

Thereafter, the first board101is heated and pressed by the hot bar3in a stacking direction (+Z direction) (see a white arrow shown inFIG. 4A), thus joining the first board101to the second board201. This in turn joins, as shown inFIG. 4B, the first electrode pad P11of the first board101to the second electrode pad P21of the second board201with the conductive joint material5.

Next, a description will be provided of a process of joining the first board including no first resist film and the second board as a comparative example.FIGS. 5A and 5Bare cross-sectional views of a first board100including no first resist film and the second board201, sequentially showing the process of joining the first board100and the second board201as the comparative example. Note that the joining process shown inFIGS. 5A and 5Bis the same or approximately the same as the joining process shown inFIGS. 4A and 4B; thus, no description will be provided of some of the joining process.

First, as shown inFIG. 5A, the first board100and the second board201are prepared. The first board100differs from the above-described first board101in that the first board100includes no first resist film. The first board100is identical or similar in other components, elements, and features as the first board101. Then, the conductive paste5P is applied (or printed) to the surface of the second electrode pad P21of the second board201.

Next, the first board100is held by suction by the hot bar3and then provided (placed) on the second board201. Specifically, the first board100is provided on the second board201to cause the first electrode pad P11of the first board100and the second electrode pad P21of the second board201to face each other. At this time, the main surface S1(first main surface) of the first insulating substrate10faces the main surface PS1(second main surface) of the second board201.

Thereafter, the first board100is heated and pressed by the hot bar3in a stacking direction (+Z direction) (see a white arrow shown inFIG. 5A), thus joining the first board100to the second board201. This in turn joins, as shown inFIG. 5B, the first electrode pad P11of the first board100to the second electrode pad P21of the second board201with the conductive joint material5.

As shown inFIGS. 5A and 5B, when the first board100including no first resist film is joined to the second board201by the hot bar3, excessive pressure is applied to a joint section between the first electrode pad P11and the second electrode pad P21during application of heat and pressure. This may cause the conductive joint material to be scattered from the above-described joint section (see a scattered portion SP shown inFIG. 5B) or cause the conductive joint material to be excessively wet-spread from the joint section (see a wet-spread portion WP shown inFIG. 5B). This in turn may cause a short circuit at an unintended section (for example, a short circuit between the second electrode pads P21and P23shown inFIG. 5B) or may provide a capacitance between other conductors (for example, between the scattered portion SP and the conductor41shown inFIG. 5B). These lead to a change in electrical characteristics.

On the other hand, according to the first preferred embodiment, during application of heat and pressure by the hot bar3(at the time of joining the first board101), the first resist film1defines and functions as a bank to significantly reduce or prevent scattering or wet-spreading of the conductive joint material from the joint section between the first electrode pad P11and the second electrode pad P21(to bring a scattering range of the conductive joint material into a joint range MR shown inFIG. 2). Therefore, a change in characteristics due to scattering or excessive wet-spreading of the conductive joint material during application of heat and pressure is able to be significantly reduced or prevented.

Further, according to the first preferred embodiment, as shown inFIG. 2, the thickness (H1) of the first resist film1located closer to the first electrode pad P11than any conductor provided on the main surface S1is larger than the thickness (H2) of the first electrode pad P11(H1>H2). Excessive pressure is able to be significantly reduced or prevented from being applied to the joint section between the first electrode pad P11and the second electrode pad P21during application of heat and pressure by the hot bar3. This in turn further reduces or prevents scattering or excessive wet-spreading of the conductive joint material from the above-described joint section during application of heat and pressure.

In the first preferred embodiment, as shown inFIGS. 1A, 1B, 2, and the like, the first resist film1is spaced away from the first electrode pad P11with a gap provided between the first resist film1and the first electrode pad P11(clearance resist structure). Accordingly, as compared to a case where the first resist film1covers some of the first electrode pad P11(a case where the first resist film1has an over-resist structure with respect to the first electrode pad P11), the thickness of the first resist film1defining or functioning as a bank for the conductive joint material5is able to be easily adjusted. That is, the thickness of the first resist film1is able to be easily adjusted to a thickness that prevents the conductive joint material from being scattered or excessively wet-spread.

Further, in the first preferred embodiment, the first resist film1surrounds the whole circumference of the first electrode pad P11in plan view of the main surface S1(when viewed along the Z-axis). The first electrode pad P11is surrounded by the first resist film1. Therefore, as compared to a case where the first electrode pad P11is not surrounded by the first resist film1, scattering or excessive wet-spreading of the conductive joint material from the joint section during application of heat and pressure is able to be significantly reduced or prevented.

In the first preferred embodiment, the first insulating substrate10is flexible. Even when the first board101comes into contact with the second board201during application of heat and pressure by the hot bar3, the first insulating substrate10is able to be deformed (for example, to define or function as a shock absorber) to significantly reduce or prevent damage to the first board101or the second board201.

Note that, in the first preferred embodiment, a description has been provided of an example where the conductive paste5P is applied (or printed) to the surface of the second electrode pad P21, but the present invention is not limited to these components, elements, and features, and the conductive paste5P may be applied (or printed) to a surface of the first electrode pad P11.

In the first preferred embodiment, a description has been provided of a method to apply (or print) the conductive paste5P to the surface of the first electrode pad P11(or the surface of the second electrode pad P21) in the joining process. However, the surface of the first electrode pad P11(or the surface of the second electrode pad P21) may be pre-coated with a predetermined amount of conductive paste. Adjusting, in advance, the amount of the conductive paste5P with which the surface of the first electrode pad P11(or the surface of the second electrode pad P21) is pre-coated is able to significantly reduce or prevent the scattering of the conductive joint material from the joint section during application of heat and pressure, as compared to a case where an excessive amount of the conductive joint material5is applied to the joint section.

Second Preferred Embodiment

In a second preferred embodiment of the present invention, a description will be provided of an example of the first board including a plurality of first electrode pads.

FIG. 6Ais an external perspective view of a first board102according to a second preferred embodiment, andFIG. 6Bis a plan view of the first board102.FIG. 7is a cross-sectional view of the first board102. InFIGS. 6A and 6B, first electrode pads P11, P12are shown in the form of a dot pattern for easy understanding of the structure.

The first board102includes a first insulating substrate10A, the plurality of first electrode pads P11, P12, a first resist film1A, first conductors61,62, interlayer connection conductors V1, V2, and the like. Note that the first board102includes components or elements (a conductor, a component, and the like) in addition to those described above, but the components or elements are not shown. The first board102differs from the first board101according to the first preferred embodiment in that the first board102includes the plurality of first electrode pads P11, P12, the first conductors61,62, and the interlayer connection conductors V1, V2.

A description will be provided below of differences from the first board101according to the first preferred embodiment.

The first insulating substrate10A is a cuboid or substantially cuboid insulating element and includes main surfaces S1, S2on opposite sides of the first insulating substrate10A. Specifically, the first insulating substrate10A is a resin flat plate including a laminate of a plurality of insulating substrate layers including a thermoplastic resin and having flexibility. The plurality of insulating substrate layers are preferably sheets primarily including, for example, a liquid crystal polymer (LCP) or polyetheretherketone (PEEK).

In the second preferred embodiment, the main surface S1of the first insulating substrate10A corresponds to the “first main surface”.

The first electrode pads P11, P12are rectangular or substantially rectangular conductor patterns provided on the main surface S1. The first electrode pads P11, P12are located at, adjacent to, or in a vicinity of a center of the main surface S1along a Y-axis and side by side along an X-axis.

The first resist film1A is a protective film provided all or substantially all over the main surface S1and located closer to the first electrode pads P11, P12than any conductor provided on the main surface S1. The first resist film1A includes openings CP11, CP12at positions corresponding to the first electrode pads P11, P12, respectively. Therefore, providing the first resist film1A on the main surface S1exposes the first electrode pads P11, P12. As shown inFIGS. 6A, 6B, and 7, the first resist film1A is spaced away from the first electrode pads P11, P12with a gap provided between the first resist film1A and the first electrode pads P11, P12. That is, the first resist film1A has a clearance resist structure with respect to the first electrode pads P11, P12.

Note that, as shown inFIG. 6B, the first resist film1A surrounds entire or substantially entire circumferences of the first electrode pads P11, P12in plan view of the main surface S1(when viewed along the Z-axis). Further, some of the first resist film1A is located between the first electrode pads P11, P12.

The first conductors61,62are conductor patterns provided in the first insulating substrate10A. The interlayer connection conductors V1, V2are provided in the first insulating substrate10A. The first conductor61is electrically connected to the first electrode pad P11via the interlayer connection conductor V1. The first conductor62is electrically connected to the first electrode pad P12via the interlayer connection conductor V2. The first conductors61,62are conductor patterns each preferably made of, for example, a Cu foil.

The first board102according to the second preferred embodiment has the following advantageous effects in addition to the advantageous effects described in the first preferred embodiment.

In the second preferred embodiment, at least some of the first resist film1A defining or functioning as a bank for the conductive joint material is provided between the plurality of first electrode pads P11, P12. Therefore, even when the conductive joint material is scattered or the like from the joint section between the first electrode pads P11and P12during application of heat and pressure, a short circuit between the plurality of first electrode pads P11, P12is able to be significantly reduced or prevented.

Further, in the second preferred embodiment, the first electrode pad P11is electrically connected to the interlayer connection conductor V1and the first conductor61provided in the first insulating substrate10A. Further, the first electrode pad P12is electrically connected to the interlayer connection conductor V2and the first conductor62provided in the first insulating substrate10A. As compared to a case where the first electrode pad is not electrically connected to either the first conductor or the interlayer connection conductor, the first electrode pads P11, P12are less likely to separate from the surface of the first insulating substrate10.

Note that, in the second preferred embodiment, a description has been provided of an example where the first electrode pads P11, P12are electrically connected to the first conductors61,62provided in the first insulating substrate10A via the interlayer connection conductors V1, V2. However, the present invention is not limited to this example. Even when the first electrode pad is electrically connected to a conductor provided on the main surface S2of the first insulating substrate10A via the interlayer connection conductor, the same or similar advantageous effects as described above are able to be provided.

Third Preferred Embodiment

In a third preferred embodiment of the present invention, a description will be provided of an example where the second board is flexible.

FIG. 8is an external perspective view of a main portion of a cable401according to the third preferred embodiment. The cable401according to the third preferred embodiment is a flexible linear (long) cable and includes a first board103and a second board203joined together with a conductive joint material.

In the third preferred embodiment, the second board203corresponds to the “mounting board”.

FIG. 9is an enlarged exploded perspective view of a joint portion between the first board103and the second board203according to the third preferred embodiment. Note that, inFIG. 8, the first electrode pad P11and the second electrode pad P21are shown in the form of a dot pattern for easy understanding of the structure.

The first board103includes a first insulating substrate10B, the first electrode pad P11, a first resist film1B, a plurality of reinforcing electrode pads EP11, EP12, a connector51, and the like. Note that the first board103includes a signal conductor, a ground conductor, and the like in addition to those described above, but they are not shown. The first board103differs from the first board101according to the first preferred embodiment in the shape of the first insulating substrate10B. Further, the first board103differs from the first board101in that the first board103includes the plurality of reinforcing electrode pads EP11, EP12and the connector51.

A description will be provided below of differences from the first board101according to the first preferred embodiment.

The first insulating substrate10B is a long (linear) insulating element whose longitudinal axis coincides with the X-axis and has main surfaces S1F, S1R and a main surface S2on opposite sides of the first insulating substrate10B. The first insulating substrate10B is a resin flat plate including a laminate of a plurality of insulating substrate layers including a thermoplastic resin and having flexibility.

In the third preferred embodiment, the main surface S1F of the first insulating substrate10B corresponds to the “first main surface”.

In the third preferred embodiment, the X-axis corresponds to a “first direction”.

As shown inFIG. 8, the first insulating substrate10B includes a rigid portion RP1and a flexible portion FP1. The rigid portion RP1is larger in lamination number of insulating substrate layers than the flexible portion FP1. Therefore, the rigid portion RP1is harder and stiffer than the flexible portion FP1. Further, the flexible portion FP1is suppler and more flexible than the rigid portion RP1.

The first electrode pad P11is a rectangular or substantially rectangular conductor pattern provided on the main surface S1. The first electrode pad P11is electrically connected to the signal conductor (not shown) of the first board103. The plurality of reinforcing electrode pads EP11, EP12are linear conductor patterns provided on the main surface S1F and extending along the Y-axis. The plurality of reinforcing electrode pads EP11, EP12are electrically connected to the ground conductor (not shown) of the first board103.

The first electrode pad P11and the plurality of reinforcing electrode pads EP11, EP12are provided adjacent to or in a vicinity of a first end of the first insulating substrate10B (a left end of the first insulating substrate10B inFIG. 8). As shown inFIG. 9, the plurality of reinforcing electrode pads EP11, EP12are provided with the first electrode pad P11located between the reinforcing electrode pads EP11, EP12along the X-axis in plan view of the main surface S1F (when viewed along the Z-axis).

The first resist film1B is a protective film provided all or substantially all over the main surface S1F and located closer to the first electrode pad P11than any conductor provided on the main surface S1F. The first resist film1B includes an opening at a position corresponding to the first electrode pad P11. Providing the first resist film1B on the main surface S1F exposes the first electrode pad P11and the plurality of reinforcing electrode pads EP11, EP12. As shown inFIG. 9, the first resist film1B is spaced away from the first electrode pad P11with a gap provided between the first resist film1B and the first electrode pad P11. That is, the first resist film1has a clearance resist structure with respect to the first electrode pad P11.

Note that, although not shown, the plurality of reinforcing electrode pads EP11, EP12each correspond to some of the conductor pattern (corresponding to a “second conductor”) provided on the main surface S1F that is not covered by the first resist film1B. Specifically, the first resist film1B includes openings at positions corresponding to the plurality of reinforcing electrode pads EP11, EP12. These openings are smaller in area than the conductor pattern. Therefore, providing the first resist film1B on the main surface S1F exposes some (the reinforcing electrode pads EP11, EP12) of the conductor pattern. As described above, the first resist film1B covers some of the conductor pattern provided on the main surface S1F. That is, the reinforcing electrode pads EP11, EP12have an over-resist structure.

The connector51is mounted on the main surface S2of the first insulating substrate10B and is provided adjacent to or in a vicinity of a second end of the first insulating substrate10B (a right end of the first insulating substrate10B inFIG. 8). The connector51is electrically continuous with the signal conductor, the ground conductor, and the like of the first board103(not shown).

Next, a description will be provided of the second board. The second board203includes a second insulating substrate20B, the second electrode pad P21, reinforcing electrode pads EP21, EP22, a second resist film2B, a connector52, and the like. Note that the second board203includes a signal conductor, a ground conductor, and the like in addition to those described above, but they are not shown. The second board203differs from the second board201according to the first preferred embodiment in the shape of the second insulating substrate20B. Further, the second board203differs from the second board201in that the second board203includes the second resist film2B, the plurality of reinforcing electrode pads EP21, EP22, and the connector52.

A description will be provided below of differences from the second board201according to the first preferred embodiment.

The second insulating substrate20B is a long (linear) insulating element whose longitudinal axis coincides with the X-axis and includes main surfaces PS1F, PS1R and a main surface PS2on opposite sides of the second insulating substrate20B. The second insulating substrate20B is a resin flat plate including a laminate of a plurality of insulating substrate layers including a thermoplastic resin and having flexibility.

In the third preferred embodiment, the main surface PS1F of the second insulating substrate20B corresponds to the “second main surface”.

As shown inFIG. 8, the second insulating substrate20B includes a rigid portion RP2and a flexible portion FP2. The rigid portion RP2is larger in lamination number of insulating substrate layers than the flexible portion FP2. Therefore, the rigid portion RP2is harder and stiffer than the flexible portion FP2. Further, the flexible portion FP2is suppler and more flexible than the rigid portion RP2.

The second electrode pad P21is a rectangular or substantially rectangular conductor pattern provided on the main surface PS1F. The second electrode pad P21is electrically connected to the signal conductor (not shown) of the second board203. The plurality of reinforcing electrode pads EP21, EP22are linear conductor patterns provided on the main surface PS1F and extending along the Y-axis. The plurality of reinforcing electrode pads EP21, EP22are electrically connected to the ground conductor (not shown) of the second board203.

The second electrode pad P21and the plurality of reinforcing electrode pads EP21, EP22are provided adjacent to or in a vicinity of a first end of the second insulating substrate20B (a right end of the second insulating substrate20B inFIG. 8). As shown inFIG. 9, the plurality of reinforcing electrode pads EP21, EP22are provided with the second electrode pad P21located between the reinforcing electrode pads EP21, EP22along the X-axis in plan view of the main surface PS1F (when viewed along the Z-axis).

The second resist film2B is a protective film provided all or substantially all over the main surface PS1F and located closer to the second electrode pad P21than any conductor provided on the main surface PS1F. The second resist film2B includes an opening at a position corresponding to the second electrode pad P21. Providing the second resist film2B on the main surface PS1F exposes the second electrode pad P21. As shown inFIG. 9, the second resist film2B is spaced away from the second electrode pad P21with a gap provided between the second resist film2B and the second electrode pad P21(clearance resist structure). Note that, as shown inFIG. 9, the second resist film2B surrounds the entire or substantially the entire circumference of the second electrode pad P21in plan view of the main surface PS1F (when viewed along the Z-axis). The second resist film2B is a solder resist film including a thermosetting resin such as an epoxy resin (EP) or a coverlay film including, for example, polyimide (PI) or polyethylene terephthalate (PET).

Note that, although not shown, the plurality of reinforcing electrode pads EP21, EP22each correspond to some of the conductor pattern provided on the main surface PS1F that is not covered by the second resist film2B. Specifically, the second resist film2B includes openings at positions corresponding to the plurality of reinforcing electrode pads EP21, EP22. These openings are smaller in area than the conductor pattern. Therefore, providing the second resist film2B on the main surface PS1F exposes some (the reinforcing electrode pads EP21, EP22) of the conductor pattern. As described above, the second resist film2B covers some of the conductor pattern provided on the main surface PS1F (over-resist structure).

Further, although not shown, the second resist film2B is preferably thicker than the second electrode pad P21.

The connector52is mounted on the main surface PS1R of the second insulating substrate20B and is provided adjacent to or in a vicinity of a second end of the second insulating substrate20B (a left end of the second insulating substrate20B inFIG. 8). The connector52is electrically continuous with the signal conductor, the ground conductor, and the like of the second board203(not shown).

As shown inFIG. 9, the main surface S1F (first main surface) of the first board103faces the main surface PS1F (second main surface) of the second board203with the first resist film1B and the second resist film2B interposed between the main surface S1F and the main surface PS1F. The first electrode pad P11of the first board103and the second electrode pad P21of the second board203are joined together with a conductive joint material. Further, the reinforcing electrode pad EP11of the first board103and the reinforcing electrode pad EP21of the second board203are joined together with a conductive joint material. Furthermore, the reinforcing electrode pad EP12of the first board103and the reinforcing electrode pad EP22of the second board203are joined together with a conductive joint material (not shown). As described above, joining the first board103and the second board203together defines one cable401.

The third preferred embodiment has the following advantageous effects in addition to the advantageous effects described in the first preferred embodiment.

The second board203according to the third preferred embodiment includes the second resist film2B provided on the main surface PS1F and located closer to the second electrode pad P21than any conductor provided on the main surface PS1F, with a gap provided between the second resist film2B and the second electrode pad P21. Further, the second resist film2B is thicker than the second electrode pad P21. The structure of the second electrode pad P21joined to the first electrode pad P11including a clearance resist structure further reduces or prevents scattering or excessive wet-spreading of the conductive joint material from the joint section during application of heat and pressure. This further reduces or prevents a change in characteristics due to scattering of the conductive joint material or the like.

In the third preferred embodiment, the insulating substrate (the first insulating substrate10B or the second insulating substrate20B) is flexible and long. When the board (for example, the first board) that is flexible and long is mounted on the mount board (for example, the second board) by reflow soldering, the board is likely to deform and shift in a mount position at the time of, for example, being mounted on the mount board. Accordingly, mounting the board on the mount board by a hot bar is suitable. Therefore, the advantageous features and effects obtained by providing the resist film of the present invention (the features and effects of significantly reducing or preventing scattering or wet-spreading of the conductive joint material during application of heat and pressure by the hot bar) are particularly effective when the insulating substrate is flexible and long.

Further, in the third preferred embodiment, the second insulating substrate20B is flexible. Even when the first board103comes into contact with the second board203during application of heat and pressure by the hot bar, the second insulating substrate20B is able to be deformed (for example, to define or function as a shock absorber) to significantly reduce or prevent damage to the first board103or the second board203. Note that, in the third preferred embodiment, since both the first insulating substrate10B and the second insulating substrate20B are flexible, the above-described advantageous features and effects are further improved.

Boards, for example, cables are typically provided by manufacturing the boards as a mother board and then dividing the mother board into a plurality of pieces. However, when such a mother board is divided into long (or large) boards, the number of boards thus provided is small. On the other hand, in the third preferred embodiment, joining the first board103and the second board203together defines one cable401(composite board). That is, since joining small pieces (the first board and the second board) divided from the mother board together provides one large board, the number of boards provided from the mother board (the number of provided boards) is able to be increased.

Further, the cable401according to the third preferred embodiment is a flexible and long cable. Such a long cable is bent for general use. Thus, a joint portion between the first board103and the second board203may separate due to bending stress. In the third preferred embodiment, since the plurality of reinforcing electrode pads are provided at the joint portion, joint strength of the joint portion is able to be increased to significantly reduce or prevent the separation. Further, in the third preferred embodiment, since the electrode pad is interposed between the two reinforcing electrode pads, damage to the joint section between the electrode pads due to bending stress is able to be significantly reduced or prevented.

Further, since the electrode pad having a clearance resist structure is low in joint strength against the insulating substrate, the electrode pad easily separates from the surface of the insulating substrate. On the other hand, since the reinforcing electrode pad having an over-resist structure is high in joint strength against the insulating substrate as compared to the electrode pad having a clearance resist structure, the reinforcing electrode pad is less likely to separate from the surface of the insulating substrate. In particular, in the third preferred embodiment, since the electrode pad having a clearance resist structure is interposed between the plurality of reinforcing electrode pads having an over-resist structure, the separation of the joint section is able to be significantly reduced or prevented.

Further, in the third preferred embodiment, the first electrode pad P11having a clearance resist structure (a structure where the resist film is spaced away from the electrode pad with a gap provided between the resist film and the electrode pad) is provided between the plurality of reinforcing electrode pads EP11, EP12. In other words, in the third preferred embodiment, the first electrode pad P11located closer to a large number of pads than any conductor provided on the main surface S1F (for example, the reinforcing electrode pads EP11, EP12) has a clearance resist structure. Accordingly scattering of the conductive joint material from the joint section of the first electrode pad P11during application of heat and pressure or the like is able to be significantly reduced or prevented, which in turn significantly reduces or prevents a short circuit between the large number of pads or the like. Therefore, even when the first electrode pad P11is located closer to the large number of pads than any conductor provided on the main surface S1F, a change in characteristics due to, for example, scattering of the conductive joint material during application of heat and pressure is able to be significantly reduced or prevented. Note that the above-described features and effects hold true for the relationship between the second electrode pad P21and the plurality of reinforcing electrode pads EP21, EP22.

In the third preferred embodiment, the longitudinal axis of the insulating substrate (the first insulating substrate10B and the second insulating substrate20B) coincides with the first direction (X-axis). When the longitudinal axis of the insulating substrate coincides with the first direction, bending stress including stress in the first direction generated when the insulating substrate deforms or bends tends to be applied to the joint portion between the first board103and the second board203(see a fourth preferred embodiment of the present invention as described below). Therefore, interposing the electrode pad between the plurality of reinforcing electrode pads in the first direction significantly reduces or prevents damage to the joint section between the electrode pads.

Fourth Preferred Embodiment

In a fourth preferred embodiment of the present invention, a description will be provided of an example that differs from the third preferred embodiment in the shape of the first board and the second board.

FIG. 10is an external perspective view of a main portion of a cable402according to the fourth preferred embodiment. The cable402according to the fourth preferred embodiment is a flexible crank-shaped (long) cable including a first board104and a second board204joined together with a conductive joint material.

In the fourth preferred embodiment, the second board204corresponds to the “mounting board”.

FIG. 11is an enlarged exploded perspective view of a joint portion between the first board104and the second board204according to the fourth preferred embodiment. Note that, in FIG.11, the first electrode pad P11and the second electrode pad P21are shown in the form of a dot pattern for easy understanding of the structure.

The first board104differs from the first board103according to the fourth preferred embodiment in shape of a first insulating substrate10C. Further, the first board104differs from the first board103in that the first board104further includes reinforcing electrode pads EP13, EP14. The first board104is substantially identical in other components, elements, and features as the first board103.

A description will be provided below of differences from the first board103according to the third preferred embodiment.

The first insulating substrate10C is an L-shaped insulating flat plate whose longitudinal axis coincides with the X-axis and has main surfaces S1F, S1R and a main surface S2on opposite sides of the first insulating substrate10C.

In the fourth preferred embodiment, the main surface S1F of the first insulating substrate10C corresponds to the “first main surface”. Further, the X-axis corresponds to the “first direction”, and the Y-axis corresponds to a “second direction”.

The plurality of reinforcing electrode pads EP11, EP12are linear conductor patterns provided on the main surface S1F and extending along the X-axis. The plurality of reinforcing electrode pads EP13, EP14are linear conductor patterns provided on the main surface S1F and extending along the Y-axis. The plurality of reinforcing electrode pads EP11, EP12, EP13, EP14are electrically connected to a ground conductor (not shown) of the first board104.

The first electrode pad P11and the plurality of reinforcing electrode pads EP11, EP12are provided adjacent to or in a vicinity of a first end of the first insulating substrate10C (a lower left end of the first insulating substrate10C inFIG. 10). As shown inFIG. 11, the plurality of reinforcing electrode pads EP11, EP12are provided with the first electrode pad P11interposed between the reinforcing electrode pads EP11, EP12along the Y-axis in plan view of the main surface S1F (when viewed along the Z-axis). The plurality of reinforcing electrode pads EP13, EP14are provided with the first electrode pad P11interposed between the reinforcing electrode pads EP13, EP14along the X-axis in plan view of the main surface S1F (when viewed along the Z-axis).

A first resist film1C is a protective film provided all or substantially all over the main surface S1F and located closer to the first electrode pad P11than any conductor provided on the main surface S1F. The first resist film1C is spaced away from the first electrode pad P11with a gap provided between the first resist film1C and the first electrode pad P11(clearance resist structure).

Note that, although not shown, the plurality of reinforcing electrode pads EP11, EP12, EP13, EP14each correspond to some of the conductor pattern (corresponding to the “second conductor”) provided on the main surface S1F that is not covered by the first resist film1C. Specifically, the first resist film1C has openings at positions corresponding to the plurality of reinforcing electrode pads EP11, EP12, EP13, EP14. These openings are smaller in area than the second conductor. Therefore, providing the first resist film1C on the main surface S1F exposes some (the reinforcing electrode pads EP11, EP12, EP13, EP14) of the second conductor. As described above, the first resist film1C covers some of the second conductor provided on the main surface S1F (over-resist structure).

Next, a description will be provided of the second board. The second board204differs from the second board203according to the third preferred embodiment in shape of a second insulating substrate20C. Further, the second board204differs from the second board203in that the second board204further includes reinforcing electrode pads EP23, EP24. The second board204is substantially identical in other components, elements, and features as the second board203.

A description will be provided below of differences from the second board203according to the third preferred embodiment.

The second insulating substrate20C is an L-shaped insulating flat plate whose longitudinal axis coincides with the X-axis and has main surfaces PS1F, PS1R and a main surface PS2on opposite sides of the second insulating substrate20C.

In the fourth preferred embodiment, the main surface PS1F of the second insulating substrate20C corresponds to the “second main surface”.

The plurality of reinforcing electrode pads EP21, EP22are linear conductor patterns provided on the main surface PS1F and extending along the X-axis. The plurality of reinforcing electrode pads EP23, EP24are linear conductor patterns provided on the main surface PS1F and extending along the Y-axis. The plurality of reinforcing electrode pads EP21, EP22, EP23, EP24are electrically connected to a ground conductor (not shown) of the second board204.

The second electrode pad P21and the plurality of reinforcing electrode pads EP21, EP22are provided adjacent to or in a vicinity of a first end of the second insulating substrate20C (an upper right end of the second insulating substrate20C inFIG. 10). As shown inFIG. 11, the plurality of reinforcing electrode pads EP21, EP22are provided with the second electrode pad P21interposed between the reinforcing electrode pads EP21, EP22along the Y-axis in plan view of the main surface PS1F (when viewed along the Z-axis). The plurality of reinforcing electrode pads EP23, EP24are provided with the second electrode pad P21interposed between the reinforcing electrode pads EP23, EP24along the X-axis in plan view of the main surface PS1F (when viewed along the Z-axis).

The second resist film2C is a protective film provided all or substantially all over the main surface PS1F and located closer to the second electrode pad P21than any conductor provided on the main surface PS1F. The second resist film2C is spaced away from the second electrode pad P21with a gap provided between the second resist film2C and the second electrode pad P21(clearance resist structure).

Note that, although not shown, the plurality of reinforcing electrode pads EP21, EP22, EP23, EP24each correspond to some of the conductor pattern provided on the main surface PS1F that is not covered by the second resist film2C. Specifically, the second resist film2C has openings at positions corresponding to the plurality of reinforcing electrode pads EP21, EP22, EP23, EP24. These openings are smaller in area than the conductor pattern. Therefore, providing the second resist film2C on the main surface PS1F exposes some (the reinforcing electrode pads EP21, EP22, EP23, EP24) of the conductor pattern. As described above, the second resist film2C covers some of the conductor pattern provided on the main surface PS1F (over-resist structure).

As shown inFIG. 11, the main surface S1F (first main surface) of the first board104faces the main surface PS1F (second main surface) of the second board204with the first resist film1C and the second resist film2C interposed between the main surface S1F and the main surface PS1F. The first electrode pad P11of the first board104and the second electrode pad P21of the second board204are joined together with a conductive joint material. Further, the reinforcing electrode pad EP11and the reinforcing electrode pad EP21are joined together with a conductive joint material. Further, the reinforcing electrode pad EP12and the reinforcing electrode pad EP22are joined together with a conductive joint material. Further, the reinforcing electrode pad EP13and the reinforcing electrode pad EP23are joined together with a conductive joint material. Further, the reinforcing electrode pad EP14and the reinforcing electrode pad EP24are joined together with a conductive joint material (not shown). As described above, joining the first board104and the second board204together defines one cable402.

The cable402according to the fourth preferred embodiment is used, for example, as follows.FIG. 12is a perspective view of a main portion of an electronic device302according to the fourth preferred embodiment.

The electronic device302includes the cable402, mount boards501,502, and the like. A large number of electronic components and the like are mounted on the mount boards501,502, but the electronic components and the like are not shown. The mount boards501,502are, for example, printed wiring boards.

As shown inFIG. 12, the cable402has bent portions CR1, CR2. Specifically, the cable402is connected between the mount boards501and502with the flexible portions (the flexible portion FP1of the first board104and the flexible portion FP2of the second board204shown inFIG. 10) bent. The connector51of the cable402is connected to a receptacle (not shown) mounted on the mount board501. The connector52of the cable402is connected to a receptacle72mounted on the mount board502.

The fourth preferred embodiment has the following advantageous effects in addition to the advantageous effects described in the third preferred embodiment.

In the fourth preferred embodiment, the plurality of reinforcing electrode pads EP13, EP14are provided with the first electrode pad P11interposed between the reinforcing electrode pads EP13, EP14along the first direction (X-axis) in plan view of the main surface S1F (when viewed along the Z-axis). Further, the plurality of reinforcing electrode pads EP11, EP12are provided with the first electrode pad P11interposed between the reinforcing electrode pads EP11, EP12along the second direction (Y-axis) in plan view of the main surface S1F (when viewed along the Z-axis). The electrode pad being interposed between the four reinforcing electrode pads further reduces or prevents damage to the joint section of the electrode pad due to bending stress generated when the insulating substrate bends.

Other Preferred Embodiments

In each of the above preferred embodiments, examples where the first insulating substrate and the second insulating substrate are cuboid or substantially cuboid or L-shaped flat plates have been described, but the shapes of the first insulating substrate and the second insulating substrate may be changed within a scope in which the advantageous features and effects of the present invention are able to be provided. The first insulating substrate and the second insulating substrate may have, for example, a polygonal shape, a circular or substantially circular shape, an elliptical shape, a T-shape, a Y-shape, a crank shape, or the like in plan view.

In each of the above preferred embodiments, an example where the first insulating substrate is a resin flat plate primarily including a thermoplastic resin, or a laminate of a plurality of insulating substrate layers including a thermoplastic resin has been described, but the present invention is not limited to these specific components, elements, and features. The first insulating substrate may be, for example, a flat plate including a thermosetting resin such as, for example, an epoxy resin or may be a dielectric ceramic such as a low temperature co-fired ceramic (LTCC). Further, the first insulating substrate may be a composite laminate of a plurality of resins, and, for example, may include a laminate of a thermosetting resin such as a glass/epoxy substrate and a thermoplastic resin. Further, the first insulating substrate that is a laminate is not limited to surfaces being fused together by applying heat and pressure to a laminate of a plurality of insulating substrate layers, and an adhesive layer may be provided between the insulating substrate layers. Note that the second insulating substrate is not limited to the specific components, elements, and features described in each of the preferred embodiments, as with the above-described first insulating substrate.

Further, in each of the above preferred embodiments, an example where the first electrode pads P11, P12and the second electrode pad P21are rectangular or substantially rectangular conductor patterns has been described, but the present invention is not limited to these specific components, elements, and features. The shape, number, and the like of the first electrode pads and the second electrode pads may be changed within a scope in which the advantageous features and effects of the present invention are able to be provided. The first electrode pad and the second electrode pad may have, for example, a linear shape, a polygonal shape, a circular or substantially circular shape, an elliptical shape, an arc shape, an annular shape, an L-shape, a T-shape, a Y-shape, a crank shape, or the like.

In each of the above preferred embodiments, an example where the board (the first board and the second board) includes two or four linear reinforcing electrode pads has been described, but the shape, number, and the like of the reinforcing electrode pads may be changed within a scope in which the advantageous features and effects of the present invention are able to be provided. The reinforcing electrode pads may have, for example, a linear shape, a polygonal shape, a circular or substantially circular shape, an elliptical shape, an arc shape, an annular shape, an L-shape, a T-shape, a Y-shape, a crank shape, or the like.

Note that, for example, a conductor pattern other than the signal conductor or the ground conductor may be provided on the first board (board) or the second board (mounting board). Further, a frequency filter, for example, an inductor, a capacitor, or any type of filter (a low-pass filter, a high-pass filter, a band-pass filter, a band elimination filter) may include a conductor pattern on the first board or the second board. Further, various transmission lines (for example, a strip line, a microstrip line, a coplanar line, and the like) may be provided on the first board or the second board.

Further, various components, for example, a chip component may be mounted on (or embedded in) the first board (board) or the second board (mounting board).