JP7371407B2 - cable - Google Patents

Description

The present invention relates to cables, and relates to techniques that are effective when applied to cables that include a shield layer having a plating layer, for example.

Japanese Patent No. 6245402 (Patent Document 1) describes a technique for forming a shield layer from a plating layer in a cable including a shield layer.

Patent No. 6245402

For example, there is a multicore cable that has a plurality of conductor wires that function as signal lines, an insulating layer that covers the plurality of conductor wires, and a shield layer that covers the insulating layer. Among the multicore cables configured in this way, some cables have an oval cross-section in the longitudinal direction.

Here, the elliptical shape in this specification refers to a closed curve having a short axis and a long axis, and is used in a broad concept including not only an elliptical shape but also a substantially elliptical shape and a compound elliptical shape. . In particular, the elliptical shape in this specification also includes a closed curve made up of two opposing parallel straight lines and two circular arcs connecting the ends of the two straight lines.

The present inventor has found that, in an oval multicore cable, for example, when adopting a configuration in which the shield layer is formed from a plating layer and a solder layer is formed in a part of the region on the plating layer, We have newly discovered that the circular shape is a factor that reduces the reliability of multicore cables. Therefore, it is desired to improve the reliability of oval multicore cables.

Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

The cable in one embodiment has an oval cross-sectional shape perpendicular to the longitudinal direction. This cable includes a shield layer composed of a plurality of conductor wires, an insulating layer covering the plurality of conductor wires, a plating layer covering the insulating layer, and a solder layer formed on the first region of the shield layer. Equipped with Here, the solder layer is made of a material containing tin, silver, and copper. At this time, the silver content in the material is 2.5% by mass or more and 3.5% by mass or less, and the copper content in the material is 2.0% by mass or more and 3.0% by mass. % or less.

According to one embodiment, cable reliability can be improved.

FIG. 2 is a diagram showing the configuration of a multicore cable that is a differential signal transmission cable. It is a figure explaining the structure of the end part of a multicore cable. Using pre-soldering technology, a solder layer is formed on the surface of the conductor wire exposed in the exposed conductor wire area of the multi-core cable and on the surface of the shield layer exposed in the exposed shield layer area of the multi-core cable. FIG. 1 is a flowchart illustrating a cable manufacturing process using pre-soldering technology. FIG. 3 is a diagram for explaining an "edge effect." FIG. 3 is a diagram for explaining an "edge effect." FIG. 2 is a schematic diagram showing an example of forming a solder layer on the surface of a shield layer exposed from an oblong multicore cable using a "conventional solder material." FIG. 3 is a schematic diagram showing an example of forming a solder layer on the surface of a shield layer exposed from an oblong multicore cable using an "effective solder material." FIG. 2 is a graph showing the relationship between the immersion time of a multicore cable in molten solder and the amount of dissolution of a plating layer.

In all the drawings for explaining the embodiment, the same members are designated by the same reference numerals in principle, and repeated explanations thereof will be omitted. Note that, in order to make the drawings easier to understand, hatching may be added even in a plan view.

<Cable configuration>
FIG. 1 is a diagram showing the configuration of a multicore cable 1 that functions as a differential signal transmission cable.

In FIG. 1, a multicore cable 1 includes a pair of conductor wires 10a and 10b that function as signal lines through which differential signals propagate, an insulating layer 11 that covers the conductor wires 10a and 10b, and an insulating layer 11 and a sheath 13 that covers the shield layer 12.

Each of the conductor wire 10a and the conductor wire 10b is made of, for example, a copper wire or a copper alloy wire. On the other hand, the insulating layer 11 is made of, for example, polyethylene resin or fluororesin. Further, the shield layer 12 is made of a plating layer made of copper, for example, while the sheath 13 called a jacket is made of an insulating resin.

The shield layer 12 is often composed of a metal foil tape, but in recent years, from the viewpoint of improving the transmission characteristics of signals propagating through the conductor wires 10a and 10b, a plated layer has been used instead of the metal foil tape. Constructing the shield layer 12 is being considered.

Below, first, the reason why the transmission characteristics of signals propagating through the conductor wire 10a and the conductor wire 10b is improved when the shield layer 12 is made of a plating layer will be explained.

For example, when the shield layer 12 is made of a metal foil tape, the metal foil tape is not fixed to the insulating layer 11, so the metal foil tape tends to loosen. If the metal foil tape becomes loose, a gap may be created between the insulating layer 11 and the shield layer 12.

In this regard, when a gap exists between the insulating layer 11 and the shield layer 12, a phase difference occurs between the signal propagating through the conductor line 10a and the signal propagating through the conductor line 10b. This phenomenon is called internal skew, and when internal skew occurs, the signal transmission characteristics of the multicore cable 1 deteriorate. Therefore, in order to improve the transmission performance of the multicore cable 1, it is being considered to fix the shield layer 12 to the insulating layer 11 so that no gap is formed between the insulating layer 11 and the shield layer 12. . Specifically, it is being considered to form the shield layer 12 not from a metal foil tape but from a plating layer. For example, a plating layer can be formed on the surface of the insulating layer 11 by using an electroless plating method. At this time, since the plating layer is formed so as to be fixed to the insulating layer 11, if the shield layer 12 is formed from the plating layer, a gap may be generated between the insulating layer 11 and the shield layer 12. can be suppressed. As a result, according to the multicore cable 1 in which the shield layer 12 is formed from a plating layer, the signal phase shift caused by the air gap can be suppressed, so that the signal transmission characteristics of the multicore cable 1 can be improved. For the above reasons, it can be seen that by forming the shield layer 12 from a plating layer instead of the metal foil tape, the transmission characteristics of the signals propagating through the conductor wires 10a and 10b can be improved.

Furthermore, when the shield layer 12 is formed from a plating layer, the thickness of the shield layer 12 can be made thinner than when the shield layer 12 is formed from a metal foil tape. Therefore, the multicore cable 1 in which the shield layer 12 is formed of a plating layer has the advantage that the multicore cable 1 can be made smaller in diameter and lighter in weight.

<Cable end configuration>
At both ends of the multicore cable 1 described above, the conductor wires 10a and 10b and the shield layer 12 are connected to a printed circuit board or a connector, respectively. Therefore, the ends of the multicore cable 1 are processed so that the conductor wires 10a and 10b and the shield layer 12 can be connected to a printed circuit board or a connector.

Below, the configuration of the end portion of the multicore cable 1 processed so as to be connected to a printed circuit board or a connector will be described with reference to the drawings.

FIG. 2 is a diagram illustrating the configuration of the end portion of the multicore cable 1. As shown in FIG.

In FIG. 2, a connection area 100 is provided at the end of the multicore cable 1 for connecting the multicore cable 1 to a printed circuit board or a connector. This connection region 100 is composed of a conductor wire exposed region 101 where the conductor wires 10a and 10b are exposed, and a shield layer exposed region 102 where the shield layer 12 is exposed. The multicore cable 1 is electrically connected to the printed circuit board or connector by connecting each of the exposed conductor wire region 101 and the exposed shield layer region 102 to the printed circuit board or connector. Specifically, the multicore cable 1 is electrically connected to the printed circuit board or connector by soldering each of the exposed conductor wire region 101 and the exposed shield layer region 102 to the printed circuit board or connector.

<Difficulty in soldering the shield layer consisting of a plating layer>
However, when connecting a shield layer made of a plating layer to a printed circuit board or connector by soldering, it is necessary to ensure mechanical connection strength in addition to electrical connection. That is, when connecting a plating layer to a printed circuit board or a connector by soldering, it is necessary to reliably connect the solder and the plating layer. Regarding this point, in addition to the plating layer having a thin film thickness of approximately 3 μm, the surface of the plating layer still has a modified layer (oxide layer) caused by minute irregularities and chemicals. The plating layer has poor solder wettability. As a result, the difficulty level of solder processing technology for realizing reliable connection between the plating layer and the solder increases. Specifically, the surface of the plating layer requires long-term high-temperature heat treatment and the use of highly active flux. Therefore, in the multi-core cable 1 that uses the shield layer 12 made of a plating layer, it is technically difficult to connect the shield layer 12 to a printed circuit board or connector by soldering, and thus some measures are required.

<Usefulness of preliminary soldering technology>
In the multicore cable 1, which is difficult to solder connect to a printed circuit board or connector in this way, the surfaces of the conductor wires 10a and 10b exposed in the conductor wire exposed area 101 of the multicore cable 1 and the multicore Forming a thin solder layer on the surface of the shield layer 12 exposed in the shield layer exposed region 102 of the cable 1 is being considered. In this specification, this technique will be referred to as a preliminary soldering technique.

For example, FIG. 3 shows the surface of the conductor wire exposed in the conductor wire exposed region 101 of the multicore cable 1 and the shield layer exposed region 102 (first region) of the multicore cable 1 using the preliminary soldering technique. FIG. 3 is a diagram schematically showing how a solder layer 20 is formed on the surface of the shield layer exposed to the surface of the shield layer. In particular, in FIG. 3, the area drawn using dots indicates that a solder layer is formed. This solder layer is formed to cover at least a portion of the shield layer exposed from the sheath 13 covering a portion of the shield layer.

When such preliminary soldering technology is used, when connecting the multi-core cable 1 to a printed circuit board or connector by soldering, for example, the shield layer 12 itself consisting of a plating layer is not connected to the mounting solder; The solder layer formed on the surface of layer 12 and the mounting solder are connected. Therefore, by using the pre-soldering technique, it is possible to perform solder connection in a relatively short time and at a low temperature, and as a result, there is an advantage that defects in the solder connection process can be reduced.

In particular, if a problem occurs when connecting the multi-core cable 1 to a printed circuit board or connector by soldering, not only the multi-core cable 1 but also the printed circuit board and connector will be defective, which will have a large impact on manufacturing costs. . In this regard, the use of pre-soldering technology can reduce defects in the soldering process. This can prevent the product itself from becoming a defective product. This means that by using pre-soldering technology, the rate of defective products such as the printed circuit board itself or the connector itself can be reduced, and thus pre-soldering technology contributes to reducing manufacturing costs. It turns out that this is a useful technique.

In addition, by using pre-soldering technology, soldering work becomes easier, so workers can perform soldering work without having to acquire advanced skills, and it is also easy to mechanize soldering work. become.

Furthermore, by using pre-soldering techniques, solder connections can be made in a relatively short time and at low temperatures. This makes it possible to use a low-activity flux, making it unnecessary to clean flux residue after soldering.

<Cable manufacturing method using pre-soldering technology>
Next, a method of manufacturing a cable using the above-described preliminary soldering technique will be described.

FIG. 4 is a flowchart illustrating a cable manufacturing process using pre-soldering technology.

In FIG. 4, first, a conductor wire made of, for example, a copper wire or a copper alloy wire is prepared (S101). Then, an insulating layer is formed to cover the conductor wire (S102). This insulating layer can be made of polyethylene resin, for example. Next, for example, by using an electroless plating method, a plating layer is formed to cover the surface of the insulating layer (S103). This plating layer becomes a shield layer. Here, the plating layer may be formed from multiple layers. For example, a plating layer may be formed by electrolytic plating on the outer periphery of a plating layer formed by electroless plating. Subsequently, a sheath is formed to cover the shield layer made of a plating layer (S104). This sheath can be formed from an insulating resin. A cable can be manufactured in the manner described above.

Next, in the following process, a process of processing the end portion of the cable is performed. Specifically, first, for example, by using mechanical means, a connection area including a shield layer exposed area where the plating layer is exposed and a conductor line exposed area where the conductor wire is exposed is formed at the end of the cable. (S105). After that, flux is applied to the surface of the plating layer and the surface of the conductor wire exposed in the connection region (S106). Then, the surface of the plating layer coated with flux and the surface of the conductor wire are immersed in the molten solder (S107). As a result, as shown in FIG. 3, for example, the solder shown by dots on the surface of the shield layer 12 (plated layer) exposed in the connection area 100 of the multicore cable 1 and the surfaces of the conductor wires 10a and 10b can be soldered. A layer is formed. In the preliminary soldering technique, a predetermined solder alloy is used, and the thickness of the solder layer is controlled by controlling the temperature of the molten solder and the immersion time of the multicore cable 1. On the other hand, the surface of the insulating layer 11 exposed in the connection region 100 of the multicore cable 1 repels solder, so no solder layer is formed thereon. As a result, even if the surface of the plating layer coated with flux and the surfaces of the conductor wires 10a and 10b are immersed in molten solder, there will be no short circuit between the conductor wires 10a and 10b and the shield layer 12. . In the manner described above, the multicore cable 1 in which the solder layer is formed on the surfaces of the conductor wires 10a and 10b exposed from the ends of the multicore cable 1 and on the surface of the shield layer 12 can be manufactured.

<Consideration of improvement>
In the process of forming a solder layer on the surface of a plating layer using a preliminary soldering technique, a flux application process and a molten solder dipping process are performed. Through these steps, first, the oxide layer formed on the surface of the plating layer is removed by reacting with the flux applied to the surface of the plating layer, thereby cleaning the surface of the plating layer. Thereafter, the plating layer is dissolved by molten solder to a predetermined depth from the surface of the cleaned plating layer. This phenomenon is called "meltback." Thereafter, a metal compound film (alloy film) is formed between the surface of the "melted back" plating layer and the molten solder, thereby achieving stable bonding between the plating layer and the solder layer.

Here, the present inventor newly discovered that in the multicore cable 1 having an oval shape, the "meltback amount" of the plating layer differs depending on the location. Specifically, the present inventor has discovered that the "meltback amount" of the plating layer in the long axis direction of the oval shape is larger than the "meltback amount" of the plating layer in the short axis direction of the oval shape. I found it.

This phenomenon can be explained by the "edge effect."

FIGS. 5 and 6 are diagrams for explaining the "edge effect."

First, in FIG. 5, consider "meltback" at point A, which exists on the flat surface of the shield layer 12 made of a plating layer. When molten solder comes into contact with the flat surface of the shield layer 12, it is considered that point A receives "melt back" from the molten solder existing within the range of angle θ1. On the other hand, in FIG. 6, consider "melt back" at a point B located at a corner of the surface of the shield layer 12 made of a plating layer. At point B, it is considered that "melt back" occurs from the molten solder existing in the range of angle θ2. At this time, the angle θ1 shown in FIG. 5 is 180 degrees, whereas the angle θ2 shown in FIG. 6 is larger than 180 degrees. This means that the influence from the molten solder at point B on the corner is greater than the influence from the molten solder at point A on the flat surface. Since it is considered that the "meltback speed" increases as the influence from the molten solder increases, the "meltback amount" at point B is larger than the "meltback amount" at point A.

This phenomenon is the "edge effect." That is, the "edge effect" in "meltback" caused by molten solder is an effect in which the "meltback speed" at the corners is greater than the "meltback speed" at the flat surface.

Here, the solder material used in the preliminary soldering technique described above is a lead-free solder material, taking into consideration its compatibility with the mounting solder used when connecting the multi-core cable 1 to the printed circuit board or connector. is often used. Specifically, the solder material used in the preliminary soldering technique is a solder material containing tin, silver, and copper, with a tin content of 96.5% by mass and a silver content of 3. A solder material having a copper content of 0.0% by mass and a copper content of 0.5% by mass is used. This solder material will be referred to herein as "conventional solder material."

When forming a solder layer on the plating layer constituting the shield layer 12 of the oval multicore cable 1, if a "conventional solder material" is used as the molten solder, an "edge effect" is also added, resulting in a long The inventors have newly discovered that "meltback" progresses more than the thickness of the plating layer in the long axis direction of the circular shape. That is, the present inventors have newly discovered that when a "conventional solder material" is used as molten solder, the plating layer disappears in the long axis direction of the oval shape. The disappearance of the plating layer means that the insulating layer 11 disposed below the plating layer comes into direct contact with the molten solder. In this case, the mechanical adhesion that had been formed between the insulating layer 11 and the shield layer 12, which is a plating layer, is lost, and as a result, the molten solder is repelled from the insulating layer 11. This not only increases the possibility that electrical disconnection or poor connection will occur in the multicore cable 1, but also may cause deterioration of the transmission characteristics of the multicore cable 1. Furthermore, even when mounting the multi-core cable 1 on a printed circuit board or connector with mounting solder, it is difficult to ensure adhesion with the mounting solder in areas where the plating layer has disappeared and the insulating layer 11 has been exposed. Become. As a result, there is a possibility that a connection failure (falling off or separation) may occur between the multicore cable 1 and the printed circuit board or connector. From the above, when "conventional solder material" is used as molten solder, "edge effect" is also added, and the plating layer constituting the shield layer 12 disappears in the long axis direction of the oval shape, leaving room for improvement. It becomes manifest.

Specifically, FIG. 7 is a schematic diagram showing an example of forming a solder layer 20 on the surface of the shield layer 12 exposed from the oval multicore cable 1 using a "conventional solder material."

In FIG. 7, region AR indicates a part of the region in the short axis direction of the oval shape. In the enlarged view of region AR, a shield layer 12 made of a plating layer is formed on the insulating layer 11, and an alloy film 20a is formed between the shield layer 12 and the solder layer 20. In this way, in the region AR that is the region in the short axis direction of the oval shape, the shield layer 12 made of a plating layer remains, and the alloy film 20a is formed between the shield layer 12 and the solder layer 20. As a result, it can be seen that stable bonding between the shield layer 12 and the solder layer 20 is achieved. In other words, even if a "conventional solder material" with a high "meltback speed" is used, the "edge effect" does not become apparent in the short axis direction of the oval shape, and as a result, the shield layer 12 consisting of a plating layer Don't "melt back" more than necessary. From this, it is possible to realize highly reliable bonding between the shield layer 12 and the solder layer 20 in the region in the short axis direction of the oval shape.

On the other hand, in FIG. 7, region BR indicates a part of the region in the long axis direction of the oval shape. In the enlarged view of the region BR, it can be seen that a part of the shield layer 12 made of a plating layer formed on the insulating layer 11 has disappeared. This is because when using a "conventional solder material" with a high "meltback speed", the shield layer 12 consisting of a plating layer becomes " This is because it will result in a "meltback." As a result, the alloy film 20a is insufficiently formed in the region BR, which is the region in the long axis direction of the oval shape, and it becomes difficult to realize stable bonding between the shield layer 12 and the solder layer 20. In other words, if you use a "conventional solder material" with a high "meltback speed", the "edge effect" will also be added, and as a result, the "meltback" will progress more than necessary in the long axis direction of the oval shape, resulting in the shielding layer being damaged. This results in the disappearance of the plating layer constituting 12. When such disappearance of the plating layer occurs, the insulating layer 11 disposed below the plating layer comes into direct contact with the molten solder, and the molten solder is repelled from the insulating layer 11. Therefore, as shown in the enlarged view of the region BR in FIG. 7, the solder layer 20 is difficult to be formed in the region where the shield layer 12 made of the plating layer has disappeared. This means that there is an increased possibility that electrical disconnection or poor connection will occur in the multicore cable 1, as well as a risk of poor connection (dropping or separation) between the multicore cable 1 and the printed circuit board or connector. This means that there is an increased risk of being invited.

From the above, if a "conventional solder material" with a high "meltback speed" is used as a solder material used in preliminary soldering technology, the "meltback amount" of the plating layer will be large, so for example, "edge In the region in the long axis direction of the oval shape where the "effect" becomes apparent, the plating layer disappears. The disappearance of the plating layer causes electrical disconnections and poor connections in the multicore cable 1, as well as poor connections (falling off and separation) between the multicore cable 1 and the printed circuit board or connector. It also becomes. Therefore, in this embodiment, measures are taken to prevent the loss of the plating layer from becoming apparent. Below, the technical idea of this embodiment in which this device is applied will be explained.

<Basic idea of embodiment>
The basic idea of this embodiment is to use a solder material that has a lower "meltback speed" than the "conventional solder material" rather than a "conventional solder material" as the solder material used in the preliminary soldering technique. It is. For example, when forming a solder layer on the shield layer of an oval multi-core cable using pre-soldering technology, an "edge effect" becomes apparent in the long axis direction of the oval shape. do. Therefore, the reduction in the film thickness of the plating layer constituting the shield layer is greater in the long axis direction of the oval shape than in the short axis direction of the oval shape. Therefore, the disappearance of the plating layer becomes a problem particularly in the long axis direction of the oval shape where the "edge effect" becomes obvious. Furthermore, the disappearance of the plating layer naturally depends on the "meltback speed" of the solder material. Therefore, the main factors that cause the disappearance of the plating layer constituting the shield layer are the "edge effect" and the "meltback speed" of the solder material.

In this regard, since the "edge effect" inevitably exists in oval multicore cables, it is difficult to prevent the plating layer from disappearing by suppressing the "edge effect" itself. it is conceivable that.

Therefore, in this embodiment, instead of focusing on suppressing the "edge effect" itself, the focus is on obtaining a solder material that has a lower "meltback speed" than "conventional solder materials." This is because, for example, if it is possible to use a solder material with a lower ``meltback speed'' than ``conventional solder materials,'' it is possible to suppress the disappearance of the plating layer even if an ``edge effect'' exists. This is because it can be done.

From the above, the basic idea of this embodiment is to use a solder material that has a lower "meltback speed" than "conventional solder materials" by devising the composition of the solder material so that the plating layer disappears. The idea is to suppress the

Below, first, useful knowledge for obtaining a solder material having a lower "meltback speed" than "conventional solder materials" will be explained.

For example, if the melting point of the solder material can be lowered, the temperature of the molten solder can be lowered. At this time, as the temperature of the molten solder decreases, the "meltback speed" decreases. This is because as the temperature of the molten solder decreases, the amount of copper that can be dissolved into the molten solder decreases. That is, the plating layer constituting the shield layer is a copper film, and "melt back" occurs when copper melts from the plating layer into the molten solder. At this time, if the amount of copper that can be dissolved in the molten solder is small, the melting of copper from the plating layer is suppressed, which means that "melt back" is less likely to occur. Therefore, in order to suppress the disappearance of the plating layer, it seems effective to lower the melting point of the solder material. However, lowering the melting point of the solder material means that activation by flux and cleaning of the surface of the plating layer (removal of the oxide film formed on the surface of the plating layer) may become insufficient. means. Therefore, lowering the melting point of the solder material in order to lower its "meltback speed" is not considered appropriate from the perspective of achieving stable bonding between the plating layer and the solder layer. .

Therefore, in this embodiment, in order to obtain a solder material having a lower "meltback speed" than "conventional solder materials", a different approach is adopted instead of lowering the melting point of the solder material. . This alternative approach is based on the following useful insights.

That is, a useful finding for obtaining a solder material having a lower "meltback rate" than "conventional solder materials" is to increase the content of copper in the solder material. This is because increasing the content of copper in the solder material means that the amount of copper already dissolved in the molten solder is large, and as a result, the leaching of copper from the plating layer into the molten solder is suppressed. This is because "meltback" is less likely to occur. Therefore, in order to suppress the disappearance of the plating layer, it can be considered that increasing the copper content in the solder material is effective.

However, increasing the content of copper in the solder material increases the melting point of the solder material. In this case, increasing the content of copper in the solder material causes a decrease in the "meltback rate", and increasing the temperature of the molten solder causes an increase in the "meltback rate". Therefore, it is important to adjust the contradictory phenomena of an increase in the "meltback rate" due to an increase in the temperature of molten solder and a decrease in the "meltback rate" due to an increase in the content of copper in the solder material. It is. In other words, it is important to increase the copper content in the solder material while suppressing an increase in the melting point of the solder material as much as possible. Furthermore, suppressing an increase in the melting point of the solder material is also important from the following viewpoints. For example, since the insulating layer constituting the multicore cable is made of polyethylene resin, if the melting point of the solder material is made too high, the polyethylene resin constituting the insulating layer will deteriorate. Therefore, suppressing the increase in the melting point of the solder material as much as possible is necessary not only from the viewpoint of suppressing an increase in the "meltback rate" but also from the viewpoint of suppressing deterioration of the insulating layer.

In this regard, increasing the silver content of the solder material lowers the melting point of the solder material. Therefore, in this embodiment, while increasing the copper content in the solder material, the silver content in the solder material is also maintained. As a result, according to the present embodiment, it is possible to reduce the "meltback speed" while suppressing the increase in the melting point of the solder material as much as possible. Based on the above, in this embodiment, the composition of the solder material is devised to suppress the disappearance of the plating layer by using a solder material with a lower "meltback speed" than "conventional solder materials". The basic idea is embodied in the approach of increasing the copper content in the solder material while maintaining the silver content in the solder material.

<Effective "solder material" that embodies the basic idea>
In the following, a "solder material" that embodies the basic idea of this embodiment will be explained.

A "solder material" that embodies the basic idea of this embodiment will be referred to as an "effective solder material." The "effective solder material" in this embodiment is used for a multicore cable whose cross section perpendicular to the longitudinal direction is oval. This multi-core cable consists of a shield layer consisting of multiple conductor wires, an insulating layer covering the multiple conductor wires, a plating layer covering the insulating layer, and a solder layer formed on the exposed area of the shield layer. Equipped with. At this time, the "effective solder material" in this embodiment is used when forming the solder layer, and specifically, the "effective solder material" contains tin, silver, and copper. And "effective solder material" in this embodiment
The silver content is 2.5% by mass or more and 3.5% by mass or less, and the copper content is 2.0% by mass or more and 3.0% by mass or less. The "effective solder material" then contains tin and unavoidable impurities as the remainder of the composition. However, the remainder of the composition of the "effective solder material" is not limited to tin and unavoidable impurities, and may contain other materials.

Here, if the copper content in the "effective solder material" is less than 2.0% by mass and the silver content is less than 2.5% by mass, the "meltback rate" increases. , there is a possibility that the plating layer (shield layer) will disappear in the region in the long axis direction of the oval shape. On the other hand, when the content of copper in the "effective solder material" exceeds 3.0% by mass, the melting point of the molten solder becomes high, and deterioration of the polyethylene resin constituting the insulating layer becomes more likely to occur. Furthermore, if the silver content in the "effective solder material" exceeds 3.5% by mass, the manufacturing cost of the multicore cable will increase because silver is expensive. Therefore, (1) suppressing the disappearance of the plating layer by reducing the "meltback speed"; (2) suppressing the increase in the melting point of molten solder and suppressing the deterioration of the polyethylene resin; In order to achieve (3) suppressing the increase in the manufacturing cost of multi-core cables, it is desirable to employ the "effective solder material" in this embodiment. In particular, to give one example, it is desirable that the silver content be 3.0% by mass and the copper content be 2.5% by mass.

The "effective solder material" in this embodiment has great technical significance when used as a material for a solder layer formed on a shield layer made of a plating layer. That is, the shield layer made of a plating layer has a thickness of, for example, about 3 μm, which is very thin. For this reason, for example, if a "conventional solder material" with a high "meltback speed" is used, the disappearance of the shield layer becomes obvious, especially in the region of the shield layer where the "edge effect" becomes obvious. This is because the thickness of the shield layer itself made of a plating layer is very thin.

On the other hand, when the shield layer is composed of a metal foil sheet, the thickness of the metal foil sheet is 10 μm, which is thicker than the plating layer, which is about 3 μm. Disappearance does not become manifest.

When the shield layer is composed of a plated layer in this way, the thickness of the plated layer itself is very thin, so that the disappearance of the shield layer due to "meltback" becomes obvious. Therefore, the "effective solder material" in this embodiment has great technical significance in that it can suppress the disappearance of the shield layer due to "meltback" by applying it when the shield layer is composed of a plating layer. It can be said that it has

FIG. 8 is a schematic diagram showing an example of forming a solder layer 20 on the surface of the shield layer 12 exposed from the oval multicore cable 1 using an "effective solder material."

In FIG. 8, region AR indicates a part of the region in the short axis direction of the oval shape. In the enlarged view of region AR, a shield layer 12 made of a plating layer is formed on the insulating layer 11, and an alloy film 20a is formed between the shield layer 12 and the solder layer 20. In this way, in the region AR that is the region in the short axis direction of the oval shape, the shield layer 12 made of a plating layer remains, and the alloy film 20a is formed between the shield layer 12 and the solder layer 20. As a result, it can be seen that stable bonding between the shield layer 12 and the solder layer 20 is realized. In other words, even if a "conventional solder material" with a high "meltback speed" is used, the "edge effect" does not become apparent in the short axis direction of the oval shape, and as a result, the shield layer 12 consisting of a plating layer Don't "melt back" more than necessary. From this, it is possible to realize highly reliable bonding between the shield layer 12 and the solder layer 20 in the region in the short axis direction of the oval shape.

Next, in FIG. 8, region BR indicates a part of the region in the long axis direction of the oval shape. In the present embodiment, in the enlarged view of region BR, it can be seen that shield layer 12 made of a plating layer formed on insulating layer 11 does not disappear. This is because we use an ``effective solder material'' that has a lower ``meltback speed'' than ``conventional solder materials'', so even if the ``edge effect'' becomes apparent in the long axis direction of the oval shape, This is also because the shield layer 12 made of a plating layer is prevented from being "melted back" more than necessary. As a result, in this embodiment, the alloy film 20a is sufficiently formed even in the region BR, which is the region in the long axis direction of the oval shape, so that stable bonding between the shield layer 12 and the solder layer 20 can be achieved. It can be realized. That is, in this embodiment, by using an "effective solder material" with a small "meltback speed", even if an "edge effect" exists, "melt melt" is prevented in the long axis direction of the oval shape. Since "back" does not progress more than necessary, the plating layer constituting the shield layer 12 is prevented from disappearing. Therefore, according to the present embodiment, it is possible to suppress the occurrence of electrical disconnection or poor connection in the multicore cable 1, and improve the reliability of the multicore cable 1.

Note that, as shown in FIG. 8, according to the present embodiment, the plating layer does not disappear in the region BR, but the thickness of the plating layer in the region BR is smaller than the thickness of the plating layer in the region AR. Become. This is because the "edge effect" is more pronounced in the region BR than in the region AR. However, in the region BR, even if the thickness of the plating layer is thin, the plating layer itself does not disappear, so there is no effect on the reliability of the multicore cable.

<Verification of effectiveness>
Next, an explanation will be given of the effect that proves that the "effective solder material" in this embodiment can suppress the disappearance of the plating layer. Specifically, the solder material used in the preliminary soldering technique has a composition with a tin content of 94.5% by mass, a silver content of 3.0% by mass, and a copper content of 2.5% by mass. It will be explained that "meltback speed" can be appropriately controlled by using "effective solder material".

FIG. 9 is a graph showing the relationship between the immersion time (au: arbitrary unit) for immersing a multicore cable in molten solder and the amount of dissolution of the plating layer (μm). In FIG. 9, the horizontal axis shows the immersion time, and the vertical axis shows the amount of dissolution of the plating layer. Here, before the multicore cable is immersed in molten solder, the thickness of the plating layer constituting the shield layer is 3 μm. When the plating layer is immersed in molten solder, "melt back" occurs, causing the plating layer to melt.

In FIG. 9, graph (1) is a graph showing the relationship between the immersion time and the amount of dissolution of the plating layer when a "conventional solder material" is used. The soldering temperature in graph (1) is 250°C. In graph (1), the solid line indicates the results in the region AR in FIG. 7, for example, while the broken line indicates the results in the region BR in FIG. 7, for example. In graph (1), by setting the immersion time to about "2.5 unit hours", the "meltback amount" (dissolution amount of the plating layer) in the area AR in FIG. 7 becomes about 1.5 μm. On the other hand, in graph (1), by setting the immersion time to about 2.5 unit hours, the "meltback amount" (dissolution amount of the plating layer) in region BR of FIG. 7 is about 2.0 μm. Become. From this, it can be seen that even for the same immersion time, the "meltback amount" of the region BR becomes larger than the "meltback amount" of the region AR due to the "edge effect."

In graph (1), it is necessary to provide a margin for the immersion time in consideration of variations in the immersion time of the multicore cable in the molten solder. At this time, for example, if the immersion time is "3.5 unit hours", the "meltback amount" (dissolution amount of the plating layer) in the area AR is about 2.5 μm, as shown in FIG. On the other hand, the "meltback amount" (the amount of dissolution of the plating layer) in the region BR reaches about 3.0 μm.

This indicates that when the "conventional solder material" is used, the plating layer disappears in the region BR where the "edge effect" becomes apparent. Therefore, it can be seen that when using the "conventional solder material", the plating layer disappears within the dipping time range that takes into account the insertion time difference of the multi-core cable and the work variation.

On the other hand, in FIG. 9, graph (2) is a graph showing the relationship between the immersion time and the amount of dissolution of the plating layer when the "effective solder material" in this embodiment is used. The soldering temperature in graph (2) is 310°C. In graph (2), the solid line indicates the results in the region AR in FIG. 8, for example, while the broken line indicates the results in the region BR in FIG. 8, for example. In graph (2), by setting the immersion time to about 4.5 unit hours, the "meltback amount" (dissolution amount of the plating layer) in the area AR in FIG. 8 becomes about 1.5 μm. On the other hand, in graph (2), by setting the immersion time to about "4.5 unit hours", the "meltback amount" (dissolution amount of the plating layer) in region BR of FIG. 8 is about 1.8 μm. Become. From this, even for the same immersion time, the "meltback amount" of the region BR becomes larger than the "meltback amount" of the region AR due to the "edge effect."

In graph (2), it is necessary to provide a margin for the immersion time in consideration of the insertion time difference of the multi-core cable and work variations. At this time, for example, even if the immersion time is "5.5 unit hours", the "meltback amount" (dissolution amount of the plating layer) in the area AR is about 2.0 μm, as shown in FIG. On the other hand, the "meltback amount" (the amount of dissolution of the plating layer) in the region BR falls within about 2.2 μm.

This means that when the "effective solder material" in this embodiment is used, the disappearance of the plating layer is suppressed even in the region BR where the "edge effect" becomes apparent. Therefore, when using the "effective solder material" in this embodiment, it is possible to effectively suppress the loss of the plating layer even within the dipping time range that takes into account the insertion time difference and work variation of the multi-core cable. Become.

Here, while the conventional soldering temperature is about 250°C, the soldering temperature in this embodiment is about 310°C. In this case, by increasing the soldering temperature, even a multi-core cable whose shield layer is made of a plating layer can be activated with flux in about the same time as normal soldering. On the other hand, the results shown in FIG. 9 confirm that even if the soldering temperature becomes slightly higher, the "meltback speed" can be kept low because a solder material with a high copper content is used. In addition, in normal soldering work, if the soldering work is not performed within about 3 unit hours, the disappearance of the plating layer will become obvious, whereas in this embodiment, the "effective solder material" is used. Therefore, the soldering work can be extended to approximately 5 hours. Therefore, according to this embodiment, it is possible to have a large work margin for soldering work.

The invention made by the present inventor has been specifically explained based on the embodiments thereof, but the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the gist thereof. Needless to say.

1 Multicore cable 10a Conductor wire 10b Conductor wire 11 Insulating layer 12 Shield layer 13 Sheath 20 Solder layer 20a Alloy film 100 Connection area 101 Conductor wire exposed area 102 Shield layer exposed area

Claims (4)

A cable whose cross-sectional shape perpendicular to the longitudinal direction is an oval shape,
multiple conductor wires,
an insulating layer covering the plurality of conductor wires;
a shield layer made of a copper film plating layer covering the insulating layer;
a sheath covering a portion of the shield layer;
a solder layer covering at least a portion of the shield layer exposed from the sheath;
Equipped with
The solder layer is made of a material containing silver and copper, with the remainder being tin and unavoidable impurities,
In the material, the content of silver is 2.5% by mass or more3 . 5% by mass or less, and the copper content is 2.0% by mass or more3 . 0% by mass or less,
an alloy film is provided between the solder layer and the shield layer,
The cable , wherein the plating layer covered with the solder layer does not disappear in the long axis direction of the oval shape. The cable according to claim 1,
The cable wherein the thickness of the plating layer in the long axis direction of the oval shape is smaller than the thickness of the plating layer in the short axis direction of the oval shape. The cable according to claim 1 or 2,
The cable, wherein the plating layer has a thickness of 3 μm or less. The cable according to any one of claims 1 to 3,
The cable is a differential signal transmission cable.

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