JP5181876B2 - Flat cable manufacturing method - Google Patents

Description

  The present invention relates to a flat cable used for an electronic device or the like and a manufacturing method thereof.

  As electronic devices become smaller and lighter, electronic components and wiring components mounted on these devices are becoming smaller. In particular, wiring members for electrical wiring are required to be capable of high-density wiring in a limited space. As such a wiring member, a flat cable is known in which a plurality of rectangular conductors are arranged on a single plane and an insulating film is laminated from both sides of the arrangement surface.

In this flat cable, tin (Sn) plating is applied to a conductor as a film for improving solderability.
However, it is known that a tin-plated conductor generates acicular crystals (whiskers) on the surface of the conductor due to receiving compressive stress for electrical contact with the connector terminals. In particular, in a flat cable in which the distance between conductors is extremely narrow, this whisker may cause a short circuit.

  In order to prevent such a short circuit due to whiskers, the conductive substrate contains 0.1 to 15% by weight of at least one of bismuth (Bi), copper (Cu), silver (Ag), and zinc (Zn). It is known that a tin alloy plating is formed, and a zinc plating, silver plating, tin-zinc alloy plating, tin-silver alloy plating or tin-bismuth alloy plating is formed on the upper layer, and heat treatment such as energization annealing is performed. (For example, refer to Patent Document 1).

JP 2007-46150 A

  However, under the above processing conditions, it is difficult to sufficiently suppress the generation of whiskers. In particular, if the heat treatment temperature is not appropriate, even if whisker generation is suppressed, the contact resistance increases and the cause of poor conduction with the connector. End up.

  An object of the present invention is to provide a flat cable in which generation of whiskers is sufficiently suppressed and an increase in contact resistance is also suppressed, and a manufacturing method for manufacturing the flat cable.

The flat cable according to the present invention that can solve the above problems is a flat cable in which a plurality of conductors arranged in parallel are covered with an insulator,
The conductor is formed by forming an alloy layer made of an alloy containing bismuth and zinc in tin on the surface of a base material made of copper or a copper alloy,
The alloy layer contains 1.0% by weight to 4.0% by weight of bismuth and 0.2% by weight to 2.0% by weight of zinc with respect to tin, and has a thickness of 0.3 μm to 0%. .9 μm or less.

The flat cable manufacturing method according to the present invention is a flat cable manufacturing method in which a plurality of conductors arranged in parallel are covered with an insulator,
A first plating layer in which 1.0 wt% or more and 4.0 wt% or less of bismuth is contained in tin on the surface of a base material made of copper or a copper alloy constituting the conductor; A surface treatment step of forming a second plating layer containing 0.0 wt% or less of zinc in tin so that the total thickness is 0.3 μm or more and 0.9 μm or less;
A heat treatment step of heating the conductor at a temperature of 270 ° C. or higher and 290 ° C. or lower;
A cable forming step of arranging a plurality of the conductors in parallel and covering them with an insulator is performed.

  Moreover, it is preferable that the said heat processing process passes the said conductor in a high temperature atmosphere (270 degreeC or more and 290 degrees C or less), and heats it.

  According to the flat cable of the present invention, the alloy layer made of an alloy in which bismuth and zinc are contained in the aforementioned amounts in tin has a conductor formed on the surface of the base material made of copper or a copper alloy, and the alloy layer Since the material and thickness are set as described above, the generation of whiskers can be sufficiently suppressed, and the increase in contact resistance can be reliably suppressed.

  Moreover, according to the flat cable manufacturing method of the present invention, the first plating layer in which 1.0 wt% or more and 4.0 wt% or less of bismuth is contained in tin on the surface of the base material made of copper or copper alloy. And a second plating layer in which 0.2 wt% or more and 2.0 wt% or less of zinc is contained in tin, a conductor formed so that the total thickness becomes 0.3 μm or more and 0.9 μm or less By heating at 270 ° C. or more and 290 ° C. or less, the first plating layer and the second plating layer can be integrated to form an alloy layer in which the alloy amount of tin and copper is an appropriate amount. Thereby, generation | occurrence | production of a whisker can fully be suppressed, and also the increase in contact resistance can be suppressed reliably, and also the improvement effect of favorable solderability can be acquired.

Hereinafter, an example of an embodiment of a flat cable and a method for manufacturing the same according to the present invention will be described with reference to the drawings.
1 is a plan view showing a flat cable according to the present invention, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, FIG. 3 is a side view of a conductor exposed portion at the end of the flat cable, and FIG. It is sectional drawing.
As shown in FIGS. 1 and 2, the flat cable 1 includes a plurality of (10 in the present embodiment) flat conductors (conductors) 2 arranged on a plane at a predetermined parallel pitch. An insulating film (insulator) 3 is stuck (laminated) on each of the two surfaces. Note that the insulator covering the flat conductor 2 may be formed by extruding an insulating resin instead of a film.

  The insulating film 3 includes an insulating resin layer 4 and an insulating adhesive layer 5. For example, the insulating resin layer 4 is a resin such as polyester, polyimide, or PPS, and the insulating adhesive layer 5 is a polyester adhesive or flame retardant. PVC. Two insulating films 3 are bonded to the flat conductor 2 with the surface of the insulating adhesive layer 5 facing the flat conductor 2. Thus, electrical insulation between the rectangular conductors 2 is achieved.

The both ends in the longitudinal direction of the flat cable 1 are conductor exposed portions 6 in which the insulating film 3 is stuck only on one surface and a plurality of flat conductors 2 are exposed on the other surface. It functions as a connection terminal that can be connected to the elastic contact piece.
As shown in FIG. 3, a terminal reinforcing tape 7 made of an insulating resin such as polyester is attached to the surface of the conductor exposed portion 6 on the side where the flat conductor 2 is not exposed. Supports to prevent deformation.

  In this embodiment, the thickness of the flat conductor 2 is 35 μm or more and 50 μm or less, the width dimension is about 0.3 mm, and the parallel pitch of the ten flat conductors 2 is about 0.5 mm. As shown in FIG. 4, the flat conductor 2 has a structure in which an alloy layer 12 is laminated on a base material 11 having a rectangular cross section. In the present embodiment, the alloy layer 12 is formed on the entire outer periphery of the substrate 11. As the substrate 11, copper (Cu), silver (Ag) -copper (Cu) alloy, tin (Sn) -copper (Cu) alloy, or the like is used.

The alloy layer 12 around the substrate 11 is made of an alloy in which bismuth (Bi) and zinc (Zn) are contained in tin (Sn).
The material of the alloy layer 12 contains 1.0% by weight to 4.0% by weight of bismuth and 0.2% by weight to 2.0% by weight of zinc with respect to tin. The thickness of the alloy layer 12 is not less than 0.3 μm and not more than 0.9 μm.

The thickness of the alloy layer 12 is related to the parallel pitch of the flat conductors 2. In the above example, since the parallel pitch of the rectangular conductors 2 is 0.5 mm and the width of the rectangular conductors 2 is 0.3 mm, the interval between the rectangular conductors 2 is 0.2 mm. This in order to suppress sufficiently a short circuit between the conductors by tin whiskers when has to do with 0.9μm hereinafter the alloy layer 12 containing tin. On the other hand, the effect of tin plating cannot be exhibited unless the alloy layer 12 containing tin is 0.3 μm or more.
When the parallel pitch of the flat conductors 2 is 0.3 mm, the distance between the flat conductors 2 is shortened, so that a short circuit due to a tin whisker does not occur, and the allowable whisker length is further shortened. On the other hand, since the width of the flat conductor 2 is reduced, the amount of tin contained in the alloy layer 12 around the flat conductor 2 is reduced. Accordingly, whisker elongation is reduced. Therefore, even when the parallel pitch of the rectangular conductors 2 is 0.3 mm, the thickness of the alloy layer 12 is set in the range of 0.3 μm to 0.9 μm while exhibiting the effect of tin plating. The short circuit between the rectangular conductors 2 due to the whisker can be sufficiently suppressed.

Next, the case where the above flat cable 1 is manufactured will be described.
FIG. 5 is a cross-sectional view of a rectangular conductor treated in the surface treatment process, FIG. 6 is a perspective view showing a heat treatment process, and FIG. 7 is a perspective view showing a cable forming process.
As shown in FIG. 5, first, a plating process is performed around the base material 11 constituting the flat conductor 2 (surface treatment process).
Specifically, the first plating layer 21 is formed by plating a surface of the base material 11 with a tin-bismuth alloy, and the second plating is further performed by plating the surface with a tin-zinc alloy. Layer 22 is formed.

The first plating layer 21 is 1.0 wt% or more and 4.0 wt% or less of bismuth with respect to tin, and the second plating layer 22 is 0.2 wt% or more and 2.0 wt% of zinc with respect to tin. % Or less.
The total thickness of the first plating layer 21 and the second plating layer 22 is 0.3 μm or more and 0.9 μm or less. In the present embodiment, the thicknesses of the first plating layer 21 and the second plating layer 22 are each 0.3 μm, and the total thickness is 0.6 μm.

Next, heat treatment is performed on the flat conductor 2 in which the first plating layer 21 and the second plating layer 22 are formed on the surface of the base material 11 (heat treatment step).
As shown in FIG. 6, a heating device 31 is used to heat-treat the flat conductor 2. The heating device 31 is obtained by winding a Kanthal wire 33 around a heating pipe 32 made of a stainless material and having a length of about 8 m. By supplying power to the Kanthal wire 33, the heating pipe 31 is heated. A high-temperature atmosphere is generated in 32. The temperature of the high-temperature atmosphere in the heating pipe 32 is 270 ° C. or higher and 290 ° C. or lower.

Then, the rectangular conductor 2 on which the first plating layer 21 and the second plating layer 22 are formed is passed through the heating pipe 32 of the heating device 31 at a linear velocity of about 160 m / min. In this way, the flat conductor 2 is heated by the high temperature atmosphere of the heating device 31 for about 3 seconds. Thereby, the 1st plating layer 21 and the 2nd plating layer 22 are united by diffusion of tin by heat treatment, and become the alloy layer 12 made of an alloy containing bismuth and zinc in tin.
In addition, the heating temperature with respect to the flat conductor 2 can be equalize | homogenized in the circumferential direction of a cross section by producing a high temperature atmosphere with the cylindrical heating pipe 32, and allowing the flat conductor 2 to pass through the center.

  Here, if the temperature of the heat treatment is too high (over 290 ° C.), the alloy amount of tin and copper in the alloy layer 12 increases and the contact resistance increases (for example, the contact resistance becomes 50 mΩ or more). ). If the heat treatment temperature is too low (below 270 ° C.), the amount of tin-copper alloy is reduced, whisker generation cannot be sufficiently suppressed, and the effect of improving solderability is reduced. This will affect the soldering at the exposed portion 6.

  On the other hand, in this embodiment, in the heat treatment step, the temperature of the high-temperature atmosphere through which the flat conductor 2 is passed is set to 270 ° C. or more and 290 ° C. or less, so that the alloy amount of tin and copper in the alloy layer 12 is appropriate. The amount can be made small. Thereby, it is possible to obtain the flat conductor 2 in which the generation of whiskers is sufficiently suppressed and the increase in contact resistance is suppressed, and a good soldering improvement effect can be obtained. The time for which the flat conductor 2 passes through the heating pipe 32, that is, the heating time is several seconds. In the present invention, the heating temperature affects the suppression of whisker and the increase of contact resistance rather than the heating time.

  Next, as shown in FIG. 7, the rectangular conductors 2 are fed from a plurality of reels 41 around which the heat-treated rectangular conductors 2 are wound up, arranged on the same plane at a predetermined parallel pitch, and arranged rectangular conductors. 2, the long insulating film 3 is sent out from the reel 42, passed between the heater rollers 43, and taken up on the take-up roller 44 (cable forming step).

  The insulating film 3 has its insulating adhesive layer 5 side facing the flat conductor 2 side. Thereby, the insulating adhesive layer 5 of the insulating film 3 is melted by passing between the heater rollers 43, and the insulating film 3 is formed on the plurality of flat conductors 2 arranged on the plane from above and below the arrangement surface. A series of long flat cables 1 are formed which are bonded together by the insulating adhesive layer 5 and the rectangular conductors 2 are arranged on a plane and covered with an insulator (insulating resin layer 4 and insulating adhesive layer 5). . The heater roller 43 may have a mechanism in which a heater portion for heating the insulating film 3 and a roller portion for pressing the insulating film 3 are separate mechanisms.

  In the cable forming process, instead of attaching the insulating film 3, an insulating resin may be extruded and covered around the flat conductor 2.

  In order to provide the conductor exposed portion 6 shown in FIG. 1 on one insulating film 3, it is preferable to form a window portion opened in a part in the longitudinal direction. A window part is provided in the location used as the edge part of the flat cable 1 in the longitudinal direction. Moreover, the excess part (part called an ear | edge) of the width direction of the insulating film 3 is cut | disconnected and removed. Thereby, the location where the insulating film 3 was connected to the longitudinal direction by the width direction both ends of a window part is removed. After that, the long flat cable is cut at the window portion to form the flat cable 1 for each predetermined length.

  In the flat cable 1 manufactured in this manner, a connector is fitted to the conductor exposed portion 6 and, after 1000 hours, the presence or absence of whiskers longer than 50 μm is observed. Not confirmed.

As described above, according to the flat cable 1 of the present embodiment, the flat conductor 2 has the alloy layer 12 on the surface of the base material 11 made of copper or a copper alloy, and the alloy layer 12 is made of tin. On the other hand, it contains 1.0 to 4.0% by weight of bismuth and 0.2 to 2.0% by weight of zinc.
When the thickness of the flat conductor 2 is 35 μm to 50 μm, the width of the flat conductor 2 is 0.15 mm to 0.3 mm, and the thickness of the alloy layer 12 is 0.3 μm to 0.9 μm, the tin whisker is In order to suppress the occurrence, it is necessary to add bismuth and zinc to the tin plating layer by 1.0 wt% or more and 0.2 wt% or more, respectively. The addition of only one could not sufficiently suppress the generation of tin whiskers, and even if the addition amount of either one was less than the above amount, the generation of tin whiskers could not be sufficiently suppressed.

  As described above, by performing heat treatment at a temperature of 270 ° C. or more and 290 ° C. or less, the copper in the base material 11 moves to the plating layer, and a quaternary alloy of tin, copper, bismuth, and zinc is formed. It is considered that bismuth and zinc are contained in combination at the above concentrations, and an alloy structure in which the generation of tin whiskers is sufficiently suppressed is obtained. Here, when the bismuth or zinc contained in the alloy layer exceeds 4.0% by weight and 2.0% by weight, respectively, even if the heat treatment temperature of the flat conductor 2 is 270 ° C. or more and 290 ° C. or less, the contact resistance increases and 50 mΩ. The following contact resistance was difficult. Therefore, in order not to cause the problem of contact resistance, the addition amounts of bismuth and zinc must be 4.0% by weight or less and 2.0% by weight or less, respectively.

  When the tin on the surface of the flat conductor 2 is increased, whiskers are likely to be generated. However, if the thickness of the tin layer (alloy layer 12) is too thin, solderability is deteriorated. In the flat conductor 2 of the flat cable 1, since the thickness of the alloy layer 12 is 0.3 μm or more and 0.9 μm or less, the occurrence of whiskers can be sufficiently suppressed, and the solderability is also good.

  Further, according to the above flat cable manufacturing method, the first plating layer in which 1.0 wt% or more and 4.0 wt% or less of bismuth is contained in tin on the surface of the base material 11 made of copper or a copper alloy. 21 and the second plating layer 22 containing 0.2 wt% or more and 2.0 wt% or less of zinc in tin are formed so that the total thickness becomes 0.3 μm or more and 0.9 μm or less. By heating the flat conductor 2 at a temperature of 270 ° C. or more and 290 ° C. or less, the alloy layer 12 in which the first plating layer 21 and the second plating layer 22 are integrated can be obtained. In the alloy layer 12, the alloy amount of tin and copper is set to an appropriate amount, thereby sufficiently suppressing the generation of whiskers and obtaining an effect of improving the solderability, and further having a contact resistance of 50 mΩ. It can be as follows. Therefore, it is possible to manufacture the flat cable 1 in which the generation of whiskers is sufficiently suppressed and the contact resistance is also well suppressed.

  In addition, since the flat conductor 2 is heated at a predetermined linear velocity in a high temperature atmosphere of 270 ° C. or more and 290 ° C. or less formed in the heating pipe 32 of the heating device 31, the productivity is increased. Can be improved.

It is a top view which shows the example of embodiment of the flat cable which concerns on this invention. It is arrow AA sectional drawing of FIG. It is a side view of the conductor exposure part in the edge part of the flat cable of FIG. It is sectional drawing of the conductor contained in the flat cable of FIG. It is sectional drawing of the conductor processed at the surface treatment process. It is a perspective view which shows the example of a heat processing process. It is a perspective view which shows the example of a cable formation process.

Explanation of symbols

1: flat cable, 2: flat conductor (conductor), 3: insulating film (insulator), 11: base material, 12: alloy layer, 21: first plating layer, 22: second plating layer

Claims (2)

A method of manufacturing a flat cable in which a plurality of conductors arranged in parallel are covered with an insulator,
The conductor is a rectangular conductor having a thickness of 35 μm or more and 50 μm or less and a width of 0.15 mm or more and 0.3 mm or less,
A first plating layer in which 1.0 wt% or more and 4.0 wt% or less of bismuth is contained in tin on the surface of a base material made of copper or a copper alloy constituting the conductor; A surface treatment step of forming a second plating layer containing 0.0 wt% or less of zinc in tin so that the total thickness is 0.3 μm or more and 0.9 μm or less;
A heat treatment step of heating the conductor at a temperature of 270 ° C. or higher and 290 ° C. or lower;
A flat cable manufacturing method comprising: performing a cable forming step in which a plurality of conductors are arranged in parallel and covered with an insulator. It is a manufacturing method of the flat cable according to claim 1 ,
The said heat processing process passes the said conductor in the high temperature atmosphere of 270 degreeC or more and 290 degrees C or less, and heats it, The manufacturing method of the flat cable characterized by the above-mentioned.

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