JP2007123209A - Method of manufacturing flexible flat cable and conductor for flexible flat cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain generation of whiskers on the surface of a conductor of a flexible flat cable surely and to a large extent. <P>SOLUTION: The flexible flat cable has an alloy layer 11 of Cu<SB>3</SB>Sn<SB>1</SB>(a copper-tin system) on a base material 10 of Cu (copper), as well as a conductor with an alloy layer 12 of Cu<SB>6</SB>Sn<SB>5</SB>(a copper-tin system) formed on the above alloy layer 11. With this, a hardness of the surface of the conductor is heightened to have its stress deformation alleviated, and generation of whiskers on the surface of the conductor is surely restrained to a large extent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a flexible flat cable and a conductor for a flexible flat cable, and particularly relates to a measure for suppressing the occurrence of whiskers (needle-like single crystals).

  Conventionally, a flexible flat cable (hereinafter referred to as FFC) has been used as an internal wiring material for various electronic devices such as various external storage devices (CD-ROM drive, DVD-ROM drive, etc.) such as digital cameras, printers, mobile phones, and personal computers. It is used.

  The FFC is used for connection between printed circuit boards of the electronic devices. Specifically, for example, conductors (wires) exposed at both ends of the FFC are inserted into terminal portions (contacts) of a fitting type connector attached to a printed circuit board, and then the lock mechanism portion of the connector is closed. The tip part (contact part) of the terminal part of the connector contacts the FFC conductor.

  Conventionally, the terminal portion of the connector and the conductor of the FFC have been subjected to metal plating, for example, tin-lead alloy (Sn—Pb) plating, in order to improve connection performance. However, in recent years, tin (Sn) plating is applied to the terminal portion of the connector and the conductor of the FFC as the demand for Pb-free (lead-free) increases due to environmental problems. It has become.

  However, with this Pb-free (lead-free), whisker (needle-shaped single crystal) may be generated in the terminal portion of the connector when the FFC conductor is in contact with the terminal portion of the connector. In other words, Pb-free has caused whisker generation. Whisker is a beard-like crystal product generated on the surface of the plating film, and causes a short circuit between conductors.

  As measures to suppress the occurrence of this whisker, connector manufacturers have adopted various measures such as reflow, bismuth (Sn-Bi) plating, silver (Ag) plating, and tin-copper (Sn-Cu) plating on the connector terminal. Treated.

  Thereby, although the terminal part surface of the connector became hard (hardness became high) and whisker generation | occurrence | production on the connector side came to be suppressed, whisker came to generate | occur | produce from the FFC side.

  This is because the surface of the FFC conductor subjected to Sn plating is softer than the surface of the terminal portion of the connector subjected to various countermeasures as a countermeasure against whisker generation (because the hardness is small). It is considered that a compressive stress from the terminal portion of the connector is applied to the layer, and whiskers are generated due to “deformation and swelling” of the Sn plating layer of the FFC conductor. There is a need for measures to suppress the occurrence of whiskers on the FFC side.

  In addition, as what gave the countermeasure which suppresses generation | occurrence | production of a whisker, although described in patent document 1, FFC and its manufacturing method are known.

In Patent Document 1, tin alloy plating is performed on a rolled conductor material, the tin alloy plated conductor material is heated to about 200 ° C., and the heat-treated tin alloy plated conductor material is further disclosed. By performing the heat treatment by annealing up to about 180 to 250 ° C., the crystal particles on the surface of the tin alloy plating are formed on the processed material after the processing, that is, the plating conductor unit composed of a plurality of conductors and insulating materials. It is disclosed that it becomes finer and suppresses the generation of whiskers.
Japanese Patent No. 3675471

  However, although Patent Document 1 describes that a second heat treatment is performed by annealing up to a maximum of about 250 ° C. with respect to a plated conductor portion unit having a tin alloy-plated conductive wire material (conductor). The plating thickness of the alloy plating is not described or suggested.

  Therefore, in the thing of patent document 1, it is thought that the plating thickness of a tin alloy plating is 1.5 micrometers or more which is a common thickness for those skilled in the art.

  For example, even if the second heat treatment is performed on the plating conductor unit having the tin alloy plating conductor material (conductor) on which the tin alloy plating with a plating thickness of 1.5 μm is applied, the tin alloy plating layer is 1 Since the thickness is 5 μm, the hardness of the conductor surface does not increase. That is, the hardness of the conductor surface does not increase.

  Therefore, when the FFC is fitted to the connector, the contact portion (fitting portion) with the connector terminal portion of the tin alloy plated conductor material (conductor) constituting the plated conductor portion unit is compressed from the connector terminal portion. When stress is applied, “deformation or bulge” occurs in the tin alloy plating layer, that is, a dislocation phenomenon occurs due to the influence of the stress, thereby generating whiskers.

  In other words, Patent Literature 1 has a problem that whisker generation on the FFC side cannot be reliably suppressed.

  Then, an object of this invention is to provide the flexible flat cable and the conductor for flexible flat cables which can suppress generation | occurrence | production of the whisker on the conductor surface reliably and significantly.

In order to solve the above-described problem, the flexible flat cable according to the first aspect of the present invention has a Cu ₃ Sn ₁ (copper-tin-based) alloy layer formed on a substrate made of Cu (copper). And a conductor having a Cu ₆ Sn ₅ (copper-tin-based) alloy layer formed on the alloy layer.

  As a result, the conductor in which two alloy layers (copper-tin alloy layer) are formed on the base material has a high hardness on the conductor surface, so that stress deformation on the conductor surface is reduced. The generation of whiskers on the conductor surface can be reliably and greatly suppressed.

In order to solve the above problems, the method for producing a flexible flat cable conductor of the present invention according to claim 2 is a method for producing a conductor used in the flexible flat cable according to claim 1, and is Cu (copper). A first step of performing annealing treatment at a first temperature on the base material on which Sn (tin) plating has been performed around the base material formed in step 1, and the base material subjected to the annealing treatment. An alloy layer of Cu ₃ Sn ₁ (copper-tin) is formed on the material, and annealing is performed at a second temperature so that an alloy layer of Cu ₆ Sn ₅ (copper-tin) is formed on the alloy layer. And a second step of performing processing.

As described above, the Cu ₃ Sn ₁ alloy layer and the Cu ₆ are formed from the lower part of the Sn plating because the conductor is subjected to the annealing process of the first process and the annealing process of the second process twice. The Sn ₅ alloy layer is diffused and generated, that is, the Cu ₃ Sn ₁ alloy layer is formed on the base material, and the Cu ₆ Sn ₅ alloy layer is further diffused and generated on the alloy layer. Since the surface hardness is increased, stress deformation on the conductor surface can be reduced. In addition, the Cu ₃ Sn ₁ alloy layer and the Cu ₆ Sn ₅ alloy layer are diffused and generated due to the two annealing processes performed on the conductor in this way, so that the Sn plating, that is, the Sn layer thin film Therefore, the hardness of the conductor surface is further increased, and the stress deformation of the conductor surface can be further reduced. In addition, since Sn grows and the crystals are large and the conductor surface becomes uniform, stress deformation on the conductor surface can be reduced. In this way, due to the annealing process being performed twice on the conductor, the hardness of the conductor surface is increased by the two alloy layers formed by diffusion, and the hardness of the conductor surface is reduced by thinning the Sn layer. Further, since the crystal is large and the conductor surface becomes uniform due to the growth of Sn crystal grains, the stress deformation of the conductor surface is reduced, and the occurrence of whiskers on the conductor surface can be surely and greatly suppressed.

  According to a third aspect of the present invention, in addition to the structure of the second aspect of the present invention, the Sn (tin) plating has a plating thickness of 0.7 μm.

As described above, the Cu ₃ Sn ₁ alloy layer and the Cu ₆ Sn ₅ alloy layer are diffused and generated due to the two annealing processes performed on the conductor, and the two alloy layers are diffused and generated. Thus, when Sn plating with a plating thickness of 0.7 μm is thinned, that is, when the Sn layer is thinned, the Sn layer has a thickness of less than 0.7 μm. As a result, the stress deformation on the conductor surface can be further reduced, and the occurrence of whiskers on the conductor surface can be reliably and greatly suppressed.

  According to the present invention, the conductor in which the two alloy layers (copper-tin alloy layer) are formed on the base material has a high hardness on the conductor surface, so that the stress deformation on the conductor surface. Is reduced, and an effective effect that the generation of whiskers on the conductor surface can be surely and greatly suppressed is obtained.

Further, according to the present invention, the Cu ₃ Sn ₁ alloy layer and the Cu ₆ Sn ₅ alloy layer are diffused and generated due to the annealing process being performed twice on the conductor. In addition, since the two alloy layers are diffused and produced, Sn plating thinning, that is, Sn layer thinning progresses, and the hardness of the conductor surface further increases. The stress deformation can be reduced, and an effective effect that the generation of whiskers on the conductor surface can be surely and greatly suppressed is obtained.

  Hereinafter, the best mode for carrying out the present invention will be described more specifically with reference to the drawings. Here, in the accompanying drawings, the same reference numerals are given to the same members, and duplicate descriptions are omitted. In addition, since description here is the best form by which this invention is implemented, this invention is not limited to the said form.

  (Embodiment)

  FIG. 1 is a diagram illustrating an FFC conductor according to the present invention, FIG. 2 is a process diagram illustrating a manufacturing procedure of the FFC conductor according to the present invention, FIG. 3 is a diagram illustrating FFC according to the present embodiment, and FIG. FIG. 5 is a diagram showing a photograph of a result of observing a cross section of the FFC conductor according to the present invention with a transmission electron microscope, FIG. 5 is a diagram showing a photograph of a result of observing the surface of the FFC conductor according to the present invention with an electron microscope, FIG. 6 is a diagram showing a photograph of the result of observing a cross section of the FFC conductor of the comparative example with a transmission electron microscope, FIG. 7 is a diagram showing a photograph of the result of observing the surface of the FFC conductor of the comparative example with an electron microscope, FIG. 8 is a diagram showing a photograph of the result of observing the contact portion (fitting portion) of the FFC conductor after fitting the FFC having the FFC conductor according to the present invention with a predetermined connector, using a metal microscope. 9 is F which has the conductor for FFC of a comparative example. The figure which shows the photograph of the result of having observed the contact part (fitting part) of the said FFC conductor after fitting C with the predetermined | prescribed connector with a metal microscope, FIG. 10: FFC which has the FFC conductor which concerns on this invention The figure explaining suppression of the whisker in the contact part (fitting part) at the time of fitting this to a predetermined connector, FIG. 11 is a contact part (fitting when FFC having a conventional FFC conductor is fitted to a predetermined connector ( It is a figure explaining generation | occurrence | production of the whisker in a fitting part.

  A conductor (conductive wire) used in a flexible flat cable (FFC) according to an embodiment of the present invention will be described with reference to FIG.

  1A is a perspective view showing an outline of a conductor (hereinafter referred to as an FFC conductor) 1 used for FFC, and FIG. 1B is an enlarged cross-sectional view of a main part A of FIG. It is.

As shown in FIG. 1A, the FFC conductor 1 has a base material (flat conductor) 10 formed of a flat soft copper wire (Cu) material, and as shown in FIG. 1B. In addition, a Cu ₃ Sn ₁ (copper-tin) first alloy layer 11 is formed on a Cu (copper) base material (flat rectangular conductor) 10, and Cu ₁ Cu is formed on the first alloy layer 11. _A second alloy layer 12 of ₆ Sn ₅ (copper-tin) is formed, and a surface layer 13 of pure Sn (tin) is further formed on the second alloy layer 12.

  In the present embodiment, the total thickness D of the first alloy layer 11, the second alloy layer 12, and the surface layer 13 is set to 0.7 μm. This thickness D 0.7 μm corresponds to the plating thickness (0.7 μm) of the Sn plating film described later.

  A method for manufacturing the FFC conductor 1 will be described with reference to FIG. FIG. 2 is a process diagram showing a procedure for manufacturing the FFC conductor 1.

  First, an Sn (tin) plating film having a predetermined plating thickness is formed by electroplating around a wire made of Cu (copper) (step S10). Here, the plating thickness of the Sn plating film is set to 0.7 μm, and is managed by the Kocourt method (electrolytic plating film thickness measurement).

  In the present embodiment, the plating thickness of the Sn plating film is set to 0.7 μm for the following reason. That is, if the plating thickness is selected based on whisker suppression, the case where the plating thickness is thin is more advantageous than the case where the plating thickness is thick, and specifically, 0.5 μm or less is desirable. On the other hand, if the plating thickness is selected based on the fitting characteristics (contact reliability) with the connector, the case where the plating thickness is thicker is more advantageous than the case where the plating thickness is thin, and more specifically, more than 0.5 μm is desirable. Therefore, in the present embodiment, both the whisker suppression and the contact reliability are considered (particularly, contact reliability is considered) and the plating thickness tolerance is taken into consideration, so that the Sn plating plating thickness is set to 0.7 μm. I have to.

  In this specification, Sn plating includes pure Sn plating and alloy containing Sn (Sn alloy) plating. However, in the following description, the Sn plating is pure Sn plating.

  The Cu wire rod having a plating thickness of 0.7 μm and subjected to pure Sn plating is subjected to a rolling process (rolling process) (step S20) to form a flat conductor, that is, the base material 10.

  Next, the base material (flat conductor) 10 is subjected to an annealing process (first annealing process) at a first temperature (step S30). In this first annealing treatment, the base material 10 is heated at a temperature of 400 to 500 ° C. for a time of 0.1 to 0.3 sec (seconds), and after this heating time is completed, the base material 10 is submerged in water. Cool quickly by cooling. By performing such an annealing treatment, the hardened copper wire that is the base of the base material can be softened to form the base material (flat conductor) 10 formed of a flat soft copper wire material.

Then, with respect to the substrate 10 to first annealing process is performed, as shown in FIG. 1 (b), _Cu 3 Sn ₁ on the substrate 10 - first alloy layer (copper-tin-based) 11 Is formed at the second temperature so that a second alloy layer 12 of Cu ₆ Sn ₅ (copper-tin) is formed on the first alloy layer 11 (second annealing treatment). Is performed (step S40).

  In this second annealing treatment, the base material 10 is heated at a temperature of 270 to 280 ° C. for a time of 5 to 10 sec (seconds), and after this heating time is finished, the base material 10 is naturally cooled, for example, by slow cooling. To do.

  In the present embodiment, the second annealing treatment is performed based on a temperature of 270 to 280 ° C. and a time of 5 to 10 sec. However, these heating temperature and heating time are merely examples, and the first It is possible to employ a heating temperature and a heating time that satisfy the conditions under which the first alloy layer 11 and the second alloy layer 12 are produced by diffusion. For example, it is possible to set the heating temperature to 260 ° C. and the heating time to 20 seconds.

  As described above, in the present embodiment, the Cu (copper) base material, that is, the conductor subjected to Sn (tin) plating, is subjected to the annealing process in the first step (step S30) and the second step. Two annealing processes of annealing process (step S40) will be performed.

Thus, due to the annealing treatment twice to the substrate 10 is performed, the first alloy layer 11 in FIG. 1 as shown in (b), Cu ₃ Sn ₁ from pure Sn plating lower And a second alloy layer 12 of Cu ₆ Sn ₅ are diffused and generated, that is, a first alloy layer (Cu ₃ Sn ₁ ) is generated on the substrate 10, and further, a first alloy layer 11 is formed on the first alloy layer 11. Two alloy layers (Cu ₆ Sn ₅ ) are produced by diffusion. Therefore, the surface hardness of the FFC conductor 1 is increased by the two alloy layers 11 and 12, and stress deformation of the surface (conductor surface) of the FFC conductor 1 can be reduced.

  Further, as described above, the two alloy layers 11 and 12 are diffused and produced, whereby the thin Sn plating film (Sn layer) is made thinner, and the surface layer 13 is formed. Therefore, the thin Sn plating film, that is, the surface layer 13 that is thinned increases the surface hardness of the FFC conductor 1 and can further reduce stress deformation on the surface (conductor surface) of the FFC conductor 1.

  Further, pure Sn grows and the Sn crystal grows, and the conductor surface of the FFC conductor 1, that is, the surface of the surface layer 13 becomes uniform. Therefore, the stress deformation of the surface (conductor surface) of the FFC conductor 1 is reduced. Can be reduced.

  As described above, in the present embodiment, the surface of the FFC conductor 1 is formed by the two alloy layers 11 and 12 that are diffusion-generated due to the annealing process being performed twice on the base material 10. The hardness of the pure Sn plating film (Sn layer), that is, the surface of the surface layer 13 (the surface of the FFC conductor 1) is increased and the pure Sn grows in crystal grains and the crystals become large. By making the surface of the FFC conductor 1 uniform, stress deformation on the conductor surface of the FFC conductor 1 is reduced, and the occurrence of whiskers on the conductor surface can be reliably and greatly suppressed.

  Next, the FFC according to the embodiment of the present invention will be described with reference to FIG. 3A is a plan view of a single-sided conductor exposed type FFC, and FIG. 3B is a cross-sectional view taken along line BB in FIG. 3A.

  3A and 3B, the FFC includes a plurality of conductors 1, an insulating sheet (insulator) 2 that covers each of the conductors 1, and a reinforcing tape 3.

  The plurality of conductors 1 are conductors manufactured (manufactured) by the manufacturing procedure shown in FIG. 2, set to a size of a predetermined length L, and arranged in parallel at a predetermined interval.

  The two insulating sheets (insulators) 2 are set to a length (L-2d) so that each conductor 1 is exposed by a predetermined length d from both ends of a plurality of conductors 1 having a predetermined length. Yes.

  A plurality of conductors 1 are interposed between the two insulating sheets 2 such that the conductors are exposed by a predetermined length d from both ends, and the two insulating sheets 2 are heat-fused to be integrated. Made it. That is, in the plurality of conductors 1, portions other than the conductor having a predetermined length d are covered with the front and back insulating sheets 2. An example of the insulating sheet 4 is a polyester resin.

  The conductor 1 is exposed on the surface (one surface) side of both ends of the FFC. The back surface (the other surface) of both ends of the FFC is covered with the reinforcing tape 3 with the reinforcing tape 4 attached. That is, in this FFC, a conductor exposed portion is provided only on one side of both end portions.

  1: Conductor for FFC according to the embodiment

  In this embodiment, the plating material = pure Sn, the plating thickness = 0.7 μm (Coolour method), the plating method = electroplating, and the first annealing treatment, the heating temperature = 400 to 500 ° C., the heating time = 0.1 In the second annealing process, 0.3 sec, cooling method = rapid cooling, heating temperature = 270-280 ° C., heating time = 5-10 sec, cooling method = slow cooling, and shown in FIG. The conductor (FFC conductor 1) was manufactured according to the steps of the manufacturing procedure of the conductor. The surface hardness of the FFC conductor 1 according to this example was 100 or more, and most of the surface hardness was 150 to 230 at which a whisker suppressing effect was obtained.

  A cross section of the conductor thus produced was photographed at a magnification of 21000 using a transmission electron microscope. A photograph as a result of the photographing is shown in FIG. Moreover, it is the same photograph as the photograph content shown to Fig.4 (a), Comprising: The mode which expressed the range of the said each alloy layer and Sn (tin) layer (surface layer) with respect to the photograph of Fig.4 (a) clearly Is shown in FIG.

As shown in FIGS. 4A and 4B, a first alloy layer 11 of Cu ₃ Sn ₁ is formed on a base material (Cu) 10, and Cu ₆ Sn ₅ is formed on the first alloy layer 11. The second alloy layer 12 is formed. Further, an Sn layer, that is, a surface layer 13 is formed on the second alloy layer 12. The structure shown in FIGS. 4A and 4B corresponds to the cross-sectional structure of the conductor shown in FIG.

4 (a) and 4 (b), the surface layer 13 as the Sn layer is not necessarily formed uniformly on the surface. As shown in FIG. In FIG. ₅ , it can be seen that the Sn layer does not exist and the surface of the second alloy layer 12 of Cu ₆ Sn ₅ exists.

This is because Cu ₂ Sn ₁ and Cu, which are alloy layers of Cu and pure Sn, are formed from the lower part of the pure Sn plating because the annealing process is performed twice on the base material 10 on which pure Sn plating has been applied. _{This is because 6} Sn ₅ is diffused and produced, so that the thinning of the Sn layer (pure Sn plating) proceeds.

  Next, the surface of the FFC conductor 1 manufactured as described above was photographed at a magnification of 20000 times using an electron microscope. FIG. 5 shows a photograph as a result of the photographing.

  Since the substrate (flat conductor) 10 is annealed twice, and is annealed in the second annealing process, Sn on the surface of the FFC conductor 1 grows as crystal grains. As shown, the crystal of the Sn layer is large, and the surface of the FFC conductor (Sn layer) is uniform.

  2: Comparative example (conventional FFC conductor)

  (Comparative Example 1)

  Plating material = pure Sn, plating thickness = 1.5 μm (Coolour method), plating method = electroplating, heating temperature = 400 to 500 ° C., heating time = 0.1 to 0.3 sec, cooling in the first annealing treatment A conductor (FFC conductor) was produced under each condition of method = rapid cooling. That is, under the above-described conditions, a conventional FFC conductor manufacturing procedure (this corresponds to steps S10 to S30 of the current manufacturing procedure in FIG. 2) was performed. In this case, the annealing process is performed only once. The surface hardness of this conventional FFC conductor was 30-40.

  A cross section of the conventional FFC conductor thus manufactured was photographed at a magnification of 21000 times using a transmission electron microscope. A photograph as a result of the photographing is shown in FIG. Moreover, it is the same photograph as the photograph content shown to Fig.6 (a), Comprising: A mode that the range of the said alloy layer and Sn layer (surface layer) was clearly represented with respect to the photograph of Fig.6 (a) is shown in FIG.6. Shown in (b).

As shown in FIGS. 6A and 6B, an alloy layer 16 of Cu ₆ Sn ₅ is formed on the base material (Cu) 10, and a surface layer 17 as an Sn layer is further formed on the alloy layer 16. ing.

  6 (a) and 6 (b), it can be seen that the alloy layer 16 is formed in a non-uniform state rather than being divided into layers, and the Sn layer, that is, the surface layer 17 is clearly present. That is, since the conductor heated at the heating temperature of 400 to 500 ° C. is rapidly cooled, the alloy layer 16 exists in a non-uniform state without being divided into layers.

  Next, the surface of the conventional FFC conductor manufactured as described above was photographed at a magnification of 20000 times using an electron microscope. A photograph as a result of the photographing is shown in FIG.

Since the substrate (flat rectangular conductor) 10 is annealed once and rapidly cooled, the surface of the FFC conductor is in a state where the Sn layer crystal is small and rough as shown in FIG. The surface of the layer is non-uniform.
(Comparative Example 2)

Of the above-mentioned conditions in Comparative Example 1, the plating thickness was changed to 0.7 μm to produce an FFC conductor (one annealing process). In this case, the surface hardness of the FFC conductor was 70 to 80, and the surface of the FFC conductor (Sn layer) was non-uniform in a state where the crystals of the Sn layer were small and rough.
(Comparative Example 3)

  Of the above-mentioned conditions in Example 1, the plating thickness was changed to 1.5 μm to produce an FFC conductor (two annealing treatments). The surface hardness of the FFC conductor in this case was 70 to 80, compared with 150 to 230 in the case of Example 1. Further, the surface of the FFC conductor (Sn layer) was non-uniform in a state where the crystals of the Sn layer were small and rough. This case corresponds to the conductor of Patent Document 1 above.

  3: Comparison of whisker suppression effect in FFC conductors

  Next, the FFC conductor according to the present embodiment, that is, the FFC conductor manufactured by the method for manufacturing the FFC conductor according to the present invention (conductor subjected to two annealing treatments) and the conventional FFC conductor (comparative example) That is, the suppression effect of whiskers was compared with the FFC conductor manufactured by the conventional FFC conductor manufacturing method.

  That is, in any case of the FFC having the FFC conductor according to the present invention and the FFC having the FFC conductor of the prior art, two FFCs having the FFC conductor of 30 cores (poles) are used as a predetermined connector. The contact portions (fitting portions) were randomly observed at six places with a metallurgical microscope and photographed.

  The photograph of the result of having observed the contact part (fitting part) of the conductor for FFC which concerns on this invention with a metal microscope is shown in FIG. In FIG. 8, of the total of 6 photos in the upper 3 and lower 3 photos, the left photo in the upper photo was taken at 200x magnification for the contact portion, and the other 5 photos were taken at 500x magnification for the contact photos. It was taken at a magnification of.

  As is apparent with reference to FIG. 8, when the annealing process is performed twice on the base material plated with pure Sn having a plating thickness of 0.7 μm, whiskers are generated at all six contact portions. Not done. In other words, when the FFC having the FFC conductor according to the present invention is employed, it can be said that generation of whiskers can be significantly suppressed (reduced).

  On the other hand, the photograph of the result of having observed the conductor for FFC of the comparative example 1 (in the case of plating thickness 1.5micrometer) with the metal microscope is shown in FIG. In FIG. 9, of the total of 6 photos in the upper 3 and lower 3 photos, the left and middle 2 photos in the upper photo were taken at 200x magnification, and the other 4 photos were The contact portion was photographed at a magnification of 500 times.

  As is apparent with reference to FIG. 9, when the annealing process is performed once on the base material plated with pure Sn having a plating thickness of 1.5 μm, whiskers (see FIG. 9 is a bearded portion indicated by an arrow. Incidentally, it can be confirmed that whisker having a length of 130 μm is generated in the left photograph in the upper stage, and whisker having a length of 50 μm is generated in the left photograph in the lower stage.

  4: Mechanism of whisker suppression

  FIG. 10 is a diagram illustrating whisker suppression of a contact portion (fitting portion) when an FFC having an FFC conductor according to the present invention is fitted to a predetermined connector.

In FIG. 10, the copper layer corresponds to the base material 10 in FIG. 1B, the alloy layer Cu ₃ Sn ₁ corresponds to the first alloy layer 11 in FIG. 1B, and the alloy layer Cu ₆ Sn. ₅ corresponds to the second alloy layer 12 in FIG. 1B, and the tin layer corresponds to the surface layer 13 in FIG.

  The reason why whisker generation from the FFC conductor according to the present invention can be greatly suppressed is as follows.

  (1) Since the Sn layer (tin layer) is thinned as shown in FIG. 10, compressive stress is applied to the Sn layer (Sn plating layer) of the FFC conductor from the connector terminal, and the “deformation of the Sn layer” Even if “swelling” occurs or Sn dislocation occurs, the absolute amount of pure Sn is small and the generation of whiskers is reduced and greatly suppressed.

(2) Also, as shown in FIG. 10, the Sn plating thickness is 0.7 μm, which is thinner than the conventional plating thickness of 1.5 μm. In addition, the hardness of the two alloy layers (Cu ₃ Sn ₁ , Cu ₆ Sn ₅ ) is easily transmitted to the Sn layer side, and the hardness of the Sn layer surface is increased. Therefore, stress deformation of the Sn layer (Sn plating) is reduced, and the generation of stress whiskers is suppressed.

  That is, the whisker suppressing effect due to the above reason (1) and the whisker suppressing effect due to the above reason (2) are combined to further suppress the generation of whiskers.

  FIG. 11 shows a whisker in the contact portion (fitting portion) when the FFC having the FFC conductor (plating thickness 1.5 μm, in the case of one annealing treatment) of the comparative example 1 is fitted to a predetermined connector. The figure explaining a mode that this occurs is shown.

  In the comparative example 1, as shown in FIG. 11, since the plating thickness of the Sn plating is 1.5 μm, which is thicker than the plating thickness of 0.7 μm in this embodiment, the Sn of the FFC conductor is used. When a compressive stress is applied to the layer (Sn plated layer) from the terminal of the connector, the “deformation or bulge” of the Sn layer occurs, that is, a dislocation phenomenon occurs due to the stress, thereby generating whiskers.

  In addition, whisker is also generated in the comparative example 2 and the comparative example 3 due to the same phenomenon as in the comparative example 1.

  The present invention can be applied to an FFC of a type in which the surface of the conductor is exposed at one end of the FFC and the back of the conductor is exposed at the other end in addition to the FFC of the single-sided conductor exposed type. it can.

It is a figure explaining the conductor for FFC which concerns on this invention. It is process drawing which shows the manufacture procedure of the conductor for FFC which concerns on this invention. It is a figure explaining FFC concerning this embodiment. It is a figure which shows the photograph of the result of having observed the cross section of the conductor for FFC which concerns on this invention with the transmission electron microscope. It is a figure which shows the photograph of the result of having observed the surface of the conductor for FFC which concerns on this invention with an electron microscope. It is a figure which shows the photograph of the result of having observed the cross section of the conductor for FFC of a comparative example with the transmission electron microscope. It is a figure which shows the photograph of the result of having observed the surface of the conductor for FFC of a comparative example with an electron microscope. It is a figure which shows the photograph of the result of having observed the contact part (fitting part) of the said FFC conductor after fitting FFC which has the conductor for FFC which concerns on this invention in the predetermined | prescribed connector with the metal microscope. It is a figure which shows the photograph of the result of having observed the contact part (fitting part) of the said FFC conductor after fitting FFC which has the FFC conductor of a comparative example with a predetermined | prescribed connector with the metal microscope. It is a figure explaining suppression of the whisker in the contact part (fitting part) at the time of fitting FFC which has a conductor for FFC concerning the present invention on a predetermined connector. It is a figure explaining generation | occurrence | production of the whisker in the contact part (fitting part) at the time of fitting FFC which has the conductor for conventional FFC with the predetermined | prescribed connector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conductor for flexible flat cables (FFC) 2 Insulation sheet 3 Reinforcement tape 10 Base material (Cu)
11 First alloy layer (Cu ₃ Sn ₁ )
12 Second alloy layer (Cu ₆ Sn ₅ )
13 Surface layer (Sn layer)

Claims (3)

An alloy layer of Cu ₃ Sn ₁ (copper-tin system) is formed on a substrate formed of Cu (copper), and an alloy layer of Cu ₆ Sn ₅ (copper-tin system) is formed on the alloy layer. A flexible flat cable characterized by having a conductor on which is formed. It is a manufacturing method of the conductor used for the flexible flat cable according to claim 1,
A first step of performing annealing treatment at a first temperature on the base material on which Sn (tin) plating is performed around the base material formed of Cu (copper);
An alloy layer of Cu ₃ Sn ₁ (copper-tin system) is formed on the base material subjected to the annealing treatment, and an alloy of Cu ₆ Sn ₅ (copper-tin system) is formed on the alloy layer. A second step of performing an annealing process at a second temperature to form a layer;
The manufacturing method of the conductor for flexible flat cables characterized by including this. The method for manufacturing a conductor for a flexible flat cable according to claim 2, wherein a plating thickness of the Sn (tin) plating is 0.7 μm.

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