JP2012038656A - Flexible flat cable and flexible printed wiring board - Google Patents
Flexible flat cable and flexible printed wiring board Download PDFInfo
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- 238000007747 plating Methods 0.000 claims abstract description 86
- 239000004020 conductor Substances 0.000 claims abstract description 53
- 229910020830 Sn-Bi Inorganic materials 0.000 claims abstract description 42
- 229910018728 Sn—Bi Inorganic materials 0.000 claims abstract description 42
- 229910000765 intermetallic Inorganic materials 0.000 claims abstract description 15
- 238000005452 bending Methods 0.000 abstract description 18
- 230000006355 external stress Effects 0.000 abstract description 6
- 229910000679 solder Inorganic materials 0.000 abstract description 6
- 239000010410 layer Substances 0.000 description 66
- 229910045601 alloy Inorganic materials 0.000 description 8
- 239000000956 alloy Substances 0.000 description 8
- 239000000463 material Substances 0.000 description 7
- 239000010949 copper Substances 0.000 description 6
- 238000000137 annealing Methods 0.000 description 4
- 229910052718 tin Inorganic materials 0.000 description 3
- 229910000881 Cu alloy Inorganic materials 0.000 description 2
- 229910020888 Sn-Cu Inorganic materials 0.000 description 2
- 229910019204 Sn—Cu Inorganic materials 0.000 description 2
- 229910052797 bismuth Inorganic materials 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 230000035882 stress Effects 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910017482 Cu 6 Sn 5 Inorganic materials 0.000 description 1
- 229910020816 Sn Pb Inorganic materials 0.000 description 1
- 229910020836 Sn-Ag Inorganic materials 0.000 description 1
- 229910020922 Sn-Pb Inorganic materials 0.000 description 1
- 229910020988 Sn—Ag Inorganic materials 0.000 description 1
- 229910008783 Sn—Pb Inorganic materials 0.000 description 1
- 239000012790 adhesive layer Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 150000002736 metal compounds Chemical class 0.000 description 1
- 229920000728 polyester Polymers 0.000 description 1
- 229920006267 polyester film Polymers 0.000 description 1
- 230000000452 restraining effect Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 238000005491 wire drawing Methods 0.000 description 1
Landscapes
- Non-Insulated Conductors (AREA)
- Insulated Conductors (AREA)
- Parts Printed On Printed Circuit Boards (AREA)
- Coating With Molten Metal (AREA)
- Manufacturing Of Printed Wiring (AREA)
Abstract
【課題】コネクタとの嵌合など大きな外部応力がかかる環境下においても、コネクタの端子およびフレキシブルフラットケーブルの導体に形成されるめっき層やはんだから、ウィスカが発生するおそれの少ない、あるいは発生してもその長さが５０μｍ未満であり、かつ優れた耐屈曲特性を備えたフレキシブルフラットケーブルを提供する。
【解決手段】Ｓｎ系めっき層を被覆した端子１２を備えたコネクタ１１に嵌合され、端子１２と接する導体１６が内部に配設されたフレキシブルフラットケーブル１３において、導体１６の素線の周囲にＳｎ−Ｂｉ系めっき層が形成されていると共に、素線とＳｎ−Ｂｉ系めっき層との間に合計厚さが１μｍ以下の金属間化合物層が形成され、Ｓｎ−Ｂｉ系めっき層のＢｉ濃度が１０ｍａｓｓ％以上であるものである。
【選択図】図１[PROBLEMS] To reduce the occurrence or occurrence of whiskers from a plating layer or solder formed on a connector terminal and a conductor of a flexible flat cable even in an environment where a large external stress such as fitting with a connector is applied. Further, the present invention provides a flexible flat cable having a length of less than 50 μm and excellent bending resistance.
In a flexible flat cable 13 fitted with a connector 11 having a terminal 12 covered with a Sn-based plating layer and having a conductor 16 in contact with the terminal 12 disposed therein, around a strand of the conductor 16. An Sn—Bi plating layer is formed, and an intermetallic compound layer having a total thickness of 1 μm or less is formed between the strand and the Sn—Bi plating layer, and the Bi concentration of the Sn—Bi plating layer Is 10 mass% or more.
[Selection] Figure 1
Description
本発明は、配線用導体または端末接続部として電気機器に使用されるフレキシブルフラットケーブル及びフレキシブル配線基板に係り、特にコネクタに嵌合されて使用されるフレキシブルフラットケーブル及びフレキシブル配線基板に関するものである。 The present invention relates to a flexible flat cable and a flexible wiring board used in electrical equipment as a wiring conductor or terminal connection portion, and more particularly to a flexible flat cable and a flexible wiring board used by being fitted to a connector.
従来、配線材、特に銅や銅合金の表面には、配線材の酸化を防ぐために、Ｓｎ，Ａｇ，ＡｕやＮｉのめっきが施される。 Conventionally, the surface of a wiring material, particularly copper or copper alloy, is plated with Sn, Ag, Au, or Ni in order to prevent the wiring material from being oxidized.
例えば、図１に示すように、コネクタ（コネクタ部材）１１と、フレキシブルフラットケーブル（以下、ＦＦＣという）１３およびフレキシブルプリント配線基板（以下、ＦＰＣという）１４の端部１５においては、コネクタ１１の端子（金属コネクタピン）１２や、ＦＦＣ１３およびＦＰＣ１４の導体１６の表面などにめっきが施されている。中でも、Ｓｎはコストが安価であり、軟らかく嵌合の圧力で容易に変形し接触面積が増え接触抵抗が低く抑えられることから、導体１６および端子１２の表面にＳｎめっきを施したものが広く一般的に使用されている。 For example, as shown in FIG. 1, a connector (connector member) 11, a flexible flat cable (hereinafter referred to as FFC) 13, and an end portion 15 of a flexible printed wiring board (hereinafter referred to as FPC) 14 have terminals of the connector 11. The (metal connector pin) 12 and the surface of the conductor 16 of the FFC 13 and FPC 14 are plated. In particular, Sn is inexpensive and soft and easily deforms by fitting pressure, increasing the contact area and keeping the contact resistance low, so that the surfaces of the conductor 16 and the terminal 12 are Sn-plated are widely used. Has been used.
このＳｎめっき用合金として、従来は耐ウィスカ性が良好なＳｎ−Ｐｂ合金が用いられてきたが、近年は環境面での対応の観点から、Ｐｂフリー材（非鉛材）、ノンハロゲン材の使用が求められており、配線材に使用される各種材料に対してもＰｂフリー化、ノンハロゲン化が求められている。 Conventionally, Sn-Pb alloys with good whisker resistance have been used as this Sn plating alloy, but in recent years, Pb-free materials (lead-free materials) and non-halogen materials have been used from the viewpoint of environmental compatibility. Pb-free and non-halogenated are also required for various materials used for wiring materials.
ところがＳｎめっきのＰｂフリー化に伴って、特にＳｎまたはＳｎ系合金めっきにおいては、Ｓｎの針状結晶であるウィスカがめっきから発生し、ウィスカによる隣接配線間の短絡事故が問題となっている。特に、パッケージを高密度化すべく隣接配線間の配設ピッチが数百μｍ以下とされる近年のＦＦＣ１３およびＦＰＣ１４においては、隣接配線間の短絡を防止するため、ウィスカ長さは最大でも５０μｍ未満とする必要がある。 However, as Sn plating becomes Pb-free, particularly in Sn or Sn-based alloy plating, whisker which is a needle crystal of Sn is generated from the plating, and a short circuit accident between adjacent wirings due to the whisker becomes a problem. In particular, in recent FFC 13 and FPC 14 in which the arrangement pitch between adjacent wirings is several hundred μm or less in order to increase the density of the package, the whisker length is less than 50 μm at the maximum in order to prevent short circuit between adjacent wirings. There is a need to.
ウィスカの発生原因の一つとして考えられているＳｎめっき中の応力を緩和させるため、電気メッキしたＳｎをリフロー処理することにより、ウィスカの発生を低減させることが可能であるとされている。 In order to relieve stress during Sn plating, which is considered as one of the causes of whisker generation, it is said that reflow treatment of electroplated Sn can reduce the generation of whiskers.
しかし、コネクタとの嵌合など新たな外部応力がかかる場合は、リフロー処理を施してもウィスカの発生を抑えることができない。 However, when new external stress is applied such as fitting with a connector, the occurrence of whiskers cannot be suppressed even if reflow processing is performed.
この問題に対し、Ｓｎめっきに２〜４ｍａｓｓ％のＢｉを添加した合金めっきによりウィスカを抑制することが提案されている（例えば、特許文献１〜７参照）。 In order to solve this problem, it has been proposed to suppress whiskers by alloy plating in which 2 to 4 mass% Bi is added to Sn plating (see, for example, Patent Documents 1 to 7).
しかし、本発明者らの検討により、ＦＦＣを嵌合するコネクタの端子上のＳｎ系めっき層の厚さによっては、ＦＦＣ側の導体上に例えば２〜４ｍａｓｓ％のＢｉを含有したＳｎ−Ｂｉ合金めっき層を被覆しても、コネクタの端子側のＳｎ系めっき層から最大長さ５０μｍ以上の長いウィスカが成長することが確認されている。 However, according to the study by the present inventors, depending on the thickness of the Sn plating layer on the terminal of the connector that fits the FFC, for example, an Sn-Bi alloy containing 2 to 4 mass% Bi on the conductor on the FFC side. Even when the plating layer is covered, it has been confirmed that a long whisker having a maximum length of 50 μm or more grows from the Sn-based plating layer on the terminal side of the connector.
また、一方で、Ｂｉの添加量を１５ｍａｓｓ％以上とすると、めっき層が硬くなり、ひび割れなどの不都合が生じやすくなり、耐屈曲特性が低下してしまうことが報告されている（例えば、特許文献４，５参照）。 On the other hand, it has been reported that if the amount of Bi added is 15 mass% or more, the plating layer becomes hard, inconveniences such as cracks are likely to occur, and the bending resistance is reduced (for example, Patent Documents). 4, 5).
以上の事情を考慮して創案された本発明の目的は、特にコネクタとの嵌合など大きな外部応力がかかる環境下においても、コネクタの端子およびフレキシブルフラットケーブルの導体に形成されるめっき層やはんだから、ウィスカが発生するおそれの少ない、あるいは発生してもその長さが５０μｍ未満であり、かつ優れた耐屈曲特性を備えたフレキシブルフラットケーブルおよびフレキシブルプリント配線基板を提供することにある。 The object of the present invention created in view of the above circumstances is to provide a plating layer or solder formed on the connector terminal and the conductor of the flexible flat cable, particularly in an environment where a large external stress such as fitting with the connector is applied. Accordingly, it is an object of the present invention to provide a flexible flat cable and a flexible printed wiring board that are less likely to generate whiskers or that have a length of less than 50 μm and that have excellent bending resistance.
上記目的を達成するために本発明は、Ｓｎ系めっき層を被覆した端子を備えたコネクタに嵌合され、前記端子と接する導体が内部に配設されたフレキシブルフラットケーブルにおいて、前記導体の素線の周囲にＳｎ−Ｂｉ系めっき層が形成されていると共に、前記素線と前記Ｓｎ−Ｂｉ系めっき層との間に合計厚さが１μｍ以下の金属間化合物層が形成され、前記Ｓｎ−Ｂｉ系めっき層のＢｉ濃度が１０ｍａｓｓ％以上であるフレキシブルフラットケーブルである。 In order to achieve the above object, the present invention provides a flexible flat cable that is fitted to a connector having a terminal coated with a Sn-based plating layer, and in which a conductor in contact with the terminal is disposed. And an Sn-Bi plating layer is formed around the wire, and an intermetallic compound layer having a total thickness of 1 μm or less is formed between the strand and the Sn—Bi plating layer, and the Sn—Bi This is a flexible flat cable in which the Bi concentration of the system plating layer is 10 mass% or more.
前記端子のＳｎ系めっき層の厚さは、前記導体のＳｎ−Ｂｉ系めっき層の厚さよりも薄くされてもよい。 The thickness of the Sn plating layer of the terminal may be made thinner than the thickness of the Sn—Bi plating layer of the conductor.
また本発明はＳｎ系めっき層を被覆した端子を備えたコネクタに嵌合され、前記端子と接する導体が内部に配設されたフレキシブルプリント配線基板において、前記導体の素線の周囲にＳｎ−Ｂｉ系めっき層が形成されていると共に、前記素線と前記Ｓｎ−Ｂｉ系めっき層との間に合計厚さが１μｍ以下の金属間化合物層が形成され、前記Ｓｎ−Ｂｉ系めっき層のＢｉ濃度が１０ｍａｓｓ％以上であるフレキシブルプリント配線基板である。 Further, the present invention is a flexible printed wiring board which is fitted to a connector having a terminal coated with a Sn-based plating layer, and a conductor in contact with the terminal is disposed therein, and Sn-Bi around the conductor wire. An intermetallic compound layer having a total thickness of 1 μm or less is formed between the element wire and the Sn—Bi plating layer, and the Bi concentration of the Sn—Bi plating layer Is a flexible printed wiring board having 10 mass% or more.
前記端子のＳｎ系めっき層の厚さは、前記導体のＳｎ−Ｂｉ系めっき層の厚さよりも薄くされてもよい。 The thickness of the Sn plating layer of the terminal may be made thinner than the thickness of the Sn—Bi plating layer of the conductor.
本発明によれば、コネクタとの嵌合など大きな外部応力がかかる環境下においても、コネクタの端子およびフレキシブルフラットケーブルの導体に形成されるめっき層やはんだから、ウィスカが発生するおそれの少ない、あるいは発生してもその長さが５０μｍ未満であり、かつ優れた耐屈曲特性を備えたフレキシブルフラットケーブルおよびフレキシブルプリント配線基板を提供できる。 According to the present invention, whisker is less likely to be generated from the plating layer or solder formed on the connector terminal and the conductor of the flexible flat cable even under an environment where a large external stress such as fitting with the connector is applied, or Even if it occurs, it is possible to provide a flexible flat cable and a flexible printed wiring board having a length of less than 50 μm and excellent bending resistance.
以下に、本発明の実施の形態について図面に基づき説明する。 Embodiments of the present invention will be described below with reference to the drawings.
図１は、フレキシブルフラットケーブル（ＦＦＣ）およびフレキシブルプリント配線基板（ＦＰＣ）をコネクタに嵌合する接続構造を示す図である。 FIG. 1 is a view showing a connection structure for fitting a flexible flat cable (FFC) and a flexible printed wiring board (FPC) to a connector.
図１に示すように、複数の導体１６が所定の間隔で並行に配列され、その両面を、絶縁フィルム１７でラミネートされてなるＦＦＣ１３またはＦＰＣ１４の端部１５は、導体１６が絶縁フィルム１７から露出されており、端部１５がコネクタ１１に嵌合されると、コネクタ１１が備える端子１２とＦＦＣ１３およびＦＰＣ１４の導体１６とが接触して、端子１２と導体１６とが電気的に接続される。 As shown in FIG. 1, the end portions 15 of the FFC 13 or the FPC 14 in which a plurality of conductors 16 are arranged in parallel at predetermined intervals and both surfaces thereof are laminated with the insulating film 17 are exposed from the insulating film 17. When the end 15 is fitted to the connector 11, the terminal 12 provided in the connector 11 contacts the conductor 16 of the FFC 13 and the FPC 14, and the terminal 12 and the conductor 16 are electrically connected.
導体１６の素線はＣｕまたはＣｕ合金からなる。また、導体１６の素線の周囲と、端子１２の端子部材の周囲には、耐酸化性を向上させるために、Ｓｎ系めっき層が形成されている。 The strands of the conductor 16 are made of Cu or Cu alloy. An Sn-based plating layer is formed around the strands of the conductor 16 and the terminal member of the terminal 12 in order to improve oxidation resistance.
ＦＦＣ１３またはＦＰＣ１４と、コネクタ１１との接続は、導体１６が端子１２から受ける外部応力によって拘束されて為されており、Ｓｎ系めっき層に外部応力がかかると、その応力を緩和すべく、図２に示すように、導体１６と端子１２との接点（嵌合部）近傍からＳｎの針状結晶であるウィスカ１８が発生・成長する。ウィスカ１８の成長が進行すると、隣接する配線から成長したウィスカ１８と接するなどし、隣接配線間の短絡事故が発生するおそれがある。 The connection between the FFC 13 or the FPC 14 and the connector 11 is made by restraining the external stress received by the conductor 16 from the terminal 12. When an external stress is applied to the Sn-based plating layer, the stress is reduced as shown in FIG. 2, whiskers 18, which are Sn needle crystals, are generated and grow from the vicinity of the contact (fitting portion) between the conductor 16 and the terminal 12. As the growth of the whisker 18 progresses, the whisker 18 grown from the adjacent wiring may come into contact, and a short-circuit accident between the adjacent wirings may occur.
そこで従来から導体１６からのウィスカ１８の発生・成長を抑制するために、Ｓｎ系めっき層にＢｉを添加したＳｎ−Ｂｉ系めっき層を導体１６に用いることが行われている。このとき、過剰なＢｉの添加はＦＦＣ１３およびＦＰＣ１４の耐屈曲特性を低下させるため、Ｂｉの添加量は数ｍａｓｓ％程度とされてきた。 Therefore, in order to suppress the generation and growth of whiskers 18 from the conductor 16, an Sn—Bi based plating layer in which Bi is added to the Sn based plating layer is conventionally used for the conductor 16. At this time, excessive addition of Bi lowers the bending resistance of the FFC 13 and FPC 14, and therefore the amount of Bi added has been about several mass%.
一方、本発明者らが鋭意研究した結果、ＦＦＣ１３およびＦＰＣ１４と、コネクタ１１との接続構造においては、導体１６からのウィスカ１８の発生を抑制することに加えて、コネクタ１１の端子１２から成長するウィスカ１８を抑制することが重要であることが分かった。ウィスカ１８の成長に寄与するＳｎ原子はＳｎ系めっき層から供給されており、ＦＦＣ１３およびＦＰＣ１４の導体１６と比較して、めっき厚さを大きくされることが多いコネクタ１１の端子１２には、より長いウィスカ１８が成長しやすいことが原因である。そのため、ＦＦＣ１３およびＦＰＣ１４の導体１６のＳｎ系めっき層にＢｉ濃度が数ｍａｓｓ％のＳｎ−Ｂｉ系めっき合金を用いても、コネクタ１１の端子１２からウィスカ１８が発生するため、十分な耐ウィスカ特性が得られないことが分かった。 On the other hand, as a result of intensive studies by the present inventors, in the connection structure between the FFC 13 and the FPC 14 and the connector 11, in addition to suppressing the generation of the whisker 18 from the conductor 16, it grows from the terminal 12 of the connector 11. It has been found that suppressing whisker 18 is important. The Sn atoms contributing to the growth of the whisker 18 are supplied from the Sn-based plating layer, and compared to the conductors 16 of the FFC 13 and the FPC 14, the terminal 12 of the connector 11, whose plating thickness is often increased, is more This is because the long whisker 18 is easy to grow. Therefore, even if a Sn-Bi plating alloy having a Bi concentration of several mass% is used for the Sn plating layer of the conductor 16 of the FFC 13 and the FPC 14, whisker 18 is generated from the terminal 12 of the connector 11. It was found that could not be obtained.
そこで本発明者らは、導体１６のＳｎ−Ｂｉ系めっき層のＢｉ濃度を変化させ、Ｂｉ濃度と、コネクタ１１の端子１２の耐ウィスカ特性との関係について鋭意検討した結果、導体１６のＳｎ−Ｂｉ系めっき層中のＢｉ濃度を１０ｍａｓｓ％以上、好ましくは２０ｍａｓｓ％以上、より好ましくは３０ｍａｓｓ％以上とすることで、十分な耐ウィスカ特性が得られることが判明した。これは、ＦＦＣ１３およびＦＰＣ１４の導体１６のＳｎ−Ｂｉ系めっき層のＢｉ濃度を高濃度にすることによって、コネクタ１１との嵌合部において、端子１２のＳｎ系めっき層へ導体１６側から拡散するＢｉの量が増大し、端子１２側で発生するウィスカ１８を抑制したものと考えられる。 Therefore, the present inventors changed the Bi concentration of the Sn—Bi plating layer of the conductor 16 and intensively studied the relationship between the Bi concentration and the whisker resistance characteristics of the terminal 12 of the connector 11, and as a result, the Sn— It has been found that sufficient whisker resistance can be obtained by setting the Bi concentration in the Bi-based plating layer to 10 mass% or more, preferably 20 mass% or more, more preferably 30 mass% or more. The diffusion of the Sn-Bi plating layer of the conductor 16 of the FFC 13 and the FPC 14 from the conductor 16 side into the Sn plating layer of the terminal 12 at the fitting portion with the connector 11 by increasing the Bi concentration. It is considered that the amount of Bi increases and the whisker 18 generated on the terminal 12 side is suppressed.
ところで、Ｓｎ−Ｂｉ系めっき層のＢｉ濃度を高濃度化すると、めっき層が硬く脆くなり、ＦＦＣ１３およびＦＰＣ１４の重要な特性である耐屈曲特性が劣化することが懸念される。しかし本発明者らは、実際に屈曲特性を決定する支配因子は、Ｓｎ系めっき層とＣｕ素線との間に形成される金属間化合物層（Ｃｕ3Ｓｎ系およびＣｕ6Ｓｎ5系）の厚さであり、Ｓｎ−Ｂｉ系めっき層中のＢｉ濃度には依存しないことを見出した。また、この金属間化合物層の合計厚さを１μｍ以下とすれば、良好な屈曲特性が得られることが分かった。なお、金属間化合物層は、通電焼鈍をしなくても、室温状態で厚さ０．３μｍ程度は形成されているため、事実上、金属間化合物層の厚さは０．３μｍ以上となる。 By the way, when the Bi concentration of the Sn—Bi plating layer is increased, the plating layer becomes hard and brittle, and there is a concern that the bending resistance, which is an important characteristic of the FFC 13 and the FPC 14, is deteriorated. However, the present inventors have determined that the controlling factor that actually determines the bending characteristics is the intermetallic compound layer (Cu 3 Sn system and Cu 6 Sn 5 system) formed between the Sn-based plating layer and the Cu element wire. It was found that the thickness was not dependent on the Bi concentration in the Sn-Bi plating layer. Further, it was found that if the total thickness of the intermetallic compound layer is 1 μm or less, good bending characteristics can be obtained. In addition, since the intermetallic compound layer is formed with a thickness of about 0.3 μm at room temperature without performing the electric annealing, the thickness of the intermetallic compound layer is practically 0.3 μm or more.
以上の検討結果を踏まえた本実施の形態にかかるＦＦＣ１３およびＦＰＣ１４は、導体１６の素線の周囲にＳｎ−Ｂｉ系めっき層が形成されていると共に、素線とＳｎ−Ｂｉ系めっき層との間に合計厚さが１μｍ以下の金属間化合物層が形成され、Ｓｎ−Ｂｉ系めっき層のＢｉ濃度が１０ｍａｓｓ％以上であることを特徴とする。 In the FFC 13 and the FPC 14 according to the present embodiment based on the above examination results, an Sn—Bi based plating layer is formed around the strand of the conductor 16, and the wire and the Sn—Bi based plating layer An intermetallic compound layer having a total thickness of 1 μm or less is formed therebetween, and the Bi concentration of the Sn—Bi-based plating layer is 10 mass% or more.
導体１６にＳｎ−Ｂｉ系めっき層を形成する際において、初期のＢｉ濃度は必ずしも１０ｍａｓｓ％以上とならなくても良い。これは、導体１６の製造工程において、めっき処理後のリフロー処理あるいはアニール処理により、めっき層とＣｕ素線との界面でＳｎ−Ｃｕ系金属間化合物相が成長してめっき層中のＳｎが消費されるため、Ｓｎ−Ｂｉ系めっき層中のＢｉ濃度が初期より上昇するからである。したがって、この熱処理後における導体１６のＳｎ−Ｂｉ系めっき層中のＢｉ濃度が１０ｍａｓｓ％以上であればよい。 When the Sn—Bi plating layer is formed on the conductor 16, the initial Bi concentration does not necessarily have to be 10 mass% or more. This is because the Sn—Cu intermetallic compound phase grows at the interface between the plating layer and the Cu element wire by the reflow treatment after the plating treatment or the annealing treatment in the manufacturing process of the conductor 16, and the Sn in the plating layer is consumed. This is because the Bi concentration in the Sn—Bi plating layer increases from the initial stage. Therefore, the Bi concentration in the Sn—Bi plating layer of the conductor 16 after this heat treatment may be 10 mass% or more.
また、Ｓｎ−Ｂｉ系めっき層にＺｎを添加することも有効であるが、Ｚｎの添加量が多すぎると、Ｓｎ−Ｂｉ系めっき層の表面（すなわち導体１６の表面）に形成されるＺｎ酸化膜層が厚くなり、導体１６と端子１２との接触抵抗の増大や耐ウィスカ特性の劣化があるため、Ｚｎ添加量は微量（数ｍａｓｓ％）とする。 It is also effective to add Zn to the Sn—Bi-based plating layer. However, if the amount of Zn added is too large, Zn oxidation formed on the surface of the Sn—Bi-based plating layer (that is, the surface of the conductor 16). Since the film layer becomes thick and the contact resistance between the conductor 16 and the terminal 12 increases and the whisker resistance is deteriorated, the amount of Zn added is set to a very small amount (several mass%).
コネクタ１１の端子１２に形成されるＳｎ系めっき層としては、例えば、純Ｓｎめっき、Ｓｎ−Ｂｉ系めっき、Ｓｎ−Ｃｕ系めっき、Ｓｎ−Ａｇ系めっきなどを使用することができる。コネクタ１１側のＳｎ系めっき層の厚さは特に限定されるものではないが、例えば０．５μｍ〜７μｍ程度のものを使用することができる。 As a Sn system plating layer formed in the terminal 12 of the connector 11, pure Sn plating, Sn-Bi system plating, Sn-Cu system plating, Sn-Ag system plating etc. can be used, for example. The thickness of the Sn-based plating layer on the connector 11 side is not particularly limited, but for example, a thickness of about 0.5 μm to 7 μm can be used.
他方、ＦＦＣ１３およびＦＰＣ１４の導体１６に形成されているＳｎ−Ｂｉ系めっき層の厚さは、コネクタ１１の端子１２に形成されているＳｎ系めっき層の厚さよりも小さくされる。 On the other hand, the thickness of the Sn—Bi plating layer formed on the conductor 16 of the FFC 13 and the FPC 14 is made smaller than the thickness of the Sn plating layer formed on the terminal 12 of the connector 11.
以上要するに、本発明によれば、ＦＦＣ１３およびＦＰＣ１４の導体１６に形成されているＳｎ−Ｂｉ系めっき層のＢｉ濃度を１０ｍａｓｓ％以上とすることで、導体１６側からコネクタ１１の端子１２に形成されているＳｎ系めっき層にＢｉが拡散し、端子１２で発生するウィスカ１８を抑制できる。このため、コネクタ１１の構成を何ら変更することなく、ＦＦＣ１３およびＦＰＣ１４をコネクタ１１に嵌合してなる接続構造の耐ウィスカ特性を良好なものとすることができる。 In short, according to the present invention, the Bi concentration of the Sn-Bi plating layer formed on the conductor 16 of the FFC 13 and FPC 14 is set to 10 mass% or more, so that the conductor 12 is formed on the terminal 12 of the connector 11. Bi diffuses into the Sn-based plating layer, and whiskers 18 generated at the terminals 12 can be suppressed. For this reason, the whisker resistance of the connection structure formed by fitting the FFC 13 and the FPC 14 to the connector 11 can be improved without changing the configuration of the connector 11.
また、導体１６の素線と、Ｓｎ−Ｂｉ系めっき層との間に形成されている金属間化合物層の合計厚さが１μｍ以下であるため、ＦＦＣ１３およびＦＰＣ１４の耐屈曲特性を劣化させることなく、耐ウィスカ特性を改善できる。 Moreover, since the total thickness of the intermetallic compound layer formed between the strand of the conductor 16 and the Sn—Bi-based plating layer is 1 μm or less, the bending resistance characteristics of the FFC 13 and the FPC 14 are not deteriorated. The whisker resistance can be improved.
本発明は上記の実施の形態に限られるものではなく、例えば、はんだ接合により構成される接続構造に適用することも可能である。この場合、Ｓｎ系はんだ合金を用いたはんだ接合後の、接合部におけるＢｉ濃度が１０ｍａｓｓ％以上であると、接合部におけるウィスカの発生と成長を抑制することができる。 The present invention is not limited to the above embodiment, and can be applied to, for example, a connection structure configured by solder bonding. In this case, the occurrence and growth of whiskers in the joint can be suppressed when the Bi concentration in the joint after solder joining using the Sn-based solder alloy is 10 mass% or more.
以下に、本発明の実施例について説明する。 Examples of the present invention will be described below.
Ｓｎに微量のＺｎ、並びに種々の濃度のＢｉを添加しためっき合金を作製し、溶融めっき装置を用いて、Φ０．６ｍｍのＣｕ線の周囲に厚さ５μｍのめっき膜を施した。その後、冷間伸線・圧延工程を経て厚さ０．０３５ｍｍ、幅０．３ｍｍの平角線を作製した。次いで通電アニーラを使用して種々の条件でリフロー処理を施した。作製した導体は、耐屈曲性試験（左右９０°、曲げＲ＝５ｍｍ）を行い、屈曲破断回数を調査した。また、ＡＥＳ深さ方向分析により、導体表面からの各元素の濃度分布を求め、図３に示すように、金属間化合物層・Ｓｎ−Ｂｉ系めっき層の厚さや、Ｓｎ−Ｂｉ系めっき層中のＢｉ濃度（平均濃度）を求めた。 A plating alloy in which a small amount of Zn and various concentrations of Bi were added to Sn was prepared, and a plating film having a thickness of 5 μm was applied around a 0.6 mm-diameter Cu wire using a hot dipping apparatus. Thereafter, a flat wire having a thickness of 0.035 mm and a width of 0.3 mm was produced through a cold wire drawing and rolling process. Next, a reflow treatment was performed under various conditions using a current-carrying annealer. The produced conductor was subjected to a bending resistance test (90 ° left and right, bending R = 5 mm), and the number of bending breaks was investigated. In addition, the concentration distribution of each element from the conductor surface was obtained by AES depth direction analysis, and as shown in FIG. 3, the thickness of the intermetallic compound layer / Sn—Bi plating layer, and the Sn—Bi plating layer Bi concentration (average concentration) was determined.
次に、これら作製した導体を５０本、０．５ｍｍピッチで並行に配列し、その両面を、ポリエステル系接着剤層を片面に有するポリエステルフィルムでラミネートし、フレキシブルフラットケーブル（ＦＦＣ）を作製した。作製したＦＦＣ各５枚（２５０ｐｉｎ）を、Ｓｎ系めっき層厚さ２μｍの端子を備えるコネクタと嵌合し、室温に２５０ｈｒ放置した。その後、ＦＦＣをコネクタから外し、ＦＦＣ側およびコネクタ側の嵌合部で発生・成長したウィスカをＳＥＭで測長し、その最大長を求めた。 Next, 50 of these conductors prepared were arranged in parallel at a pitch of 0.5 mm, and both surfaces thereof were laminated with a polyester film having a polyester-based adhesive layer on one side to prepare a flexible flat cable (FFC). Each of the manufactured FFCs (250 pins) was fitted with a connector having a terminal with a Sn-based plating layer thickness of 2 μm and left at room temperature for 250 hours. Thereafter, the FFC was removed from the connector, and whiskers generated and grown at the FFC side and the fitting portion on the connector side were measured by SEM, and the maximum length was obtained.
作製した各導体の金属間化合物層厚さ、Ｓｎ−Ｂｉ系めっき層の厚さおよびＢｉ濃度と、各導体を用いて作製したＦＦＣの屈曲破断回数、最大ウィスカ長との関係を表１に示す。 Table 1 shows the relationship between the thickness of the intermetallic compound layer, the thickness of the Sn-Bi plating layer and the Bi concentration of each manufactured conductor, the number of bending breaks of the FFC manufactured using each conductor, and the maximum whisker length. .
表１に示すように、Ｂｉ濃度が１０ｍａｓｓ％以下である従来例１，２のＦＦＣは、最大ウィスカ長が５０μｍ以上であった。 As shown in Table 1, the FFCs of Conventional Examples 1 and 2 having a Bi concentration of 10 mass% or less had a maximum whisker length of 50 μm or more.
これに対し、導体のＳｎ−Ｂｉ系めっき層中のＢｉ濃度が１０ｍａｓｓ％以上である実施例１〜４のＦＦＣは、最大ウィスカ長が５０μｍ未満と良好な耐ウィスカ特性を示しており、Ｂｉ濃度が高くなるほどウィスカの成長が抑制された。また、金属化合物層の厚さが１μｍ以下である実施例１〜４のＦＦＣは、屈曲破断回数が２万回以上と良好な耐屈曲特性を示しており、Ｂｉ濃度が高くなることによる屈曲特性の劣化は見られなかった。 On the other hand, the FFCs of Examples 1 to 4 in which the Bi concentration in the Sn-Bi based plating layer of the conductor is 10 mass% or more show a good whisker resistance with a maximum whisker length of less than 50 μm, and the Bi concentration The higher the value, the lower the growth of whiskers. In addition, the FFCs of Examples 1 to 4 in which the thickness of the metal compound layer is 1 μm or less show a good bending resistance with a number of bending breaks of 20,000 or more, and the bending characteristics due to an increase in Bi concentration. The deterioration of was not seen.
一方、通電アニーラの条件を変えて焼鈍を強くし、金属間化合物層の厚さを大きくした比較例１では、Ｂｉ濃度が高いため耐ウィスカ特性は良好であるが、屈曲破断回数が８千回程度と、耐屈曲特性が劣化している。 On the other hand, in Comparative Example 1 in which the annealing conditions were increased by changing the conditions of the current annealing and the thickness of the intermetallic compound layer was increased, whisker resistance was good because the Bi concentration was high, but the number of bending fractures was 8,000 times. The degree and bending resistance properties are degraded.
１１ コネクタ
１２ 端子
１３ フレキシブルフラットケーブル
１６ 導体
11 Connector 12 Terminal 13 Flexible Flat Cable 16 Conductor
Claims (4)
前記導体の素線の周囲にＳｎ−Ｂｉ系めっき層が形成されていると共に、前記素線と前記Ｓｎ−Ｂｉ系めっき層との間に合計厚さが１μｍ以下の金属間化合物層が形成され、前記Ｓｎ−Ｂｉ系めっき層のＢｉ濃度が１０ｍａｓｓ％以上であることを特徴とするフレキシブルフラットケーブル。 In a flexible flat cable that is fitted to a connector having a terminal coated with a Sn-based plating layer, and a conductor in contact with the terminal is disposed inside,
An Sn—Bi plating layer is formed around the conductor wire, and an intermetallic compound layer having a total thickness of 1 μm or less is formed between the strand and the Sn—Bi plating layer. The flexible flat cable, wherein the Sn concentration of the Sn-Bi plating layer is 10 mass% or more.
前記導体の素線の周囲にＳｎ−Ｂｉ系めっき層が形成されていると共に、前記素線と前記Ｓｎ−Ｂｉ系めっき層との間に合計厚さが１μｍ以下の金属間化合物層が形成され、前記Ｓｎ−Ｂｉ系めっき層のＢｉ濃度が１０ｍａｓｓ％以上であることを特徴とするフレキシブルプリント配線基板。 In a flexible printed wiring board fitted with a connector provided with a terminal coated with a Sn-based plating layer, and a conductor in contact with the terminal is disposed inside,
An Sn—Bi plating layer is formed around the conductor wire, and an intermetallic compound layer having a total thickness of 1 μm or less is formed between the strand and the Sn—Bi plating layer. The flexible printed wiring board, wherein the Sn concentration of the Sn-Bi plating layer is 10 mass% or more.
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