GB2381963A

GB2381963A - Plated electrical terminal

Info

Publication number: GB2381963A
Application number: GB0225794A
Authority: GB
Inventors: Naoto Taguchi; Makoto Yamanashi; Eiji Fukuda; Mayayoshi Iketani
Original assignee: Yazaki Corp
Current assignee: Yazaki Corp
Priority date: 2001-11-13
Filing date: 2002-11-05
Publication date: 2003-05-14
Anticipated expiration: 2022-11-05
Also published as: DE10251507A1; GB0225794D0; GB2381963B; FR2832257A1; FR2832257B1

Abstract

In a terminal, a base member made of a copper alloy includes at least one contact portion on which a mating member is brought into contact. A nickel layer is plated on at least the contact portion of the base member. A copper layer is plated on the nickel layer. A tin layer is plated on the copper layer. The tin layer has a thickness in a range of 0.4žm to 1.1žm.

Description

TERMINAL This invention relates to a terminal used in various connectors.

Generally, a terminal, used in various connectors, comprises a base material, made of a copper alloy (such as brass), and a tin-plating layer formed on that surface of this base material for contact with a mating material (that is, a surface of a resilient contact piece of a female terminal or a surface of a male terminal). However, when such a tin-plated terminal is used at high temperatures for a long time period, there has been encountered a problem that copper (which is an easily-oxidized substance), forming the base material, diffuses into the tin-plating layer to form an oxide film on the surface of the tin-plating layer, thereby increasing a contact resistance. Therefore, Japanese Patent Publication No. 8-7960A, for example, discloses that a nickel-plating layer is interposed between a base material and a tin-plating layer to suppress the diffusion of copper.

However, when such a terminal, having the interposed nickel-plating layer, is subjected to high temperatures for a long time period, an intermetallic compound is formed as a result of mutual diffusion of the nickel-plating layer and the tin-plating layer, and therefore there is encountered a similar problem that an oxide of this intermetallic compound increases the contact resistance.

In view of such a background, Japanese Patent Publication No.

10-134869A discloses a three-layer plating terminal in which a nickel-plating layer, a copper-plating layer and a tin-plating layer are sequentially formed on

a base material. In this construction, since the nickel-plating layer and the tin-plating layer are not disposed adjacent to each other, an intermetallic compound of the two will not be formed, so that the contact resistance can be kept to a low level for a long time period.

On the other hand, it has been increasingly required for a connector to have a compact design and a high-density connection design. In order to achieve this, it is important for the terminal to offer a reduced insertion force when it is connected to a mating terminal Therefore, if the above three-layer plating terminal is so designed as to offer a reduced insertion force, it would be a very useful terminal which attains both of a low contact resistance and a low insertion force.

It is therefore an object of this invention to provide an improved terminal which is obtained by imparting a low insertion force to the above three-layer plating terminal.

In order to achieve the above object, according to the present invention, there IS provided a terminal, comprising: a base member comprised of a copper alloy, the base member including at least one contact portion on which a mating member is brought into contact; a nickel layer, plated on at least the contact portion of the base member; a copper layer, plated on the nickel layer ; and

a tin layer, plated on the copper layer and having a thickness of 1. or less.

It is thought that an insertion force is the sum of a force (shearing force), exerted for shearing an agglutinating bond between agglutinating portions of two terminals pressed against each other upon contact of the two terminals with each other under a load, and a mechanical resistance produced when the two terminals, pressed against each other, plastically deform the mating materials in their respective sliding directions upon sliding movement relative to each other. In a terminal having an uppermost layer formed by a tin-plating layer, the plastic deformation can easily occur upon insertion of the terminal since tin is soft metal, and therefore the mechanical resistance depends on this tin-plating layer. The larger the thickness of the tin-plating layer is, the larger the amount of plastic deformation is, and the mechanical resistance also increases. Therefore, in the terminal of the present invention, the thickness of the tin-plating layer is reduced into a small value of not larger than 1.1 am so as to reduce the mechanical resistance due to the plastic deformation, thereby reducing the insertion force.

The copper-plating layer and the nickel-plating layer, which form the undercoat, are composed of hard metals, respectively, and therefore these layers bear the contact load, acting on the whole plating layer, and reduce the shearing force due to the load. As a result, the contact load, acting on the tin-plating layer is also relieved, so that the amount of plastic deformation decreases. Thus, the shearing force and the mechanical resistance due to the plastic deformation are reduced, so that the insertion force is greatly reduced.

Accordingly, there can be obtained the terminal having both of the low contact resistance-design and the low insertion force-design, and this terminal can adequately meet the requirements of the smaller design and higher-density design of connectors.

It has been found that the above terminal is particularly suitably used as the type of terminal in which a contact load, acting between this terminal and the mating terminal at the time of insertion of the terminal, is 25N or less.

Accordingly, this terminal can be suitably used, for example, in a multi-pole connector for an automobile.

The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: Fig. 1 is a cross-sectional view schematically showing a layer construction of a terminal of the present invention; Fig. 2 is a cross-sectional view of a female terminal according to a first embodiment of the invention; Fig. 3 is a cross-sectional view of a female terminal according to a second embodiment of the invention; Fig. 4 is a cross-sectional view of a female terminal according to a third embodiment of the invention, Fig. 5 is a cross-sectional view of a female terminal according to a fourth embodiment of the invention,

Fig. 6 is a cross-sectional view of a female terminal according to a fifth embodiment of the invention; Fig. 7 is a graph showing the relation between a contact load and an insertion force; and Fig. 8 is a graph showing the relation between the thickness of a tin-plating layer and an insertion force.

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

Fig. 1 is a cross-sectional view schematically showing that portion of the terminal of the invention for contact with a mating material. This contact portion for the mating terminal"means a surface of a resilient contact portion of a female terminal or a surface of a male terminal. As shown in the drawings, the terminal comprises a base material 101, and a nickel-plating layer 102, a copper-plating layer 103, and a tin-plating layer 104 are sequentially formed on this base material 101. The base material 101 is composed of a copper alloy such as brass.

The nickel-plating layer 102 serves to suppress the diffusion of copper from the base material 101 into the tin-plating layer 104. The copper-plating layer 103 serves to suppress the formation of an intermetallic compound of nickel and tin. According to the intervention of these undercoats, an oxide will not be formed on the surface of the tin-plating layer 104, so that the increase of a contact resistance can be suppressed. Such a three-layer

plating terminal is similar to that disclosed in Japanese Patent Publication No.

1 0-134869A.

In the three-layer plating terminal of the present invention, the thickness of the tin-plating layer 104 is made as small as not larger than 1.1 11m. With this construction, a mechanical resistance due to plastic deformation, occurring at the time of insertion of the terminal, can be reduced.

More specifically, as will be more fully described later, the insertion force can reduced 20% or more as compared with a terminal having a tin-plating layer with a thickness of 1.5 11m. With respect to the lower limit of the thickness of the tin-plating layer 104, if this thickness is smaller than 0.4 11m, the homogeneous layer is less liable to be obtained because of the difficulty with the production, so that the mechanical characteristics become inferior Therefore, in the present invention, the thickness of the tin-plating layer 104 is in the range of between 0.4 11m and 1.1 11m.

The thickness of the nickel-plating layer 102, as well as the thickness of the copper-plating layer 103, is not limited to any specified value in so far as these layers can prevent the diffusion. However, the nickel-plating layer 102 and the copper-ptattng layer 103 are harder than the tin-plating layer 104, and serve to bear the contact load applied at the time of insertion of the terminal.

Therefore, each of the two layers need to have a certain degree of thickness.

And besides, the nickel-plating layer 102 and the copper-plating layer 103, though in a smaller amount as compared with the tin-plating layer 104, undergo plastic deformation at the time of insertion of the terminal, and therefore if the nickel-plating layer 102 and the copper-plating layer 103 become too large in thickness, this will adversely affect the bending in the

production of the terminal.

Therefore, in the present invention, preferably, the thickness of the nickel-plating layer 102 is in the range of between 0. 1 um and 0.8 m, and the thickness of the copper-plating layer 103 is in the range of between 0. 1 um and 0.8 im. When each layer thickness is within this range, the increase of the insertion force due to the plastic deformation can be suppressed while maintaining the diffusion prevention effect.

Each of the above plating layers can be formed by a known plating method. For example, an electrolytic plating method is commonly used, and the construction of its apparatus is simple, and the thickness of each layer can be relatively easily controlled, and therefore this method is preferred.

Further, in the present invention, preferably, a reflowing treatment is applied to the nickel-plating layer 102, the copper-plating layer 103 and the tin-plating layer 104 so as to form a copper-tin alloy layer. This copper-tin alloy layer is harder than the nickel-plating layer 102 and the copper-plating layer 103, and increases the hardness of the whole undercoat, so that the plastic deformation due to the load, applied at the time of insertion of the terminal, can be reduced, while the insertion force can be further reduced. And besides, part of the tin-plating layer 104 is converted into the copper-tin alloy layer, and therefore the layer thickness apparently becomes smaller than before the reflowing treatment is applied, and this contributes to a further reduction of the insertion force.

The reflowing treatment can be carried out by a known method. For example, the nickel-plating layer 102, the copper-plating layer 103 and the tin-plating layer 104 are sequentially formed on the base material 101, and

thereafter the terminal is introduced into an electric furnace. With respect to treatment conditions, generally, heat of 2320C or more is applied for a short time period.

The above three-layer construction, in which the tin-plating layer 104 has the thickness of the specified value, and the above construction, in which the copper-tin alloy layer IS added, can be applied to resilient contact pieces of various female terminals shown in Figs. 2 to 6. In each of these drawings, a male terminal (not shown) is inserted horizontally from the left side (in the drawings) toward the right side, and each of these drawings is a cross-sectional view taken along the direction of insertion of the male terminal.

Fig. 2 shows a female terminal according to a first embodiment. The female terminal 1 includes the resilient contact piece 10 provided within a receiving portion 21 having an insertion port 20 for the insertion of the male terminal therethrough. The receiving portion 21 is formed, for example, by bending a flat metal sheet into a square tubular shape. The resilient contact piece 10 comprises a rectangular flat sheet of brass which is folded back at its generally middle portion thereof, and a folded-back portion 11 is slightly bent at a suitable portion thereof, and a tip of this bent portion is curved to form a contact portion 12 for contact with the male terminal (mating member). In this embodiment, the above-mentioned three-layer plating layer (the copper-tin alloy layer may be included) is formed at least on the surface of this contact portion 12. The resilient contact piece 10 is fixedly secured at its proximal end 13 to an inner surface of an upper wall 21 a of the receiving portion 21.

In a female terminal 1 according to a second embodiment as shown in Fig 3, the resilient contact piece 10 is formed integrally with and extends

from a bottom wall 21b of a receiving portion 21. More specifically, the resilient contact piece 10 is folded back upwardly toward the inner side of the receiving portion 21 at an insertion port 20, and further a folded-back portion 11 is bent at a suitable portion thereof toward the bottom wall 21 b. A tip of the bent portion is curved to form a contact portion 12 for contact with a male terminal. In this embodiment, the above-mentioned three-layer plating layer (the copper-tin alloy layer may be included) is formed at least on the surface of this contact portion 12.

In a female terminal 1 according to a third embodiment as shown in Fig. 4, a resilient contact piece 10 is folded back to extend from a bottom wall 21 b of a receiving portion 21 toward the inner side of the receiving portion 21.

An end portion 11 a of a folded-back portion 11 is formed into a generally oval shape in facing relation to the bottom wall 21 b. A curved projection is formed at a suitable portion of the folded-back portion 11 to define a contact portion 12 for contact with a male terminal. In this embodiment, the above-mentioned three-layer plating layer (the copper-tin alloy layer may be included) is'formed at least on the surface of this contact portion 12.

In a female terminal 1 according to a fourth embodiment as shown in Fig. 5, a resilient contact piece 10 is folded back to extend from a bottom wall 21 b of a receiving portion 21 toward the inner side of the receiving portion 21.

A folded-back portion 11 is bent at a suitable portion thereof toward the bottom wall 21 b, and an end portion 11 a is cut off at a region immediately after this bent portion. A tip of the bent portion is curved to form a contact portion 12 for contact with a male terminal. In this embodiment, the above-mentioned three-layer plating layer (the copper-tin alloy layer may be included) is formed

at least on the surface of this contact portion 12.

In a female terminal 1 according to a fifth embodiment as shown in Fig. 6, a resilient contact piece 10 is folded back to extend from a bottom wall 21 b of a receiving portion 21 toward the inner side of the receiving portion 21.

A folded-back portion 11 IS bent upwardly at a suitable portion thereof, and an end portion 11 a is cut off at a suitable portion of this bent portion. The bent portion serves as a contact portion 12 for contact with a male terminal. In this embodiment, the above-mentioned three-layer plating layer (the copper-tin alloy layer may be included) is formed on the surface of this contact portion 12.

In each of the above female terminals 1, the load of contact between the female terminal and the male terminal is predetermined by the angle of folding-back of the resilient contact piece 10, the width of the resilient contact piece and so on. In the above embodiments, the contact load is adjusted to not larger than 25N.

Although not shown in the drawings, each of the female terminals may have a plurality of contact portions 12 to further reduce the insertion force.

Advantageous effects of the present invention were examined with various numeral examples It shoutd be noted that the present invention will not be limited by the numeral examples.

There were used female terminals shown respectively in Figs. 2 to 6.

First, a nickel-plating layer having a thickness of 0.5 um was formed on the contact portion of the resilient contact piece of each of the female terminals by the electrolytic plating method. Next, a copper-plating layer having a thickness of 0.5 11m was formed on the nickel-plating layer by the electrolytic plating method. Further, a tin-plating layer having a thickness of 0. 5 am was

formed on the copper-plating layer by the electrolytic plating method. Then, a reflowing treatment was carried out by applying heat of 2320C or more for a short time period.

As shown in Table 1, a contact load was adjusted, and an insertion force was measured pursuant to JASO D616-94, using a male terminal having a 1.2 J. lm thick tin-plating layer formed on its base material made of brass. For comparison purposes, an insertion force was similarly measured, using female terminals each having a 1.5 m thick tin plating layer.

Table 1

contact load 5N 10N 20N 25N female terminal Figs. 2 and 3 Fig. 4 Fig. 5 Fig. 6

The results are shown in Fig. 7, and it will be appreciated that in the terminals of the present invention (represented by crosses), the insertion force is smaller when the contact load is below 25N, as compared with the examples having the 1.5 um thick tin-plating layer (represented by circles).

On the other hand, three resilient contact pieces of female terminals were formed from a flat sheet made of brass. A nickel-plating layer having a thickness of 0.5 m was formed on that surface of each resilient contact piece for contact with a male terminal, by an electrolytic plating method. Then a copper-plating layer having a thickness of 0.5 J. Lm was formed on each nickel-plating layer by an electrolytic plating method. Further, a tin-plating layer having thicknesses of 0. 4 J. Lm, 1.1 m and 1.5 m was formed on the respective associated copper-plating layers by an electrolytic plating method.

Then, a reflowing treatment was carried out by applying heat of 2320C or more for a short time period An insertion force was measured pursuant to JASO D616-94, using the thus obtained resilient contact pieces and a male terminal having a 1.2 J. 1m thick tin-plating layer formed on its base material made of brass.

Namely, the insertion forces were measured, using the above female terminals and male terminals, and the average value and deviations were found The results are shown in Fig. 8, and it will be appreciated that when the thickness of the tin-plating layer is not larger than 1.1 m, the insertion force can be reduced 20% or more as compared with the example having a tin-plating thickness of 1.5 cm (a typical thickness in a conventional terminal).

Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.

For example, the above three-layer construction can be applied to either of a male terminal and a female terminal, and in either case, the low insertion force can be achieved. However, when this construction is applied to both of the male and female terminals, this is most effective.

Claims

1 1. A terminal, comprising: 2 a base member comprised of a copper alloy, the base member 3 including at least one contact portion on which a mating member is brought 4 into contact; 5 a nickel layer, plated on at least the contact portion of the base 6 member; 7 a copper layer, plated on the nickel layer ; and 8 a tin layer, plated on the copper layer and having a thickness of 9 1.1 Jlm or less.

1 2. The terminal as set forth in claim 1, wherein the tin layer has a 2 thickness in a range of 0. 44m to 1.1 am.

1 3. The terminal as set forth in claim 1, wherein each of the nickel layer 2 and the copper layer has a thickness in a range of 0.1 Jlm to 0. 8m.

1 4. The terminal as set forth in claim 1, further comprising a copper-tin 2 alloy layer interposed between the copper layer and the tin layer.

1 5. The terminal as set forth In claim 1, wherein a contact load 2 established between the contact portion and the mating member is so adjusted 3 as to be 25N or less.

6. The terminal as set forth in claim 1, further comprising a resilient piece, wherein the contact portion is formed on the resilient piece.

7. A terminal substantially as described with reference to any of the examples shown in the accompanying drawings.