Connector terminal material

Abstract

The aim is to achieve both a reduction in insertion force and improved solder wettability in high-temperature, high-humidity environments. [Solution] The average thickness of the nickel layer is 0.15 mm or more and 4.0 mm or less, and the average thickness of the copper-tin alloy layer is 0.15 μm or more and 0.8 μm or less. In a cross section parallel to the rolling direction of the substrate, if the area ratio of the tin layer to the total area of ​​the copper-tin alloy layer and the tin layer at the connection portion is X%, and the area ratio of the tin layer to the total area of ​​the copper-tin alloy layer and the tin layer at the soldered portion is Y%, X% is 21% or more and 50% or less, Y% is 31% or more and 90% or less, Y>X, and the difference is 10% or more.

Description

[Technical Field]

[0001] The present invention relates to a terminal material for connectors that reduces the insertion force required when fitting connectors and improves solder wettability when mounted. [Background technology]

[0002] Conventionally, connectors used to connect electrical wiring in automobiles, consumer devices, etc. have terminal pairs designed to be electrically connected when a contact piece provided on the female terminal comes into contact with a male terminal inserted into the female terminal at a predetermined contact pressure.

[0003] As such a connector (terminal), a terminal material is known in which a copper or copper alloy substrate is copper-plated and tin-plated, and then a reflow process is performed to form a copper-tin alloy layer and a tin layer on the substrate.

[0004] For example, in Patent Document 1, a terminal material having such a copper-tin alloy layer and a tin layer is disclosed in which the roughness of the substrate is controlled to control the state of exposure of the copper-tin alloy layer from the tin layer, thereby reducing the insertion force. However, the substrate must be processed in advance to control the roughness, which makes it difficult to apply this method to terminal materials for small terminals with complex shapes that are manufactured by punching and then plating.

[0005] In addition, in Patent Document 2, the insertion force is reduced by making the tin layer made of tin or a tin alloy on the copper-tin alloy layer very thin, but there is a problem in that the contact resistance increases in a high-temperature, high-humidity environment because the tin layer is small.

[0006] Furthermore, in Patent Document 3, part of the copper-tin alloy is replaced with nickel (Ni), the copper-tin alloy is made to have a steep uneven shape, and a certain amount of the tin layer is left, thereby reducing friction and preventing an increase in contact resistance in high-temperature environments; however, because the copper-tin alloy layer is steep, there is a limit to how much the insertion force can be reduced.

[0007] However, when these terminal materials are formed into terminals, fracture surfaces are created, which reduces solder wettability. To prevent this, plating and reflow processes can be performed after forming the terminal shape. However, in all terminal materials, the tin layer needs to be thin to maintain low friction, so if it takes a long time from plating to reflow or if the terminal is exposed to a high-temperature, high-humidity environment, the solder wettability will be reduced. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-100220 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-012320 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-240520 Summary of the Invention [Problem to be solved by the invention]

[0009] These terminal materials tend to have a soft tin layer on the surface that easily adheres during insertion and removal, resulting in high insertion forces. For this reason, attempts have been made to reduce the insertion force by thinning the tin layer and exposing part of the copper-tin alloy layer, but this results in insufficient solder wettability during mounting. Ensuring solder wettability requires thickening the tin layer, but this increases the insertion force. Therefore, it has been difficult to achieve both reduced insertion force and improved solder wettability. Furthermore, if nickel from the nickel layer diffuses into the copper-tin alloy layer during reflow treatment, holes will form in the nickel layer, reducing the barrier properties, and over time, an oxide layer will form on the surface of the tin layer.

[0010] The present invention has been made in view of the above circumstances, and has as its object to achieve both a reduction in insertion force and an improvement in solder wettability in a high-temperature, high-humidity environment. [Means for solving the problem]

[0011] The terminal material for a connector of the present invention comprises a substrate made of copper or a copper alloy, a coating formed thereon, the coating comprising: a nickel layer made of nickel or a nickel alloy formed on a surface of the substrate; a copper-tin alloy layer made of an alloy of copper and tin formed on the nickel layer; and a tin layer made of tin or a tin alloy formed on the copper-tin alloy layer; and the terminal material has a connecting portion to be connected to a mating side and a soldering portion to be soldered to a substrate, the average thickness of the nickel layer is 0.15 μm or more and 4.0 μm or less, and the average thickness of the copper-tin alloy layer is 0.15 μm or more and 0.8 μm or less, In a cross section parallel to the rolling direction of the base material, when a cross-sectional area ratio of the tin layer to a total area of ​​the copper-tin alloy layer and the tin layer in the connection portion is X%, and a cross-sectional area ratio of the tin layer to a total area of ​​the copper-tin alloy layer and the tin layer in the soldering portion is Y%, X% is 21% or more and 50% or less, and Y% is 31% or more and 90% or less, Y>X and the difference is 10% or more.

[0012] The nickel layer functions as a barrier to prevent the diffusion of copper and other components (base material components) from the base material at high temperatures, improving heat resistance. The greater the average thickness of this nickel layer, the higher the heat resistance, but a certain thickness is unnecessary and makes the layer more susceptible to cracking during processing. On the other hand, if the average thickness of the nickel layer is too small, the barrier function against the base material components is insufficient, reducing solder wettability and increasing contact resistance in high-temperature, high-humidity environments.

[0013] In addition, the copper-tin alloy layer and the tin layer have a composite structure in which the relatively soft tin layer on the surface is supported by the hard copper-tin alloy layer, and the interface between them has an uneven shape, which, combined with the lubricating effect of the tin layer, reduces the coefficient of friction. If the average thickness of the copper-tin alloy layer exceeds 0.8 μm, the tin layer remaining after reflow processing will be thin, resulting in high contact resistance in high-temperature, high-humidity environments and a high coefficient of friction. On the other hand, if the average thickness of the copper-tin alloy layer is less than 0.15 μm, the tin layer will be thick and the hard copper-tin alloy layer will be reduced, resulting in a high coefficient of friction. The same applies to soldered parts, but this is mainly effective in connection parts.

[0014] Regarding the cross-sectional area ratio of the copper-tin alloy layer and the tin layer in a cross section parallel to the rolling direction, as the cross-sectional area ratio of the tin layer increases, the exposed area ratio of the copper-tin alloy layer on the tin layer surface decreases, and as the cross-sectional area ratio of the tin layer decreases, the exposed area ratio increases. The connection part aims to reduce friction by lowering the cross-sectional area ratio of the tin layer and increasing the exposed area ratio of the copper-tin alloy layer. However, if the cross-sectional area ratio of the tin layer is too low, the friction coefficient will increase.

[0015] When a terminal is formed into a narrow pin shape, plating the coating often results in a difference in coating thickness between the flat and corner areas, and measuring the coating thickness at the corners is difficult. Therefore, relying solely on the average thickness of the coating on the flat surface of the terminal can make it difficult to ensure good solder wettability. Therefore, in addition to the average thickness of the copper-tin alloy layer, the cross-sectional area ratio of the tin layer to the total area of ​​the copper-tin alloy layer and the tin layer is specified. This cross-sectional area ratio of the tin layer is not necessarily strictly proportional to the exposed area ratio of the copper-tin alloy layer, but there is a certain correlation.

[0016] At the connection, if the cross-sectional area ratio of the tin layer exceeds 50%, the tin layers will adhere to each other during sliding, increasing the coefficient of friction; if it is less than 21%, the contact resistance will increase in high-temperature, high-humidity environments. In the soldered portion, if the cross-sectional area ratio of the tin layer exceeds 90%, the cross-sectional area ratio of the tin layer in the connection portion also becomes high, making it difficult to achieve low friction, and if it is less than 31%, the solder wettability decreases.

[0017] Furthermore, if the difference (YX) in the cross-sectional area ratio of the tin layer between the connection portion and the soldered portion is 10% or more, good solder wettability can be ensured even in a high-temperature, high-humidity environment.

[0018] In the terminal material for a connector of the present invention, the soldering portion may have a skewness Ssk of 0 or more of the nickel layer after the tin layer and the copper-tin alloy layer are peeled off.

[0019] Skewness Ssk is a parameter that is a three-dimensional extension of the profile curve (line roughness) parameter Rsk, and like Rsk, is a parameter that evaluates the degree of deviation (skewness: wideness) of the height distribution histogram. If the skewness Ssk is 0 or more, the height distribution is symmetrical from top to bottom, indicating that the nickel layer has few defects. If the skewness Ssk is negative, the surface has many fine valleys and many defects. Products with good Ssk of the nickel layer at the soldered joint are less likely to have high contact resistance in high-temperature, high-humidity environments. Since the Ssk of the soldered joint and the connection are considered to be roughly the same, products with no defects in the nickel layer have high barrier properties against base material components in high-temperature, high-humidity environments.

[0020] In the terminal material for connectors of the present invention, the exposed area ratio of the copper-tin alloy layer exposed from the tin layer on the surface of the coating is preferably 20% or more at the connection portion and less than 10% at the soldered portion.

[0021] In the connection part, a high exposed area ratio of the copper-tin alloy layer is preferable to reduce insertion force, and if it is less than 20%, the effect of reducing insertion force is poor. Conversely, in the soldered part, a low exposed area ratio of the copper-tin alloy layer is preferable, and if it is 10% or more, there is a risk of reduced solder wettability in a high-temperature, high-humidity environment.

[0022] For terminal materials for connectors that are fixed to a substrate by soldering, it is preferable to use a "post-plating method" in which the metal plate is plated after it has been punched out.For pin-shaped terminals, the post-plating method forms a coating on the entire surface of the connection part with the mating side and the soldering part, resulting in a terminal that has excellent insertion / removal properties with the mating terminal and excellent solder wettability. [Effects of the Invention]

[0023] According to the present invention, by forming the thickness of the tin layer, etc. between the connection portion and the soldering portion and the cross-sectional area ratio of the tin layer within a predetermined range, it is possible to achieve both a reduction in insertion force at the connection portion and an improvement in solder wettability at the soldering portion. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a plan view of a terminal material for a connector according to an embodiment of the present invention; [Figure 2] 2 is a schematic cross-sectional view of the connector terminal material of FIG. 1. [Figure 3] 2 is a flowchart showing a method for manufacturing the connector terminal material of FIG. 1. [Figure 4] 3 is a schematic cross-sectional view showing a substrate with a plating layer before a reflow treatment step of the terminal material for a connector of FIG. 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0026] [Configuration of connector terminal materials] As shown in Figure 1, the terminal material 1 for connectors in this embodiment is a terminal chain formed by connecting multiple terminal members 10 in the shape of pin terminals, and is formed by punching out a long plate material using a press process. Specifically, a plurality of elongated terminal members 10 are provided in parallel at predetermined intervals on one side of an elongated connecting member 11 of a predetermined width, extending in a direction perpendicular to the longitudinal direction of the connecting member 11. Each terminal member 10 has a pin-shaped connecting portion 13 and a soldering portion 14, which is narrower than the connecting portion 13 and continues from its tip, with the base end of the soldering portion 14 connected at a right angle to the connecting member 11. After being separated from the connecting member 11, the terminal member 10 is used by soldering the soldering portion 14 to a through-hole or the like in a circuit board or the like so as to be fixed in an electrically connected state, and the electrical connection is made by inserting the connecting portion 13 into another female terminal. For example, the plate thickness is 0.06 mm to 1.00 mm, and the width of the connection portion 13 is 0.1 mm to 2.0 mm, but Figure 1, including the shape of the terminal member 10, is just an example, and is not limited to what is shown in Figure 1, as long as it has a connection portion that is electrically connected to a mating terminal.

[0027] This connector terminal material 1 has a connection portion coating 22 and a soldering portion coating 23 formed on a substrate 21 made of copper or a copper alloy. These coatings 22, 23 have a common layer structure, with nickel layers 31, 32 made of nickel or a nickel alloy, copper-tin alloy layers 33, 34 made of an alloy of copper and tin, and tin layers 35, 36 made of tin or a tin alloy formed in this order on the substrate 21. The tin layers 35, 36 form the surface layers of the coatings 22, 23. FIG. 2 shows a cross section in the thickness direction, and the coatings 22 and 23 are formed on the entire surface of both the front and rear surfaces and both side surfaces of the substrate 21.

[0028] The composition of the substrate 21 is not particularly limited as long as it is made of copper or a copper alloy, and it may be made of a plate material made of copper or a copper alloy such as oxygen-free copper (C10200), Cu-Mg copper alloy (C18665), brass, or phosphor bronze.

[0029] The nickel layers 31, 32 have the function of suppressing the diffusion of components (substrate components) such as copper from the substrate 21 into the copper-tin alloy layers 33, 34 and the tin layers 35, 36 formed thereon. The average thickness (film thickness) of the nickel layers 31, 32 is set to be 0.15 μm or more and 4.0 μm or less for both the connection portion coating 22 and the soldering portion coating 23. The nickel layers 31, 32 have a barrier function that prevents the diffusion of components such as copper (base material components) from the base material 21 at high temperatures, thereby improving heat resistance. The greater the average thickness of these nickel layers 31, 32, the higher the heat resistance, but a certain thickness (4.0 μm) is necessary and is prone to cracking during processing. On the other hand, if the average thickness of the nickel layers 31, 32 is too small, the barrier function against the base material components becomes insufficient, resulting in high contact resistance in high-temperature, high-humidity environments. Furthermore, if the average thickness of the nickel layers 31, 32 is too small, they are prone to copper-tin alloying in high-temperature, high-humidity environments, reducing solder wettability.

[0030] In the film 23 for soldering portions, the skewness Ssk of the nickel layer 32 is preferably 0 or more. Skewness Ssk is a parameter that is a three-dimensional extension of the profile curve (line roughness) parameter Rsk, and like Rsk, is a parameter that evaluates the degree of deviation (skewness: wideness) of the height distribution histogram. During reflow, some of the nickel in the nickel plating layer diffuses into the copper-tin alloy layer. In this case, the diffusion occurs along the grain boundaries of the copper-tin alloy, so the greater the amount of diffusion, the more the nickel plating layer collapses into the shape of the grain boundaries. This state causes defects in the nickel barrier properties and reduces heat resistance (the tin layer becomes more susceptible to copper-tin alloying when heated). If the skewness Ssk is 0 or greater (a positive value), the height distribution is symmetrical from top to bottom, indicating few defects. If the skewness Ssk is negative (a negative value), the surface has many fine valleys and many defects. If the Ssk of the nickel layer 32 in the soldering portion 14 is less than 0, the heat resistance of the nickel layer 32 may decrease, which may result in a decrease in solder wettability in a high-temperature, high-humidity environment. An Ssk of 0 or more is preferable because heat resistance is maintained and solder wettability in a high-temperature, high-humidity environment does not decrease, but it is difficult to produce an Ssk of 0.6 or more. In the connection portion 13, a nickel layer 31 without defects (with an Ssk of 0 or more) is also preferable because it has a high barrier property against base material components in a high-temperature, high-humidity environment.

[0031] The composition of the nickel layers 31 and 32 is not particularly limited as long as they are made of nickel or a nickel alloy.

[0032] The copper-tin alloy layers 33, 34 are layers obtained together with the tin layers 35, 36 by sequentially forming a copper plating layer and a tin plating layer on the nickel layers 31, 32 and then reflowing them, and are formed of a composite structure consisting of only a Cu6Sn5 alloy or a mostly Cu6Sn5 alloy with a small amount of Cu3Sn alloy disposed underneath. In some cases, some of the copper in the copper plating layer remains unreacted, and a thin copper layer may exist between the nickel layer 32 and the copper-tin alloy layers 33, 34. The surfaces of these copper-tin alloy layers 33, 34, i.e., the interfaces with the tin layers 35, 36 on top of them, are formed with an uneven shape, and this is a composite structure in which the relatively soft tin layers 35, 36 on the surface are supported by the hard copper-tin alloy layers 33, 34, which, combined with the lubricating effect of the tin layers 35, 36, can reduce the coefficient of friction. In the connection film 22, a portion of the copper-tin alloy layer 33 is exposed on the surface of the tin layer 35. In the soldering film 23, a small portion of the copper-tin alloy layer 33 may also be exposed on the surface of the tin layer 35, but it is also possible that no portion is exposed.

[0033] The copper-tin alloy layers 35, 36 have an average thickness of 0.15 μm or more and 0.8 μm or less for both the connection film 22 and the soldered portion film 23. The average thickness of the copper-tin alloy layers 35, 36 is affected by the reflow treatment conditions described below and the thickness of the tin-plated layers 43, 44 and the copper-plated layer 42 during manufacturing. If the average thickness of the copper-tin alloy layers 33, 34 is less than 0.15 μm due to insufficient heating during the reflow process, the tin layers 35, 36 become thicker, reducing the hardness of the copper-tin alloy layers 33, 34, resulting in a higher coefficient of friction. If the average thickness of the copper-tin alloy layers 33, 34 exceeds 0.8 μm due to excessive generation of the copper-tin alloy layers 33, 34 during the reflow process, the tin layers 35, 36 become thinner, increasing the contact resistance in a high-temperature, high-humidity environment and the coefficient of friction. This is also true for the soldered portion 14, but is primarily effective for the connection portion 13. The copper-tin alloy layers 33 and 34 preferably have an average thickness of 0.30 μm or more and 0.65 μm or less.

[0034] In addition, in a cross section parallel to the rolling direction of the base material 21, the cross-sectional area ratio of the tin layers 35, 36 to the total area of ​​the copper-tin alloy layers 33, 34 and the tin layers 35, 36 is 21% or more and 50% or less in the connection portion coating 22, and 31% or more and 90% or less in the soldering portion coating 23.

[0035] Regarding the exposed area ratio of the copper-tin alloy layers 33, 34 and the cross-sectional area ratio of the tin layers 35, 36, as the cross-sectional area ratio of the tin layers 35, 36 increases, the exposed area ratio of the copper-tin alloy layers 33, 34 on the surfaces of the tin layers 35, 36 decreases, and as the cross-sectional area ratio of the tin layers 35, 36 decreases, the exposed area ratio of the copper-tin alloy layers 33, 34 increases.

[0036] The connecting portion 13 is designed to have low friction by reducing the cross-sectional area ratio of the tin layer 35 and increasing the exposed area ratio of the copper-tin alloy layer 33. However, if the cross-sectional area ratio of the tin layer 35 is too low, the coefficient of friction becomes high. In this connection 13, if the cross-sectional area ratio of the tin layer 35 exceeds 50%, adhesion occurs easily and it becomes difficult to reduce friction, and if it is less than 21%, the coefficient of friction becomes high and the contact resistance becomes high in a high-temperature, high-humidity environment.

[0037] In the soldering portion 14, if the cross-sectional area ratio of the tin layer 36 exceeds 90%, the cross-sectional area ratio of the tin layer 35 in the connection portion 13 also increases, making it difficult to achieve low friction, and if it is less than 31%, the solder wettability decreases. The cross-sectional area ratio of the tin layers 35, 36 is preferably 25% or more and 45% or less in the connection portion 13, and is preferably 45% or more and 75% or less in the soldered portion 14.

[0038] Furthermore, if the difference (YX) in the cross-sectional area ratio of the tin layers 35, 36 between the connection portion 13 and the soldered portion 14 is 10% or more, the soldered portion 14 can ensure good solder wettability even in a high-temperature, high-humidity environment.

[0039] The exposed area ratio of the copper-tin alloy layers 33, 34 exposed from the tin layers 35, 36 on the surfaces of the films 22, 23 is preferably 20% or more for the film 22 for the connection portions and less than 10% for the film 23 for the soldered portions. In the connection portion 13, a high exposed area ratio of the copper-tin alloy layer 33 is preferable to reduce the insertion force, and if it is less than 20%, the effect of reducing the insertion force is poor. Conversely, in the soldering portion 14, a low exposed area ratio of the copper-tin alloy layer 34 is preferable, and if it is 10% or more, there is a risk of reduced solder wettability in a high-temperature, high-humidity environment.

[0040] [Method of manufacturing connector terminal material] Next, a method for manufacturing this connector terminal material 1 will be described. The manufacturing method of this connector terminal material 1 includes a punching process in which a long, thin metal plate is punched by a press to form a chain of terminals that will become the base material 21, a pretreatment process in which the surface of the base material 21 after punching is cleaned, a plating layer forming process in which a nickel plating layer 41, a copper plating layer 42, and tin plating layers 43 and 44 are formed in this order on the surface of the base material 21, and a reflow treatment process in which the plated layer-coated base material 45 on which the three plating layers have been formed is heated and reflow-treated (see FIG. 3). The steps will be explained below in order.

[0041] (Punching process) A thin metal plate made of copper or a copper alloy wound into a coil is punched out by a press while being unwound, to form a chained-terminals body that serves as a base material 21 as shown in FIG.

[0042] (Pretreatment process) After punching, the base material 21 is subjected to pre-treatment such as degreasing and pickling to clean the surface.

[0043] (Plating layer formation process) After the pretreatment, a nickel plating layer 41 made of nickel or a nickel alloy, a copper plating layer 42 made of copper or a copper alloy, and tin plating layers 43 and 44 made of tin or a tin alloy are formed in this order on the substrate 21 as follows (see FIG. 4).

[0044] -Nickel plating layer- The pretreated surface of the substrate 21 is then subjected to nickel plating to form a nickel plating layer 41 made of nickel or a nickel alloy. A typical nickel plating bath may be used, for example, a sulfamic acid bath containing nickel sulfamate and boric acid as its main components. The temperature of the plating bath is 50°C to 60°C, and the current density is 1 A / dm 2 More than 10A / dm 2 The thickness of the nickel plating layer 41 is set to 0.15 μm or more and 4.0 μm or less.

[0045] -Copper plating layer- Copper plating is performed on the nickel plating layer 41 to form a copper plating layer 42 made of copper or a copper alloy. A common copper plating bath may be used for the copper plating, such as a copper sulfate bath containing copper sulfate and sulfuric acid as its main components. The temperature of the plating bath is 20°C to 50°C, and the current density is 1 A / dm 2 More than 10A / dm 2 The thickness of the copper plating layer 42 is set to 0.1 μm or more and 0.5 μm or less.

[0046] -Tin plating layer- A tin plating process is carried out on the copper plating layer 42 to form tin plating layers 43, 44 made of tin or a tin alloy. A common tin plating bath may be used as the plating bath for forming the tin plating layers 43, 44, for example, a methanesulfonic acid bath containing methanesulfonic acid and tin methanesulfonate as the main components. The temperature of the plating bath is 20°C or higher and 40°C or lower, and the current density is 1 A / dm2 More than 20A / dm 2 The following is said to be true.

[0047] This tin plating process is controlled so that the tin plating layers 43, 44 at the connection portion 13 and the soldered portion 14 have different thicknesses. Specifically, a plating process (electrolytic plating process) is performed on a plated substrate on which a nickel plating layer 41 and a copper plating layer 42 have been formed, while the substrate is immersed in a tin plating bath (electrolytic plating bath) and a shielding plate is placed between the electrode and the vicinity of the region that will become the connection portion 13. The shielding plate is an insulating plate made of a non-conductive resin or the like, and is made of a material that is not corroded by the plating solution (for example, vinyl chloride or acrylic resin). By appropriately setting the distance between the shielding plate, the substrate with the plated layer, and the electrode, as well as the area of ​​the shielding plate, the thickness of the tin plating layers 43, 44 on the connection portion 13 and the soldered portion 14, respectively, the thickness can be controlled. The tin plating layer 43 of the connection portion 13 is controlled to a thickness of 0.3 μm or more and 2.5 μm or less, and the tin plating layer 44 of the soldered portion 14 is controlled to a thickness of 1.0 μm or more and 4.0 μm or less. In this case, the tin plating layer 44 of the soldered portion 14 is formed thicker than the tin plating layer 43 of the connection portion 13. Instead of using this shielding plate, the thickness may be controlled by performing tin plating multiple times, at least once of which involves masking the surface of the portion that will become the connection before plating.

[0048] In this way, a nickel plating layer 41, a copper plating layer 42, and tin plating layers 43 and 44 are sequentially formed on the surface of the substrate 21, thereby obtaining a substrate 45 with three plating layers stacked on top of each other. Note that a cleaning treatment using sulfuric acid or the like is performed between each plating treatment. Before this plating process, the substrate 21 is punched into a chain terminal body by a press, and the substrate 21 is then immersed in a plating bath to form a plating layer, so that three plating layers are formed not only on the front and back surfaces of the substrate 21 but also on both side surfaces (the cut end surfaces during punching). However, the present invention can also be used in a "partial plating" process in which only a portion of the substrate is immersed in a plating bath.

[0049] (Reflow processing process) The plated layer-equipped substrate 45 on which the plated layer has been formed as described above is subjected to a reflow treatment. In the case of a long, narrow plate material (strip material) wound on a roll, this reflow treatment is performed by running the plate material in the lengthwise direction and passing it through a reflow furnace while continuously performing the above-described pretreatment and plating treatment. However, in the case of the plated layer-equipped substrate 45 of this embodiment, it is a punched material that has been punched in advance by a press into a chain of terminals of a predetermined length as shown in Fig. 1, and after the punched material is subjected to the above-described pretreatment and plating treatment, the plated layer-equipped substrate 45 is supplied to a relatively small reflow furnace and subjected to the reflow treatment. This reflow treatment is performed by heating the plated layer-attached substrate 45 to a temperature equal to or higher than the melting point of tin to melt the tin plated layers 43 and 44, and then cooling.

[0050] The connector terminal material 1 thus formed has coatings 22, 23 formed on a substrate 21 on which a plurality of terminal members 10 are continuously formed, and the coatings 22, 23 are formed in this order of nickel layers 31, 32 made of nickel or a nickel alloy, copper-tin alloy layers 33, 34 made of an alloy of copper and tin, and tin layers 35, 36 made of tin or a tin alloy. As described above, the coatings 22, 24 made of the nickel layers 31, 32, the copper-tin alloy layers 33, 34, and the tin layers 35, 36 are formed not only on the front and back surfaces of the substrate 21 but also on both side surfaces, so that the entire surface of the substrate 21 is covered with the coatings 22, 23. During the reflow treatment, the copper in the copper plating layer 42 reacts with the tin in the tin plating layers 43, 44 to form copper-tin alloy layers 33, 34 and tin layers 35, 36, but some of the copper in the copper plating layer 42 may remain unreacted, resulting in a thin copper layer between the nickel layers 31, 32 and the copper-tin alloy layers 33, 34.

[0051] In the case of a pin-shaped terminal using the terminal material 1 of this embodiment, as shown in Fig. 1, the connecting portion 13 that connects to the mating terminal is formed in a long, thin pin shape, so that not only the front and back surfaces but also the side surfaces of the terminal material 1 may come into contact with the mating terminal, but even in this case, the performance as a connector is not impaired because the coatings 22, 24 are formed on the entire front, back, and side surfaces of the connecting portion 13. In addition, because the coatings 22, 23 are formed on the entire surface, corrosion is less likely to occur.

[0052] Furthermore, since the coatings 22, 23 have the nickel layers 31, 32 that cover the substrate 21, the diffusion of components such as copper (substrate components) from the substrate 21 at high temperatures can be prevented, improving heat resistance. In addition, the copper-tin alloy layers 33, 34 and the tin layers 35, 36 have a composite structure in which the relatively soft tin layers 35, 36 on the surface are supported by the hard copper-tin alloy layers 33, 34, and the interface between them has an uneven shape, which, combined with the lubricating effect of the tin layers 35, 36, reduces the coefficient of friction.

[0053] Furthermore, the cross-sectional area ratio of the tin layers 35, 36 is set to 21% or more and 50% or less for the connection portion 13 and 31% or more and 90% or less for the soldering portion 14.This makes it less likely for adhesion of the tin layer 35 to occur in the connection portion 13, reducing the coefficient of friction, and improving the solder wettability in the soldering portion 14, thereby achieving both a reduction in insertion force and improved solder wettability in high-temperature, high-humidity environments.

[0054] In addition, the detailed configuration is not limited to that of the embodiment, and various modifications can be made within the scope that does not deviate from the spirit of the present invention. Although the nickel layers 31, 32 are set to the same thickness range in the connecting portion 13 and the soldered portion 14, they may be set to different thicknesses within that range (0.15 μm or more and 4.0 μm or less). The copper-tin alloy layers 33, 34 are set to the same thickness range in the connecting portion 13 and the soldered portion 14, but may be set to different thicknesses within that range. In addition, in the plating process, the nickel plating layer 41 and the copper plating layer 42 are set to the same thickness in both the connection portion 13 and the soldering portion 14, but they may be set to different thicknesses, as with the tin plating layers 43 and 44. [Example]

[0055] The substrate was a 0.25 mm thick sheet of alloy C18665 (CDA (Copper Development Association)). After punching out the chain-terminal shape shown in the figure, the substrate underwent electrolytic degreasing as a pretreatment, and the surface was subsequently plated with nickel, copper, and tin. Furthermore, pickling treatments were performed between each plating and after each copper plating. The conditions for electrolytic degreasing, pickling, and plating are listed in order in Table 1, and the same conditions were used in the following examples and comparative examples. In the table, RT stands for room temperature. In this case, the thickness of the nickel plating layer was adjusted by changing the plating time in the range of 13 to 350 seconds for the nickel plating process. The thickness of the copper plating layer was adjusted by changing the plating time in the range of 8 to 40 seconds for the copper plating process. The plating time in the tin plating process was set to a range of 8 to 120 seconds, and a shielding plate was used during this time to control the thickness difference between the connection part and the soldered part. In Comparative Example 4, the tin plating process was performed without using a shielding plate.

[0056] [Table 1]

[0057] The substrates with the various plating layers thus formed were subjected to a reflow treatment under the reflow conditions described in the embodiments.

[0058] After the reflow treatment, the terminal material was measured for the average thickness of each layer of the coating and the cross-sectional area ratio of the tin layer.

[0059] (average thickness of each layer) When measuring the average thickness of each layer, the measurement points were part A in Figure 1 for the connection part and part B in the same figure for the soldered part. Part A is the sliding part of the terminal, which is the center of the width direction at a position L1 = 2 mm (2 mm from the top edge of the paper in Figure 1) from the tip of the pin with a total length of L0 = 28.8 mm. Part B is the solder wetted part of the terminal, which is the center of the width direction at a position L1 x 2 = 4 mm from the side edge of the connecting part (bottom edge of Figure 1) and L1 = 2 mm from the connecting position of the terminal. The thickness of the nickel layer was measured using a fluorescent X-ray film thickness meter (FT150) manufactured by Hitachi High-Tech Science Corporation.

[0060] Regarding the average thickness of the copper-tin alloy layer, each sample was cross-sectionally processed using a focused ion beam device (FIB) (model number: SMI3050TB) manufactured by Seiko Instruments Inc., and the formed cross section (cross section parallel to the rolling direction of the substrate) was observed at a magnification of 13,000 times using a scanning ion microscope (SIM). In the cross-sectional SIM image at a tilt angle of 60°, the distance a from the interface with the nickel layer to the peak of the peak of the copper-tin alloy layer and the distance b from the interface with the nickel layer to the valley of the copper-tin alloy layer were measured at 10 arbitrary locations each, and the average was calculated and then converted into an actual length to obtain the average thickness of the copper-tin alloy layer.

[0061] (cross-sectional area ratio of tin layer) Five cross-sectional images of the entire joint and soldered portion parallel to the rolling direction of the substrate were obtained, and the obtained backscattered electron images were binarized using image processing software Image J (ver. 1.54f) so that the tin layer appeared black and the copper-tin alloy layer appeared white. The areas of the tin layer and copper-tin alloy layer were calculated, and the cross-sectional area ratio of the tin layer was calculated as tin layer / (tin layer + copper-tin alloy layer) × 100. The average of the five images was used as the measured value. The cross-sectional area ratio of the tin layer in the joint was designated X, and the cross-sectional area ratio of the tin layer in the soldered portion was designated Y. The binarization was performed with an altitude range of 255 set to 112.

[0062] The results of these measurements are shown in Table 2.

[0063] [Table 2]

[0064] In addition, the coefficient of friction, contact resistance, exposed area ratio of the copper-tin alloy layer on the surface of the tin layer, and skewness Ssk of the nickel layer were measured to evaluate solder wettability.

[0065] (coefficient of friction) The connection section of each sample was cut into a 60 mm long test piece parallel to the rolling direction and used as a substitute for a male terminal (male terminal test piece). The female terminal test pieces were all the same. The unprocessed terminal-shaped specimens of Example 13 (base material: 0.25 mm thick C18665) were cut into 60 mm x 10 mm pieces and embossed with a 1.5 mm radius at the center of the test piece. Measurements were performed using a Bruker AXS friction and wear tester (UMT-Tribolab). The convex surface of the female terminal test piece was placed horizontally, 5 mm below part A in Figure 1, so that part A was the center of the sliding area. A load of 3 N was applied to the male terminal test piece, and the female terminal test piece was slid 10 mm to a position 5 mm above part A in Figure 1. Friction coefficient data was obtained every 0.013 mm of sliding distance, and the average value of the friction coefficient obtained between sliding distances of 0.1 mm and 10 mm was taken as the friction coefficient value.

[0066] (contact resistance) Test specimens were prepared for the connection of each sample in the same way as for the coefficient of friction, and after heating them at 150°C for 250 hours, the contact resistance (mΩ) was measured. For the measurements, a friction and wear tester (UMT-Tribolab) from Bruker AXS was used, with the convex surface of the female test specimen in contact with the horizontally placed male terminal test specimen, and the contact resistance value when a load of 5 N was applied to the male terminal test specimen was measured using the four-terminal method.

[0067] (solder wettability) For solder wettability, the zero-cross time (ZCT) was measured at point B in Figure 1 using a meniscograph test on the soldered joint of each sample. Each sample was subjected to a pressure cooker test in a high-temperature, high-humidity environment (105°C, 100% RH saturation, 8 hours) using an accelerated life tester (Espec Corporation, EHS-411M). The zero-cross time was measured before and after the pressure cooker test (before and after the high-temperature, high-humidity test) using a meniscograph test. The zero-cross time was measured by immersing the sample in a Sn-3Ag-0.5Cu lead-free solder bath at a temperature of 245°C, at an immersion speed of 2 mm / sec, at a depth of 5 mm from the joint, for 10 seconds. A solder zero-cross time of 2 seconds or less was assigned an A rating, a rating of B for a time between 2 seconds and 3 seconds, and a rating of C for a time exceeding 3 seconds. A C rating indicates a failure.

[0068] (Ssk: Skewness) The skewness was measured at part A in Figure 1. The specimen was immersed in an etching solution (Raybold L-80) for removing the tin layer, exposing the underlying copper-tin alloy layer. The specimen was then immersed in an etching solution for removing the copper-tin alloy layer (a mixture of 100 g / L Raybold CopperAct S-40 and 80 mL / L sulfuric acid) to completely remove the copper-tin alloy layer and expose the underlying nickel layer. The nickel layer was then measured at nine points using a Keyence laser microscope (VK-X200) with a 150x objective lens (field of view: 96 μm × 72 μm) and no filter. The average skewness (Ssk) was calculated.

[0069] (exposed area ratio of copper-tin alloy layer) The measurement areas were designated as parts A and B in the drawing, and the surface of the tin layer was observed using an SEM (JSM-7001F manufactured by JEOL Ltd.). 2A backscattered electron image of the field of view was obtained. The obtained backscattered electron image was binarized using the image processing software Image J (ver. 1.54f) so that the copper-tin alloy layer exposed on the surface appeared black and the tin layer appeared white, and the exposed area ratio was calculated by determining the area of ​​the copper-tin alloy layer. The binarization was performed with an altitude range of 255 set to 112.

[0070] The results of these measurements are shown in Table 3.

[0071] [Table 3]

[0072] In the examples where the average thickness of the nickel layer was 0.15 μm or more and 4.0 μm or less, the average thickness of the copper-tin alloy layer was 0.15 μm or more and 0.8 μm or less, and the cross-sectional area ratio of the tin layer in the cross section was 21% or more and 50% or less at the cross-sectional area ratio X% of the connection part, and 31% or more and 90% or less at the cross-sectional area ratio Y% of the soldered part, and where the difference between Y and X was 10% or more, the friction coefficient and contact resistance were low, and the solder wettability was also good at the soldered part.

[0073] Among these, Examples 3, 5, 7, 12, and 13, which had extremely low coefficients of friction at the connection parts, had a cross-sectional area ratio of the tin layer of more than 25% but less than 54% at the connection parts and more than 45% but less than 75% at the soldered parts. Generally, the contact resistance after heating and solder wettability can be said to be good, but Example 3 had a slightly higher contact resistance after heating because the average thickness of the nickel layer was smaller, and the ZCT evaluation after the high-temperature, high-humidity test was B. The cross-sectional area ratio of the tin layer at the connection was low in Examples 4, 8, 9, 11, and 14, which had slightly higher contact resistance after heating. Example 6, which had a higher friction coefficient, had a higher cross-sectional area ratio of the tin layer at the connection.

[0074] In contrast, in Comparative Example 1, the average thickness of the nickel layer was too small, resulting in high post-heat contact resistance at the connection, a ZCT evaluation of C after the high-temperature, high-humidity test, and poor solder wettability. In Comparative Example 2, the cross-sectional area ratio of the tin layer at the connection was too low, resulting in a high friction coefficient at the connection. Furthermore, the cross-sectional area ratio of the tin layer at the soldered portion was also low, resulting in poor solder wettability after the high-temperature, high-humidity test. In Comparative Example 3, the cross-sectional area ratio of the tin layer at the connection was too high, resulting in a high friction coefficient at the connection. In Comparative Example 4, the cross-sectional area ratio of the tin layer at the soldered portion and the average thickness of the copper-tin alloy layer were almost the same, resulting in poor solder wettability at the soldered portion. In Comparative Example 5, the cross-sectional area ratio of the tin layer at the connection was too low, resulting in high post-heat contact resistance at the connection. Furthermore, the cross-sectional area ratio of the tin layer at the connection was low, resulting in a high friction coefficient. In Comparative Example 6, the average thickness of the copper-tin alloy layer was too small, resulting in a high friction coefficient at the connection. Furthermore, because the SsK of the nickel layer was low, the barrier properties of the nickel layer against the base material components were low, and the solder wettability after the high-temperature, high-humidity test was low. In Comparative Example 7, the cross-sectional area ratios of the tin layer at the connection and soldered parts were both too low, resulting in high contact resistance at the connection after heating and low solder wettability at the soldered part due to the low cross-sectional area ratio of the tin layer. In Comparative Example 8, the cross-sectional area ratio of the tin layer at the connection was slightly high and slightly low at the soldered part, resulting in a large negative difference in the cross-sectional area ratio of the tin layer between the soldered part and the connection (YX). As a result, the friction coefficient was slightly high and the solder wettability before and after the high-temperature, high-humidity test was also slightly low. [Explanation of symbols]

[0075] 1. Connector terminal material 10 Terminal materials 11 Connecting member 13 Connection 14 Soldering section 21 Base material 22. Coating for connection parts 23 Film for soldered parts 31,32 Nickel layer 33,34 Copper-tin alloy layer 35,36 tin layer 41 Nickel plating layer 42 Copper plating layer 43,44 Tin plating layer 45 Substrate with plating layer

Claims

1. a coating is formed on a substrate made of rolled copper or copper alloy material, the coating comprising: a nickel layer made of nickel or a nickel alloy formed on a surface of the substrate; a copper-tin alloy layer made of an alloy of copper and tin formed on the nickel layer; and a tin layer made of tin or a tin alloy formed on the copper-tin alloy layer; and the coating has a connection part to be connected to a counterpart and a soldering part to be soldered to a substrate, the average thickness of the nickel layer is 0.15 μm or more and 4.0 μm or less, and the average thickness of the copper-tin alloy layer is 0.15 μm or more and 0.8 μm or less, In a cross section parallel to the rolling direction of the base material and along the thickness direction, when a cross-sectional area ratio of the tin layer to a total area of ​​the copper-tin alloy layer and the tin layer in the connection portion is X%, and a cross-sectional area ratio of the tin layer to a total area of ​​the copper-tin alloy layer and the tin layer in the soldering portion is Y%, X% is 21% or more and 50% or less, and Y% is 31% or more and 90% or less, Y>X, and the difference is 10% or more; The terminal material for a connector, wherein the soldering portion has a skewness Ssk of the nickel layer after the tin layer and the copper-tin alloy layer are peeled off, of 0 or more and 0.6 or less.

2. The terminal material for a connector as described in claim 1, characterized in that the exposed area ratio of the copper-tin alloy layer exposed from the tin layer on the surface of the coating is 20% or more at the connection portion and less than 10% at the soldered portion.

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