Terminal materials for connectors

Abstract

The aim is to achieve both reduced 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 tin layer at the connection point is X%, and the area ratio of the tin layer to the total area of ​​the copper-tin alloy layer and tin layer at the soldering point is Y%, then X% is 21% or more and 50% or less, Y% is 31% or more and 90% or less, Y > X, and the difference between them is 10% or more.

Description

Technical Field

[0001] The present invention relates to a terminal material for a connector that reduces the insertion force during connector fitting and improves the solder wettability during mounting.

Background Art

[0002] Conventionally, a connector used for connecting electrical wiring in automobiles, consumer devices, etc. is designed to be electrically connected by a contact piece provided on a female terminal and a male terminal inserted into the female terminal contacting with a predetermined contact pressure. It includes a terminal pair.

[0003] As such a connector (terminal), a terminal material is known in which copper plating and tin plating are applied on a base material made of copper or a copper alloy, and a copper-tin alloy layer and a tin layer are formed on the base material by performing a reflow process.

[0004] As such a terminal material having a copper-tin alloy layer and a tin layer, for example, in Patent Document 1, the insertion force is reduced by controlling the roughness of the base material and controlling the exposed state of the copper-tin alloy layer from the tin layer. However, it is necessary to process in advance to control the roughness of the base material. Therefore, it is difficult to apply it to a terminal material that is manufactured by punching and then plating a terminal with a complex and small part shape.

[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. However, there is a problem that the contact resistance increases in a high-temperature and high-humidity environment because the tin layer is thin.

[0006] In addition, in Patent Document 3, a part of the copper-tin alloy is replaced with nickel (Ni) to make the copper-tin alloy have a steep uneven shape and leave a certain amount of the tin layer, thereby reducing friction and preventing an increase in contact resistance in a high-temperature environment. However, since the copper-tin alloy layer is steep, there is a limit to reducing the insertion force.

[0007] However, when these terminal materials are formed into terminals, fracture surfaces are created, which leads to a problem of reduced solder wettability. To prevent this, it is conceivable to perform plating and reflow treatment after forming the terminal shape. However, in all terminal materials, the tin layer needs to be thin to maintain low friction, so if there is a long time between the plating treatment and the reflow treatment, or if the material is exposed to a high temperature and high humidity environment, there is a problem of reduced solder wettability. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2007-100220 [Patent Document 2] Japanese Patent Publication No. 2011-012320 [Patent Document 3] Japanese Patent Publication No. 2014-240520 [Overview of the project] [Problems that the invention aims to solve]

[0009] In these terminal materials, the soft tin layer on the surface is prone to adhesion during insertion and removal, resulting in high insertion force. Therefore, attempts are made to reduce the insertion force by thinning the tin layer and exposing part of the copper-tin alloy layer. However, this leads to insufficient solder wettability during mounting. To ensure sufficient solder wettability, the tin layer must be thickened, which increases the insertion force. Thus, achieving both reduced insertion force and improved solder wettability has been difficult. Furthermore, during reflow processing, when nickel from the nickel layer diffuses into the copper-tin alloy layer, pores form in the nickel layer, reducing its barrier properties, and over time, an oxide layer forms on the surface of the tin layer.

[0010] This invention has been made in view of these circumstances, and aims to achieve both a reduction in insertion force and an improvement in solder wettability in high-temperature, high-humidity environments. [Means for solving the problem]

[0011] The connector terminal material of the present invention has a base material made of copper or a copper alloy, a nickel layer made of nickel or a nickel alloy formed on the surface of the base material, a copper-tin alloy layer made of a copper-tin alloy formed on the nickel layer, and a tin layer made of tin or a tin alloy formed on the copper-tin alloy layer, and has a connection portion for connection to the mating side and a soldering portion for soldering to the 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 of the substrate parallel to the rolling direction, if the ratio of the cross-sectional area of ​​the tin layer to the total area of ​​the copper-tin alloy layer and the tin layer in the connection portion is X%, and the ratio of the cross-sectional area of ​​the tin layer to the total area of ​​the copper-tin alloy layer and the tin layer in the soldered portion is Y%, then X% is 21% or more and 50% or less, and Y% is 31% or more and 90% or less. Y > X, and the difference between them is 10% or more.

[0012] The nickel layer has a barrier function that prevents the diffusion of copper and other components (substrate components) from the substrate at high temperatures, thereby improving heat resistance. The greater the average thickness of this nickel layer, the higher the heat resistance, but beyond a certain thickness it is unnecessary and prone to cracking during processing. On the other hand, if the average thickness of the nickel layer becomes too small, the barrier function against the substrate components becomes insufficient, reducing solder wettability and increasing contact resistance in high-temperature, high-humidity environments.

[0013] Furthermore, the copper-tin alloy layer and the tin layer are a composite structure in which the relatively soft tin layer on the surface is supported by the hard copper-tin alloy layer. Because the interface has an uneven shape, the coefficient of friction can be reduced in combination with the lubricating effect of the tin layer. When the average thickness of the copper-tin alloy layer exceeds 0.8 μm, the tin layer remaining after reflow soldering becomes thinner, increasing the contact resistance and friction coefficient in high-temperature and high-humidity environments. On the other hand, when the average thickness of the copper-tin alloy layer is less than 0.15 μm, the tin layer becomes thicker, and the amount of hard copper-tin alloy layer decreases, resulting in a higher friction coefficient. The same applies to soldered joints, but it is particularly effective in connection areas.

[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, a higher cross-sectional area ratio of the tin layer reduces the exposed area ratio of the copper-tin alloy layer on the surface of the tin layer, while a lower cross-sectional area ratio of the tin layer increases the exposed area ratio. At the connection point, friction is reduced 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 coefficient of friction will increase.

[0015] When terminals are formed in a narrow pin shape, plating them to form a coating easily results in differences in coating thickness between the flat and corner portions, and measuring the coating thickness at the corners is difficult. Therefore, relying solely on controlling the average thickness of the coating on the flat portion of the terminal may make it difficult to ensure good solder wettability. To address this, in addition to the average thickness of the copper-tin alloy layer, the ratio of the cross-sectional area of ​​the tin layer to the total area of ​​the copper-tin alloy layer and the tin layer is specified. This ratio of the cross-sectional area of ​​the tin layer is not strictly proportional to the exposed area ratio of the copper-tin alloy layer, but there is a certain degree of correlation.

[0016] At the connection point, 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 and high-humidity environments. In soldering joints, if the cross-sectional area ratio of the tin layer exceeds 90%, the cross-sectional area ratio of the tin layer at the connection point also increases, making it difficult to reduce friction. If it falls below 31%, solder wettability decreases.

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

[0018] In the terminal material for a connector of the present invention, it is preferable that the skewness Ssk of the nickel layer after peeling the solder layer and the copper-tin alloy layer is 0 or more.

[0019] Skewness Ssk is a parameter obtained by three-dimensionally expanding Rsk of a contour curve (line roughness) parameter, and is a parameter for evaluating the degree of deviation (skewness) of a histogram of height distribution, similar to Rsk. When this skewness Ssk is 0 or more, it indicates that the height distribution is symmetric about the vertical axis and there are few defects in the nickel layer. When the skewness Ssk is negative, it indicates a surface with many fine valleys and many defects. Those with good Ssk of the nickel layer in the soldering part are less likely to have an increase in contact resistance in a higher temperature and humidity environment. Since the Ssk of the soldering part and the connection part are considered to be almost the same, those without defects in the nickel layer have a high barrier property against the base material components in a high temperature and humidity environment.

[0020] In the terminal material for a connector of the present invention, it is preferable that the exposed area ratio of the copper-tin alloy layer exposed from the tin layer on the surface of the film is 20% or more at the connection part and less than 10% at the soldering part.

[0021] For the connection part, it is better to have a higher exposed area ratio of the copper-tin alloy layer to reduce the insertion force. If it is less than 20%, the effect of reducing the insertion force is poor. On the contrary, for the soldering part, it is better to have a lower exposed area ratio of the copper-tin alloy layer. If it is 10% or more, there is a risk of deterioration of solder wettability in a high temperature and humidity environment.

[0022] In the terminal material for a connector fixed to a substrate by soldering, it is preferable to use a "post-plating method" in which a metal plate is punched and then plated. In the case of pin-shaped terminals, by the post-plating method, films are formed on the entire surfaces of the connection part with the mating side and the soldering part, respectively, resulting in a terminal with excellent insertion and extraction properties with the mating side terminal and excellent solder wettability.

Effects of the Invention

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

[0024] [Figure 1] This is a plan view of a connector terminal material according to an embodiment of the present invention. [Figure 2] Figure 1 is a schematic cross-sectional view of a connector terminal material. [Figure 3] Figure 1 is a flowchart showing the manufacturing method for connector terminal materials. [Figure 4] Figure 2 is a schematic cross-sectional view showing a plated substrate for connector terminal material before the reflow process. [Modes for carrying out the invention]

[0025] Embodiments of the present invention will be described below with reference to the drawings.

[0026] [Composition of connector terminal materials] As shown in Figure 1, the connector terminal material 1 of this embodiment is a terminal chain formed by connecting multiple terminal members 10, each having the shape of a pin terminal, and is formed by punching out a long sheet of 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, along a direction perpendicular to the length of the connecting member 11. Each terminal member 10 has a pin-shaped connecting portion 13 and a soldering portion 14 narrower than the connecting portion 13, which are formed continuously from the tip, with the base end of the soldering portion 14 connected to the connecting member 11 at a right angle. After being detached from the connecting member 11, the terminal member 10 is used in an electrically connected state to a substrate by soldering the soldering portion 14 to a through-hole or the like on the substrate, and an electrical connection is made by inserting the connecting portion 13 into another female terminal. For example, the plate thickness is formed to be 0.06 mm or more and 1.00 mm, and the width of the connection portion 13 is formed to be 0.1 mm or more and 2.0 mm or less. However, Figure 1 is just one example, including the shape of the terminal member 10, and is not limited to what is shown in Figure 1. Any connection portion that makes an electrical connection with a mating terminal is acceptable.

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

[0028] The base material 21 is not particularly limited in composition as long as it is made of copper or a copper alloy, and is 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 and 32 have the function of suppressing the diffusion of copper and other components (substrate components) from the substrate 21 to the copper-tin alloy layers 33 and 34 and the tin layers 35 and 36 formed thereon. The average thickness (film thickness) of the nickel layers 31 and 32 is set to 0.15 μm or more and 4.0 μm or less for both the coating 22 for the connection part and the coating 23 for the soldering part. The nickel layers 31 and 32 have a barrier function that prevents the diffusion of copper and other components (substrate components) from the substrate 21 at high temperatures, thereby improving heat resistance. The greater the average thickness of these nickel layers 31 and 32, the higher the heat resistance, but a certain thickness (4.0 μm) is sufficient and anything beyond that is unnecessary, as it can easily lead to cracking during processing. On the other hand, if the average thickness of the nickel layers 31 and 32 becomes too small, the barrier function against the substrate components becomes insufficient, and the contact resistance value increases in high temperature and high humidity environments. Also, if the average thickness of the nickel layers 31 and 32 becomes too small, copper-tin alloying is more likely to occur in high temperature and high humidity environments, and solder wettability decreases.

[0030] Furthermore, in the soldering part coating 23, it is preferable that the skewness Ssk of the nickel layer 32 is 0 or greater. Skewness Ssk is a parameter that extends the contour curve (line roughness) parameter Rsk to three dimensions, and like Rsk, it is a parameter that evaluates the degree of bias (skewness: wideness) of the histogram of the height distribution. During reflow soldering, some of the nickel in the nickel plating layer diffuses into the copper-tin alloy layer. In this case, since the diffusion occurs along the grain boundaries of the copper-tin alloy, the greater the diffusion, the more the nickel plating layer collapses into the shape of the grain boundaries. This condition results in a defect in the nickel barrier, leading to reduced heat resistance (the tin layer becomes more prone to copper-tin alloying when heated). A skewness value of 0 or greater (positive value) indicates that the height distribution is symmetrical vertically and that there are few defects. A skewness value of 0 (negative value) indicates that the surface has many small valleys and that there are many defects. If the Ssk of the nickel layer 32 in the soldering portion 14 is lower than 0, the heat resistance of the nickel layer 32 will decrease, which may reduce solder wettability in high-temperature and high-humidity environments. It is preferable that the Ssk is 0 or higher, as this maintains heat resistance and prevents a decrease in solder wettability in high-temperature and high-humidity environments, but it is difficult to manufacture if the Ssk is 0.6 or higher. Furthermore, in the connection portion 13, it is preferable that the nickel layer 31 is free of defects (Ssk is 0 or higher) because it provides a high barrier against the substrate components in high-temperature and high-humidity environments.

[0031] Furthermore, 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 and 34 are obtained together with the tin layers 35 and 36 by sequentially forming a copper plating layer and a tin plating layer on top of the nickel layers 31 and 32 and then performing a reflow treatment. They are formed by a composite structure consisting of only Cu6Sn5 alloy, or mostly Cu6Sn5 alloy with a small amount of Cu3Sn alloy placed underneath. In some cases, some of the copper in the copper plating layer remains unreacted, resulting in a thin copper layer between the nickel layer 32 and the copper-tin alloy layers 33 and 34. The copper-tin alloy layers 33 and 34 have an uneven surface, that is, an interface with the tin layers 35 and 36 above them. This creates a composite structure in which the relatively soft tin layers 35 and 36 are supported by the hard copper-tin alloy layers 33 and 34. Combined with the lubricating effect of the tin layers 35 and 36, this reduces the coefficient of friction. Furthermore, in the coating 22 for the connection part, a portion of the copper-tin alloy layer 33 is exposed on the surface of the tin layer 35. In the coating 23 for the soldering part, a small portion of the copper-tin alloy layer 33 may also be exposed on the surface of the tin layer 35, but it may not be exposed at all.

[0033] The average thickness of these copper-tin alloy layers 35 and 36 is 0.15 μm to 0.8 μm for both the coating 22 for the connection part and the coating 23 for the soldering part. The average thickness of these copper-tin alloy layers 35 and 36 is affected by the reflow treatment conditions described later, as well as the thickness of the tin-plated layers 43 and 44 and the copper-plated layer 42 during manufacturing. If the average thickness of the copper-tin alloy layers 33 and 34 is less than 0.15 μm due to insufficient heating during the reflow process, the tin layers 35 and 36 become thicker, and the amount of hard copper-tin alloy layers 33 and 34 decreases, resulting in a higher coefficient of friction. If the average thickness of the copper-tin alloy layers 33 and 34 exceeds 0.8 μm due to excessive formation of copper-tin alloy layers 33 and 34 during the reflow process, the tin layers 35 and 36 become thinner, increasing the contact resistance value in high-temperature and high-humidity environments, and thus increasing the coefficient of friction. The same applies to the soldered joint 14, but it is mainly effective in the connection 13. The average thickness of these copper-tin alloy layers 33 and 34 is preferably 0.30 μm or more and 0.65 μm or less.

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

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

[0036] The connection portion 13 aims to reduce friction by lowering 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 will increase. In this connection section 13, if the cross-sectional area ratio of the tin layer 35 exceeds 50%, adhesion becomes more likely, making it difficult to reduce friction. If it is less than 21%, the coefficient of friction becomes high, resulting in high contact resistance in high-temperature and high-humidity environments.

[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 reduce friction, and if it is less than 31%, the solder wettability decreases. The cross-sectional area ratio of the tin layers 35 and 36 is preferably 25% to 45% at the connection portion 13 and preferably 45% to 75% at the soldered portion 14.

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

[0039] Furthermore, on the surfaces of the coatings 22 and 23, the exposed area ratio of the copper-tin alloy layers 33 and 34 exposed from the tin layers 35 and 36 should be 20% or more for the coating 22 for the connection part and less than 10% for the coating 23 for the soldering part. For the connection portion 13, a higher exposed area ratio of the copper-tin alloy layer 33 is preferable to reduce insertion force; if it is less than 20%, the effect of reducing insertion force is poor. Conversely, for the soldering portion 14, a lower exposed area ratio of the copper-tin alloy layer 34 is preferable; if it is 10% or more, solder wettability may decrease in high-temperature, high-humidity environments.

[0040] [Manufacturing method for connector terminal materials] Next, we will explain how to manufacture the terminal material 1 for this connector. The manufacturing method for this connector terminal material 1 includes a punching step in which a long, narrow metal plate is punched out by a press to form a terminal chain that will become a base material 21; a pre-treatment step in which the surface of the base material 21 after punching is cleaned; a plating layer formation step in which a nickel plating layer 41, a copper plating layer 42, and tin plating layers 43, 44 are sequentially formed on the surface of the base material 21; and a reflow treatment step in which the plated base material 45 with the three plating layers formed is heated and reflow treated (see Figure 3). The process will be described below in order.

[0041] (punching process) A long, narrow metal plate made of copper or a copper alloy, wound into a coil, is fed out and punched out by a press to form a terminal chain that will become the base material 21 as shown in Figure 1.

[0042] (Pre-treatment process) The base material 21 after punching is subjected to a pre-treatment to clean the surface by degreasing, pickling, etc.

[0043] (Plating layer formation process) On the pre-treated substrate 21, 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 as follows (see Figure 4).

[0044] -Nickel plating layer- A nickel plating treatment is performed on the surface of the pre-treated substrate 21 to form a nickel plating layer 41 made of nickel or a nickel alloy. A general nickel plating bath can be used; for example, a sulfamic acid bath mainly composed of nickel sulfamate and boric acid can be used. The temperature of the plating bath is 50°C to 60°C, and the current density is 1 A / dm². 2 More than 10A / dm 2 The following is specified: The thickness of this nickel plating layer 41 is specified to be between 0.15 μm and 4.0 μm.

[0045] -Copper plating layer- A copper plating treatment is performed to form a copper plating layer 42 made of copper or a copper alloy on the nickel plating layer 41. A general copper plating bath can be used for the copper plating; for example, a copper sulfate bath mainly composed of copper sulfate and sulfuric acid can be used. The plating bath temperature should be between 20°C and 50°C, and the current density should be 1 A / dm². 2 More than 10A / dm 2 The following is specified: The thickness of this copper plating layer 42 is specified to be between 0.1 μm and 0.5 μm.

[0046] -Tin plating layer- A tin plating treatment is performed to form tin plating layers 43 and 44 made of tin or a tin alloy on the copper plating layer 42. A general tin plating bath can be used as the plating bath for forming the tin plating layers 43 and 44; for example, a methanesulfonic acid bath mainly composed of methanesulfonic acid and tin methanesulfonate can be used. The plating bath temperature is 20°C to 40°C, and the current density is 1 A / dm².2 More than 20A / dm 2 The following is considered to be the case.

[0047] This tin plating process is controlled so that the tin plating layers 43 and 44 have different thicknesses at the connection point 13 and the soldered part 14. Specifically, a plated substrate having a nickel plating layer 41 and a copper plating layer 42 is immersed in a tin plating bath (electroplating bath), and a shielding plate is placed between the area that will become the connection part 13 and the electrode while the plating process (electroplating process) is performed. The shielding plate is an insulating plate made of a material that does not corrode in the plating solution, such as a non-conductive resin (for example, polyvinyl chloride or acrylic resin). By appropriately setting the distance between the shielding plate, the plated substrate, and the electrode, as well as the area of ​​the shielding plate, the thickness of the tin plating layers 43 and 44 at the connection part 13 and the soldering part 14, respectively, can be controlled. The tin plating layer 43 of the connection portion 13 is controlled to be between 0.3 μm and 2.5 μm in thickness, and the tin plating layer 44 of the soldering portion 14 is controlled to be between 1.0 μm and 4.0 μm in thickness. In this case, the tin plating layer 44 of the soldering portion 14 is formed to be thicker than the tin plating layer 43 of the connection portion 13. Alternatively, the thickness may be controlled by performing tin plating multiple times, with at least one of these processes involving masking the surface of the connecting portion before plating.

[0048] In this manner, 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 plated substrate 45 with three stacked plating layers. Between each plating process, a cleaning treatment using sulfuric acid or the like is performed. Before this plating process, the substrate 21 is in a state where it has been punched out into a chain terminal body by a press. The substrate 21 is then immersed in a plating bath to form a plating layer, so three plating layers are formed not only on both the front and back surfaces of the substrate 21, but also on both sides (the cut ends at the time of 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 the plating bath.

[0049] (Reflow process) The plated substrate 45, which has the plating layer formed as described above, is subjected to reflow processing. In the case of a long, narrow sheet material (strand material) wound on a roll, this reflow processing is carried out by running the sheet material in the length direction and passing it through a reflow oven while continuously performing the above-mentioned pretreatment and plating process. However, in the case of the plated substrate 45 of this embodiment, it is a punched material that has been punched out in advance by a press as a terminal chain of a predetermined length as shown in Figure 1. After the above-mentioned pretreatment and plating process is applied to this punched material, the plated substrate 45 is supplied to a relatively small reflow oven and subjected to reflow processing. This reflow process is performed by heating the plated substrate 45 above the melting point of tin to melt the tin plating layers 43 and 44, and then cooling it.

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

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

[0052] Furthermore, since nickel layers 31 and 32 covering the substrate 21 are formed on the coatings 22 and 23, the diffusion of copper and other components (substrate components) from the substrate 21 at high temperatures can be prevented, thereby improving heat resistance. Furthermore, the copper-tin alloy layers 33,34 and the tin layers 35,36 form a composite structure in which the relatively softer tin layers 35,36 are supported by the harder copper-tin alloy layers 33,34. Since the interface between them has an uneven shape, the coefficient of friction can be reduced in combination with the lubricating effect of the tin layers 35,36.

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

[0054] Furthermore, the detailed configuration is not limited to that of the embodiment, and various modifications can be made without departing from the spirit of the present invention. Although the nickel layers 31 and 32 were set to the same thickness range at the connection point 13 and the soldering point 14, they may be set to different thicknesses within that range (0.15 μm or more and 4.0 μm or less). Although the copper-tin alloy layers 33 and 34 were set to the same thickness range at the connection point 13 and the soldering point 14, they may be set to different thicknesses within that range. Furthermore, in the plating process, the nickel plating layer 41 and the copper plating layer 42 were set to the same thickness for both the connecting portion 13 and the soldering portion 14, but they may be set to different thicknesses, similar to the tin plating layers 43 and 44. [Examples]

[0055] A 0.25 mm thick plate of CDA (Copper Development Association) alloy symbol C18665 was used as the base material. After punching it into the terminal chain shape shown in the figure, electrolytic degreasing was performed as a pretreatment, and nickel plating, copper plating, and tin plating were applied sequentially to the surface. Pickling treatment was also performed between each plating and after copper plating. The conditions for electrolytic degreasing, pickling, and plating are shown in Table 1 in the order of the process, and the same conditions were used for the following examples and comparative examples. In the table, RT indicates room temperature. In this case, for nickel plating, the thickness of the nickel plating layer was adjusted by varying the plating time in the range of 13 to 350 seconds. For copper plating, the thickness of the copper plating layer was adjusted by varying the plating time in the range of 8 to 40 seconds. For tin plating, the plating time was set in the range of 8 to 120 seconds, and during that time, a shielding plate was used to control the thickness difference between the connection part and the soldered part. In Comparative Example 4, tin plating was performed without using a shielding plate.

[0056] [Table 1]

[0057] The plated substrates, on which various plating layers were formed in this manner, were subjected to reflow treatment. The reflow conditions were carried out within the range described in the embodiment.

[0058] For the terminal material after reflow processing, the average thickness of each coating layer and the cross-sectional area ratio of the tin layer were measured.

[0059] (Average thickness of each layer) For measuring the average thickness of each layer, the measurement area was defined as part A in Figure 1 for the connection area and part B in the same figure for the soldered area. Part A is the central part in the width direction, located at L1=2mm (2mm from the top edge of the paper in Figure 1) from the tip of the pin, which has a total length of L0=28.8mm and corresponds to the sliding part of the terminal. Part B is the central part in the width direction, located at L1×2=4mm from the side edge of the connecting part (bottom edge in Figure 1) and L1=2mm from the connecting position of the terminal. The thickness of the nickel layer was measured using a Hitachi High-Tech Science Corporation X-ray fluorescence film thickness gauge (FT150).

[0060] To determine the average thickness of the copper-tin alloy layer, each sample was cross-sectionally processed using a focused ion beam (FIB) system (model: SMI3050TB) manufactured by Seiko Instruments Inc. The formed cross-sections (parallel to the rolling direction of the substrate) were observed at a magnification of 13,000x using a scanning ion microscope (SIM). In the cross-sectional SIM image with a 60° inclination angle, the distance a from the interface with the nickel layer to 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. The average of these distances was then calculated and converted to the actual length to obtain the average thickness of the copper-tin alloy layer.

[0061] (Cross-sectional area ratio of the tin layer) Five cross-sectional images were acquired of the entire connection and soldered areas parallel to the rolling direction of the substrate. The acquired backscattered electron images were binarized using the image processing software imageJ (ver. 1.54f) so that the tin layer was black and the copper-tin alloy layer was white. After calculating the area of ​​the tin layer and the copper-tin alloy layer, the cross-sectional area ratio of the tin layer was calculated as tin layer / (tin layer + copper-tin alloy layer) × 100, and the average of the five points was taken as the measured value. Let X be the cross-sectional area ratio of the tin layer at the connection area, and Y be the cross-sectional area ratio of the tin layer at the soldered area. Binarization was performed with the intensity range set to 112 out of 255.

[0062] These measurement results are shown in Table 2.

[0063] [Table 2]

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

[0065] (Coefficient of friction) For the connection parts of each sample, a 60mm long test piece was cut parallel to the rolling direction and used as a substitute for the male terminal (male terminal test piece). For the female terminal sample, all samples were the same. Sample from Example 13 (base material: C18665 material with a plate thickness of 0.25mm) was cut to 60mm x 10mm and embossed with a radius of curvature of 1.5mm in the center of the test piece. For measurement, a friction and wear tester (UMT-Tribolab) from Bruker AXS Corporation was used. The male terminal test piece was set horizontally, and the convex surface of the female terminal test piece was brought into contact with a position 5mm below part A in Figure 1, so that part A in Figure 1 was the center of the sliding part. A load of 3N was applied to the male terminal test piece and it was slid 10mm to a position 5mm above part A in Figure 1. Friction coefficient data was acquired at every 0.013 mm sliding distance, and the average of the friction coefficients obtained between 0.1 mm and 10 mm sliding distances was used as the friction coefficient value.

[0066] (contact resistance) For each sample's connection point, test specimens were prepared in the same manner as for the coefficient of friction. These were heated at 150°C for 250 hours, and then the contact resistance (mΩ) was measured for each. For the measurement, a friction and wear tester (UMT-Tribolab) from Bruker AXS Corporation was used. The convex surface of the female test specimen was brought into contact with the horizontally positioned male terminal test specimen, and the contact resistance value was measured using the four-terminal method when a load of 5N was applied to the male terminal test specimen.

[0067] (Solder wettability) For solder wettability, the zero-crossing time (ZCT) was measured by meniscography at point B in Figure 1 at the solder joint of each sample using a weakly active flux. Each sample underwent a pressure cooker test in a high-temperature, high-humidity environment (temperature 105°C - saturated 100%RH - test time 8 hours) using an accelerated life tester (ESPEC EHS-411M), and the zero-crossing time was measured by meniscography before and after the pressure cooker test (before and after the high-temperature, high-humidity test). The zero-crossing time was measured by immersion in Sn-3Ag-0.5Cu lead-free solder at a solder bath temperature of 245°C, with an immersion speed of 2 mm / sec, an immersion depth of 5 mm from the connection point with the joint of the sample, and an immersion time of 10 seconds. A solder zero-crossing time of 2 seconds or less was rated A, a time between 2 seconds and 3 seconds was rated B, and a time exceeding 3 seconds was rated C. C was a failing grade.

[0068] (Ssk: Skewness) The skewness in section A of Figure 1 was measured. The tin layer was removed by immersion in an etching solution for stripping the tin plating (Raybolt L-80) to expose the underlying copper-tin alloy layer. Then, the copper-tin alloy layer was completely stripped by immersion in an etching solution for stripping the copper-tin alloy layer (a mixture of Raybolt CopperAct S-40 100g / L and sulfuric acid 80mL / L) to expose the underlying nickel layer. The skewness of this nickel layer was determined from the average value of skewness Ssk measured at a total of 9 points using a Keyence Corporation laser microscope (VK-X200) with an objective lens of 150x (measurement field of view 96μm × 72μm) and no filter.

[0069] (Percentage of exposed copper-tin alloy layer) The measurement area was designated as parts A and B in the drawing. Using a SEM (JSM-7001F manufactured by JEOL Ltd.), the surface of the tin layer was observed, and a measurement of 0.0028 mm was obtained at 2000x magnification. 2Backscattered electron images of the field of view were acquired. The acquired backscattered electron images were binarized using the image processing software imageJ (ver. 1.54f) so that the exposed copper-tin alloy layer on the surface appeared black and the tin layer appeared white. The exposed area ratio was calculated by determining the area of ​​the copper-tin alloy layer. Binarization was performed with the altitude range set to 112 out of 255.

[0070] These measurement results are shown in Table 3.

[0071] [Table 3]

[0072] Examples in which 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, the cross-sectional area ratio of the tin layer in the cross-section was 21% or more and 50% or less at the connection part (cross-sectional area ratio X%), and 31% or more and 90% or less at the soldering part (cross-sectional area ratio Y%), and YX had a difference of 10% or more, showed low coefficient of friction and contact resistance, and good solder wettability at the soldering part.

[0073] Among these, Examples 3, 5, 7, 12, and 13, which exhibited extremely low coefficients of friction at the connection points, had a cross-sectional area ratio of tin layers exceeding 25% but less than 54% at the connection points and exceeding 45% but less than 75% at the soldered areas. Overall, the contact resistance and solder wettability after heating were good, however, Example 3 had a slightly higher contact resistance after heating due to the smaller average thickness of the nickel layer, resulting in a ZCT evaluation of B after the high-temperature, high-humidity test. Examples 4, 8, 9, 11, and 14, which showed slightly higher contact resistance after heating, had a lower cross-sectional area ratio of the tin layer at the connection point. Example 6, which showed a higher coefficient of friction, also had a higher cross-sectional area ratio of the tin layer at the connection point.

[0074] In contrast, Comparative Example 1 had a nickel layer with an average thickness that was too small, resulting in high contact resistance at the connection after heating, a ZCT evaluation of C after the high-temperature and high-humidity test, and low solder wettability. Comparative Example 2 had a high coefficient of friction at the connection because the cross-sectional area ratio of the tin layer at the connection was too low. Also, the cross-sectional area ratio of the tin layer at the soldering point was low, resulting in low solder wettability after the high-temperature and high-humidity test. Comparative Example 3 had a high coefficient of friction at the connection because the cross-sectional area ratio of the tin layer at the connection was too high. Comparative Example 4 had almost the same cross-sectional area ratio of the tin layer at the soldering point and the average thickness of the copper-tin alloy layer at the connection point, resulting in low solder wettability at the soldering point. Comparative Example 5 had a high contact resistance at the connection after heating because the cross-sectional area ratio of the tin layer at the connection point was too low. Also, the coefficient of friction was high because the cross-sectional area ratio of the tin layer at the connection point was low. Comparative Example 6 had a high coefficient of friction at the connection point because the average thickness of the copper-tin alloy layer was too small. Furthermore, because the SsK of the nickel layer was low, the barrier properties of the nickel layer against the substrate components were low, resulting in poor solder wettability after the high-temperature, high-humidity test. In Comparative Example 7, the cross-sectional area ratio of the tin layer in both the connection and soldering areas was too low. In the connection area, the contact resistance after heating was high, and in the soldering area, the low cross-sectional area ratio of the tin layer resulted in poor solder wettability. In Comparative Example 8, the cross-sectional area ratio of the tin layer was slightly high in the connection area and slightly low in the soldering area. As a result, the difference in the cross-sectional area ratio of the tin layer between the soldering area and the connection area (YX) was significantly negative, leading to a slightly higher coefficient of friction and slightly lower solder wettability before and after the high-temperature, high-humidity test. [Explanation of symbols]

[0075] 1. Terminal material for connectors 10 Terminal components 11 Connecting member 13 Connection part 14 Soldering section 21 Base material 22 Coating for connection parts 23. Coating for soldering joints 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 Plating-coated substrate

Claims

1. A coating is formed on a base material made of copper or a copper alloy, comprising a nickel layer made of nickel or a nickel alloy formed on the surface of the base material, a copper-tin alloy layer made of a copper-tin alloy formed on the nickel layer, and a tin layer made of tin or a tin alloy formed on the copper-tin alloy layer, and also having a connecting portion for connection to the mating side and a soldering portion for soldering to the 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 of the substrate parallel to the rolling direction, if the ratio of the cross-sectional area of ​​the tin layer to the total area of ​​the copper-tin alloy layer and the tin layer in the connection portion is X%, and the ratio of the cross-sectional area of ​​the tin layer to the total area of ​​the copper-tin alloy layer and the tin layer in the soldering portion is Y%, then X% is 21% or more and 50% or less, and Y% is 31% or more and 90% or less. A terminal material for connectors characterized in that Y > X, and the difference between them is 10% or more.

2. The connector terminal material according to claim 1, characterized in that the soldered portion has a skewness Ssk of the nickel layer after the tin layer and the copper-tin alloy layer have been removed, which is 0 or greater.

3. The connector terminal material according to claim 1 or 2, characterized in that the exposure 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 soldering portion.

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