JP4847898B2 - Wiring conductor and method for manufacturing the same - Google Patents

Description

  The present invention relates to a wiring conductor and a terminal connection portion, and more particularly to a wiring conductor such as a flexible flat cable (FFC) and a flexible printed wiring board (FPC) that are used in electronic equipment and requires flexibility. It is about the method.

  Conventionally, the surface of a wiring material, particularly copper or copper alloy, is plated with Sn, Ag, Au, or Ni to prevent the wiring material from being oxidized. For example, as shown in FIG. 2, in the terminal connection part of the connector 11 and flexible flat cable (hereinafter referred to as FFC) 13, the connector pins (metal terminals) 12 of the connector (connector member) 11 and the conductors 14 of the FFC 13 The surface is plated. In particular, Sn is inexpensive and soft, so it is easily deformed by the fitting (contact) pressure to increase the contact area and keep the contact resistance low, so the surface of the wiring material was Sn plated. Things are widely used in general.

  Conventionally, Sn-Pb alloys with good whisker resistance have been used as this Sn plating alloy, but in recent years, Pb-free materials (lead-free materials) and non-halogen materials have been used from the viewpoint of environmental compatibility. Pb-free and non-halogenated are also required for various materials used for wiring materials.

JP 2002-294486 A JP 2003-293187 A

  As Sn plating becomes Pb-free, particularly in Sn or Sn-based alloy plating, whisker 21, which is a needle crystal of Sn, is generated from the plating at the terminal connection portion as shown in FIG. There is a problem that a short circuit may occur between adjacent wires (conductor 14).

  In order to relieve stress during Sn plating, which is considered as one of the causes of whisker generation, it is said that reflow treatment of electroplated Sn can reduce the generation of whiskers.

  However, when a new external stress is applied such as a fitting portion (connecting portion) with the connector, the occurrence of whiskers cannot be suppressed even if the reflow process is performed. In addition, whisker can be suppressed by electrolytic plating or electroless plating of an alloy such as Bi or Ag, but it is reported that whisker is generated by reflow treatment, compared to pure Sn. These alloy platings also have problems. At present, as an effective measure for suppressing whisker, a method of applying a thin Sn plating of 1 μm or less has been proposed, but there is a problem that the contact resistance is increased more than that in the prior art particularly when left at high temperature and high humidity ( For example, JEITA lead-free completed urgent proposal report meeting material (2005.2.17), JEITA lead-free solder practical application 2005 result report (2005.6), JP 2005-206869 A, JP 2006-45665 A reference).

  The object of the present invention, which was created in view of the above circumstances, is less likely to generate whiskers from the Sn plating film surface and the solder around the conductor, even in an environment where a large external stress such as fitting with a connector is applied. Another object of the present invention is to provide a Pb-free wiring conductor that hardly generates whiskers and does not increase contact resistance even in a high temperature and high humidity environment, and a method for manufacturing the same.

To achieve the above object, a first aspect of the invention, at least part of the surface of the core made of a metal material made of a composite material Sn-based material part is formed of Pb-free, said core and said Sn-based the Ni-P intermediate layer of a predetermined thickness between the material portion is provided, then the reflow line Ukoto, loss of Ni-P intermediate layer by diffusing the Ni-P intermediate layer in the Sn-based material part together is, on the surface of the Sn-based material part, it is one obtained by forming a composite film comprising a composite film or a Sn oxide consisting Sn oxide and P oxide and the phosphate compound, the Sn-based material part The wiring conductor is characterized in that the thickness is 1 μm or less, and the thickness of the Ni—P intermediate layer is 1/200 or more and less than 1/20 of the thickness of the Sn-based material portion .

The invention according to claim 2 is the wiring conductor according to claim 1 , wherein the Ni—P intermediate layer is made of 1 wt% or more and 15 wt% or less of P, and the balance is Ni and an inevitable impurity Ni—P alloy. .

According to a third aspect of the present invention, the Sn-based material portion is pure Sn-based, Sn-Ag-based, Sn-Ag-Cu-based, Sn-Bi-based, Sn-Bi-Ag-based, or Sn composed of Sn and inevitable impurities. The wiring conductor according to claim 1 , wherein the wiring conductor is a Cu-based Pb-free solder material.

According to a fourth aspect of the present invention, due to the reflow, a part of the Sn-based material part forms an intermetallic compound layer with a part of the constituent elements of the core material and the Ni-P intermediate layer, and the Sn-based material part remaining thickness of the pure Sn or Sn alloy 0.05μm or more, the wiring conductor according to claims 1 to 3 or less than 0.5 [mu] m.

The invention according to claim 5 is the wiring conductor according to claim 4 , wherein the remaining thickness of the pure Sn or Sn alloy in the Sn-based material portion is 0.05 μm or more and less than 0.2 μm.

In the invention of claim 6, the metal material as the core material is a conductive material having an electric conductivity of 10% IACS or more, oxygen-free copper, tough pitch copper, silver, nickel, a copper alloy material, a nickel alloy material, an aluminum alloy material Or a conductor for wiring according to any one of claims 1 to 5 , wherein the conductor is a round wire, square wire, plate, strip, or foil.

The invention of claim 7 is a method for producing a composite material in which a Pb-free Sn-based material portion is formed on at least a part of the surface of a core material made of a metal material , and performing Ni-P electrolytic plating on the core material, An Ni—P intermediate layer having a predetermined thickness is provided on at least a part of the surface of the core material, and a Pb-free Sn-based material portion is provided on the Ni—P intermediate layer by Sn plating, and wire drawing / rolling is performed to form the composite after adjusting the size and shape of the timber, carried out reflow, the Ni-P intermediate layer with abolishes Ni-P intermediate layer is diffused into the Sn-based material part, on the surface of the Sn-based material part, Sn A composite film composed of an oxide and a P oxide or a composite film composed of a Sn oxide and a phosphate compound , wherein the Sn-based material portion has a thickness of 1 μm or less, and the Ni-P intermediate layer Is 1/2 of the thickness of the Sn-based material part. 0 or more, it is a manufacturing method of the wiring conductor, characterized in that less than 1/20.

  According to the present invention, in the wiring conductor of an electronic device, oxidation of the surface of the conductor (wiring material) whose surface is plated with Sn can be prevented. As a result, even when external stress such as a fitting portion is applied, it is possible to suppress the whisker which is a needle crystal of Sn, and it is possible to solve a problem such as a short circuit between adjacent conductors. In addition, contact reliability is not impaired even in a high temperature and high humidity environment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1 (a), the wiring conductor according to a preferred embodiment of the present invention has 1 P on at least a part of the surface (outer peripheral surface) of the core material 33 made of a conductive material (metal material). A Ni—P layer (Ni—P intermediate layer) 32 having a predetermined thickness, which is made of Sn and inevitable impurities, is provided, and the Sn-based material portion 31 is plated on the Ni—P layer 32. 1 and then heat-treated (reflow treatment), as shown in FIG. 1B, the Ni-P layer 32 is diffused into the Sn-based material portion 31 and the Ni-P layer 32 disappears. . The thickness of the Ni-P layer 32 is set to 1/200 or more and less than 1/20 of the thickness of the Sn-based material portion 31, and the Ni-P layer 32 is melted during the reflow process. It is characterized by diffusing. The conductor for wiring after the heat treatment has a composite film made of Sn oxide and P oxide (or a composite film made of Sn oxide and phosphate compound) 35 on the surface of the Sn-based material portion 31, and a core material 33. And the Sn-based material part 31 have a metal material of the core material 33 and an Sn intermetallic compound layer.

  The material constituting the Sn-based material portion 31 is pure Sn-based, Sn-Ag-based, Sn-Ag-Cu-based, Sn-Bi-based, Sn-Bi-Ag-based, or Sn-Cu based on Sn and inevitable impurities. Pb-free solder material of the system is mentioned.

  As the metal material constituting the core material 33, a conductive material having an electrical conductivity of 10% IACS or more, oxygen-free copper, tough pitch copper, silver, nickel, a copper-based alloy material, a nickel-based alloy material, an aluminum-based alloy material, or an iron-based alloy Materials. Moreover, as a shape of the core material 33, a round wire, a square wire, a board, a strip, or a foil is mentioned, It does not specifically limit.

  The Sn-based material portion 31 may be provided on the entire outer peripheral surface of the core material 33, or may be provided only on the surface that is fitted and connected to the connector pin 12 shown in FIG.

  Further, the thickness of the intermetallic compound layer 34 is not particularly limited as long as the intermetallic compound layer 34 is extremely thin so as not to hinder the bending characteristics of the wiring conductor.

  Next, the manufacturing method of the wiring conductor of this Embodiment is demonstrated.

  In the present embodiment, first, the Ni—P layer 32 is provided on at least a part of the surface (outer peripheral surface) of the core material 33. This Ni-P layer 32 is formed by Ni-P electrolytic plating described later. Then, the Sn-based material portion 31 is provided by electrolytic plating or electroless plating on the Ni-P layer 32 having a predetermined thickness formed by electrolytic plating.

  Thereafter, the core material 33 provided with the Ni-P layer 32 and the Sn-based material portion 31 is subjected to wire drawing / rolling processing to be adjusted to a predetermined size / shape, and then subjected to heat treatment (reflow treatment). By this reflow process, the P component of the Ni-P layer 32 diffuses into the melted Sn-based material portion 31, and the Ni component of the Ni-P layer 32 is formed between the metal material of the core material 33 and Sn. It acts as a barrier layer for suppressing the growth of intermetallic compounds, and the Ni-P layer 32 disappears. The diffused P component is preferentially oxidized on the surface of the Sn-based material portion 31, and a composite film composed of Sn oxide and P oxide (or Sn oxide and phosphate compound is formed on the surface of the Sn-based material portion 31. Composite film) 35 formed. In addition, at the interface between the core material 33 and the Sn-based material portion 31 after the heat treatment, the metal material of the core material 33 and the intermetallic compound layer 34 of Sn are formed extremely thin. Thereby, the wiring conductor according to the present embodiment is obtained.

  The annealing temperature / time for reflow is not particularly limited, and is a temperature / time sufficient for P to diffuse.

  Next, the operation of the present embodiment will be described.

  The present inventors have found that by adding an appropriate amount of an oxidation-inhibiting element such as P into Sn, surface oxide film formation can be suppressed, whiskers can be suppressed, and increase in contact resistance under a high temperature environment can be suppressed. An application has already been filed (Japanese Patent Application No. 2006-191579).

  As a method for adding P to Sn, a hot dipping method is disclosed (see Japanese Patent No. 3005742). In the electroplating (electrolytic plating) method, it is difficult to control P to an extremely low concentration, and usually only a few percent can be controlled. For this reason, the hot dipping method is effective as the P control method, but there are problems that the line speed is slow and the cost is high. In addition, when hot-dip plating is performed in the air, P is preferentially oxidized over Sn to increase the concentration on the surface, but this high-concentration P oxide layer is scraped in a subsequent wire drawing / rolling step, and the added P is There is also a concern that it will disappear.

  Therefore, in the present embodiment, the Ni—P layer 32 by electrolytic plating is provided as an intermediate layer between the core material 33 and the Sn-based material portion 31. The thickness of the Ni-P layer 32 is 1/200 or more and less than 1/20 of the thickness of the Sn-based material portion 31, and is very thin. The P concentration of the Ni—P layer 32 is 1 wt% or more and 15 wt% or less, and the concentration can be adjusted.

  A method for producing Ni-P electrolytic plating by adding an appropriate amount of phosphorous acid to a Watt bath (mainly a mixture of nickel sulfate and nickel chloride) well known as a Ni plating bath is known. An example of plating conditions for Ni-P electrolytic plating is shown in Table 1. The thickness of the Ni-P layer 32 is adjusted by, for example, adjusting the current density and the immersion time in the Sn plating bath. The adjustment of the P concentration of the Ni-P layer 32 is, for example, the concentration of phosphorous acid. Adjust by adjusting.

  When Sn plating is performed on the Ni—P plating, a P-concentrated layer is formed at the interface between the two platings by a heat treatment such as a reflow process later. And in a reliability test, there exists a possibility that peeling may generate | occur | produce in the interface of Ni plating and P concentration layer, and there exists a problem of causing the fall of reliability.

  Therefore, in the present embodiment, the thickness of the Ni—P layer is set to be 0.3 μm or less and less than 1/20 of the thickness of the Sn-based material portion 31. Thus, during the reflow process, the Ni—P layer diffuses into the molten Sn-based material part, and part of the Ni—P layer forms an intermetallic compound layer, and the Ni—P layer disappears. For this reason, P concentration layer does not exist after reflow processing, and good reliability is obtained. Further, the Ni-P layer is amorphous and has a very hard and brittle property. If the Ni-P layer remains, the bending characteristics of the wiring conductor may be lowered. Since the -P layer disappears and disappears, such a fear disappears.

  When the thickness of the Ni-P layer is 1/20 or more of the thickness of the Sn-based material portion, the Ni-P layer cannot be lost during reflow treatment after wire drawing / rolling. Layer or P-enriched layer remains. Moreover, when the thickness of the Ni—P layer exceeds 0.3 μm after wire drawing / rolling, the Ni—P layer cannot withstand wire drawing / rolling and cracks are generated. Therefore, the thickness of the Ni—P layer is preferably 0.3 μm or less and less than 1/20 of the thickness of the Sn-based material portion 31.

  Thus, by providing a very thin Ni-P layer 32 as an intermediate layer and performing reflow treatment to diffuse and disappear, P can be added to the Sn plating (Sn-based material part 31) at an extremely low concentration. In addition, it is possible to manufacture a wiring conductor that is inexpensive, has high reliability, and has excellent bending characteristics. By applying the wiring conductor according to the present embodiment to, for example, the conductor 14 of the FFC 13 in the terminal connection portion shown in FIG. 2, it is possible to suppress the occurrence of whiskers on the surface of the conductor 14, Problems such as a short circuit between adjacent wiring members can be solved.

  Another effect of the Ni-P layer 32 is that when the metal material used as the core material 33 is, for example, pure copper or a copper alloy, the Ni of the Ni-P layer 32 is the intermetallic compound of copper and tin over time. It is to suppress the growth.

  As a countermeasure against whiskers, it has been disclosed that the thickness of the remaining Sn after the reflow process is reduced in a flexible flat cable (FFC) or a flexible printed wiring board (FPC) (see JP 2006-45665 A). However, in a high temperature holding environment, the intermetallic compound of copper and tin grows with time, and the residual Sn thickness becomes extremely thin or the intermetallic compound is exposed to the surface, thereby increasing the contact resistance. There is a problem of end.

Therefore, in the present embodiment, the Ni-P layer 32 is provided as an intermediate layer, and the growth of the intermetallic compound of copper and tin over time is suppressed by the Ni. There is no risk of thinning or exposure of intermetallic compounds to the surface. Further, due to the effect of suppressing the growth of the intermetallic compound by Ni, the remaining Sn thickness can be made thinner than before, and the whisker resistance can be further enhanced. The remaining Sn thickness, that is, the remaining thickness of pure Sn or Sn alloy of the Sn-based material part 31 is specifically adjusted to 0.05 μm or more and less than 0.5 μm, preferably 0.05 μm or more and less than 0.2 μm. Is done. Thereby, although the initial contact resistance is somewhat high, a wiring conductor with little change with time can be obtained.

  In order to produce such an effect of Ni, the thickness of the Ni-P layer 32 is preferably 1/200 or more of the thickness of the Sn-based material portion 31. If it is less than that, the amount of Ni added is too small, and thus the above-mentioned effect cannot be obtained.

  The P concentration of the Ni—P layer 32 is preferably 1 wt% or more and 15 wt% or less. It is difficult to stably produce the Ni-P layer 32 having a P concentration of more than 15 wt%, and the Ni-P layer 32 becomes hard and brittle as the P concentration increases, which makes it difficult to perform wire drawing and rolling. In addition, since the Ni-P layer 32 is an extremely thin layer, if the P concentration is less than 1 wt%, the P concentration supplied to the Sn-based material portion 31 is too small, and thus the above-described effects cannot be obtained. .

  On the other hand, when the conductor having a structure in which the Ni-P layer 32 and the Sn-based material portion 31 are provided on the core material 33, the Ni-P layer 32 is positioned on the inner layer side of the Sn-based material portion 31. Therefore, there is no possibility that the Ni-P layer 32 is scraped off by wire drawing / rolling.

  In addition, the reflow treatment is performed after the wire drawing / rolling process. Although the Ni-P layer 32 is located on the inner layer side of the Sn-based material portion 31, P is more easily oxidized than Sn. When the material part 31 melts (during the reflow process), the P component diffuses into the Sn-based material part 31 and P is oxidized prior to Sn and volatilizes from the surface, or a very thin P oxide film is formed on the surface. Form. That is, by performing the reflow process, P moves to the surface of the Sn-based material portion 31 and a very thin composite film 35 is generated on the surface of the Sn-based material portion 31. As the P diffuses, the Ni—P layer 32 disappears and is integrated with the Sn-based material portion 31. Since the thickness of the Sn-based material portion 31 is 20 to 200 times the thickness of the Ni-P layer 32, the P concentration in the entire integrated Sn-based material portion 31 is extremely low.

  Furthermore, since the composite film 35 is formed on the surface of the Sn-based material portion 31 after the reflow process, it is possible to prevent the Sn on the inner layer side of the composite film 35 from being oxidized and suppress the generation of whiskers. Is done. Since the composite film 35 suppresses the growth of Sn oxide film even in a high temperature and high humidity environment, an increase in contact resistance can be suppressed.

  Table 2 shows an example according to the above-described embodiment and a comparative example.

  First, after making the conductor for flexible flat cables of the Ni-P layer thickness and composition and initial Sn thickness shown in Table 2, they were subjected to reflow treatment by energization heating. The Ni—P layer before reflow treatment and the initial Sn thickness were determined from the thickness of each layer before drawing and rolling, and the thickness of each layer after drawing and rolling was determined by proportional calculation.

  Further, the remaining Sn thickness of the conductor after the reflow treatment was measured by an electrochemical method called a Kokuru method. The bending characteristic (number of bending breaks) was measured by measuring the number of times until the conductor breaks when the bending diameter is R = 4 mm and the left and right are bent at 90 °.

  Next, each conductor was laminated with a PET film coated with an adhesive to produce an FFC. Thereafter, whisker characteristics (whisker generation rate, maximum length) were evaluated by fitting each FFC and a non-plated connector at room temperature for 500 hours. Moreover, each FFC and the connector are fitted to measure the initial contact resistance, and then the contact resistance after being left in a high-temperature and high-humidity environment (85 ° C. and 85% Rh) for 500 hours is obtained to obtain an increase. Contact resistance characteristics were evaluated.

  In Examples 1 to 4, the thickness of the Ni—P layer, the P concentration, and the remaining Sn thickness after the reflow treatment are within the scope of the present invention, and have good bending characteristics, whisker characteristics, and contact resistance characteristics. It was. The thinner the remaining Sn thickness, the better the whisker characteristics. When the remaining Sn thickness was 0.1 μm, the generation of whiskers could be completely suppressed. As a result of surface analysis of each conductor, it was confirmed that a composite film composed of Sn oxide and P oxide or a composite film composed of Sn oxide and phosphate compound was formed on the surface. In particular, when the residual Sn thickness was 0.1 μm, the initial contact resistance value was slightly higher, but the contact resistance did not increase even after being left at high temperature and high humidity, and good contact resistance could be obtained.

  On the other hand, Comparative Example 1 does not have a Ni-P layer as an intermediate layer, and the growth inhibiting effect of Ni intermetallic compound and the oxidation inhibiting effect of P cannot be obtained. The contact resistance characteristics when left untreated were inferior.

  In Comparative Example 2, since the Ni-P layer is too thick compared to the initial Sn thickness (Ni-P layer / initial Sn layer = 1/2), the Ni-P layer or the P enriched layer after the reflow treatment As a result, the bending properties were extremely inferior.

  In Comparative Example 3, since the P concentration of the Ni-P layer is too low to sufficiently obtain the effect of suppressing oxidation of P, surface oxidation proceeds when left at high temperature and high humidity, resulting in increased contact resistance. It was.

It is an expansion schematic diagram of the plating part of the conductor for wiring based on suitable one Embodiment of this invention. FIG. 1A shows a state before heat treatment, and FIG. 1B shows a state after heat treatment. It is a figure which shows the example of a fitting of a connector and FFC. It is a figure which shows the mode of the expansion of a fitting part, generation | occurrence | production of a whisker, and the short circuit between adjacent wiring.

Explanation of symbols

31 Sn-based material part 32 Ni-P intermediate layer 33 Core material 35 Composite film

Claims (7)

At least part of the surface of the core made of a metal material made of a composite material Sn-based material part is formed of Pb-free, the Ni-P intermediate layer of a predetermined thickness between the core material and the Sn-based material part provided, then a reflow line Ukoto, the Ni-P intermediate layer is diffused into the Sn-based material part with abolishes Ni-P intermediate layer, on the surface of the Sn-based material part, a Sn oxide A composite film made of P oxide or a composite film made of Sn oxide and a phosphate compound is formed, and the thickness of the Sn-based material portion is 1 μm or less, and the thickness of the Ni-P intermediate layer Is a conductor for wiring, wherein the thickness is 1/200 or more and less than 1/20 of the thickness of the Sn-based material portion . The wiring conductor according to claim 1 , wherein the Ni—P intermediate layer is made of 1 wt% or more and 15 wt% or less of P, and the balance is Ni and an inevitable impurity Ni—P alloy. The Sn-based material portion is pure Sn-based, Sn-Ag-based, Sn-Ag-Cu-based, Sn-Bi-based, Sn-Bi-Ag-based, or Sn-Cu-based Pb-free made of Sn and inevitable impurities. The wiring conductor according to claim 1 , wherein the wiring conductor is a solder material. By the reflow, a part of the Sn-based material part forms an intermetallic compound layer with a part of the constituent elements of the core material and the Ni-P intermediate layer, and the remaining Sn or Sn alloy of the Sn-based material part remains. The wiring conductor according to claim 1, wherein the thickness is 0.05 μm or more and less than 0.5 μm. The conductor for wiring according to claim 4 , wherein the remaining thickness of pure Sn or Sn alloy in the Sn-based material part is 0.05 μm or more and less than 0.2 μm. The core metal material is a conductive material having an electrical conductivity of 10% IACS or more, oxygen-free copper, tough pitch copper, silver, nickel, a copper alloy material, a nickel alloy material, an aluminum alloy material, or an iron alloy material. The wiring conductor according to any one of claims 1 to 5 , wherein the wiring conductor is configured and has a round wire, a square wire, a plate, a strip, or a foil. A method of manufacturing a composite material in which a Pb-free Sn-based material portion is formed on at least a part of a surface of a core material made of a metal material , wherein Ni-P electrolytic plating is performed on the core material, and at least a part of the surface of the core material Is provided with a Ni-P intermediate layer of a predetermined thickness, a Pb-free Sn-based material part is provided on the Ni-P intermediate layer by Sn plating, and wire drawing and rolling are performed to adjust the size and shape of the composite material. after performs reflow, the Ni-P intermediate layer is diffused into the Sn-based material part with abolishes Ni-P intermediate layer, on the surface of the Sn-based material part, the Sn oxide and P oxides A composite film made of Sn oxide and a phosphate compound , wherein the Sn-based material part has a thickness of 1 μm or less, and the Ni-P intermediate layer has a thickness of the Sn-based film. 1/200 or more of material part thickness, 1/20 A method for manufacturing a wiring conductor, which is a fully.

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