JP2008066493A - Lead wire, lead terminal for aluminum electrolytic capacitors, and aluminum electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the generation of a whisker even in a portion where this lead wire is welded to an aluminum lead which is most likely easy to generate a tin whisker, wherein tin atoms form an intermetallic compound with nickel atoms. <P>SOLUTION: A lead wire 10 consists of a copper layer 12, a nickel layer 13 and a tin layer 14 laminated on the surface of a steel wire 11 in sequence from inside. In this lead wire 10, even in a portion where melt-integration is carried out with an aluminum lead which is most likely easy to generate the tin whisker, the tin atoms form the intermetallic compound with nickel atoms, and mix with steel atoms, copper atoms, and aluminum atoms. Hence, this prevents tin atoms from gathering together to build tin particle which serves as the source of generation of the whisker. Moreover, since rare metal is not needed, it is cheap and there is also no worry of the scarcity of resources. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lead wire, a lead terminal for an aluminum electrolytic capacitor, and an aluminum electrolytic capacitor.

  Conventionally, solder plating (tin-lead alloy plating) has been applied to the surface of a metal core wire such as a copper wire or a copper-clad steel wire so that the lead wire of an electronic component such as a capacitor can be easily soldered to a printed circuit board. Solder plating has been widely used because it has low cost and good solderability and has excellent characteristics that solderability does not deteriorate even when placed in a bad environment such as high temperature and high humidity. However, since lead contained in solder is toxic, the use of solder containing lead in electrical products is prohibited.

  When lead plating is used to remove lead from the lead plating and tin plating is no longer toxic, whiskers (whisker-shaped tin single crystals) grow from the tin plating layer, which may cause an electrical short circuit accident. In order to prevent this, for example, an invention in which tin-palladium alloy plating is applied to the surface of tin plating has been proposed (Patent Document 1).

An aluminum electrolytic capacitor uses an aluminum lead (aluminum wire) as a core material for winding an aluminum foil, and the lead wire is welded to the aluminum lead for external connection. Conventional lead wires have been solder-plated on the surface of a copper-clad steel wire or the like, but since the lead in the solder plating is toxic, solder plating is becoming unusable. Whiskering does not occur if solder plating is used, but whiskering tends to occur especially from the welded portion between the aluminum lead and the lead wire. As a countermeasure, an invention has been proposed in which the tin plating surface of the lead wire is oxidized to form tin oxide (Patent Document 2).
JP 9-45579 A JP 2004-31950 A

  The structure in which tin-palladium alloy plating is applied to the surface of the tin plating to prevent whisker growth from the tin plating layer of the lead wire is a rare metal and expensive palladium. There is a risk of shortage. For this reason, it is desired to prevent whiskers without using rare metals.

  As a countermeasure against whisker in the welded part of aluminum lead and lead wire of aluminum electrolytic capacitor, the method of oxidizing tin plating surface of lead wire to tin oxide is that whisker is generated if there is too little tin oxide and if there is too much tin oxide Lead wire solderability is reduced. Therefore, an appropriate amount of tin oxide must be formed, but it is difficult to control.

  The lead wire according to claim 1 is a lead wire formed by laminating a copper layer, a nickel layer, and a tin layer in order from the inside on the surface of the steel element wire.

  In the lead wire of the present invention, even in the portion fused and integrated with the aluminum lead where tin whisker is most likely to be generated, the tin atom forms an intermetallic compound with the nickel atom and melts with the iron atom, copper atom and aluminum atom on an atomic scale. For this reason, it is possible to prevent tin atoms from gathering to form tin particles that become a whisker generation source. Moreover, since no rare metal is required, it is inexpensive and there is no fear of resource shortage. Further, since the nickel layer can be formed with high precision by a plating method, it is not necessary to perform difficult control to form an appropriate amount of tin oxide.

  The lead wire according to claim 2 is a lead wire according to claim 1, wherein a tin alloy layer containing at least one of silver, bismuth, copper, indium and zinc is further laminated on the outermost layer. is there.

  By using a tin alloy layer containing at least one of silver, bismuth, copper, indium, and zinc as the outermost layer of the lead wire, the melting point can be lowered and solderability can be improved as compared with pure tin. The melting point of pure tin is 232 ° C., but the melting point of the tin-5 wt% bismuth alloy is 228 ° C., the melting point of the tin—0.7 wt% copper alloy is 229 ° C., and so on. Similarly, tin-silver alloy, tin-indium alloy, and tin-zinc alloy can be lowered in melting point.

  A lead wire according to claim 3 is the lead wire according to claim 1 or 2, wherein the nickel layer has a thickness of 0.5 μm to 5 μm.

  If the thickness of the nickel layer is less than 0.5 μm, there may be a shortage of nickel atoms when the tin atom forms an intermetallic compound with the nickel atom. If the thickness of the nickel layer exceeds 5 μm, the lead wire becomes too hard. Easily break. For this reason, the thickness of the nickel layer is suitably 0.5 μm to 5 μm.

  The lead terminal for an aluminum electrolytic capacitor according to claim 4, wherein the lead wire formed by laminating a copper layer, a nickel layer, and a tin layer in this order from the inside to the surface of the steel element wire and an aluminum lead are welded. Terminal.

  The lead terminal for an aluminum electrolytic capacitor of the present invention is suitable as a lead terminal for an aluminum electrolytic capacitor because whisker generation is prevented at all locations including the portion where the lead wire and the aluminum lead are welded.

  The lead terminal for an aluminum electrolytic capacitor according to claim 5, wherein the lead terminal for the aluminum electrolytic capacitor according to claim 4 is a tin alloy layer further comprising at least one of silver, bismuth, copper, indium and zinc as an outermost layer. Is a lead terminal for an aluminum electrolytic capacitor in which a lead wire formed by laminating and an aluminum lead are welded.

  The lead terminal for an aluminum electrolytic capacitor of the present invention prevents whiskers from occurring at all locations including the portion where the lead wire and the aluminum lead are welded, and the lead wire has particularly good solderability. Is preferred.

  The aluminum electrolytic capacitor according to claim 6 has a lead terminal for an aluminum electrolytic capacitor in which a lead wire formed by laminating a copper layer, a nickel layer, and a tin layer in this order from the inside to the surface of a steel element wire and an aluminum lead are welded. It is an aluminum electrolytic capacitor.

  Since the aluminum electrolytic capacitor of the present invention does not generate whiskers in the lead wires, it is possible to prevent an electrical short accident after being mounted on a printed circuit board.

  The aluminum electrolytic capacitor according to claim 7 is the aluminum electrolytic capacitor according to claim 6, further comprising a tin alloy layer containing at least one of silver, bismuth, copper, indium, and zinc laminated on the outermost layer. An aluminum electrolytic capacitor having a lead terminal for an aluminum electrolytic capacitor in which a wire and an aluminum lead are welded.

  The aluminum electrolytic capacitor of the present invention has particularly good lead wire solderability when mounted on a printed circuit board. Moreover, since there is no whisker generation of the lead wire, it is possible to prevent an electrical short accident after being mounted on the printed circuit board.

  The lead wire of the present invention can prevent the generation of whiskers even at the welded portion with the aluminum lead where tin whiskers are most likely to occur. Moreover, since no rare metal is required, it is inexpensive and there is no fear of resource shortage. Since the nickel layer can be formed with high accuracy by a plating method, it is not necessary to perform difficult control to form an appropriate amount of tin oxide. The lead terminal for a capacitor of the present invention is suitable as a lead terminal for an aluminum electrolytic capacitor because whisker generation is prevented at all locations including a portion where a lead wire and an aluminum lead are welded. Since the aluminum electrolytic capacitor of the present invention does not generate whiskers in the lead wires, it is possible to prevent an electrical short accident after being mounted on a printed circuit board.

  First, the mechanism of whisker growth from the tin plating layer of a conventional tin plating lead will be described. FIG. 1 is a schematic view of a conventional lead wire 100 that is not subjected to whisker countermeasures, in which lead is simply removed by tin plating from solder plating of a copper-coated steel wire. As shown in FIG. 1, a copper layer 102 and a tin layer 103 are sequentially laminated concentrically on the surface of a steel wire 101 by a plating method to form a lead wire 100 having a diameter of 0.5 mm. Yes.

  Conventionally, in the case of a combination of a copper underlayer and a tin layer, it is known that the temperature at which tin whiskers are most likely to occur is room temperature. However, according to the inventor's experiment, even if the lead wire 100 is not subjected to whisker countermeasures, whisker generation is completely observed even if it is left at room temperature for 60 days if it is not subjected to processing such as welding. I couldn't. Whisker is known to occur within a few days when it occurs, and it is predicted that it will not occur even if left for a long time.

  However, one end of the same conventional lead wire 100 is butted against one end of the aluminum lead 20 as shown in FIG. 2 (a), and resistance welding is performed. Similarly, when left at room temperature, whiskers are generated in only one day. I understood. This imitates an actual structure when the lead wire 100 is used for an aluminum electrolytic capacitor, and a similar whisker is generated even in an actual aluminum electrolytic capacitor.

  FIG. 2B is an enlarged schematic view of a butt-welded portion between the lead wire 100 and the aluminum lead 20 immediately after welding (a portion of a broken-line circle 21 in FIG. 2A). At the time of resistance welding, the abutted portion becomes as high as 2000 ° C., so that the tips of the lead wire 100 and the aluminum lead 20 are melted and integrated to be solidified.

  FIG. 2C is an enlarged schematic view of a welded portion between the lead wire 100 and the aluminum lead 20 after 24 hours from welding. As shown in FIG. 2C, a large number of tin whiskers 104 are characteristically formed only in the portion 22 where the lead wire 100 and the aluminum lead 20 are fused and integrated. However, whiskers are not seen at all in the same lead wire 100 away from the melt-integrated portion 22.

  According to the inventor's estimation, the reason why the whisker 104 is generated only in the portion 22 where the lead wire 100 and the aluminum lead 20 are fused and integrated is as follows. As shown in the sectional view of the melt-integrated portion 22 in FIG. 3A, in the portion 22 where the lead wire 100 and the aluminum lead 20 are melt-integrated, iron atoms, copper atoms, and aluminum leads derived from the lead wire 100 are obtained. Aluminum atoms from 20 are melting on an atomic scale. However, since the tin atoms derived from the tin layer 103 of the lead wire 100 do not melt with each other, they gather to form tin particles 105 having a diameter of several μm to several tens of μm. When the melted portion is solidified, a strong compressive stress is applied to the tin particles 105.

  As shown in the cross-sectional view of the melt-integrated portion 22 in FIG. 3 (b), a whisker-like single crystal of tin is formed to relieve this compressive stress, and the whisker 104 is extruded from the surface of the melt-integrated portion 22. Become. Since the compressive stress is not applied to the tin layer 103 on the surface of the lead wire 100 away from the melt-integrated portion 22, no whisker is generated.

  Next, FIG. 4 is a schematic view of the lead wire 10 of the first embodiment of the present invention in which countermeasures against whiskers are taken. As shown in FIG. 4, the lead wire 10 of the present invention is formed on the surface of the steel wire 11 in order by a copper layer 12 having a thickness of 20 μm, a nickel layer 13 having a thickness of 2 μm, and a tin layer 14 having a thickness of 12 μm. A lead wire 10 having a diameter of 0.5 mm is laminated. At this time, the thickness of the nickel layer 13 is suitably 0.5 μm to 5 μm. The reason is that when the thickness of the nickel layer 13 is less than 0.5 μm, there is a possibility that the nickel atoms will be insufficient when the tin atoms form an intermetallic compound with the nickel atoms, and when the thickness of the nickel layer 13 exceeds 5 μm. This is because the lead wire becomes too hard and easily breaks.

  One end of the lead wire 10 of the present invention was butted against one end of the aluminum lead 20 as shown in FIG. 5 (a) and resistance-welded was made and allowed to stand at room temperature for 60 days, but no whiskers were found. FIG. 5B is an enlarged schematic view immediately after welding of the welded portion 23 between the lead wire 10 and the aluminum lead 20 of the present invention. At the time of resistance welding, the welded portion that is abutted becomes as high as 2000 ° C., so that the leading ends of the lead wire 10 and the aluminum lead 20 are melted and integrated together and solidified. The appearance immediately after welding is the same as that of the conventional lead wire 100 (FIG. 2 (b)) that is not subjected to whisker countermeasures. However, in the lead wire 10 of the present invention, the whisker is also seen from the melted and integrated portion 24 even after being left for 60 days. Never occurred. That is, the appearance after leaving for 60 days is also as shown in FIG. As a result, it is predicted that whiskers will not occur even if the lead wire 10 of the present invention is left for a long period of time.

The inventor presumes why the whisker does not occur from the portion 24 fused and integrated with the lead wire 10 of the present invention as follows. As shown in the sectional view of the melt-integrated portion 24 in FIG. 5C, in the portion 24 in which the lead wire 10 and the aluminum lead 20 are melt-integrated, the iron atoms, copper atoms, and aluminum leads 20 derived from the lead wire 10 are used. The derived aluminum atoms are melting on an atomic scale. On the other hand, the tin atom derived from the tin layer 14 forms an intermetallic compound (presumed to be Ni ₃ Sn ₄ ) with the nickel atom derived from the nickel layer 13 and can be dissolved on an atomic scale with iron atoms, copper atoms, and aluminum atoms. . For this reason, unlike the conventional lead wire 100 which does not take a countermeasure against whisker, tin atoms do not collect to form tin particles. Since tin particles are a source of whisker, the lead wire 10 of the present invention in which tin particles are not formed has no source of whisker. Therefore, whiskers are not generated from the melted and integrated portion 24 in the lead wire 10 of the present invention even if left for a long time.

  Since the lead wire is necessary for external connection of the aluminum electrolytic capacitor and the aluminum lead is necessary as a core material of the aluminum electrolytic capacitor, the lead wire 10 and the aluminum lead 20 are always used for the aluminum electrolytic capacitor as shown in FIG. There is a melt-integrated portion 24. When the tin particles 105 are formed in the melted and integrated portion of the lead wire 10 and the aluminum lead 20 as shown in FIG. 3A, a compressive stress is applied to the tin particles 105, and thus there is a probability that a tin whisker 104 is generated. Become very expensive. Therefore, in order to prevent the tin whisker 104 in the aluminum electrolytic capacitor, it is necessary that the tin particles 105 are not formed in the melt-integrated portion of the lead wire and the aluminum lead. However, if the particle size of the tin particles 105 is about 1 μm or less, the whisker 104 is unlikely to be generated because the compressive stress applied to the tin particles 105 is small. Even if the whisker 104 is generated, a long (several tens of μm or more) whisker 104 is not formed because the tin particles 105 contain a small amount of tin atoms. Accordingly, it is considered that there is no actual damage caused by the whisker 104 even if the tin particles 105 having a particle size of about 1 μm or less are present.

  Next, FIG. 6 is a schematic view of the lead wire 30 of the second embodiment of the present invention in which countermeasures against whiskers are taken. As shown in FIG. 6, in the lead wire 30 of the second embodiment of the present invention, the copper layer 32 has a thickness of 20 μm, the nickel layer 33 has a thickness of 2 μm, and the tin layer 34 has a thickness on the surface of the steel wire 31. A lead wire 30 having a diameter of 0.5 mm is formed by laminating a 12 μm, tin-5 wt% bismuth alloy layer 35 with a thickness of 2 μm by plating. At this time, the thickness of the nickel layer 33 is suitably 0.5 μm to 5 μm, and the thickness of the tin-5 wt% bismuth alloy layer 35 is suitably 1 μm to 3 μm.

  The mechanism for preventing tin whisker generation in the lead wire 30 of the second embodiment of the present invention is the same as that of the lead wire 10 of the first embodiment. The merit of the lead wire 30 of the second embodiment is that the outermost layer is a tin-5 wt% bismuth alloy 35, and therefore the melting point is lower than that of the lead wire 10 of the first embodiment in which the outermost layer is a pure tin layer 14 and soldered. It is a good thing. For this reason, when the aluminum electrolytic capacitor using the lead wire 30 of the second embodiment is mounted on a printed board, the yield of soldering and the reliability are higher.

  The lead wire and aluminum lead of the present invention can be welded by a conventional resistance welding method, and a lead terminal for an aluminum electrolytic capacitor can be manufactured.

  Moreover, an aluminum electrolytic capacitor can be manufactured by the conventional manufacturing method using the lead terminal for aluminum electrolytic capacitors of this invention.

  The lead wire of the present invention can prevent the generation of whiskers even at the welded portion with the aluminum lead where tin whiskers are most likely to occur. Moreover, since no rare metal is required, it is inexpensive and there is no fear of resource shortage. The lead terminal for an aluminum electrolytic capacitor of the present invention is suitable as a lead terminal for an aluminum electrolytic capacitor because whisker generation is prevented at all locations including the portion where the lead wire and the aluminum lead are welded. Since the aluminum electrolytic capacitor of the present invention does not generate whiskers in the lead wires, it is possible to prevent an electrical short accident after being mounted on a printed circuit board.

Schematic diagram of conventional lead wire without whisker countermeasures (A) Conventional lead wire and aluminum lead welding diagram (b) Enlarged schematic view of conventional lead wire and aluminum lead welded portion immediately after welding (c) Conventional lead wire and aluminum lead welded portion after whisker generation Schematic diagram of (A) Cross-sectional view of welded portion of conventional lead wire and aluminum lead immediately after welding (b) Cross-sectional view of welded portion of conventional lead wire and aluminum lead after whisker generation Schematic diagram of the lead wire of the first embodiment of the present invention (A) Welded drawing of the lead wire and aluminum lead of the present invention (b) Magnified schematic diagram of the welded portion of the lead wire and aluminum lead of the present invention immediately after welding (c) of the welded portion of the lead wire and aluminum lead of the present invention Cross section Schematic diagram of the lead wire of the second embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Lead wire 11 Steel element wire 12 Copper layer 13 Nickel layer 14 Tin layer 20 Aluminum lead 21 Welded part 22 Part where lead wire and aluminum lead are fused and integrated 23 Welded part 24 Part where lead wire and aluminum lead are fused and integrated 30 Lead wire 31 Steel strand 32 Copper layer 33 Nickel layer 34 Tin layer 35 Tin-5 wt% bismuth alloy layer 100 Lead wire 101 Steel strand 102 Copper layer 103 Tin layer 104 Whisker 105 Tin particles

Claims (7)

  A lead wire in which a copper layer, a nickel layer, and a tin layer are laminated on the surface of a steel wire in order from the inside.   The lead wire according to claim 1, wherein a tin alloy layer containing at least one of silver, bismuth, copper, indium and zinc is further laminated on the outermost layer.   3. The lead wire according to claim 1, wherein the nickel layer has a thickness of 0.5 μm to 5 μm.   A lead terminal for an aluminum electrolytic capacitor in which a lead wire in which a copper layer, a nickel layer, and a tin layer are laminated in this order on the surface of a steel wire and an aluminum lead are welded.   5. The lead terminal for an aluminum electrolytic capacitor according to claim 4, further comprising: a lead wire in which a tin alloy layer containing at least one of silver, bismuth, copper, indium, and zinc is laminated on the outermost layer; and an aluminum lead; Lead terminal for aluminum electrolytic capacitors welded with.   The aluminum electrolytic capacitor which has the lead terminal for aluminum electrolytic capacitors which welded the lead wire by which a copper layer, a nickel layer, and a tin layer were laminated | stacked in order from the inner side on the steel strand surface, and the aluminum lead. The aluminum electrolytic capacitor according to claim 6, wherein a lead wire in which a tin alloy layer containing at least one of silver, bismuth, copper, indium, and zinc is further laminated on the outermost layer, and an aluminum lead are welded. An aluminum electrolytic capacitor having lead terminals for an aluminum electrolytic capacitor.

Images