JP4798343B2 - Aluminum electrolytic capacitor - Google Patents

Description

  The present invention relates to an aluminum electrolytic capacitor, and more particularly, to a countermeasure against Sn (tin) whisker that occurs with lead-free lead terminals.

  In an aluminum electrolytic capacitor, a lead terminal is attached to an anode foil and a cathode foil made of an aluminum material constituting a capacitor element, and the lead terminal passes through a sealing body that seals an opening of an exterior case to the outside. Pulled out.

  Usually, the lead terminal is a tab terminal that has a flat portion crushed in the shape of a feather plate on one end of an aluminum bar, and the other end is a round bar, but can be soldered to the circuit board Therefore, a copper-coated steel wire (CP wire) having a plating layer on the surface is welded to the round bar portion of the tab terminal as an external lead wire.

  From the viewpoint of environmental protection in recent years, in order to cope with lead-free lead terminals as well, a copper-coated steel wire plated with Sn 100% is often used. The Sn plating thickness is about 12 μm, and usually no Sn whisker (whisker-like crystal) is generated from the surface.

  However, Al, Sn, Cu, Fe, and the like are mixed in the welded portion of the round terminal portion of the tab terminal and the external lead wire, and particularly when the aluminum layer is exposed to the outside air, the Sn layer is caused by hydration or oxidation reaction. It is known that the stress acts on the Sn whisker and the Sn whisker is generated with a tremendous momentum.

  The lead terminal is pulled out to the outside through a terminal insertion hole formed in the sealing body. Conventionally, the terminal insertion hole has the same diameter as that of the round bar portion, and the welded portion is exposed to the outside. Since the structure is exposed to the outside air, Sn whiskers are likely to grow. When the growth is remarkable, the whiskers are scattered on the circuit board, and in the worst case, there is a risk of shorting the electronic circuit. .

  In order to relieve stress on Sn of dissimilar metals that cause Sn whiskers, for example, in the invention described in Patent Document 1, it is proposed to contain Bi (bismuth) in Sn that becomes a plating layer. According to this, although the growth of Sn whisker can be suppressed to some extent, the same effect has not been obtained for all the lead terminals.

JP 2000-12386 A

  Therefore, an object of the present invention is to suppress the growth of Sn whiskers by adding a device that hardly increases the cost to the sealing body, so that even if Sn whiskers are generated, they are not scattered outside.

In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that a capacitor element formed by winding an anode foil and a cathode foil made of an aluminum material each having a lead terminal attached thereto via a separator, and the capacitor element The lead terminal includes a bottomed cylindrical outer case that is stored together with a predetermined electrolytic substance, and a sealing rubber that is provided with a terminal insertion hole for the lead terminal and is attached to an opening of the outer case. but the tab terminal made of aluminum material having a flat portion and a round bar portion, and a lead-out lead wire welded to an end portion of the round bar portion having a plating layer containing tin free of lead in the surface An aluminum electrolytic capacitor in which the lead terminal is inserted into the terminal insertion hole, and the external lead wire is drawn out of the outer case, in the terminal insertion hole of the sealing rubber. A round bar fitting hole round bar portion of the tab terminal is fitted, the outer lead leads in communication with the rod fitting hole includes a lead wire insertion hole to be inserted, and And a welded portion storage portion for storing a welded portion between the round bar portion and the external lead wire between the round bar fitting hole and the lead wire insertion hole, and is included in the plating layer. to prevent leakage to the outside as well as suppress the generation and growth of whiskers at the weld due to tin are, in diameter than the diameter of the pore size on Kigaibu lead leads of the lead wire insertion hole, the upper is characterized in that Ki溶 contact portion is prevented directly exposed to the outside air is shut off from the outside.

According to a second aspect of the present invention, in the first aspect, the lead wire insertion hole has a hole diameter of 80 to 90 % with respect to the diameter of the external lead wire.

  According to a third aspect of the present invention, in the first or second aspect, the axial length of the lead wire insertion hole is 0.2 mm or more.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the axial length of the lead wire insertion hole is 20% or more of the thickness of the sealing rubber.

  According to the first aspect of the present invention, a round bar fitting hole into which the round bar portion of the tab terminal is fitted into the terminal insertion hole of the sealing rubber, and the external lead is connected to the round bar fitting hole. The lead wire insertion hole through which the wire is inserted is included, and the diameter of the lead wire insertion hole is made smaller than the diameter of the external lead wire. Since it is not directly exposed, it is possible to suppress the generation of Sn whiskers when the Sn plating layer is provided.

  According to the second aspect of the present invention, the lead wire insertion hole has a hole diameter of 70 to 99.9% with respect to the diameter of the external lead wire. The external lead wire can be inserted into the lead wire insertion hole without applying a load.

  According to the invention of claim 3, the lead rubber insertion hole has an axial length of 0.2 mm or more. Even if the Sn whisker grows to the maximum, the sealing rubber is not pierced.

  According to the invention of claim 4, wherein the axial length of the lead wire insertion hole is 20% or more of the thickness of the sealing rubber, the sealing property of the sealing rubber can be maintained well, and the productivity at the time of assembly is increased. It can be good.

  Next, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

  As shown in the sectional view of FIG. 1, this aluminum electrolytic capacitor includes a capacitor element 1 having a pair of lead terminals 2 and 2. As shown in FIG. 2, the capacitor element 1 is formed by winding an anode foil 1a made of an aluminum material to which lead terminals 2 are attached and a cathode foil 1b in a spiral shape through a separator paper (not shown). .

  The capacitor element 1 is accommodated in a bottomed cylindrical outer case 3 with a predetermined electrolytic substance, and the opening of the outer case 3 is sealed with a sealing rubber 4. The sealing rubber 4 is provided with terminal insertion holes 5 and 5, and the tip ends of the lead terminals 2 and 2 are drawn out through the terminal insertion holes 5 and 5.

  Actually, the sealing rubber 4 is housed in the outer case 3 together with the capacitor element 1 in the state of being attached to the lead terminals 2 and 2, and then formed in the lateral throttle groove 3a of the outer case 3 and the outer case. 3 is fixed airtightly in the opening of the outer case 3 by caulking of the edge 3b.

  The exterior case 3 may be a commonly used aluminum case. Butyl rubber or the like may be used for the sealing rubber 4 and does not need to be a special rubber material. The electrolyte substance is usually a water-based or organic liquid electrolyte, but a solid electrolyte may also be used.

  As shown in FIG. 2, the lead terminal 2 includes a tab terminal 21 and an external lead wire 22. The tab terminal 21 is made of an aluminum material, and includes a flat portion 21a and a round bar portion 21b that are press-molded into a battledore shape.

  This type of tab terminal 21 can be obtained by cutting a round aluminum bar material to a predetermined length and pressing one end thereof, and the flat portion 21a is caulking needle or welded to the anode foil 1a and the cathode foil. 1b.

  For the external lead wire 22, a copper-coated steel wire (CP wire) is usually used. The external lead 22 is provided with a plating layer on the surface in order to improve the solderability to the circuit board. However, in the case of Pb (lead) free, the plating layer is mainly Sn 100% plated or Sn / Bi ( 0.5%) plating or the like is applied.

  The external lead wire 22 has a smaller diameter than the round bar portion 21b of the tab terminal 21 and is welded to the end surface of the round bar portion 21b. Reference numeral 23 is attached to the weld. When the plating layer on the surface is Sn 100% plating, the plating layer other than the welded portion 23 is stable, but in the welded portion 23, Al, Sn, Cu, Fe, etc. are mixed and exposed to the outside air. Then, stress acts on the Sn layer due to the hydration or oxidation reaction of Al, and Sn whisker (beard-like crystal) 23a is generated and grows with a tremendous momentum. In Sn / Bi (0.5%) plating, whisker growth is mitigated as compared with Sn 100%, but whisker is generated.

  In order to suppress the generation and growth of Sn whiskers 23a in the welded portion 23, the terminal insertion hole 5 is configured as shown in FIG. FIG. 3 is an enlarged cross-sectional view of the terminal insertion hole 5 together with the welded portion 23 of the lead terminal 2. The terminal insertion hole 5 is a large-diameter round bar fitting hole 51 into which the round bar part 21b is fitted. And a small-diameter lead wire insertion hole 52 through which the external lead wire 22 is inserted, and a welded portion storage portion 53 formed therebetween.

  The round bar fitting hole 51, the welded portion storage portion 53, and the lead wire insertion hole 52 are coaxially connected. The round bar fitting hole 51 may be a hole having a diameter substantially the same as or slightly smaller than the diameter of the round bar portion 21b. On the other hand, the lead wire insertion hole 52 has a smaller diameter than the external lead wire 22 in order to block the welded portion 23 from the outside.

  Even if the lead wire insertion hole 52 has a small diameter, if the lead wire insertion hole 52 is too small, the lead wire may be bent or the capacitor element 1 may be stressed when the external lead wire 22 is inserted. The diameter of the external lead wire 22 is φ1 and the inner diameter of the lead wire insertion hole 52 is φ2, and φ2 is preferably 70 to 99.9% (particularly 80 to 90%) of φ1. In order to improve the lead wire insertion property, it is also effective to heat and melt the tip of the lead wire to round it.

  Further, it is known that the Sn whisker 23a grows up to a maximum of 200 μm in a moisture-resistant storage at 60 ° C., a relative humidity of 95%, and 1000 hours. For this reason, it is preferable that the axial length (depth) L of the lead wire insertion hole 52 is 0.2 mm or more. This means that when the lead terminal 2 is inserted into the terminal insertion hole 5, the thickness from the lower end of the welded portion 23 to the lower surface of the sealing rubber 4 is required to be 0.2 mm or more.

  From the viewpoint of sealing performance at the lead wire insertion hole 52 and productivity during assembly, the axial length L of the lead wire insertion hole 52 is preferably 20% or more of the thickness of the sealing rubber 4. .

  In order to suppress generation and growth of the Sn whisker 23a, the welded portion storage portion 53 is a funnel so as to be in close contact with the welded portion 23 between the large-diameter round bar fitting hole 51 and the small-diameter lead wire insertion hole 52. It is formed in a shape.

  According to the configuration described above, when the lead terminal 2 is inserted into the terminal insertion hole 5, the welded portion 23 is blocked from the outside by the lead wire insertion hole 52, and the inner surface of the welded portion storage portion 53 is in close contact with the welded portion 23. Therefore, the Sn whisker 23a is hardly generated in the welded portion 23, and even if the Sn whisker 23a is generated, its growth is suppressed and does not reach the outside of the capacitor. Therefore, when mounted on a circuit board, it is possible to prevent the occurrence of a short circuit in the electronic circuit over a long period of time.

Referring to FIG. 3, as an example of the present invention, a lead-coated lead wire 22 of lead terminal 2 is made of a copper-coated steel wire having a diameter of 100% Sn and a copper-coated steel wire having a diameter of 0.45 mm. Twenty aluminum electrolytic capacitors of 10V 100 μF (outer diameter 6.3 mm, axial length 5.0 mm) were made on trial with the inner diameter of the wire insertion hole 52 being 0.36 mm (80% of 0.45 mm).
The comparative example is an aluminum electrolytic capacitor of 10 V 100 μF (outer diameter 6.3 mm, axial length 5.0 mm) in which the terminal insertion hole 5 is almost the same diameter as the round bar portion 21b over the entire length and the welded portion 23 is exposed to the outside. (20 prototypes).

Both the inventive example and the comparative example were subjected to a moisture-resistant storage test at 60 ° C., a relative humidity of 95%, and 1000 hours, and the growth of Sn whiskers and the occurrence rate of Sn whiskers having a length of 30 μm or more were observed.
This observation was performed every 200 hours, 400 hours, 600 hours, 800 hours, and 1000 hours. However, in the example of the present invention, since the welded portion cannot be seen from the outside, four pieces are extracted every time, and the welded portion 23 is extracted. The length of whisker was measured by removing the rubber covering.

The observation result of the length of Sn whisker is shown in FIG. As can be seen, in the comparative example, since the welded portion 23 is exposed to a humidity atmosphere, the stress on the Sn plating layer at the welded portion 23 acts, and the growth of Sn whiskers is intense, reaching 200 μm after 800 hours. did.
On the other hand, in the example of the present invention, since the welded portion 23 is cut off from the humidity atmosphere, the maximum length of the Sn whisker is suppressed to about 1/6 of the comparative example, and the welded portion 23 does not directly contact the outside air. There is an effect.

Next, the observation result of Sn whisker incidence with a length of 30 μm or more is shown in FIG. In the comparative example, the incidence rate of Sn whisker having a length of 30 μm or more increased with time, and the occurrence rate reached about 60% when 800 hours passed.
On the other hand, in the example of the present invention, the occurrence rate of Sn whisker having a length of 30 μm or more after about 400 hours is about 5%, and thereafter the Sn whisker does not grow and the occurrence rate is about 1000 hours. 5% is maintained.

  As described above, according to the present invention, the whisker growth, which has been a problem when using, for example, a Sn 100% plated lead wire as the external lead wire, is suppressed from the request for Pb-free. Even if this occurs, a highly reliable aluminum electrolytic capacitor that can be safely mounted on a circuit board for a long period of time is provided, and its industrial applicability is great. .

The typical sectional view showing the basic composition of the aluminum electrolytic capacitor by the present invention. The perspective view which shows the lead terminal used for the said aluminum electrolytic capacitor. Sectional drawing which shows the principal part of this invention. The graph which shows the growth length of Sn whisker. The graph which shows Sn whisker incidence rate whose length is 30 micrometers or more.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor element 2 Lead terminal 21 Tab terminal 21a Flat part 21b Round bar part 22 Outer lead wire 23 Welding part 3 Exterior case 4 Sealing rubber 5 Terminal insertion hole 51 Round bar fitting hole 52 Lead wire insertion hole 53 Welding part accommodating part

Claims (4)

A capacitor element formed by winding an anode foil and a cathode foil made of an aluminum material each having a lead terminal attached thereto via a separator, and a bottomed cylindrical outer case in which the capacitor element is accommodated together with a predetermined electrolytic substance; A tab made of an aluminum material, wherein the lead terminal has a flat portion and a round bar portion, the terminal insertion hole for the lead terminal being perforated and a sealing rubber attached to the opening of the exterior case Comprising a terminal and an external lead wire having a plated layer containing no tin on the surface and containing tin , welded to the end of the round bar, the lead terminal being inserted into the terminal insertion hole, In the aluminum electrolytic capacitor in which the external lead wire is drawn out of the outer case,
The sealing rubber terminal insertion hole has a round bar fitting hole into which the round bar portion of the tab terminal is fitted, and a lead that communicates with the round bar fitting hole and into which the external lead wire is inserted. A welded portion storage portion that includes a wire insertion hole and that accommodates a welded portion between the round bar portion and the external lead wire between the round bar fitting hole and the lead wire insertion hole. Prepared,
To prevent leakage to the outside as well as suppress the generation and growth of whiskers at the weld due to the tin contained in the plating layer, the diameter of the lead wire insertion hole of the upper Kigaibu lead lead a smaller diameter than the diameter, aluminum electrolytic capacitors, characterized in that the upper Ki溶 contact portion is so not exposed to the outside air is shut off from the outside. The aluminum electrolytic capacitor according to claim 1, wherein a hole diameter of the lead wire insertion hole is 80 to 90 % with respect to a diameter of the external lead wire.   The aluminum electrolytic capacitor according to claim 1 or 2, wherein an axial length of the lead wire insertion hole is 0.2 mm or more.   4. The aluminum electrolytic capacitor according to claim 1, wherein an axial length of the lead wire insertion hole is 20% or more of a thickness of the sealing rubber. 5.

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