JP5044772B2 - Capacitor lead terminal welding method - Google Patents

Description

  The present invention relates to a metal-plated lead wire (CP wire) mainly composed of tin and a wire made of aluminum or the like, particularly to a method for welding a lead terminal for a capacitor.

Conventionally, the welding method for lead terminals for capacitors is to use a wire made of aluminum or the like and a lead wire (CP wire), that is, the surface of a wire based on iron, copper, etc., plated with extremely high purity tin. There is a method of joining by an arc stud welding method or the like.
However, this method has a problem that tin whiskers are generated on the surface of the weld bead.
Even if the whisker is not recognized immediately after welding, the whisker is generated and grows with the lapse of time. Therefore, there is a concern that the whisker may come into contact with the whisker when it is mounted on a circuit board, causing a short circuit.
Against this background, the Japan Electronics and Information Technology Association (JEITA) is standardizing electronic device whisker test methods, and drafting JIS drafts and international proposals for the International Electrotechnical Commission (IEC) are planned.

Up to now, lead wires plated with tin containing lead have been used for the purpose of improving soldering characteristics in the post-process of electrolytic capacitor fabrication. In this case, it is known that whiskers do not occur. However, in recent years, as interest in global environmental issues has increased, there has been an increasing demand for reducing the use of lead.
From such a background, the use of lead-plated lead wires (CP wires) that do not contain lead is urgently needed, but a method that can completely prevent the occurrence of the above whiskers has not yet been disclosed.

Therefore, as a conventional method for suppressing the occurrence of whiskers, a method using a lead wire plated with tin containing a metal such as bismuth (see Patent Document 1), and cleaning the lead wire with an alkaline cleaning liquid as a pretreatment for welding・ Method of heating after drying (see Patent Document 2), method of heating in an oxygen atmosphere as post-welding treatment, and inorganic acid salt including silicate and borate within several milliseconds to 1 second after welding There is a method of dipping in the heated aqueous solution (see Patent Document 3).
Further, as a related technique, a surface treatment agent for solder containing a benzimidazole compound and a salt thereof for obtaining a tin alloy plating that suppresses the generation of whiskers is disclosed (see Patent Document 4).
Also, for the purpose of improving the welding strength with lead-free tin-plated copper lead terminals, arc welding is performed after preheating (by means of blowing an inert gas such as heated argon or nitrogen) at a temperature close to the melting temperature of tin. A method (see Patent Document 5) is disclosed.

Although the method as described above is disclosed, the generation of the whisker has not been completely prevented by the method using bismuth-tin alloy plating that does not contain lead.
Further, there is a problem in terms of cost because it is applied not only to the tip portion of the lead wire (CP wire) that becomes a part of the weld bead generated by the whisker but also to the entire portion including the portion that does not require alloy plating.

In the method of heating the lead wire (CP wire) after washing and drying with an alkaline cleaning liquid as a pretreatment for welding, the generation of the whisker cannot be completely prevented as in the above-described method.
In addition, there is a problem in productivity and cost, such as heating for a long time (about 21 minutes) under complicated production process management.

  A method of heating in an oxygen atmosphere for a long time (10-60 minutes) as a post-welding treatment, and immersing a silicate or borate in a heated aqueous solution containing an inorganic acid salt within a few milliseconds to 1 second after the end of welding. In the method to do, there is not only a problem in productivity and cost because it requires further post-processes such as the heating step and immersion step after welding the lead wire (CP wire) and the aluminum tab in the same manner as described above. The whisker length has a suppression effect of about 100 μm to 170 μm and has not yet been prevented.

  Also, in the case of arc welding after preheating by blowing only heated inert gas, even if the welding strength is improved, tin that causes whisker is present on the surface of the weld bead so that whisker generation can be prevented. Has not reached.

This whisker does not occur even when the lead wire (CP wire) is heated and melted and solidified alone, and almost all the generation factors are formed during the solidification process of molten metal (made of aluminum, tin, etc.) by welding. This has been found by the inventors' research.
Therefore, in the pre-welding process and post-welding process performed on the surface of the above-described weld metal, it is difficult to obtain the effect of completely preventing the whisker as well as suppressing the whisker length to less than 100 μm.

  Accordingly, the inventors of the present application, as a welding shield gas welding method for capacitor lead terminals that can prevent the generation of whiskers by blocking the generation / growth in the welding process in which the generation factors of whiskers are formed, A method of welding a lead wire and an aluminum tab using a mixed gas of an inert gas and an active gas was invented, and a patent application was filed (see Patent Document 6).

  However, with the above method, whisker generation probability decreased and whisker length could be shortened, but whisker could still not be completely suppressed.

JP 2000-12386 A JP 2000-277398 A JP 2004-31950 A Japanese Patent Laid-Open No. 2004-156094 JP 2004-335859 A JP 2006-339185 A

  The present invention provides a lead terminal for a capacitor that can prevent generation of further needle-shaped whiskers by post-processing in addition to blocking generation / growth in the welding process in which the generation factor of needle-shaped whiskers is formed. The object is to provide a welding method.

The present invention relates to a method for welding a lead terminal for a capacitor that welds an aluminum tab and a lead wire plated with metal mainly composed of tin, and as a post-treatment of welding using an inert gas as a welding shield gas The ultrasonic wave is irradiated to at least the lead wire of the capacitor lead terminal and the welded portion of the aluminum tab . In addition, a mixed gas of an inert gas and an active gas is used as the welding shield gas.
According to this, by irradiating the lead terminal with ultrasonic waves after welding the lead terminal, physical vibrations are given to the welded part between the lead wire and the aluminum tab, in particular, in the welded part where the tin and aluminum are solidified. By applying compressive stress to the applied residual tensile stress, the internal stress can be relaxed and the occurrence of needle-like whiskers can be suppressed.

In addition, the capacitor lead terminal is characterized by suppressing the occurrence of needle-like whiskers by irradiating ultrasonic waves in a solution in a stage (latent period) where whiskers have not yet appeared after welding. Yes.
In other words, the cause of the generation of needle-like whiskers is thought to be that tin atoms are pushed out of the plating film and grow in an oxidizing atmosphere due to the release of stress generated in the plating film in the process after welding.
Since there is a certain latent period before the metal film is pushed out of the plating film, ultrasonic waves are irradiated during this latent period.

In addition, a glycerin solution is used as the solution. It is characterized by suppressing the occurrence of needle-like whiskers in the oxidizing atmosphere after welding by irradiating glycerin with ultrasonic waves to form a reduction reaction field.
Although all the phenomena have not been clarified, hydrogen generated by decomposition of the molecular structure of glycerin, which is a liquid containing polyol (compound containing two or more hydroxyl groups), by irradiating glycerin with ultrasonic waves. It is assumed that a reducing atmosphere reaction field is formed.
Incidentally, the inventors have confirmed that the generation of needle-like whiskers is promoted in an oxidizing atmosphere.

  By using the present invention, in addition to blocking the generation and growth of needle-like whiskers in the welding process in which the cause of whisker formation is formed, post-treatment by ultrasonic irradiation can prevent further whisker generation. it can.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
As an example of the welding method of the electrolytic capacitor and the electric double layer capacitor lead terminal according to the present invention, a system configuration diagram of the arc stud welding method shown in FIGS. 1 and 2 will be described.
1 is a gas cylinder filled with argon gas, 2 is a gas cylinder filled with oxygen gas, 3 is a mixer, 4 is a shield nozzle, 5 is a gas cylinder filled with helium gas, 6 is an arc stud welding device, 7 is one electrode, 8 is a lead wire (CP wire), 9 is the other electrode, 10 is an aluminum wire, and 11 is a shielding gas.
Hereinafter, explanation will be made with the lead terminals for electrolytic capacitors.
As shown in FIG. 1, a mixer 3 for supplying and mixing each gas from a gas cylinder 1 filled with argon gas and a gas cylinder 2 filled with oxygen gas is provided, and a welding shield gas mixed at a predetermined ratio by the mixer 3. A plurality of shield nozzles 4 for supplying 11 are provided.
The lead wire (CP wire) 8 is gripped by one electrode 7 of the arc stud welding device 6, and the aluminum tab 10 is gripped by the other electrode 9, and the tip of the lead wire (CP wire) 8 and the tip of the aluminum tab 10 are It arrange | positions so that the welding shield gas 11 may be supplied from the said shield nozzle 4 to a contact point, ie, a welding part.

The lead terminal is composed of a lead wire (CP wire) 8 and an aluminum tab 10, and the aluminum tab 10 is formed by processing a round bar-shaped aluminum wire of about 0.5 to 2 mm to form a flat part and a round bar part. The round bar and the lead wire (CP wire) 8 are welded to form a lead terminal.
The flat portion of the aluminum wire is connected to an electrode foil not shown here.
The lead wire (CP wire) 8 is a round rod-shaped wire, and for this wire, for example, a wire formed by forming a copper film on the surface of a mild steel wire having a diameter of about 0.3 to 1.2 mm is used.
In addition to mild steel wire, pure copper wire, copper alloy wire, or other metal wires may be used for this wire.
The surface of the lead wire (CP wire) is subjected to metal plating mainly composed of tin such as tin or tin-bismuth.

Next, the welding method of the lead terminal for electrolytic capacitors of this invention is demonstrated.
As shown in FIG. 2, the tip of the lead wire (CP wire) 8 and the tip of the round bar portion of the aluminum tab 10 are arranged to face each other at a constant interval, and the electrode 7 of the arc stud welding device 6 is operated to lead the lead wire. (CP wire) 8 is brought into contact with the tip of the round bar portion of the aluminum tab 10 and the arc stud welding device 6 is operated to supply the welding shield gas 11 from the shield nozzle 4 to lead the lead 8 and the aluminum tab 10. And shield the welded part.
In this state, by separating the lead wire (CP wire) 8 from the aluminum tab 10, an arc is generated between the tip of the lead wire (CP wire) 8 and the tip of the round bar portion of the aluminum tab 10, and the opposing leads The tip of the wire (CP wire) 8 and the tip of the round bar portion of the aluminum tab 10 are melted.
In this state, when the lead wire (CP wire) 8 is moved and brought into contact with the tip of the round bar portion of the aluminum tab 10, the lead wire (CP wire) 8 and the aluminum tab 10 are melted and solidified between the metals. The round bar is welded.

Conventionally, when a lead wire plated with pure tin (CP wire) that does not use lead by using 100% argon gas as a shielding gas and an aluminum wire are joined by arc stud welding, the needle is removed from the weld bead as shown in FIG. The whisker 12 is generated and grows over time.
The inventor has clarified that the whisker 12 is generated from a portion where tin (Sn) plated on the surface of the lead wire (CP wire) is dispersed and solidified in the weld metal (Al).
Therefore, it is impossible to prevent the whisker 12 from being generated by the known method using the weld bead surface treatment as described above.

  The cause of this is that whisker is a large crystal without distortion due to recrystallization (recrystallization temperature 0 to 25 ° C.) of island-shaped tin (Sn) that has been strained by the stress received from welding aluminum (Al). There is a hypothesis that it is a changing phenomenon, but it is not clear.

  Therefore, as an example of a welding method for solving this phenomenon, as shown in FIG. 1, argon gas 1 which is an inert gas and oxygen gas 2 which is an active gas are mixed in a mixer 3 by 75 to 90% and 25 to 10%, respectively. The lead wire (CP wire) 8 and the aluminum wire 10 are welded by the arc stud welding device 6 as shown in FIG.

  As a result, tin (Sn) plated on the surface of the lead wire (CP wire) is agglomerated and solidified into the weld metal, and tin (Sn) is dispersed and solidified in the aluminum (Al) surface layer of the weld metal. It will not be done. By performing this reaction in the process of melt solidification by arc welding, it becomes possible to prevent the generation of whiskers.

  Further, helium gas 5 having a high potential gradient (high arc plasma energy) is added to the above-described mixed gas within a range where the effect of the oxygen gas 2 is not hindered, and the weld bead is smoothed, so that tin (Sn) remains in the uneven portion. Thus, the reliability of preventing the occurrence of the whisker can be improved.

  The metal plating of the lead wire (CP wire) 8 may be metal plating mainly composed of tin, and includes those containing other metal materials such as tin-bismuth.

In addition, the welding method includes not only the arc stud welding method of the above embodiment but also other gas shield welding methods (laser welding method, micro TIG welding method, etc.).
Furthermore, a method of welding in a chamber capable of forming a similar gas atmosphere is also included.

As described above, the capacitor lead terminals welded by the above-described arc stud welding method or the like are subjected to further suppression processing of the needle-like whisker by the post-processing shown in FIG.
13 is a capacitor lead terminal, 14 is an ultrasonic generator, 15 is a bath, 16 is a storage tank, and 17 is an ultrasonic transducer.
First, as shown in FIG. 4, the welded capacitor lead terminal 13 is housed in an ultrasonic generator 14 and irradiated with ultrasonic waves for a predetermined time.
In this ultrasonic generator 14, an ultrasonic transducer 17 is installed on the lower surface of the storage tank 16, the outside of the storage tank 16 is filled with water, and the storage tank 16 for storing the capacitor lead terminals 13 is the above-described storage tank 16. It is installed so as to be adjacent to the ultrasonic transducer 17.
The storage tank 16 is filled with a glycerin solution, and the capacitor lead terminals 13 are stored in the storage tank 16.
In this state, the ultrasonic vibrator 17 of the ultrasonic generator 14 is operated to irradiate the capacitor lead terminal 13 with ultrasonic waves.

  Here, as Example 1, the state of the welded portion of the capacitor lead terminal after filling the storage tank of the ultrasonic generator with a glycerin solution and irradiating ultrasonic waves at 40 kHz for 6 hours is shown in FIG. As the welding shield gas of Example 1, a capacitor lead terminal welded by an arc stud welding method using a mixed gas composed of argon gas and oxygen gas is used.

  In Example 1, as shown in the scanning electron microscope (SEM) photograph of FIG. 5, massive Sn was detected from the surface of the welded portion of the capacitor lead terminal, but needle-like whiskers were not generated. Rather, the object of the present invention has been achieved.

It is a system block diagram explaining the gas shielding method of this invention. It is explanatory drawing explaining the state at the time of completion | finish of gas shield welding. It is explanatory drawing explaining a whisker generation | occurrence | production form. It is explanatory drawing explaining the ultrasonic irradiation method of this invention. 2 is a scanning electron microscope (SEM) photograph of a welded portion of a capacitor lead terminal of Example 1. FIG.

Explanation of symbols

1 Argon gas cylinder 2 Oxygen gas cylinder 3 Mixer 4 Shield nozzle 5 Helium gas cylinder 6 Arc stud welding device 7 One electrode 8 Lead wire (CP wire)
9 Other electrode 10 Aluminum wire 11 Shield gas 12 Whisker 13 Capacitor lead terminal 14 Ultrasonic generator 15 Bath 16 Storage tank 17 Ultrasonic vibrator

Claims (4)

A welding method of a lead terminal for a capacitor for welding a lead wire mainly plated with tin and an aluminum tab, and for the capacitor as a post-treatment of welding using an inert gas as a welding shield gas A welding method for a capacitor lead terminal, wherein ultrasonic waves are applied to at least a welded portion of the lead terminal and the aluminum tab of the lead terminal.   2. The capacitor lead terminal welding method according to claim 1, wherein a mixed gas of an inert gas and an active gas is used as the welding shield gas. 3. The method for welding a capacitor lead terminal according to claim 1, wherein the capacitor lead terminal is irradiated with an ultrasonic wave in a solution during a latent period until a whisker after welding appears. .   The method for welding lead terminals for capacitors according to claim 3, wherein a glycerin solution is used as the solution.

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