JPS597208B2 - Capacitor manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a capacitor, and particularly to an improvement in a method for reforming capacitor pellets in a solid electrolytic capacitor.

In general, this type of capacitor is made by press-molding metal powder with valve action, such as tantalum, niobium, aluminum, titanium, etc., into a cylindrical shape and sintering it.The surface of the capacitor pellet is then chemically treated with ζ An oxide layer is formed as a dielectric layer, and then a semiconductor layer is formed on the oxide layer by repeating the deposition and thermal decomposition operations of the semiconductor mother liquid several times.

However, during this decomposition process, the oxide layer tends to deteriorate due to thermal stress and the like, resulting in a decrease in dielectric strength.

Therefore, after each decomposition step or as appropriate, reconstitution is performed for the purpose of repairing this oxidized layer.

This regeneration is carried out as follows. That is, for example, a capacitor pellet after forming a semiconductor layer is immersed in an electrolytic solution whose concentration is slightly lower than that used in chemical formation, and a DC voltage is applied to the capacitor pellet.

This re-formation voltage is applied by applying a constant voltage based on the expected withstand voltage of the capacitor to be re-formed.

However, in this method, since a voltage is suddenly applied to the capacitor, the oxide layer may not be repaired and may be destroyed all at once.

Therefore, a voltage application method has been proposed in which the applied voltage is increased linearly or logarithmically with respect to the elapsed time. However, if the rate of increase is too fast, the As the applied voltage increases, some capacitors have their oxidized layers destroyed without being repaired, resulting in some capacitors becoming defective.

Of course, it would be possible to slow down the rising speed of the applied voltage to allow enough time for repair, but doing so would require a very long time for re-formation, reducing work efficiency. Therefore, it is not suitable for mass production.

Therefore, in view of the above-mentioned drawbacks, this invention reduces the incidence of characteristic defects by increasing the voltage applied during re-forming in a stepwise manner, thereby taking the time necessary for repair without significantly increasing the re-forming time. Examples will be described below.

First, an oxide layer and a semiconductor layer are formed by a conventional method on the surface of a capacitor pellet made by press-molding metal powder having a valve action into a cylinder shape and sintering it.

Thereafter, the capacitor pellet is immersed in a re-forming solution (electrolytic solution) whose concentration is slightly lower than that of the chemical re-forming solution, and connected to a re-forming power source.

This reconversion power source is configured so that the voltage increases stepwise as will be described later.

Then, the re-forming voltage in this power source is divided into, for example, 10 steps, and the holding time of each step is set to 3 minutes, the voltage is increased, and the re-forming operation is performed.

According to this embodiment, since the oxide layer is reliably repaired at each step, it is possible to significantly reduce the incidence of characteristic defects such as leakage current that are thought to depend on the state of repair.

In this respect, 35V10 using Kunkle powder in the above example
When using capacitor pellets of lower μ class, the defective rate was 3%, whereas in the conventional example it was 8%.

It is generally known that the oxide layer is repaired by re-formation, but since there is a certain speed of repair, if the rate of increase of the re-formation voltage is made higher than the speed of repair of the oxide layer, the withstand voltage will increase. Dielectric breakdown occurs when the voltage drops below the reconstitution voltage.

Therefore, by increasing the reformation voltage stepwise, sufficient time can be secured for repairing the oxide layer (this not only reduces the incidence of characteristic defects but also improves the reliability of the capacitor).

In addition, the reconstitution time can be set almost the same as the conventional example, so
Workability is not hindered.

Next, a circuit example of a reconversion power source used in the method of this invention will be explained.

In FIG. 1, reference numeral 1 denotes a pulse generator, which generates short pulses of a fixed size at fixed time intervals.

2 is a diode, and 3 is a capacitor, and each time a pulse is supplied to the capacitor 3 from the pulse generator 1 through the diode 2, its charging voltage increases stepwise.

Reference numeral 4 denotes a field effect transistor, which amplifies the input voltage and outputs it by flowing a current proportional to the charging voltage of the capacitor 3 from the B power source to the resistor 5.

6 is an upper limit voltage setting circuit, which outputs the input voltage as it is up to a certain set voltage, but when it exceeds that, outputs a fixed set voltage. 9 is a booster that supplies the input voltage value with a large current.

The output waveform obtained by this circuit is as shown in FIG.

That is, the voltage rises stepwise at regular time intervals, reaches a certain upper limit set voltage E1, and is maintained at that value.

This output voltage is applied between the container 10 filled with the reconstitution liquid and the capacitor pellets 11 immersed therein, thereby performing reconstitution.

The rise width per step of the applied voltage E, the holding time of each step, and the voltage rise limit may be appropriately selected depending on the type of capacitor.

In addition to the method of setting the upper limit of the applied voltage as described above, there is also a method of setting the upper limit of the current flowing through the capacitor undergoing re-formation.

FIG. 3 shows the configuration of a power supply circuit incorporating an upper limit current setting circuit 6' in place of the upper limit voltage setting circuit 6 described above.

In this case, in order to detect the current flowing through the capacitor 11, a detection resistor 12 is inserted in series with the capacitor 11, the resistance value of which is sufficiently lower than that of the re-forming section 10.11.

The voltage at both ends is compared with a reference voltage 14 by a comparator 13, and sent through a NOT circuit 15 to a gate circuit 16 as an output for turning the gate circuit ON or OFF.

That is, only when the voltage across the detection resistor 12 is lower than the reference voltage 14, a high level output is sent to the gate circuit 16.
The output voltage of the electrical effect transistor 4 is sent as it is to the PUSK 9, and when the voltage across the detection resistor 12 exceeds the reference voltage 14, a low level output is sent to the gate circuit so that no output is produced. Make it.

When reconstitution is performed using such a circuit, the current flowing through the reconstituted capacitor 11 changes as shown by the dotted chain in FIG. 2.

In other words, each time the voltage increases step by step, a charging current of approximately constant width flows in an increasing pulse waveform, and the leakage current value decreases to a value corresponding to the applied voltage and insulation properties of the capacitor at that point, and the leakage current gradually increases. The current increases.

When a certain set value (1) is reached, the current supply is stopped and the re-formation is completed.

This upper limit current value is selected according to the allowable leakage current value of the capacitor 11 undergoing re-formation.

When reconstitution is performed in this way, the capacitor 1
The withstand voltage is restored to the highest voltage value that can be restored.

Therefore, production efficiency can be increased by recording the applied voltage at the upper limit value and classifying each capacitor into grades based on withstand voltage.

Next, an example of a power supply circuit that smooths the rise of each step of the applied voltage waveform to reduce the impact on the capacitor undergoing re-formation will be described.

FIG. 4 shows the power supply circuit of FIG. 1 in which a capacitor 17 is connected in parallel to the output section of the field effect transistor 4 via a resistor 18.

In this way, the voltage appearing at the output of the field effect transistor 4 is charged with a time constant defined by the capacitor 17 and the resistor 18, and is then sent to the PUSK 9.

Therefore, the output voltage waveform of the power supply circuit rises smoothly and rises stepwise, as shown in FIG.

In this case, better results can be expected from the repair.

Note that, in place of the upper limit voltage setting circuit 6, it is of course possible to incorporate the above-mentioned upper limit current setting circuit 6'.

Further, as another power supply circuit configuration, there is one in which the capacitor 11 undergoing re-formation is charged little by little at intervals, and the charging voltage is increased in steps to perform the re-formation.

Examples of the circuit are shown in FIGS. 6 and 7.

In FIG. 6, reference numeral 19 denotes a pulse generator that supplies short pulses of a fixed size at fixed time intervals.

This pulse generator 19 has a sufficiently larger current capacity than the pulse generator 1 shown in FIGS. 1, 3, and 4, and supplies reconstitution current without the amplifier 4 or booster 9 It is possible.

In the case of FIG. 6, the capacitor 11 to be reconstituted is gradually charged via the diode 20 every cycle of the pulse generator, and the charging voltage increases.

This voltage waveform becomes as shown in FIG.

That is, the charging voltage E of the reconstituted capacitor 11 rises stepwise every cycle of the pulse generator 19, but as the voltage rises, the amount of voltage drop E due to leakage current increases. The waveform has a tail.

Finally, the output voltage E of the pulse generator 19.

A sawtooth waveform is repeated, with a peak at , and a drop E1 proportional to the leakage current of the capacitor 11.

Furthermore, in the circuit of FIG. 6, a variable resistor 21 is inserted in series between the diode 20 and the capacitor 11 to be reconstituted, as shown in FIG.

In this way, the capacitor 11 is charged with an RC time constant, so that the rise of the voltage waveform that rises in steps becomes smooth as shown in Figure 9.
Better results can be expected from the repair.

Note that by changing the resistance value of the variable resistor 21, the slope of the rise can be changed arbitrarily.

In the present invention, the capacitor pellet is not limited to the sintered type of the above embodiment, but may be a metal wire having a valve action, or may be crushed or wound into a coil.

Furthermore, it may be one in which foil-like metal is wound, such as an aluminum electrolytic capacitor.

As explained above, in the present invention, since the reconstitution of capacitor pellets made of a metal member having a valve action is carried out by applying a voltage that increases stepwise at predetermined time intervals, the reconstitution treatment time is It is possible to improve the repairability of the oxide layer, reduce the failure rate of capacitor characteristics, and improve reliability without increasing the oxidation layer.

[Brief explanation of drawings]

1 to 9 show different embodiments of the power supply circuit used in the present invention and their output voltage waveforms, respectively.

Claims (1)

[Claims] 1. A method for manufacturing a capacitor, which comprises applying a stepwise increasing voltage to a capacitor pellet made of a metal member having a valve action to perform reconstitution.