Application Notes for Tantalum Solid Electrolytic Capacitor
1. Operating Voltage
Tantalum Solid Electrolytic Capacitor shall be operated at the rated voltage or lower.
Rated voltage: The “rated voltage” refers to the maximum DC voltage that is allowed to be continuously applied between the capacitor
terminals at the rated temperature.
Surge voltage: The “surge voltage” refers to the voltage that is allowed to be instantaneously applied to the capacitor at the rated
temperature or the maximum working temperature. The capacitor shall withstand the voltage when a 30-second cycle of application of
the voltage through a 1000 Ω series resistance is repeated 1000 times in 6-minute periods.
When designing the circuit, the equipment’s required reliability must be considered and appropriate voltage derating must be performed.
2. Application that contain AC Voltage
Special attention to the following 3 items.
(1) The sum of the DC bias voltage and the positive peak value of the AC voltage should not exceed the rated voltage.
(2) Reverse voltage should not exceed the allowable values of the negative peak AC voltage.
(3) Ripple voltage should not exceed the allowable values.
3. Permissible Reverse Voltage
If reverse voltage exceeding the value shown in the following table is applied to the capacitor, there is a fear of a fluctuation of leakage
current and an increase in failure rate. To avoid the permissible reverse voltage, use the capacitor under bias voltage as required.
The above specifications apply for accidental reverse voltage. If reverse voltage is constantly applied to the capacitor, use it with
non-polar connection.
4. Permissible Ripple Voltage
Permissible ripple voltage is determined by the loss of element and heat radiation of case
and lead wire.
This is influenced by capacitance, frequency of ripple, ESR and operating temperature.
The permissible ripple voltage values are shown in our technical document.
5. Application on low-impedance circuit
The failure rate of low impedance circuit at 0.1Ω/V is about five times greater than that of a 1Ω/V circuit. To curtail this higher failure rate,
tantalum capacitors used in low impedance circuits, such as filters for power supplies, particularly switching power supplies, or for noise
by-passing, require that operating voltage be derated to less than half of the rated voltage. Actually, less than 1/3 of the rated voltage is
recommended.
6. Non Polar Application
Tantalum capacitors can be used as a non-polar unit if two capacitors are connected “BACK-TO-BACK” when reserve voltage is applied
at a more than permissible value, or in a purely AC circuit. The two capacitors should both be of the same rated voltage and capacitance
tolerance, and they should both be twice the required capacitance value.
Ripple Voltage: Permissible Ripple Voltage shall not exceed the value allowed for either C1 or C2 (This will be the same, as the
capacitors should be identical.)
Capacitance:(C1×C2)/(C1 + C2)
Leakage Current: If terminal A is (+), the Leakage Current will be equal to C1’s Leakage Current.
If terminal B is (+), the Leakage Current will be equal to C2’s Leakage Current.
7. Soldering
7.1. Preheating
To obtain optimal reliability and solderability conditions, capacitors should be pre-heated at 130 to 200 °C for approximately 60 to 120
seconds.
7.2. Soldering
The body of the capacitor shall not exceed 260 °C during soldering.
(1) Reflow Soldering
Reflow soldering is a process in which the capacitors are mounted on a printed board with solder paste. There are two methods of
Reflow Soldering: Direct and Atmospheric Heat.
· Direct Heat (Hot plate)
During the Direct Heat method, the capacitor has been positioned on a printed board, which is then placed upon a hot plate.
The capacitor maintains a lower temperature than the substrate, which in turn stays at a lower temperature than the hot plate.
· Atmospheric Heat
a) VPS (Vapor Phase Soldering)
During VPS,the substrate is heated by an inert liquid with a high boiling point. The temperature of the capacitor’s body and the
temperature of the substrate are about the same as the atmosphere. This temperature should be below 240°C.
b) Near and Far IR Ray
Due to the heat absorption of the capacitor’s body, the internal temperature of the capacitors may be 20 ~ 30°C higher than the
setting temperature and may exceed 260°C.
Temperature control is crucial in maintaining a temperature of 260 °C or lower.
c) Convention Oven
An infrared ray is the main source of heat in this process. The temperature of the substrate and the capacitors can be maintained
at a similar level by the circulation of heated air, or an inert gas.