Tantulum Capacitor Design Guide

• High volumetric efficiency.
• Stable electrical performance over temperature (T.C. 12%).
• Operating temperature range -55°C to +125°C, 2/3 Vr (linear derating) above +85°C, CGT series is derated above +40°C.
• Better frequency characteristics than aluminum electrolytics.
• Self-Healing, no wear out mechanism. No degradation in performance or reliability.
• No limitation on shelf life.

Surge voltages may be applied up to ten times in an hour for periods up to 30 seconds at a time. They are not intended for continuous operation and should not be used as a parameter for design. See table below.

Voltage derating improves the operating reliability of a tantalum capacitor. Select a higher voltage rated part (30% to 70%) than the maximum line voltage. In the case of low impedance circuits, the tantalum capacitor is likely to be stressed by current surges. In circuits which undergo rapid charge/discharge, a protective resistor of 1.0 ohm per applied volt is recommended. If this is impossible, a voltage-derating factor of up to 70% is recommended. A combination of tantalum capacitors can be connected in series to increase working voltage of the equivalent capacitor. In many power supply topologies where the di/dt
through the capacitor is limited, such as most implementations of buck (current mode), forward converter and flyback, the requirement for series resistance is decreased to 0.1 ohm per applied volt. This level of resistance is used as a basis for the series resistance variable in a 1%/1000 hours 60% confidence level reference. This is what steady state life tests are based on. Certain test circuits such as ICT are likely to subject the capacitor to large voltage and current transients, which will not be seen in normal use. This should be taken into account when considering the capacitors rated voltage.

A small amount of reverse voltage is permissible for short periods. It is not intended to cover continuous operation.

Maximum reverse voltages are:

+25°C 10% of rated voltage not exceeding 1.0 volt
+85°C 3% of rated voltage not exceeding 0.5 volt
+125°C 1% of rated voltage not exceeding 0.1 volt

Tantalum capacitors are polar devices. A non-polar effect can be created by connecting two devices, arranged back-to-back (- to-back (- to -). The capacitance value of each part should be twice the required capacitance value, equal tolerance and rated voltage. For example, two PCT10/35DK devices connected in a back-to-back configuration would result in a non-polar 5MFD, 35volt device.

In DC-DC converters, the input side is typically fed from voltage sources, which are not regulated and are of nominally low impedance. This type of application severely stresses the capacitor. A higher than normal failure rate level may be experienced. Maximum voltage derating and use of low ESR devices is recommended.

Higher capacitances and even lower ESR
Values can be achieved by connecting tantalum capacitors in parallel.

Electrostatic Discharge
Tantalum capacitors demonstrate no sensitivity to ESD.

Flammability UL Rating UL94 VO, Oxygen Index 35%. Epoxy, Hysol MG 33.

Ripple current ratings for all devices can be calculated. For 25°C ripple current ratings, take the square root of the part's free air maximum power dissipation in watts (from the table below) divided by the maximum ESR rating of the component listed in the catalog in ohms (where applicable, convert milliohm values to ohms). Apply the temperature correction factor for temperature above 25°C.

DC Leakage current is dependent on the voltage applied, elapsed time of voltage applied and temperature. Leakage current is measured after 3-5 minutes application of the rated voltage at +20°C. Leakage current increases with higher temperatures and can be mitigated by increasing the voltage rating of the part. Leakage current drops rapidly below the parts initial value when reduced voltages are applied. Voltage derating of the component has the effect of decreasing leakage as shown in the graph below. This will also give a significant increase in the reliability of the part for any application.

Soldering Capacitors

• Soldering temperature and time should be the minimum for a good connection.
  
• Recommended soldering profiles are designed to insure that the temperature of the internal construction of the capacitors does not exceed +220°C.
  
• Positioning capacitors near components radiating heat such as power transistors should be avoided.
  
• Allow for an increase to ESR ratings of 1.25 x catalog limit post PCB assembly.

Lead-free RoHS compliant, 100% Sn termination finish
Legislation is being developed worldwide to reduce the lead content and other hazardous substances in electronic products. This will reduce the environmental impact when such products are discarded. Nemco products are lead-free devices which meet RoHS requirements. Optional suffix codes have been added to our part numbering system so either 90/10 Sn/Pb or 100% Sn (lead-free) can be specified. The following general information applies to lead-free surface mount devices.

IR reflow
Pre-heating: 150°C +/- 15°C / 60-90s
Maximum peak temperature: 240°C - 260°C, 250°C max recommended, 10 seconds maximum time at peak, 3 reflow cycles.
Ramp rate: 2-3°C/sec.
Maximum time (cumulative) above 230°C 40 seconds.
Cool down should not be forced. 6°C/sec. is recommended.

Wave soldering
PCT, LSR, MCT and CGT: Maximum peak temperature: 250°C - 260°C for 3-5 seconds max (250°C max recommended)
TB: Maximum peak temperature: 230°C - 250°C for 3-5 seconds max (240°C max recommended)
All other parameters remain the same as for IR reflow.

Hand soldering
Soldering iron tip diameter: select to fit application
Maximum tip temperature: +370°C
Maximum exposure time: 3 seconds
Apply heat to pad, not the terminations.

Recommended solder alloy for reflow: SnAgCu
lead-free (100% Sn) termination finish is compatible with all common lead-free solder pastes including SnCu, SnCuAgBi, etc.
Recommended solder alloy for wave soldering: SnCu
Recommended solder alloy for hand soldering: SnAgCu

Forward compatibility
Parts with Sn/Pb can be used in a lead-free process depending on the solder and solder temperature.
Solders with Bi are not compatible.

Backward compatibility
Lead-free parts (100% Sn termination finish) can be used in a Sn/Pb process. The 100% Sn (Tin) termination finish is compatible
with existing Sn/Pb solder pastes / systems in use today.

RoHS
Nemco lead-free product complies with EU Directive 2002/95/EC on the Restriction of Hazardous Substances requirements.

JEDEC Standard JESD97
Nemco lead-free surface mount devices are in accordance with category e3 terminations.

MSL
PCT, LSR, MCT and TB series moisture sensitivity level per IPC/Jedec J-STD-020B is level 1.
CGT series moisture sensitivity level per IPC/Jedec J-STD-020B is level 3.

Visual standard
Lead-free solder joints are not as bright as tin-lead pastes and the fillet may not be as large.

Resin color
The encapsulant resin color may darken due to the increase in temperature required for the paste.

Self alignment
lead-free solder pastes do not allow the same self alignment as lead containing systems, Standard mounting pads are acceptable,
but machine set up may need to be modified.

Reliability
PCT, LSR, MCT and TB series are 1% per 1,000 hours at 85°C, Vr with 0.1Ω / V series impedance, 60% confidence level.
CGT series is 0.2% per 1,000 hours at 85°C, 0.5xVr with 0.1Ω / V series impedance, 60% confidence level.

Soldering conditions
Fluxes containing acids must not be used.

Cooling
After soldering, the assembly should preferably be allowed to cool naturally to room temperature. In the event that assisted cooling
is used, the rate of change in temperature should not exceed that used in reflow.