When it comes to selecting a surface mount tantalum capacitor, the first choice is whether to use a precision molded part or a conformally coated device.
The most common choice for commercial applications is the precision molded capacitor. They possess precise dimensional repeatability to EIA standards for ease of PCB mounting, and are available in standard, high temperature, low ESR, fail safe and even stacked versions for bulk capacitance solutions. Molded tantalum capacitors are also manufactured in lead-frameless (commonly known as face-down) configurations for low profile mounting.
However, a conformal coated tantalum capacitor offers the highest volumetric efficiency of any surface mount tantalum capacitor, and provides low ESR performance as well as a three-fold improvement in ESL performance over standard molded parts.
CONFORMAL COATED CAPACITOR UPSIDE
As a conformal coated tantalum capacitor does not possess a lead frame, mounting profiles as low as 1.0mm are achievable (see Vishay 572D Series), and the maximum usage of the package outline provided by this configuration also means up to 50%+ more capacitance is available in a comparable footprint to a molded device.
This “lead-frameless” design also suppresses distortion, which can make them an excellent choice for high end audio circuits. AVX, for example, produces the F95 series of conformal coated tantalum capacitor which has been optimized to achieve high level sound production.
Conformal coated tantalum capacitors are also available in dual anode ultra low ESR versions (see Vishay 597D Series) and fused versions for fail safe operation (see Vishay T96 Series).
CONFORMAL COATED CAPACITOR DOWNSIDE
Conformal coated capacitors are resin dipped products, rather than injection molded parts. This introduces a non-uniformity into the end product which is a bane to production people using fast pick and place machines that pick up parts for assembly with vacuum tweezers.
The ability to rework these parts is also limited, as a wayward hot iron can easily destroy the device is situ.
CONFORMAL COATED CAPACITORS CURRENTLY IN PRODUCTION
There are 22 series of conformal coated tantalum capacitors in production today; three are manufactured by AVX (these parts were formerly part of the Nichicon range of tantalum capacitors), and the other nineteen are part of the Vishay Sprague portfolio of tantalum capacitors.
Capacitance range across all series is 0.1µF to 2,200µF and working voltage range 2Vdc – 75Vdc.
The AVX range comprises standard commercial, low profile & high CV, and the audio optimized version previously mentioned, while the extensive Vishay Sprague range comprises commercial, COTS, medical, military, low profile, ultra low ESR and fail safe versions.
So if it’s a design that places maximum priority on volumetric efficiency and low ESR, such as a medical implantable device or hearing aid, a conformally coated tantalum capacitor may be worth considering, taking into account the caveats mentioned above. You can check out the complete industry range below, or better still, ask Capacitor Faks to send you all the information you need.