Molded Guide

www.vishay.com

Vishay Sprague

Revision: 12-Sep-17

1

Document Number: 40074

THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT

Guide for Molded Tantalum Capacitors

INTRODUCTION

Tantalum electrolytic capacitors are the preferred choice in

applications where volumetric efficiency, stable electrical

parameters, high reliability, and long service life are primary

considerations. The stability and resistance to elevated

temperatures of the tantalum / tantalum oxide / manganese

dioxide

system

make

solid

tantalum

capacitors

an

appropriate choice for today's surface mount assembly

technology.

Vishay Sprague has been a pioneer and leader in this field,

producing a large variety of tantalum capacitor types for

consumer, industrial, automotive, military, and aerospace

electronic applications.

Tantalum is not found in its pure state. Rather, it is

commonly found in a number of oxide minerals, often in

combination with Columbium ore. This combination is

known as “tantalite” when its contents are more than

one-half tantalum. Important sources of tantalite include

Australia, Brazil, Canada, China, and several African

countries. Synthetic tantalite concentrates produced from

tin slags in Thailand, Malaysia, and Brazil are also a

significant raw material for tantalum production.

Electronic

applications,

and

particularly

capacitors,

consume the largest share of world tantalum production.

Other important applications for tantalum include cutting

tools (tantalum carbide), high temperature super alloys,

chemical processing equipment, medical implants, and

military ordnance.

Vishay Sprague is a major user of tantalum materials in the

form of powder and wire for capacitor elements and rod and

sheet for high temperature vacuum processing.

THE BASICS OF TANTALUM CAPACITORS

Most

metals

form

crystalline

oxides

which

are

non-protecting, such as rust on iron or black oxide on

copper. A few metals form dense, stable, tightly adhering,

electrically insulating oxides. These are the so-called

“valve”metals and include titanium, zirconium, niobium,

tantalum, hafnium, and aluminum. Only a few of these

permit

the

accurate

control

of

oxide

thickness

by

electrochemical means. Of these, the most valuable for the

electronics industry are aluminum and tantalum.

Capacitors are basic to all kinds of electrical equipment,

from radios and television sets to missile controls and

automobile ignitions. Their function is to store an electrical

charge for later use.

Capacitors consist of two conducting surfaces, usually

metal plates, whose function is to conduct electricity. They

are separated by an insulating material or dielectric. The

dielectric used in all tantalum electrolytic capacitors is

tantalum pentoxide.

Tantalum pentoxide compound possesses high-dielectric

strength and a high-dielectric constant. As capacitors are

being manufactured, a film of tantalum pentoxide is applied

to their electrodes by means of an electrolytic process. The

film is applied in various thicknesses and at various voltages

and although transparent to begin with, it takes on different

colors as light refracts through it. This coloring occurs on the

tantalum electrodes of all types of tantalum capacitors.

Rating for rating, tantalum capacitors tend to have as much

as three times better capacitance / volume efficiency than

aluminum electrolytic capacitors. An approximation of the

capacitance / volume efficiency of other types of capacitors

may be inferred from the following table, which shows the

dielectric constant ranges of the various materials used in

each type. Note that tantalum pentoxide has a dielectric

constant of 26, some three times greater than that of

aluminum oxide. This, in addition to the fact that extremely

thin films can be deposited during the electrolytic process

mentioned earlier, makes the tantalum capacitor extremely

efficient with respect to the number of microfarads available

per unit volume. The capacitance of any capacitor is

determined by the surface area of the two conducting

plates, the distance between the plates, and the dielectric

constant of the insulating material between the plates.

In the tantalum electrolytic capacitor, the distance between

the plates is very small since it is only the thickness of the

tantalum pentoxide film. As the dielectric constant of the

tantalum pentoxide is high, the capacitance of a tantalum

capacitor is high if the area of the plates is large:





where

C = capacitance

e = dielectric constant

A = surface area of the dielectric

t = thickness of the dielectric

Tantalum

capacitors

contain

either

liquid

or

solid

electrolytes. In solid electrolyte capacitors, a dry material

(manganese dioxide) forms the cathode plate. A tantalum

lead is embedded in or welded to the pellet, which is in turn

connected to a termination or lead wire. The drawings show

the construction details of the surface mount types of

tantalum capacitors shown in this catalog.

COMPARISON OF CAPACITOR



DIELECTRIC CONSTANTS

DIELECTRIC

e

DIELECTRIC CONSTANT

Air or vacuum

1.0

Paper

2.0 to 6.0

Plastic

2.1 to 6.0

Mineral oil

2.2 to 2.3

Silicone oil

2.7 to 2.8

Quartz

3.8 to 4.4

Glass

4.8 to 8.0

Porcelain

5.1 to 5.9

Mica

5.4 to 8.7

Aluminum oxide

8.4

Tantalum pentoxide

26

Ceramic

12 to 400K

C

eA

t

-------

=