Film Capacitors - Introduction - Philips Semiconductors / NXP Semiconductors

1996 Oct 21 5

Philips Components

Film capacitors Introduction

FILM CAPACITORS

The dielectric material of a film capacitor is a plastic or paper film. In the table below, an overview is given of the film

dielectrics used in Philips film capacitor products.

Film dielectrics used in Philips ﬁlm capacitor products

Note

1. P = paper; KT = polyethylene terephthalate; KC = polycarbonate; KPS = polyphenylene sulfide; KS = polystyrene;

KP = polypropylene.

Because of their typical properties, the polyester and polycarbonate dielectrics are used in general purpose applications

where a small bias DC voltage and small AC voltages at low frequencies are usual. The most important properties are

the high capacitance per volume for polyester and, the capacitance stability over a wide temperature range for

polycarbonate.

A rather new dielectric is polyphenylene sulfide (KPS). Its high melting point allows it to be used in a non-encapsulated

SMD product. The properties of KPS determine the stability of the product characteristics.

Polypropylene and polystyrene films are used in high frequency or high voltage applications due to their very low

dissipation factor and high dielectric strength.

Paper film is still used in capacitors for mains applications, as for example in interference suppression capacitors.

Typical properties as functions of temperature or frequency are illustrated in Figs 1 to 4.

PARAMETER DIELECTRIC(1) UNIT

P KT KC KPS KS KP

Dielectric constant:

at 1 kHz 3.0 3.3 2.8 3.0 2.4 2.2

Dissipation factor (×10−4)

at 1 kHz 50 50 12 3 2 1

at 10 kHz 120 110 50 6 2 2

at 100 kHz 200 170 100 12 2 2

at 1 MHz 300 200 110 18 4 4

Volume resistivity 10+16 10+17 10+17 10+17 10+18 10+18 Ωcm

Dielectric strength 100 400 300 250 500 600 V/µm

Maximum application

temperature 100 125 125 150 85 100 °C

Power density:

at 10 kHz 67 50 21 2.5 0.67 0.6 W/cm3

1996 Oct 21 6

Philips Components

Film capacitors Introduction

Fig.1 Capacitance change as a function of ambient free air temperature at 1 kHz; typical curves.

handbook, full pagewidth

DRINL01

100

−2

−4

−60 −20 60

20 Tamb (°C)

140

KPS

∆C

C

(%)

Fig.2 Dissipation factor as a function of frequency at 20 °C; typical curves.

handbook, full pagewidth

DRINL02

105

104

103

102

103

102

f (Hz)

dissipation

factor

(× 10−4)KT

KPS

1996 Oct 21 7

Philips Components

Film capacitors Introduction

Fig.3 Dissipation factor as a function of ambient free air temperature at 1 kHz; typical curves.

ndbook, full pagewidth

DRINL03

−60 −20 20 60 100 140

103

10−1

102

dissipation

factor

(× 10−4)

Tamb (°C)

KPS

Fig.4 Insulation resistance as a function of ambient free air temperature; typical curves.

handbook, full pagewidth

DRINL04

−60 −20 20 60 100 140

107

103

106

104

105

Tamb (°C)

Rins

(MΩ)

KPS

1996 Oct 21 8

Philips Components

Film capacitors Introduction

CONSTRUCTION OF THE CAPACITOR CELL

The type of electrode used determines whether the

capacitor is a metallized film or film/foil type.

The electrodes used for metallized film capacitors consist

of a thin metal layer with a thickness of approximately

30 to 50 nm. The electrodes of film/foil capacitors have

discrete metal foils with thicknesses of approximately

5to10µm.

Due to their construction, film/foil capacitors can carry

higher currents than metallized ones, but are larger in

volume.

Metallized capacitors have a self-healing behaviour as an

intrinsic characteristic. All capacitor cells are low inductive

wound, except for the SMD products which are produced

by stacked film technology.

Depending on the AC voltage, single or series

constructions are used. Single section capacitors are

normally used for products with an AC rating up to

275 V (AC). Series constructions are used for higher

voltages.

GENERAL DEFINITIONS

Rated voltage (URdc)

The maximum DC voltage (in V) which may be

continuously applied to a capacitor at any operating

ambient temperature below the rated temperature.

Category voltage (UC)

The maximum AC voltage (or DC voltage) which may be

applied continuously to a capacitor at its upper category

temperature.

Rated AC voltage (URac)

The maximum RMS voltage (in V) of specified frequency

(mostly 50 Hz), which may be continuously applied to a

capacitor at any operating ambient temperature below the

rated temperature.

Capacitance

The capacitance of a capacitor is the capacitive part of the

equivalent circuit composed of capacitance, series

resistance and inductance.

Rated capacitance

The rated capacitance, normally marked on the product, is

the value for which the capacitor has been designed.

Capacitance tolerance

The percentage of the allowed deviation of the

capacitance from the rated capacitance is measured at a

free air ambient temperature of 23 ±1°C and RH of

50 ±2%.

Tolerance coding in accordance with

“IEC 62”

A letter “A” indicates that the tolerance is defined in the

type specification or customer detail specification.

Temperature coefﬁcient and cyclic drift of

capacitance

The terms characterizing these two properties apply to

capacitors of which the variations of capacitance as a

function of temperature are linear or approximately linear

and can be expressed with a certain precision.

PERCENTAGE OF

DEVIATION LETTER CODE

±1.0% F

±2.0% G

±5.0% J

±10.0% K

±20.0% M

Fig.5 Simplified equivalent circuit.

handbook, halfpage

DRINL06

ESR

1996 Oct 21 9

Philips Components

Film capacitors Introduction

TEMPERATURE COEFFICIENT OF CAPACITANCE

The rate of capacitance change with temperature,

measured over the specified temperature range. It is

normally expressed in parts per million per Kelvin (10−6/K).

TEMPERATURE CYCLIC DRIFT OF CAPACITANCE

The maximum irreversible variation of capacitance

observed at room temperature during or after the

completion of a number of specified temperature cycles. It

is usually expressed as a percentage of the capacitance

related to a reference temperature. This is normally 20 °C.

Rated voltage pulse slope (dV/dt)

The maximum voltage pulse slope that the capacitor can

withstand with a pulse voltage equal to the rated voltage.

For pulse voltages other than the rated voltage, the

maximum voltage pulse slope may be multiplied by URdc

and divided by the applied voltage.

The voltage pulse slope multiplied by the capacitance

gives the peak current for the capacitor.

Dissipation factor and equivalent series resistance

The dissipation factor or tangent of loss angle (tan δ) is the

power loss of the capacitor divided by the reactive power

of the capacitor at a sinusoidal voltage of specified

frequency.

The equivalent series resistance (ESR) is the resistive part

of the equivalent circuit composed of capacitance, series

resistance and inductance.

Insulation resistance and time constant

The insulation resistance (Rins) is defined by the applied

DC voltage divided by the leakage current after a well

defined minimum time.

The time constant is the product (in seconds) of the

nominal capacitance and the insulation resistance

between the leads.

Fig.6 Simplified equivalent circuit.

handbook, halfpage

DRINL06

ESR

Ambient temperature

The ambient temperature is the temperature of the air

surrounding the component.

Climatic category

The climatic category code (e.g. 50/100/56) indicates to

which climatic category a film capacitor type belongs.The

category is indicated by a series of three sets of digits

separated by oblique strokes corresponding to the

minimum ambient temperature of operation, the maximum

temperature of operation and the number of days of

exposure to damp heat (Steady state - test Ca)

respectively that they will withstand.

Category temperature range

The range of ambient temperatures for which the capacitor

has been designed to operate continuously. This is

defined by the temperature limits of the appropriate

category.

Upper category temperature

The maximum ambient temperature for which a capacitor

has been designed to operate continuously at category

voltage.

Lower category temperature

The minimum ambient temperature for which a capacitor

has been designed to operate continuously.

Rated temperature

The maximum ambient temperature at which the rated

voltage may be applied continuously.

Maximum application temperature

The equivalent of the upper category temperature.

Self-healing

The process by which the electrical properties of a

metallized capacitor, after a local breakdown, are rapidly

and essentially restored to the values before the

breakdown.

Temperature characteristic of capacitance

The term characterizing this property applies mainly to

capacitors of which the variations of capacitance as a

function of temperature, linear or non-linear, cannot be

expressed with precision and certainty.

1996 Oct 21 10

Philips Components

Film capacitors Introduction

The temperature characteristic of capacitance is the

maximum reversible variation of capacitance, produced

over a given temperature range within the category

temperature range.

It is expressed normally as a percentage of the

capacitance related to a reference temperature of 20 °C.

Storage temperature

The temperature range with a RH of maximum 80%

without condensation at which the initial characteristics

can be guaranteed for at least 2 years.

Maximum power dissipation

The power dissipated by a capacitor is a function of the

voltage (Uesr) across or the current (I) through the

equivalent series resistance ESR and is expressed by:

Given that for film capacitors

the formula can be simplified to:

or with

the formula becomes:

PUesr2

ESR

--------------

PESRI

×=

Fig.7 Simplified equivalent circuit.

handbook, halfpage

DRINL05

Uesr

ESR

Uesr2ESR2

ESR21ω2C2

⁄+

-------------------------------------------- U2

×=

δtan ωC ESR 0.1«××=

Uesr2ESR2ω2C2U2

×××=

ESR δωC⁄tan=

PωC×=δU2

×tan×

Pδtan

ωC×

-------------- I2

×=

For the tan δ we take the maximum value found in the

specification, C is in farads and . U or I are

assumed to be known.

The maximum permissible power dissipation (Pmax), which

depends on the dimensions of the capacitor and on the

ambient free air temperature are given in the specification.

In applications where sinewaves occur, we have to take for

U the RMS-voltage or for I the RMS-current of the

sinewave.

In applications where periodic signals occur, the signal has

to be expressed in Fourier-terms:

with U0 the DC voltage, Uk and Ik (the voltage and current

of the k-th harmonic respectively) the formula for the

dissipated power becomes:

and tan δkis the tan δ at the k-th harmonic.

ω2πf=

kkωtΦ

+()sin×

k1=

∞

∑

kkωtΦ

+()sin×

k1=

∞

∑

Pkωc×δ

-------

×tan××

k1=

∞

∑

Pδ

tan Ik

2k×ω×C×

---------------------------------

k1=

∞

∑

1996 Oct 21 11

Philips Components

Film capacitors Introduction

TEST INFORMATION

Robustness of leads

TENSILE STRENGTH OF LEADS (Ua)

(LOAD IN LEAD AXIS DIRECTION)

Lead diameter 0.5, 0.6 and 0.8 mm: load 10 N, 10 s.

BENDING (Ub)

Lead diameter 0.5, 0.6 and 0.8 mm: load 5 N, 4 ×90°.

Lead diameter 1.0 mm: load 10 N, 4 ×90°.

TORSION (Uc) (FOR AXIAL CAPACITORS ONLY)

Severity 1: three rotations of 360°.

Severity 2: two rotations of 180°.

Rapid change of temperature (Na)

The rapid change of temperature test is intended to

determine the effect on capacitors of a succession of

temperature changes and consists of 5 cycles of

30 minutes at lower category temperature and 30 minutes

at higher category temperature.

Dry heat (Ba)

This test determines the ability of the capacitors to be used

or stored at high temperature. The standard test is

16 hours at upper category temperature.

Damp heat cyclic (Db)

This test determines the suitability of capacitors for use

and storage under conditions of high humidity when

combined with cyclic temperature changes and, in

general, producing condensation on the surface of the

capacitor.

One cycle consists of 24 hours exposure to 55 °C and

95 to 100% relative humidity (RH).

Cold (Aa)

This test determines the ability of the capacitors to be used

or stored at low temperature. The standard test is 2 hours

at the lower category temperature.

Damp heat steady state (Ca)

This test determines the suitability of capacitors for use

and storage under conditions of high humidity.

The test is primarily intended to permit observation of the

effects of high humidity at constant temperature over a

specified period.

The capacitors are exposed to a damp heat environment

which is maintained at a temperature of 40 °C and a RH of

90 to 95% for the number of days specified by the third set

of digits of the climatic category code.

Soldering conditions

With regard to the resistance to soldering heat and the

solderability, our products comply with

“IEC 384-1”

and the

additional type specifications.

For our precision capacitors where capacitance stability is

important, we refer to the paragraph “Soldering conditions”

in the type specification.

In the tables

“Quick reference test requirements”

overview is given for the various soldering parameters per

product type.

Solvent resistance of components

Soldered capacitors may be cleaned using appropriate

cleansing agents, such as alcohol, fluorhydro-carbons or

their mixtures. Solvents or cleansing agents based on

chlorohydrocarbons or ketones should not to be used, as

they may attack the capacitor or the encapsulation.

After cleaning it is always recommended to dry the

components carefully.

Special attention should be given to non or partially

encapsulated products (e.g. KS 424 ... 431).