Technology

© EPCOS AG 2016

2

Fig. 1: Cross section of a metalized film capacitor

Fig. 2: Self-healing property of a metalized film capacitor

Metallized film capacitors (fig.1)

have the advantage that for

certain failures in the dielectric the

capacitor will not go into short

thanks to the ultrathin metallized

electrode (thickness typical 10 to

100 nm) and the use of aluminium

as material for the electrodes. If a

breakdown occurs, the aluminium

will evaporate around the break-

down spot and immediately

oxidize to Al

excellent insulator. So the

breakdown spot becomes high-

impedance and is insulated from

the rest of the capacitor. The

insulated area is formed in a few

microseconds and ensures the full

functionality of the capacitor after

breakdown.

This behaviour is called

“clearing”

or

“self-healing” (fig. 2). In prin-

ciple there should not be any

further clearing during the service

life, since all capacitors are

typically “cleared” with a voltage

of 1.5 times the rated voltage

during the production process.

Additionally, to limit the energy

dissipation during a clearing event,

for some designs at least one

electrode is divided into segments,

connected by small links or fuses.

The capacitors are typically

named “segmented” or

“structured” metalized film

capacitors. See fig. 3 example of

a “T-segmentation”:

EPCOS possesses different

winding technologies:

 The stacked technology,

typically used for PCC film

capacitors, for which the film is

already wound flat on the

winding machine. This tech-

nology offers the highest fill

factor and the lowest ESR.

 The flat pressed winding tech-

nology which is most commonly

used on the market for this type

of application today. This tech-

nology offers the lowest costs at

a good performance.

Typical rated voltages (V):

IGBT

rated

voltage

PCC capacitor

Rated

voltage

Maximum

voltage

1)

650 - 705 450

500

750

500

550

1200

900

950

1) For limited time, please refer to data sheet

The rated voltage is defined as the

continuous operating voltage tak-

ing into account for the calculation

of the expected lifetime.

The maximum voltage is the

maximum operating voltage to be

applied on the capacitor for short

operations (e.g. up to 10% of the

expected calculated lifetime).

A detailed lifetime calculation

based on a mission profile (voltage,

temperature) can be submitted

upon request.

Film assembly

Self-healing property

1) Metal-end spray layer

4) Heavy-edge

2) Free margin

5) Dielectric

3) Metallization, flat or CSP

(with or without structure)

1) Organic dielectric

7) Boundary layer between

2) Metalized electrodes

plasma zone and

3) Material displacing shock wave

dielectric

4) Air gap

8) Break down channel

5, 6) Plasma discharge zone

9) Dielectric in gas zone

10) Isolation area