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construction is mainly used for capacitors with
smaller capacitance (100pF through 0.1µF).
The advantage of this construction
is the easy contactability of the metal foil electrodes
and the good pulse strength.
A breakdown in the
dielectric film of a F capacitor leads to an irreversible
short circuit and thus, to failure.
To avoid breakdowns caused
by weak spots in the dielectric, the insulating film
chosen is always thicker than theoretically required by
the values which are determined from the specific
breakdown strength of the material. Films of less than 4
µm are not used for F capacitors because of their high
proportion of weak points.
The necessity for thicker insulating film has an
unfavorable effect on the size and the material used. In
order to achieve a particular capacitance with thicker
insulating film, the length of the band also has to be
increased by the same amount. Thicker insulating film
therefore squares the volume of the winding element.
A weak spot occurs, when
depressions meet on the upper and lower surfaces of the
film. The dielectric must then be at least thick enough
to have just the required breakdown strength.
Advantage: High pulse loading capacity due to good contact of the
terminating wires to the metal foil electrodes.
WIMA types with