6 FILM AND FOIL CAPACITORS Film and foil capacitors are the most commonly used
capacitors in the industry. Their essential differentiator
is the dielectric used and its properties.
Film capacitors come in capacitance ranges from as
small as 5pF to as large as 100uF. A special subcategory
are plastic film capacitors, which use polystyrene, polycarbonate
or Teflon as their dielectrics. These work well
under high temperature, have smaller tolerances, very
long service life and a high reliability.
On metallized foil capacitors the conductive film is
sprayed onto each side of the dielectric. This has selfhealing
properties, so that much thinner dielectric films
can be used. These devices feature high capacitance
values with smaller case sizes.
The materials used to protect capacitors have a major
influence on their service life. They must provide sealing
and mechanical, thermal and chemical resistance.
For capacitors exposed to harsh conditions, materials
must withstand temperatures and temperature cycles,
particulates, electrostatic discharges (ESD), electromagnetic
interference (EMI), vibration, impacts, high
voltage, humidity and other chemical aggression.
Film and Foil
Capacitors