The
metallized type of construction also makes it possible to
produce wound capacitors with larger capacitance values
in small sizes (~ 0.01µF through 100µF and
larger). In the case of M capacitors, thin layers of
aluminium (~ 0.03µm) are vacuum-deposited on the
insulating film as conducting electrodes. In the case of
a breakdown, the short circuit current causes the thin
metal coating to evaporate around the point of failure,
without reducing the quality of the dielectric. An
insulating area is formed, the capacitor remains intact (self-healing). The capacitance loss of a few pF
which this causes, is of no importance.
With metallized capacitors, the
breakdown strength of the insulating film can be used to
the full. During the production of the capacitors the
weak points are burnt out. This makes it possible to use
the thinnest insulating films right down to < 1µm in thickness.
In contrast to the
advantages of the small dimensions and the self-healing
properties of metallized capacitors, there is the
disadvantage of a limited current loading capacity as a
result of the thin, vacuum-deposited metal layers.
Advantage: Construction with the most favorable capacitance/volume
value.
