Design of EMI Capacitors
EPCOS EMI capacitors use polypropylene (PP) film metalized with a thin layer of Zinc (Zn).
The following key points have made this design suitable to IEC/UL testing, holding a minimum
size.
Overvoltage AC capability with very high temperature Endurance test of IEC60384-14
(4
th
edition) / UL60384-14 (2
nd
edition) must be performed at 1.25 × V
R
at maximum tempera-
ture, during 1000 hours, with a capacitance drift less than 10%.
Higher breakdown voltage withstanding if compared to other film metallizations, like Aluminum.
IEC60384-14 (4
th
edition) / UL60384-14 (2
nd
edition) establishes high voltage tests performed
at 4.3 × V
R
1 minute, impulse testing at 2500 V for C= 1 µF and active flammability tests.
Damp heat steady state: 40 °C/ 93% RH / 56 days. (without voltage or current load)
Effect of humidity on capacitance stability
Long contact of a film capacitor with humidity can produce irreversible effects. Direct contact with
liquid water or excess exposure to high ambient humidity or dew will eventually remove the film
metallization and thus destroy the capacitor. Plastic boxed capacitors must be properly tested in
the final application at the worst expected conditions of temperature and humidity in order to
check if any parameter drift may provoke a circuit malfunction.
In case of penetration of humidity through the film, the layer of Zinc can be degraded, specially
under AC operation (change of polarity), accelerated by the temperature, provoking an increment
of the serial resistance of the electrode and eventually a reduction of the capacitance value.
For DC operation, the parameter drift is much less.
Plastic boxes and resins can not protect 100% against humidity. Metal enclosures, resin potting or
coatings or similar measures by customers in their applications will offer additional protection
against humidity penetration.
Display of ordering codes for EPCOS products
The ordering code for one and the same product can be represented differently in data sheets,
data books, other publications and the website of EPCOS, or in order-related documents such as
shipping notes, order confirmations and product labels. The varying representations of the or-
dering codes are due to different processes employed and do not affect the specifications
of the respective products. Detailed information can be found on the Internet under
www.epcos.com/orderingcodes.
B32924*4 ... B32926*4
X2 / 350 V AC
Page 16 of 21Please read Cautions and warnings and
Important notes at the end of this document.
