Technology
Film assembly
Process flow
1) Metal-end spray layer
2) Free margin
3) Metallization, flat or CSP
w. / wo. structuring
4) Heavy-edge
5) Precise extension and
“wavy-smooth” cut
1) Winding of capacitor element 5) Testing of active winding
with metallized film
6) Wiring, e.g. with busbar and
2) Metal-end spray
encapsulation
3) Thermal treatment
7) 100% final inspection
4) Sawing of active winding
Fig. 2:
Main working steps
Fig. 1:
Cross sections of film/foil assembly
Film assembly
At least two dielectric films are
wound in parallel to form a cap-
acitor element. Fig. 1 shows the
film/foil arrangements in a cross-
sectional view for common PCC
designs: the diagram shows the
most common standard version
with the metallization on one side.
The winding technology
This developed winding tech-
nology can be used to implement
absolutely flat and wrinkle-free
stacked windings in “power cap
1)
dimensions” for PCC using
metallized polymer films, starting
with PP down to 2.5 μm and PET
of 1.8 μm, Fig. 2, 3. The PCC
process flowchart describes the
main production steps. The
flexibility and extremely high
process quality of the production
line and the polygon winder (PW)
are important for this application.
A special “wavy-smooth” cut
combination produces a maxi-
mum effective contact surface via
a defined small offset and pre-
cisely wound master capacitors
allowing a specially optimized
metal-spraying and contacting
process. The result is an out-
standingly high pulse-current
handling capability far beyond the
minimum requirements laid down
in IEC and EN standards and
©
EPCOS AG - Edition October 2013
without the contact edge problem,
a well-known and dangerous
constriction effect at the film
edges of low-cost MKP windings.
Process flow
The process flow for PCC with
power cap formatted stacked
windings is shown in Fig. 2.
Contacting of windings
The end faces of the windings are
contacted by metal spraying
(Schooping) to ensure a reliable
and low-inductance connection
between the metallized film layers
and to the connection system.
After this working step the cap-
acitor windings will be connected
with leads e. g. busbars which are
welded onto the metal-end spray
layer, Fig. 3.
Impregnation and sealing
The active winding elements are
heated and dried for a defined
period in vacuum. In this way, air
and moisture are extracted from
the inner capacitor to avoid any
oxidation effects at the electrodes
or any partial discharges. This
process step ensures excellent -
+capacitance stability and a long
useful life.
The Low Power designs are
boxed (resin-filled) or
unpackaged (naked).
1) PCCs can naturally also be designed with
flat windings.
Fig. 3:
Left
- stacked-winding;
right
- flat capacitor winding with copper busbars which are
welded onto the metal-end spray layer, ready for assembly
2
51mcu
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