2
VARISTOR
PRODUCTS
Varistor Products
115 www.littelfuse.com
CA Varistor Series
High Energy Industrial Disc
Passivation Layer
The standard CA Series is supplied with passivation layer around the
outside perimeter of the disc forming an electrical insulator as detailed in
the dimensional drawing. The CA Series is also available without a
passivation layer for applications where the customer provides a suitable
encapsulation or potting material as recommended below.
(See Ordering Information.)
Encapsulated Recommendations
After lead attachment, the disc/lead assembly may be coated or
encapsulated in a package to provide electrical insulation and isolation
from environmental contamination as required by the application.
Coating/Filler materials for containers may include silicones,
polyurethanes, and some epoxy resins.Two examples of acceptable
polyurethanes are Dexter Hysol (US7013, parts A and B) and Rhenatech
(resin 4714, hardener 4900), or their equivalents. Materials containing
halogens, sulfides, or alkalines are not recommended.
Electrode Metallization
The standard CA Series is supplied with sintered silver electrodes on
CA32 devices and arc-sprayed copper-over-aluminum electrodes for CA40
and CA60 series. CA40 parts are also available with sintered silver elec-
trode, see “Ordering information.”In general, when discs are stacked to
attain a specific operating voltage or energy capability, the copper finish is
typically chosen. Likewise, the copper finish is used with high temperature
lead attach soldering operations (wave solder). The silver metallization is
typically used for solder reflow lead attach operations (I-R, Vapour-Phase).
The recommended temperature profile of a belt-fed convection oven is
shown in Figure 13.
Stacking and Contact Pressure
Recommendations
When applications require the stacking of Littelfuse CA discs or when
electrical connection is made by pressure contacts, the minimum pres-
sure applied to the disc electrode surface should be 2.2kGs (5 pounds).
The maximum recommended pressure applied to the disc electrode is
dependent upon diameter size and is given in the following table.