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www.littelfuse.com
Varistor Products
NA Varistor Series
Passivation Layer
The standard NA Series is supplied with passivation layer around the
outside perimeter of the disc forming an electrical insulator as detailed in
the dimensional drawing.
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 NA Series is supplied with a sintered silver metallization for the
electrode finish. 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 6.
Stacking and Contact Pressure
Recommendations
When applications require the stacking of Littelfuse NA 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
16N/CM
2
(23LBs/IN
2
).
Packaging and Shipping
The NA Series is supplied in bulk for shipment. Discs are packaged in
compartmentalized cartons to protect from scratching or edge-chipping
during shipment.
