Brochure

Varistors Introduction
TECHNICAL NOTE
Technical Note
www.vishay.com
Vishay BCcomponents
Revision: 04-Sep-13
2
Document Number: 29079
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FIRING
The pressed products are first pre-fired to burn out the
binder. They are then fired for a controlled period and
temperature until the required electrical characteristics are
obtained. Regular visual and electrical checks are made on
the fired batch.
METALLIZATION
The fired ceramic discs are metallized on both sides with a
silver content layer to produce good low resisitive electrical
contacts. Metallization is achieved by screen printing. Visual
checks are made regularly and a solderability test is carried
out in each production batch.
ATTACHING LEADS
Leads are automatically soldered to the metallized faces
and regular strength tests are made. Three types of lead
configuration are available; one with straight leads, one with
straight leads and flange, and one with kinked leads.
LACQUERING
The components are coated by immersing them in a special
non flammable ochre epoxy lacquer. Two coats are applied
and the lacquer is cured. Regular tests to check the coating
thickness are made.
ELECTRICAL TESTING (100 %)
The voltage of each component is normally checked at
two reference currents (1 mA and another according to the
application). Any rejects are automatically separated for
further evaluation.
MARKING
All components are laser marked with type identification,
voltage rating and date code.
QUALITY
APPROVALS
• UL 1449 ed. 3 according file E332800
• VDE following IEC 61051-1/2 according file 40002622 or
40013495
• CSA file 219883 and cUL according file E332800
The term ‘QUALITY ASSESSMENT’ is defined as the
continuous surveillance by the manufacturer of a product to
ensure that it conforms to the requirements to which it was
made.
PRODUCT AND PROCESS RELEASE
Recognized reliability criteria are designed into each new
product and process from the beginning. Evaluation goes
far beyond target specifications and heavy emphasis is
placed upon reliability. Before production release, new
varistors must successfully complete an extended series of
life tests under extreme conditions.
MONITORING INCOMING MATERIALS
Apart from carrying out physical and chemical checks on
incoming raw materials, a very close liaison with material
suppliers is maintained. Incoming inspection and product
results are gradually fed back to them, so ensuring that they
also maintain the highest quality standards.
IN-LINE CONTROL
The manufacturing centre operates in accordance with the
requirements of IEC 61051-1 and UL 1449 . Each operator is
actively engaged in quality checking. In addition, in-line
inspectors and manufacturing operators make regulated
spot checks as a part of our Statistical Process Control
(SPC).
FINAL INSPECTION AND TEST (100 %)
At the end of production, each varistor is inspected and
tested prior to packing.
LOT TESTING
Before any lot is released, it undergoes a series of special lot
tests under the supervision of the Quality department.
PERIODIC SAMPLE TESTING
Component samples are periodically sent to the Quality
laboratory for rigorous climatic and endurance tests to
IEC/UL requirements. Data from these tests provide a
valuable means of exposing long term trends that might
otherwise pass unnoticed. The results of these tests are
further used to improve the production process.
FIELD INFORMATION
The most accurate method of assessing quality is
monitoring performances of the devices in the field.
Customer feedback is actively encouraged and the
information is used to study how the components may be
further improved. This close relationship with customers is
based on mutual trust built up over many years of
co-operation.
encapsulation electrodesintergranular boundary
leads
100
V
(V)
I (µA)
3