B59421A0075A062_1007 Datasheet, PDF (27/32 Pages) EPCOS – PTC thermistors as limit temperature sensors

Sensors
Limit temperature sensors, EIA sizes 0402, 0603 and 0805
Superior series
When subjecting leads to mechanical stress, the following should be observed:
Tensile stress on leads
During mounting and operation tensile forces on the leads are to be avoided.
Bending of leads
Bending of the leads directly on the thermistor body is not permissible.
A lead may be bent at a minimum distance of twice the wire's diameter +2 mm from the solder
joint on the thermistor body. During bending the wire must be mechanically relieved at its outlet.
The bending radius should be at least 0.75 mm.
Twisting of leads
The twisting (torsion) by 180° of a lead bent by 90° is permissible at 6 mm from the bottom of the
thermistor body.
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Sealing and potting
When thermistors are sealed or potted, there must be no mechanical stress through differing ther-
mal expansion in the curing process and during later operation. In the curing process the upper
category temperature of the thermistor must not be exceeded. It is also necessary to ensure that
the potting compound is chemically inert.
Sealing and potting compounds may degenerate the titanate ceramic of PTC thermistors and lead
to the formation of low-ohmic conduction bridges. In conjunction with a change in dissipation con-
ditions due to the potting compound, local overheating may finally damage the thermistor.
Therefore sealing and potting should be avoided whenever possible.
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Cleaning
You may use common cleaners based on organic solvents (eg dowanol or alcohol) to clean ce-
ramic and solder joints.
For sufficient cleaning flux must be completely removed.
Solvents may cause plastic encapsulations to swell or detach. So be sure to check the suitability
of a solvent before using it.
Caution is required with ultrasonic processes. If the sound power is too high, for example, it can
degrade the adhesive strength of the terminal metallization or couse the encapsulation to detach.
After cleaning drying is promptly necessary.
Please read Cautions and warnings and
Important notes at the end of this document.
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