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10/09

Ferrites and accessories

Cautions and warnings

Mechanical stress and mounting

Ferrite cores have to meet mechanical requirements during assembling and for a growing number

of applications. Since ferrites are ceramic materials one has to be aware of their special behavior

under mechanical load.

Just like any ceramic material, ferrite cores are brittle and sensitive to any shock, fast changing or

tensile load. Especially fast cooling rates under ultrasonic cleaning, high static and cyclic loads can

cause cracks or failure of the ferrite cores.

For detailed information see Data Book 2007, chapter "General - Definitions, 8.1".

Stresses in the core affect not only the mechanical but also the magnetic properties. It is apparent

that the initial permeability is dependent on the stress state of the core. The higher the stresses are

in the core, the lower the value for the initial permeability. Thus, the embedding medium should offer

the greatest possible elasticity.

For detailed information see Data Book 2007, chapter "General - Definitions, 8.2".

Heating up

Ferrites can run hot during operation at higher flux densities and higher frequencies.

NiZn-materials

The magnetic properties of NiZn-materials can change irreversibly when exposed to strong

magnetic fields.

Processing notes

– The start of the winding process should be soft. Otherwise, the flanges may be destroyed.

– Excessive winding forces may damage the flanges or squeeze the tube so that the cores can no

longer be mounted.

– Excessive soldering time at high temperature (>300 °C) may affect coplanarity or pin

arrangement.

– Not following the processing notes for soldering of the J-leg terminals may cause solderability

problems at the transformer because of contamination with tin oxide (SnO) from the tin bath or

burned insulation from the wire. For detailed information see Data Book 2007, chapter

"Processing notes, 2.2".

– The dimensions of the pin hole arrangement are fixed and should be understood as an ideal

recommendation for drilling the printed circuit board. In order to avoid problems when mounting

the transformer, customers should make allowances for manufacturing tolerances in the drilling

and pick-and-place processes by increasing the diameter of the pin holes.