Why do thick film resistors have maximum a power spec for short (<10us) pulses?

[dvm]

Many manufacturors specify a maximum power pulse load for very short
pulses. I would expect a kind of 1/t behaviour, just as for normal
resistors.

I know that there is a maximum voltage limit, which gives maximum
power, but this limit should almost never be reached for low ohmic
resistors (100Ohm or less).

D.v.M

 

[Boris Mohar]

Many manufacturors specify a maximum power pulse load for very short
pulses. I would expect a kind of 1/t behaviour, just as for normal
resistors.

I know that there is a maximum voltage limit, which gives maximum
power, but this limit should almost never be reached for low ohmic
resistors (100Ohm or less).

D.v.M

Thermal shock. All of the heating happens on one side of the ceramic
substrate.

 

[dvm]

Thermal shock. All of the heating happens on one side of the ceramic
substrate.

Yes, but I see for short pulses no difference between round resistors
and thick film chip resistors. For round resistors the 1/t
relationship is otfen seen in the datasheets.

D.v.M

 

[legg]

Yes, but I see for short pulses no difference between round resistors
and thick film chip resistors. For round resistors the 1/t
relationship is otfen seen in the datasheets.

The film current density distribution after laser-trimming the chip
resistor is nowhere near as uniform as for the larger radial-bodied
components.

The larger bodies are threatened only by unintentional hotspots due to
film irregularities. In the smaller bodies, this hotspot is built-in,
to be within 'acceptible' limits. Those limits are reflected in the
pulse spec.

RL