[volt-nuts] Oil and molded components
Dr. Frank Stellmach
drfrank.stellmach at freenet.de
Wed Dec 16 17:19:50 UTC 2009
I would be careful on the selection of the oil for the molded Z201.
The oil must be highly isolating, very pure, absolutely humidity free,
and must not contain acids or other substances which might affect the
From the vishay site, one learns, that the metal can type is
hermetically tight, and if its oil filled, neither oxygen, nor water
vapor can degrade the resistor element. These two properties only lead
to the ultra stable 2ppm/6years drift.
On the other hand, the molded type has a drift of 20ppm/yr., which means
the resitive element is vulnerable to both, despite the mold compound.
It's well known, that molded ICs also need a coating on the chip, and
that water vapor diffuses into the mold, if the device is exposed to
free air. (cracking during reflow soldering will occur)
So, if the Z201 is put into an oil bath, the mold copound will soak up
the oil like a sponge, and the oil (and other substances)might diffuse
to the resistor element.
On the other hand, if the appropriate, pure oil has been selected, such
an oil bath would reduce temperature drift AND degradation drift in one
Btw.: I have seen a designation of such an oil recently, perhaps it was
on the Vishay technical site, describing the VHP types.
Best regards - Frank
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