[volt-nuts] Oil and molded components
ed_palmer at sasktel.net
Wed Dec 16 13:40:10 EST 2009
Dr. Frank Stellmach wrote:
> 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
> resistor element.
> 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
> 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)
Earlier in this thread there was mention of resistors that were coated
with shellac or lacquer. Would it be possible to coat a molded resistor
to seal it from air, moisture, or oil? Perhaps one of the high-voltage
varnishes like this:
> 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 instance.
> 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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