[volt-nuts] Oil and molded components

[Dr. Frank Stellmach]

Hi,

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 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 
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