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

Dr. Frank Stellmach wrote: > 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) > 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: http://www.action-electronics.com/msds/GC10-9002%20Spec%20Sheet.pdf Ed > 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 >

Ed Palmer wrote: > snip > > > 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: > http://www.action-electronics.com/msds/GC10-9002%20Spec%20Sheet.pdf > > Ed Hi Ed, Let me forewarn everyone that starting research in WIKI over such subjects will get you buried into hours and hours of torture from which your brain will eventually emerged with a headache. While WIKI is quite good for a general brush of knowledge, it is by no means a complete treatise of any subject. Interestingly WIKI (information) groups shellac and varnish as kissing cousins. What surprised me is shellac, made from an insect {uck} is used to coat candy. So watch out for those M&M’s ! The varnish page was less disturbing. However, both do not really answer the questions we have for our applications. So what is needed is to approach or search companies that provide shellac/varnish materials for the electrical industries and see if there are any “WHITE” papers describing the details of such magic. It seems that there are many variations of shellac/varnish {all considered resins} with varying properties and clearly shows the need for a chemist. I know one real chemist. I met him at a favorite little local restaurant dive where he hangs out. However, when you ask him questions you mainly get incomplete phrases {forget sentences}, so I think he has sniffed a few to many formulas. In all fairness, he really is a nice person. So the upshot is some research is needed to get a better grip on the subject. I think not one formula fits all. GC electronics has a number of “coatings” for different purposes but seemingly all similar, at least their writeups look that way. That is why I hate painting. Just too many choices ! AND never, ever take a female with you to a paint store. Unless Fluke, Genrad and others would talked about why they use such-and-such for their products, we are left up to our own devices. Well worth the read is the WIKI for shellac: http://en.wikipedia.org/wiki/Shellac And for varnish: http://en.wikipedia.org/wiki/Varnish For mineral oil: http://en.wikipedia.org/wiki/Mineral_oil Bill....WB6BNQ

In a number of precision decade boxes I have, the resistors are wound on Mica cards and painted with red varnish. I'm pretty well certain this is the red Glyptal which has been around for ages (since WW II for sure). The Glyptal company is very much in business. A caution about painting and varnishing things: When they dry, they shrink. I saw somebody paint the heat shield shroud of a spacecraft launch vehicle. The paint shrank and the shroud did not separate. $54 M went into the Pacific. -John =========== > Ed Palmer wrote: > >> snip >> > >> 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: >> http://www.action-electronics.com/msds/GC10-9002%20Spec%20Sheet.pdf >> >> Ed > > Hi Ed, > > Let me forewarn everyone that starting research in WIKI over such subjects > will > get you buried into hours and hours of torture from which your brain will > eventually emerged with a headache. While WIKI is quite good for a > general brush > of knowledge, it is by no means a complete treatise of any subject. > > Interestingly WIKI (information) groups shellac and varnish as kissing > cousins. > What surprised me is shellac, made from an insect {uck} is used to coat > candy. > So watch out for those M&M’s ! > > The varnish page was less disturbing. However, both do not really answer > the > questions we have for our applications. So what is needed is to approach > or > search companies that provide shellac/varnish materials for the electrical > industries and see if there are any “WHITE” papers describing the details > of such > magic. > > It seems that there are many variations of shellac/varnish {all considered > resins} with varying properties and clearly shows the need for a chemist. > I know > one real chemist. I met him at a favorite little local restaurant dive > where he > hangs out. However, when you ask him questions you mainly get incomplete > phrases > {forget sentences}, so I think he has sniffed a few to many formulas. In > all > fairness, he really is a nice person. > > So the upshot is some research is needed to get a better grip on the > subject. I > think not one formula fits all. GC electronics has a number of “coatings” > for > different purposes but seemingly all similar, at least their writeups look > that > way. > > That is why I hate painting. Just too many choices ! AND never, ever > take a > female with you to a paint store. Unless Fluke, Genrad and others would > talked > about why they use such-and-such for their products, we are left up to our > own > devices. > > Well worth the read is the WIKI for shellac: > > http://en.wikipedia.org/wiki/Shellac > > And for varnish: > > http://en.wikipedia.org/wiki/Varnish > > For mineral oil: > > http://en.wikipedia.org/wiki/Mineral_oil > > > Bill....WB6BNQ > > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > >