Electronics > Metrology

MLCCs encapsulated in glass?

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Found them in the scrap box.  No idea where from are they.  The size is similar with that of a glass diode, and what is inside the glass looks like a MLCC capacitor.  The marking is 104Z 50V 8220.  I guess they are 100nF/50V MLCC in glass case.

Never seen such glass encapsulated capacitors.  Searched online and couldn't find any.

Anybody know what are these for, and why a glass case for a 0.1uF/50V, anyway?

I've got some of those too, stripped from prototype boards - surprisingly, about 30+ years ago, certainly before we were using smd on our boards. There were/are epoxy encapsulated ones in the same form factor.

I've no idea if the glass encapsulation is intended to improve reliability. I suppose they would be more tolerant of physical stress than epoxy ones (auto lead bending, auto insertion machines?) and moisture-proof. Mine are 100nF decouplers too.

I have seen these odd looking caps used for decoupling in old computer boards (I remember a ZX81 RAM expansion board). So these are not precision caps, more like small size low ESR / ESL caps.  These could be class 3 ceramic caps, using some special surface effects.

An old datasheet.

Kleinstein is right. They were good for automatic insertion, small for the time, quite robust, MIL grade.
Used mostly as decoupling caps..
I also remember if from Sinclair ZX81, they were used in modems, mainframe...

Thank you all, pretty clear now.

Was hoping for something high precision, but they are just nice looking vintage, probably from the week 20 of 1982.

Seems this glass encapsulated MLCCs can still be bought as NOS.  Searching for Unitrode I found some on ebay, https://www.ebay.co.uk/itm/100x-Unitrode-axial-100nf-50v-ceramic-capacitor-0-1uf-C104-202-104-0-1uf-/391907472239 and from the last picture on ebay, the label says tolerance is +80% -20%.


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