i was re-reading this topic. you used SibaTit . you know where that name comes from ?
SIemens BArium TItanate capacitor.
They are nothing but class II capacitors which we commonly call X7R , Y5V (and others)
all the ceramic SMD's (class II of course, class i uses a different material ) we buy these days are barium titanate.
They are strange beasts...
- they age :an x7r can lose up to 5% after 10000 hours, a y5v up to 20%. just by sitting there, doing nothing. When you solder them this effect "resets" . Loss is greatest in the first 10 hours after "reset" (it's logaritmic). so dont use them in opamp filters , or timing applications.
- they are voltage dependent
- they exhibit microphony (barium titanate is a piezoelectric material) . you can make them "sing" , but they can also pick up audio. NEVER use them in frequency loops or opamp feedback circuits in systems subject to large vibrations. They will pick up vibration and create a signal !
the ones you used are the early models ( basically a tube that was squashed down). the later versions are much smaller and basically a 1206 with two legs and overmolded.
Philips(bc components/vishay) produces an orange variant of that.
Hello free_electron,
yes I know, I simply had them lying around since the 1980ties, I think.
I bought these to assemble a 128kB memory extension card for my APPLE ][e clone
These were ceramic capacitors with higher ESR, I guess, to supress the glitches from the DRAM chips (don't remember correctly anymore).
I just mentioned this strange name SiBaTit so nobody wondered about these blue capacitors.
This problem with high C-V ceramic capacitors is really a pain. As Ta capacitors are not allowed/wanted any more, our engineers use e.g. 22µF/6.3V X7R or X7S capacitors behind a 5V LOD regulator, and some brands, even for these Automotive grade ceramics, show an excessive capacitance drop to 30%, or below, with DC bias
, over time and over temperature, so that the LOD soon starts oscillation. I really mean, that this 22µF might drop to < 6µF!
This effect was, or is not so prominent with lower CxV capacitors, like these 100nF blocking caps, and with reasonable compliance voltage, i.e. operating voltage well below nominal / max voltage rating.
Singing ceramic capacitors are quite rare, we have more problems with singing coils, sitting in SMPSUs.
Root cause is a subharmonic due to loose coil windings.
Frank