What's different abut ceramic caps these days?

[Mark Hammer]

That's not a question about quality, or anything unique to this year, or whatever.

Rather, as I'm installing some ceramics into a board, I can't help but be struck by the difference in size of the ceramic caps now, compared to 30-40 years ago.  When it comes to electrolytics, and a comparable shrinkage in size, I can understand that on the basis of discovery of new materials, and especially methods for producing ultra-thin film that can be wrapped and wrapped and wrapped and still not reach any appreciable diameter.  Higher voltage ratings in smaller packages is also a result of using newer materials to make those thin sheets that get wrapped.

But what has resulted in smaller ceramic disc caps?  I'm afraid I'm ignorant in that respect.  Anybody have a simple explanation/recounting?

Are these changes of the sort that have produced different specs and properties for ceramic caps in recent years?

[aron]

Multilayer?

http://www.freepatentsonline.com/y2011/0141659.html

[frank_p]

I think it's all about how the EIA class the behavior of the cap (not the electroceramic's dielectric properties of the reciepe of the powder mix): mainly temperature stability ( : ...and 'perhaps' as a consequence microphony in our relative special case of interest).  The lower the class (ex: class I: COG (or NPO) ), the bigger the cap will be and the better the general electrical properties will be (including stability in aging).  But since temperature of the cap is mainly due to power dissipation in high frequencies due to losses, it's more applicable to RF issues.  If we go down in class (2, 3 and 4) smaller physical sizes, higher dielectric constants (think 100 for pure titanium dioxyde $$$ ceramics and 1000's for 'powder mixes' (about 5 for the average plastics...)) and higher breakdown voltages we can get, at the expense of lower temperature stabilty (higher temperature coefficient slope: lets say higher (+X -Y) tolerances values) and increase in the microphonics behavior with other ceramics or additives.  My impression is that reduction of size is a desired characteristic, especially since the diameter of the cap will grow relatively high for the 'more than small value' non-multilayer ceramic cap (for the general and hobby buyer).  So the real question would be, what class and then, what category of disc cap we really need (or 'blindly buy') for the audio stuff.  Sure, smaller and cheaper, sells well; and who know the receipe of the 'powder mix' or even the three letter code that is not printed...

[wavley]

I agree with Aaron on the multilayer thing.  At my job with work a lot with American Technical Ceramics stuff and they're constantly coming up with ways to make bigger values in smaller packages by using multilayer designs, I actually spoke with them in depth about this at the International Microwave Symposium in June because we were not enjoying the failure rate of .1uF film caps at cryogenic temperatures (it's still pretty good considering the circumstances, but we have less with ceramic)  they weren't quite there in a package size that we could easily retrofit in our amp bodies without some machining, but they were a lot closer then they were a couple of years ago.

[boogietone]

A lot of research as been done over the past decades on the production of ceramic materials. One area that has received much attention is the use of smaller particle sizes down the submicron scale. Controlling the nucleation and growth of ceramic crystals can be a pretty delicate balance of chemistry, temperature, time, and mechanical handling. So, it is not just the use of different ceramic materials but the use of "better" versions of the same powders.