Small glass capacitors polarized?

[Paul Koning]

> On Sep 27, 2015, at 2:03 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
> 
> Hey, everyone: those little glass capacitors (well, the casing is glass - I'm
> not sure what's inside) that one often sees used as per-chip noise/spike
> supression caps (often 0.01 uF or some such size) on 1970s/1980s vintage
> boards: are those things polarized, or can I put them in either way around?

Glass?  Do you mean ceramic?

The only polarized capacitors in the sense that they suffer damage if installed backwards are the various flavors of electrolytics.

There are a few other capacitor types that come with a recommended installation direction; paper-insulated wound foil ones are a classic example.  But that's because the way they are constructed means that one plate ends up being the outer layer of the assembly, which means that's the side that should be grounded for best noise reduction in bypass applications.  That's a functional difference, not a reliability issue.  Another example are the classic tubular ceramic capacitors I remember seeing in Europe (but not in the USA) for the same reason.

Anything with flat layers, like mica, ceramic disk, or surface mount ceramics, isn't going to care at all about polarization for either of these reasons.

	paul