NOS caps

[Bucksears]

So, my girlfriend's father is an EE. Has LOADS of old parts (ICs, caps, resistors, transistors, etc). He doesn't use a lot of them anymore (he's in his 80's and just tinkers), so he let me 'take whatever I need'.
I got some ceramic caps, but was wondering about the lifespan of them. They're unused, but I have no idea how long they've been down there; probably since the 70's or 80's.

If they're unused, would the spec on them 'shift' at all? i.e. are they still any good?

[R.G.]

Ceramic caps have no shelf life wearout mechanisms that I'm aware of, except possibly corrosion on the leads making them hard to solder.

Electros are the ones which self-rot.

[Mark Hammer]

While electrolytics "self-rot", the question I have to ask is whether that self-rot is an aspect of all electrolytcs, regardless of size, date of manufacture, size, etc., or whether it is the sort of thing that applies mostly to electros of a certain generation.

I can easily desolder and remove a couple of dozen 10uf/35v submini caps from any old 8-bit or 16-bit Soundblaster card.  They are, at worst maybe 15 years old, and are clearly of a different construction than the behemoths I used to buy in the 70's, of the same capacitance and voltage rating.  Do these each come with the same count-down-to-uselessness?

[JKowalski]

ALL electrolytic caps degrade over time. It's not a question of when they were made - the degradation comes from the basic design of electrolytics.

Any other caps should be fine, however.

[R.G.]

ALL electrolytic caps degrade over time. It's not a question of when they were made - the degradation comes from the basic design of electrolytics.

Any other caps should be fine, however.

Dead correct.

While electrolytics "self-rot", the question I have to ask is whether that self-rot is an aspect of all electrolytcs, regardless of size, date of manufacture, size, etc., or whether it is the sort of thing that applies mostly to electros of a certain generation.

I can easily desolder and remove a couple of dozen 10uf/35v submini caps from any old 8-bit or 16-bit Soundblaster card.  They are, at worst maybe 15 years old, and are clearly of a different construction than the behemoths I used to buy in the 70's, of the same capacitance and voltage rating.  Do these each come with the same count-down-to-uselessness?

They all do. Different filling fluids may make them do it at a faster or slower rate, but eventually they all get there. I paid $50 (roughly) for a 1950's hardcover book on electrolytic cap manufacture to get some tech answers that are no longer commonly available. More fun than a night at the movies, and about the same price - 

Progress in electro caps is in either the foils, the oxide layer formation, or the electrolyte. Progress in foils has been in the direction of very pure foils which are not only very thin (smaller "dead volume" between the active surfaces) but also etched to increase the surface area by eating pits into the surface. Progress in oxide formation took a huge step when it went from formed-in-place to formed-in-a-tank, then wound into the final cap, and of course in consistency through hyper-fine control of the bath, the forming current, etc.

Progress in the electrolyte is what has given us the very long lives we now enjoy as compared to the originals. I now understand that the electrolyte fluids don't contain water any more, so it does not evaporate away; this was the reason for so-called "dry electrolytics" being advertised; no water. The fluids used now are not very fluid at standard temperatures, do not boil easily under overheating, and contain chemicals to retard them eating the oxide and to help the oxide self-heal. But as far as I can tell, nobody has yet cut the rate of decay to zero. In a metalized mylar cap, the rate at which the mylar decomposes and lets the metalization short is effectively zero. They'll probably fail in several millenia, but to me they may as well be eternal. Not so electros.