Should I eat -- er, solder -- this? On the aging and toughness of ceramic disc capacitors.

August 22, 2008 4:30 AM

Should I eat – er, solder – this? I'm building a preamp and I just discovered that I'm low on 0.1μF 50v ceramic disc capacitors. My question is about whether it's worth trying to salvage more from another (already disassembled) piece of equipment.

I noticed that I have lots of green ceramic disc caps with happy little 104s on them (don't know the voltage, but it seems improbable that it's less than 50v) on the carcass of a portable CD player which I've already largely disassembled in order to liberate its DC motors. I don't think I have the means to accurately test the caps. They are old.

So, the question: how hardy are these things? When they have been put on the board, they will have been through two solderings and a desoldering, plus however many years of portable CD-playing service. Worth a try, or go to the damn store and get some new capacitors ffs? Thank you.

posted by Your Time Machine Sucks to technology (10 comments total)

I'd give it a shot. I think the circuit board is more susceptible to heat damage from soldering than the cap.

On the other hand, a new capacitor ought to set you back 15 cents, so why bother?
posted by gjc at 4:50 AM on August 22, 2008 [1 favorite]

If you need the NOW, cannibalize. The ceramics don't wear out and a 50V rating is pretty low. Check the actual voltage that will appear on the caps and I would be surprised if it's anywhere near 50V.
posted by FauxScot at 4:53 AM on August 22, 2008 [1 favorite]

I know, I know, but it's kind of a pain in the ass to go to the store. The 11-cent capacitors require running a gantlet of anti-theft measures (OH NOES SHE MIGHT TAKE OUR 11-CENT CAPACITOR!), one of whom is the smolderingly angry man at the desk where you have to put in a request for the capacitors, after waiting in a line.

Oh, here is a straw poll that I'm also curious about: if you do pcb soldering with an adjustable temperature iron, what temperature is your soldering iron set to?
posted by Your Time Machine Sucks at 4:58 AM on August 22, 2008

Depends on the component, I guess. Resistors, caps etc: sort of medium. IC's, relays, whatever: pretty fucking high. SMD stuff, no idea. High and quick though, presumably.
posted by nicolas léonard sadi carnot at 5:18 AM on August 22, 2008 [1 favorite]

I was curious about degrees celsius, if you know.
posted by Your Time Machine Sucks at 5:26 AM on August 22, 2008

I was curious about degrees celsius, if you know.

In the region of 350 degrees centigrade.

Or more precisely, that's where it's set at the moment, but if something isn't going to my satisfaction sometimes I'll turn it up higher.

Some components include hand soldering instructions (including recommended temperatures) in their datasheets.
posted by Mike1024 at 6:43 AM on August 22, 2008 [1 favorite]

OK, preamp just turned on and worked on the first go -- thank you both for sparing me Angry Capacitor Desk Man!
posted by Your Time Machine Sucks at 6:51 AM on August 22, 2008

I see you're in Germany, so why not just order stuff like this from Reichelt (the German equivalent of Mouser/Digikey)? Is there a reason you have to go buy them from a brick n' mortar?
posted by DecemberBoy at 6:23 PM on August 22, 2008

Ordering online (from Farnell usually, not Reichelt since it hasn't yet happened that they had every part I needed in stock) is how I got in this fix -- I left 3 capacitors off of my otherwise-complete order :) . Waiting another 4-6 days and paying 6 Euros plus however much petroleum use to ship €0.33 of parts wouldn't make sense since I didn't need anything else right now. My local Conrad, obnoxious as they are (and good lord, they are), is a bike ride away, and the defunct CD player was lurking under my desk, so that was an easy call.
posted by Your Time Machine Sucks at 3:04 PM on August 23, 2008

if you do pcb soldering with an adjustable temperature iron, what temperature is your soldering iron set to?

One interesting aspect to this.. Due to the physics of heat flow, a hotter iron can mean keeping the component cooler! Basically, if you have a really hot iron, and you move really fast, the lead might already be soldered properly before the heat energy has had chance to reach the part. Obviously this doesn't apply as much with SMT parts, but that isn't an issue here.

In general, I'm with Mike1024, it is more about feel than numbers. I'm sure that stops being true for certain kinds of precision work though -- due to especially heat sensitive components, or whatever..


As for the original question, I think the only reason not to do it would be temperature rating and tolerance. For example, I doubt the caps in your ex-CD-player are NP0.. If you don't know what NP0 is (or even if you do) here's a great tutorial on real world capacitors.
posted by Chuckles at 2:14 AM on August 27, 2008