Getting to dislike tantalum caps
rdawson16 at hotmail.com
Sun Feb 14 18:49:30 CST 2010
Further, anybody that does radio restoration knows the first step is to "De Cap it"
Pull all electrolytics and replace.
Ceramic non polar is the way...
> Date: Mon, 15 Feb 2010 00:32:02 +0000
> From: classiccmp at philpem.me.uk
> Subject: Re: Getting to dislike tantalum caps
> Teo Zenios wrote:
> > The aluminum electrolytic were the ones with problems.
> True, that. Google "Capacitor Plague."
> It's been happening since the turn of the century, if not a bit earlier.
> AIUI there are at least three different explanations:
> - Early SMD electrolytics (the tin-can-on-plastic-base ones) tended
> to suffer from failures of the sealing plug. Basically, convection or IR
> soldering made the rubber plug deform, and after a while the cap would
> just dry out, or leak all over the PCB.
> - Later SMD capacitors had to be soldered with incredibly exact
> thermal profiles. Some contract manufacturers upped the peak temperature
> to get the solder joints to flow better. Catch: this also buggered up
> the rubber seals on electrolytic caps. Same result as above.
> - The "industrial espionage" explanation. Some jerkoff stole a
> chemical formula for a low-ESR capacitor electrolyte from a major
> Japanese capacitor manufacturer (I've heard the name Rubycon banded
> about). Of course they only got part of the formula; it was missing a
> few stabilising chemicals. Result: fzzt-boom after about 500 hours
> runtime, or electrolyte leaking all over the PCB...
> And then there's "just plain crap parts." Panasonic, Chemi-Con and
> Rubycon are usually safe bets (though there are a lot of fake and
> knock-off parts about -- e.g. "Rulycon" and "Fuhjyuu" -- the latter has
> the audacity to use a very slightly modified version of Hitachi's logo).
> There's a database of capacitor manufacturers and their logos here --
> <http://capacitor.web.fc2.com/>. The page is in Japanese, but Google
> translates it into (mostly) readable English.
> > Tantalums are nice as long as you don't have a voltage spike (they hate
> > going above their rated voltage and short).
> This is why I usually spec them 50 to 100% higher than the highest
> voltage I expect to see on the power line the cap is filtering. That is
> to say, if I'm using a tantalum cap on a 5V line, I'll put a 7.5 or 10V
> capacitor in there.
> > At least when the aluminum
> > electrolytic leak/go bad they just quit working (open), hopefully not
> > eating the circuit board.
> Though more often than not, they *do* eat the PCB when they pack in,
> especially the SMD ones...
> classiccmp at philpem.me.uk
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