Getting to dislike tantalum caps

Date: Mon, 15 Feb 2010 00:32:02 +0000 From: classiccmp at philpem.me.uk To: Subject: Re: Getting to dislike tantalum caps Teo Zenios wrote: 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. 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. Though more often than not, they *do* eat the PCB when they pack in, especially the SMD ones... -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/