What happened to electrolytic capacitors in the 21st century?

There was a period of time where lots of capacitors were made with a dodgy electrolyte, especially by some large Taiwanese manufacturers. The capacitors looked OK in a wide variety of tests when new, but they didn't age well. Because it took a few years for the capacitors to fail, and the high failure rate to become known, an awful lot of them had been produced and built into things before people realised there was a problem. It then took a few more years to for the things to leave circulation.

Exactly why these manufacturers had electrolyte problems is not completely clear. They were using new, water based electrolytes which had been developed in Japan and worked very well. Presumably the cheaper manufacturers had missed something or cut some corners while reproducing (or ripping off) the Japanese research.

The type of capacitor affected was cheap, large capacitance, low ESR capacitors. These are the kind of thing that appears in huge numbers of consumer devices, so the problem became known in the wider community. Plus, the failure mode of these capacitors was rupture and venting, so it was easy for even people unfamiliar with electronics to see which component was at fault when their motherboard stopped working.

Wikipedia has an article about it: Capacitor Plague

Industrial espionage gone wrong. Verified many years after the fact.

Though it was suspected from nearly the beginning. (Article courstesy of The Wayback Machine, since the original is gone from the web.)

Basic story: Guy leaves Japanese capacitor manufacturer Rubycon and goes to work for a company in China, taking a copy of the electrolyte formula for high performance aluminum electrolytic capacitors with him.

Later, part of his chinese staff leaves and goes to work for a capacitor manufacturer in Taiwan. They also took a copy of the Rubycon formula, but mangled it somewhere along the way.

So, the manufacturer in Taiwan builds what he thinks are valuable, high quality caps manufactured using Rubycon's formula. He sells them at a good price, but cheaper than Rubycon and promises the same quality.

Loads of companies buy and install these caps, then the things start failing in droves.

During the 70's the Mil-Std-HDBK217 calculations for MTBF included an acceleration factor inverse to the circuit ESR. This implied surge currents and thermal rise which in turn follow Arhennius effects of localized degradation. Out gassing is a primary early warning with a bulged lid.

Also recall,SMPS development were on the rise as material cost pressures demanded lower cost and lower ESR parts. This implies ignoring the natural failure modes of circuit ESR in order to get high efficiency converters.

So the trend to see more SMPS cap failures is partly due to th designers ignoring the aging effects on ESR and the inherent thermal runaway when self heating followed.

True, new technology electrolytics have improved as well as the conductor surface finish to lower ESR in the foil. Rising costs in tantalum from places like Russia forced companies to switch to Aluminum electrolytics.

one must evaluate MTBF on a case by case if the root cause was:

• bad design,
• bad parts,
• bad process (no clean or Aqua clean flux with acidic residue, or excess thermal spike on reflow profile, etc.).

A high end modem does not validate if they used high quality qualified parts with MTBF verification done inhouse and maybe just trusted the supplier.

Generally the best capacitor MTBF comes from companies in Japan, Taiwan and China a distant 3rd due to the QA reliability and process control verification diligence required for long life parts. Material contamination is a major cause in cap fabrication.

**** The biggest improvement in Aluminum Electrolytic's is the charge/discharge time constant T=ESR x C has reduced to same or better as tantalum in low ESR grade, in some cases but not all. You have to compute this next time you choose a cap that needs to be low ESR and compare 10 parts with 1 @ 10x the value for a large bridge Cap. If it is smaller, chances you get a lower ESR and higher SRF or if in the same size voltage and family just the same constant T.
Ultra low ESR Caps. are now <1~20us while general purpose are 100us to >1ms.****