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I'm trying to design my project, Super OSD, to be as reliable as possible. I want it to work good as new when 5 years old. I hate unreliable products, environmentally it's a waste, and economically it's expensive.

To that end, I'm avoiding electrolytic capacitors, and I've spec'd everything at least 1.5x, most 2x where size/cost permits. However, I am still having to use tantalum bead caps for the on-board regulators of the microcontrollers.

Are there any other things I should be aware of?

Thomas O
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3 Answers3

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If you use appropriate derating guidelines for electrolytic capacitors (keeping the ripple current in check, ensuring they stay well below their maximum temperature rating) they can last a very long time and still provide adequate performance. I've seen capacitors come out of 15 year-old equipment and still 'work' to some degree.

Fans have a limited lifespan depending on how fast you operate them. They tend to gradually fail over time.

If you have a primarily surface-mount design, consider conformal coating to help limit exposure to the elements and mitigate oxidation, etc. Products in the field for years which have some air exposure can very easily get several millimeters of dust, which makes a very effective thermal blanket.

Make sure that, if you're using RoHS parts, that you're not using parts prone to tin whiskering. (This is another area where conformal coating can be helpful).

Adam Lawrence
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    Yes, please don't have a fear of aluminum electrolytics without justification. Just because some of them fail doesn't mean that the technology is fundamentally flawed and should be avoided. CDE has some really nice literature on them http://www.cde.com/catalogs/AEappGUIDE.pdf True, high temperatures can dry out the electrolyte, but as an example a cap rated for 2000 hr @ 105 °C will last 15 years at a quite balmy 45 °C. +1 – Nick T Nov 04 '10 at 16:35
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    As for fans, consider magnetic bearing fans. The actually have no moving components in traditional sense and there's no wear during normal use. Still, it's a good idea to clean them once in a while just to make sure that dust doesn't go into the bearing. I have a couple of laptops with them and can say that they work great. – AndrejaKo Nov 04 '10 at 17:21
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    Better to avoid fans if at all possible using higher performing power handling components (supplies, switches, controllers). I think his board is fairly low power so this isn't a major issue. – Nick T Nov 04 '10 at 17:31
  • Low power stuff. No fans necessary. – Thomas O Nov 04 '10 at 20:34
  • If you want to taste the military-aerospace way, you replace all electrolytic caps with tantalum caps. – Tim Williscroft Nov 04 '10 at 23:04
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People already named ceramic SMD as alternative. But there are even better things. Look at stacked film SMD caps which are even more reliable, can stand mechanical stress, self heal and acoustically immune.

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How big do you need your caps to be?

You can get ceramic 100uF/6.3V low-ESR caps in 1210 packages.

IOW: You can solve most power supply problems with ceramic SMD caps that are superior to electrolytics in just about every way.

dren.dk
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  • Yep, I'm using 22u/10V caps in 0805 packages on the output. – Thomas O Nov 05 '10 at 11:43
  • You can also create problems, too - if your PCB is subject to mechanical stress (specifically flex) your SM caps can easily become non-fusible heat sources and burn holes into the board. – Adam Lawrence Nov 05 '10 at 18:35