Rad Hard vs. Rad Tolerant

Just what the names imply. Rad-hard means that the device is immune to the effects of radiation (up to some limit). Rad-tolerant means that the device can operate in a particular radiation environment, as long as certain precautions and mitigations are taken. For instance, a Xilinx gate array is rad-tolerant, and can be used successfully by implementing a scrubbing and error correcting algorithm on the program code. Or, a device may have a non-destructive failure which can be corrected by applying a reset or cycling power.

There's a bunch of good info on radiation at www.klabs.org

I also have quite a bit of info on my hard drive if you have a specific question.

If a device is constructed with RHA ICs and some non RHA discrete transistors and diodes etc..., then a sample is radiation tested to 1019.7 condition A (fast dose rate). All silicon components used are wafer controlled to the specific sample that was tested.

ie. if a wafer change occurs radiation testing will be done again.

Can that device be considered rad hard if the statistical analysis shows the post radiation parameters of the completed device will stay within tolerances?

You can consider it rad-hard. Whether the agency you're designing for will is another story. I'd try to get rad-hard transistors and diodes, where possible. Most diodes are rad-hard. (Microsemi has some good application notes on this). Bipolar transistors seem to be except for displacement damage.

Both Goddard and Johnson Space Centers have some public testing data available on their websites.

But, in general, yes - if you test it and it's good, then it's good. Assuming you have traceability on the wafer lots, etc. And assuming your radiation testing is appropriate to your operating environment.

We plan to use a couple of plastic parts in our system, which is being designed for interplanetary space - a very harsh environment, and we're simply going to buy a large number from a single lot, and test the crap out of them and hope our parts people sign off on it.

Thank you for your input. Looking around on the internet leads me to believe the line between Rad Tolerant and Rad Hard is a bit sketchy at best. I will look on the sites you suggested. If you have any additional input I would appreciate it.

Thanks Again

I have been in the Radiation Effects Industry for more than 30 years and the definition I would use for the difference between Rad Hard and Rad Tolerant is this: Rad Hard is something the was developed with radiation effects in mind, they tweaked the process to improve the hardness or the monitor the process for its radiation effects metrics. Rad Tolerant is something that is not produced with radiation in mind, but due to using a particular technology or particular construct they get a level of radiation tolerance. However, this product is not monitored for its radiation hardness and can be changed at any time to improve other attributes and radiation hardness will suffer. This is a very important question you must ask when dealing with any semiconductor supplier because they will market something as Rad Hard when in fact it is Rad Tolerant and you don't figure it out until it is in your system and you fail a rad qual test. Yes, Rad Hard is expensive but well worth the dollars when compare to a redesign after a qual or a failure on orbit!

This is a topic near and dear to my heart!

Brian Triggs

Director, Rad Hard Program Quality

Semicoa Corporation

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