How thermal testing can help increase reliability of electronic systems?

How thermal testing can help increase reliability of electronic systems?

I never thought I would be a daily blogger, but after having read Nazita’s entry on the Quantas/A80/RR case I realized we can sweep the street in front of our own doors. Well, Nazita speaks about faith. I agree, faith is important, for example when I do my yoga exercises I also believe yoga helps me a lot. I believe, because I feel its positive effects, but I do not know, how it works exactly. When designing electronic systems, faith alone does not help. One needs real knowledge about the behavior of the system that will be manufactured - and in cases like the above quoted incident, life of hundreds of people may depend on it: think of fly-by-wire for example. In this particular case onboard safety system helped detect the problem and take corrective action. Thanks G (and the designers), these systems did not fail end helped safe landing of the aircraft.

In general, we do not want onboard electronics of any aircraft to fail. This is just one example of safety critical systems where high level of reliability is a must. There are similar needs in the automotive industry for example. The everyday use of the electric cars is not yet here but electronics is vital for today’s conventional cars already.

According to a study of the US Air Force Avionics Integrity Program from about two decades ago failure of electronics systems in about 55% of all cases was due to thermal issues. This figure is being quoted since then. Actually, I have my personal evidence for this from my own history of using a PC at home. My actual PC at home broke down twice. The first breakdown was something I could smell and see - there was a smoke signal issued by the machine: the controller IC in its hard-drive electronics simply burnt out. The second computer breakdown I had was when my 7 years old no-name PC stopped working completely. In this case I was not sure if it was a real hardware failure. I suspected that either the BIOS has forgotten its contents or my well known operating system gave up after 7 years of service. So, the ratio is 50-50.

Thus, making sure that we eliminate half of the possible failures is really very important. With such an action we can double the reliability of our systems. The question is, how one can achieve reducing the number of thermal problems? Of course with thermal-aware design. By doing so, we can eliminate our own failures.

But how about the failures of our suppliers? What can we do if we have to build our systems using all kinds of components (packaged IC chips, diodes, transistors), thermal interface materials, heat-sinks and other cooling assemblies? We have to make sure that all the components are reliable and the final assembly is also good. A typical failure mechanism which leads to thermal problems is when the thermal interface materials degrade, or thermal interfaces (such as die attach) delaminate. And this is something that can be observed by thermal transient measurement based structural analysis. A nice example of this got recently published at the THERMINIC Workshop held in October in Barcelona: with a joint effort of the Pannon University (Veszprém, Hungary) and BME (Budapest, Hungary) long term stability of LEDs aimed at streetlighting applications was studied. The usual LM80 LED testing procedure was combined with thermal transient measurements. In many cases degradation of the applied TIM material was found during these tests, but other failures like delamanition of the LED from its MCPCB substrate was also among the major degradation mechanisms. And this is just one example which shows how thermal transient testing can be used to increase product reliability. Further examples will be shown in one of our coming webinars. So, if you are interested, come and sign up for this event! See you next time!

Andras

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