Highly Accelerated Life Test (HALT) chamber manufacturer Qualmark recently completed an interesting study, where it compared test data from 47 HALT tests in 1995-96 to data from 47 tests in 2007-08. The purpose of the study was to gauge the effect of the transition from the use of through hole printed circuit boards (PCBs) that were predominately used in the 1990s to the surface mount PCBs predominantly used today.
The order of the applied stresses was the same in all tests:
- Cold step
- Hot step
- Rapid thermal
- Vibration
- Combined vibration and rapid thermal
The study found that, in general, the surface mount PCBs fared much better from a vibration standpoint. There was a 58% reduction in the fraction of vibration failures versus the earlier data.
On the other hand, the fraction of failures due to rapid thermal stresses more than doubled for surface mount PCBs, as compared to older through hole versions.
Additionally, the earlier data showed that 20% of the failures discovered in HALT required the extreme stresses of the combined environment. The figure increased to 32% for the latter test group. This would seem to indicate that today’s electronics are more robust, although in the earlier group, there were 5.0 failures per test, as compared to 6.25 failures in the more recent group.
Although there were some differences between the test groups (e.g. the types of products tested) it seems clear that HALT testing is still relevant and necessary for today’s surface mount electronics, especially in the combined vibration and rapid thermal environment.
For more on HALT testing, register for MET Laboratories’ January 11, 2011 webinar: “HALT Testing Effectively”