Difference between Reliability Growth Testing and say, HALT?

[Steve]

Can anyone explain the fundamental difference between Reliability Growth Testing and other testing like HALT?

I know that with HALT I can't quantify the reliability.

[Tarik El-Azzouzi]

The term HALT is a qualitative testing method and stands for highly accelerated life testing. It is not a method that quantifies the life characteristics of the product. It is used to obtain an idea about the type of failures that can happen and to uncover some failure modes and the failure mechanisms that lead to them.
Qualitative tests are performed on small samples with the specimens subjected to a single severe level of stress, to a number of stresses or to a time-varying stress (i.e. stress cycling, cold to hot, etc.). If the specimen survives, it passes the test. Otherwise, appropriate actions will be taken to improve the product's design in order to eliminate the cause(s) of failure.

Usually, no improvements on the design are made during HALT.

For more info about HALT, refer to: http://www.weibull.com/AccelTestWeb/types_of_accelerated_tests.htm.


Reliability Growth on the other hand is a quantitative methodology; it is used to analyze the improvements made on a product design and verify whether a certain reliability goal has been reached. It is usually performed in normal conditions (unlike HALT which is performed in highly stressed conditions). In general, the first prototypes produced during the development of a new complex system will contain design, manufacturing and/or engineering deficiencies. Because of these deficiencies the initial reliability of the prototypes may be below the system's reliability goal or requirement. In order to identify and correct these deficiencies, the prototypes are often subjected to a rigorous testing program. During testing, problem areas are identified and appropriate corrective actions (or redesign) are taken. Reliability growth is the improvement in the reliability of a product (component, subsystem or system) over a period of time due to changes in the product's design and/or the manufacturing process. A reliability growth program is a well-structured process of finding reliability problems by testing, incorporating corrective actions and monitoring the increase of the product's reliability throughout the test phases. For more info about Reliabilty Growth, refer to: http://www.weibull.com/relgrowthwebcontents.htm#Introduction.

[Steve]

That's pretty much what I thought.

Usually, no improvements on the design are made during HALT.

By this I suppose you mean that improvements are made AFTER the HALT is complete, as opposed to RGT where improvements are made as you go along.

Why couldn't one combine accelerated testing with RGT?

[atari_400]

Actually, you can make changes to the product in HALT and retest in order to validate the changes/improvements that have been made.

[halthassnz]

Hi Guys,

Maybe I can explain a little further about HALT's use during the development phase:

You are correct in saying that the you cannot qualify a products life using HALT. There is no way to extrapolate meaningful MTBF data from a "standard" HALT test.
HALT is definately used to improve the product. When you conduct HALT you are specifically attempting to stimulate dormant faults to the surface where they can be analyzed and corrected.
What you can do is use HALT to improve the product prior to conducting a RDT. For example: HALT will tell you your temperature operating limits (and having conducted a thorough HALT you will have improved these limits).
This data can be fed into an RDT to allow you to increase the temperature swing for thermal cycling, and therefore reduce your test time. You would need to apply an acceleration formula to achieve this.In my experience its essential to HALT first, make your improvements, and then run your RDT. Typically you will find very similar failure modes within the two tests (depending upon what testing you conduct in an RDT).

The difference of course is that HALT only takes a few days to complete, whilst RDT's can take months or even years depending upon the confidence level required.

Cheers,

[Powertron]

Does anyone have any recommendations on the type of HALT tests that should be performed on a Desktop 40W power supply to identify any design or manufacturing weaknesses? I am presently planning to thermal cycle a total of five power supplies (1 hour at rated load and rated voltage at each temperature extreme) within their data sheet limits of 0C to 40C for one day and then extend the temperature limits by each day until I see one failure (i.e. the second day the units would be thermal cycled between -5C and 50C, the third day -10C and 60C, the fourth day -15C and 70C, the fifth day -20C and 80C). Is this test sufficient?