Properly performed HALT and HASS have been shown to be extremely effective in terms of cost and reliability obtained. Commonly made mistakes can be prevented by education on the correct principles and applications of the methods.
HALT & HASS in a Nutshell
Highly Accelerated Life Tests (HALT) are run during the design phase of a program to find design weaknesses and eliminate them. Any stress that exposes design weaknesses that would show up in the normal environments is suitable even if these stresses do not occur in the normal environments to which the product will be exposed. This is due to the crossover effect.
For example, a particular design fault may show up very quickly due to vibration and only slowly due to temperature cycling. If the normal environment does not include vibration, many people will not respond to the design faults found during vibration only to find that the faults show up much later due to thermal cycling in the field. One must address the failure mode and mechanism, not the stress used to expose the flaw or weakness. Stressing continues until all weaknesses which could cause field failures are found and fixed.
Many failure modes occur in a relationship that is exponential with the stress level, that is, higher level stresses accelerate the failure way out of proportion to the stress applied. That is why the step stress approach is used-to compress time, hence the name Time Compression™.
What’s the difference between HALT and HASS?
Highly Accelerated Stress Screens (HASS) are run during production in order to find process problems such as poor solder joints. Again, time compression techniques and the cross over effect are employed to speed the process and to reduce costs. Tests called Safety of Screen are run to prove that the HASS profiles leave enough life in the product.
It is frequently profitable to go beyond this when the costs of HASS are included, that is, more robustness will frequently reduce the cost of HASS more than the cost of the improvement. In both processes, there are several steps that all must be done in sequence and these are:
1. Precipitation – change a latent defect into a patent one.
2. Detection – determine that a fault has been precipitated. This requires coverage and resolution in the test equipment.
3. Failure Analysis – determine why the failure occurred.
4. Corrective Action – implement the fix.
5. Corrective Action Verification – demonstrate that the fix did indeed cure the problem.
6. Data Base – put the problem, failure analysis, corrective action and corrective action verification into a data base which is accessible to all that may need it.
It is strongly suggested that correct training in the techniques be obtained before attempting them as many incorrect applications using the names HALT and HASS have been observed, many of them leading to negative results or at best no improvement. More than a few incorrect applications of the methods have led to major disasters. Used correctly, the methods always produce cost savings, design time reduction, improved reliability and improved customer satisfaction.
An Assessment of the Strengths and Weaknesses of Your Company’s Reliability Process
Why Would I Need A Reliability Plan Assessment?
Our instructors can help you obtain an individual assessment of the strengths and weaknesses of your company’s reliability process and implement a plan of action. A company that wishes to evolve to the level of having world class reliability may have no idea as to where to start or they may be stuck at an interim plateau. As in many other endeavors, we seek out the best examples of successful companies and pattern our activities to best replicate the ideal. No one company is the perfect example, however, a collection of the best reliability practices spanning the best companies does provide a picture of the ideal. Having established this picture of best practices, we then pursue the goal of making our company look and function “just like the ideal picture.” Sounds simple doesn’t it? Like many other things, this is much easier to say than it is to actually carry out. Someone needs to assemble the ideal picture, drawing from many industries over an extended period of time. Profound knowledge must always guide the implementation process.
Dr. Deming said it best in chapter three of his book entitled “Out Of The Crisis.” The following is an exact quote from Chapter three, “Diseases and Obstacles,” on page 143:
A Common Obstacle:
“Anyone that comes to try to help us must understand all about our business.”
“All evidence points to the fallacy of this supposition. Competent men in every position, if they are doing their best, know all that there is to know about their work except how to improve it. Help toward improvement can come only from some other kind of knowledge. Help may come from outside the company, combined with knowledge already possessed by people within the company but not being utilized.” Dr. Edwards Deming.
Reliability is a discipline that transcends any individual industry but can be optimized by drawing from the best of a diverse array of industries. The Reliability Program Plan Assessment is a 30 year collection of the best of the best across such industries as automotive, telecom, machine tools, electronics, computers, home appliance, and power tools.
The Reliability Program Plan Assessment is the type of help that many companies are looking for when internal resources are inadequate or when external revitalization is needed.
Making your company function like the “ideal picture” will require the following:
- Wanting and championing change with sincerity.
- Realizing that no single “silver bullet” will cure all ills.
- Understand the strategy and details contained in the ideal picture of best practices.
- Evaluating your strengths and weaknesses in execution of each step in the ideal picture as compared to other industries.
- Developing action plans for improvement in areas of weakness.
- This should function under the Plan – Do – Study – Act process.
- Institutionalize this as an on-going process so that it functions without the constant attention of outside consultants.
Call us at 303/ 655-3051 or send an email to: [email protected] to find out more!
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