Highly Accelerated Life Tests and Highly Accelerated Stress Screens (HALT & HASS) Helping to reduce time to marke

1. Highly Accelerated Life Tests and Highly Accelerated Stress Screens (HALT & HASS) Helping to reduce time to market and improve cost efficiency Chris Bowles TÜV Product Service Tel: +44 (0)1489 558150 Email: cbowles@tuvps.co.uk

2. What is HALT / HASS ? • HALT (Highly Accelerated Life Test) and HASS (Highly Accelerated Stress Screen) are recognisedas powerful tools for improving product reliability, reducing time to market, reducing warranty costs and increasing customer satisfaction.

3. HALT HALT (Highly Accelerated Life Test) Hari Mountogianakis

4. HALT • In HALT the goal is to over stress the product, induce failures and improve reliability. • After uncovering and understanding the failure modes, corrective action can be taken to push out the operating limits of the product as far as possible. • A HALT is performed in the early stages of the design progress. • HALT is not a test to pass or fail. It is a process of discovery and design optimization. Hari Mountogianakis

5. HALT • Although the failure modes are induced by overstresses, they are typically valid failure modes that would show up in the field. • HALT determines the weakest parts in the design of the product. The overstresses applied, are accelerating the precipitation of these failures and allow an early correction in only 3 to 5 days. • HALT is the opportunity to find most, if not all of the failures that would show up in qualification testing (often even more).

6. The HALT Environment • The stresses applied during HALT are thermal extremes, rapid thermal transitions, vibration, and a combination of thermal and vibration stress. • Low temperature step stress. • High temperature step stress • Rapid thermal cycles • Vibration step stress • Combined environment cycles

7. The HALT Environment • Low temperature step stress Hari Mountogianakis

8. The HALT Environment • High Temperature Step Stress Hari Mountogianakis

9. The HALT Environment • Rapid Thermal Cycles Hari Mountogianakis

10. The HALT Environment • Vibration Step Stress Hari Mountogianakis

11. The HALT Environment • The vibration system is utilises repetitive shock hammers, exiting 6 DOF over a wide bandwidth (2Hz to 10kHz). Vibration in Six Degrees Of Freedom (6DOF) Hari Mountogianakis

12. The HALT Environment • Combined Environment Cycles Hari Mountogianakis

13. Typical HALT Failures • High/ Low temperature: Marginal components/design and process issues. • Thermal Cycles: Thermal coefficient of expansion mismatches, weak solder joints, PCB mounting problems. • Vibration: Weak solder joints, poor PCB design, poor component mounting. • Combined: All of the above Hari Mountogianakis

14. HALT Equipment Stress • In addition to the HALT environment the equipment under test must be function checked and stressed. • Voltage margining • Power cycling • Frequency changes • Clock variations Hari Mountogianakis

15. Preparing for HALT • Sample size is typically 4 to 6 units allowing detailed verification of the failure modes found and insure that no failure mode is missed. • A critical factor during HALT is a high resolution monitoring with functional test equipment. It must ensure that relevant functions and signals can be monitored, diagnosed as well as stimulated. • Prior to HALT equipment coverings and enclosures may be modified to aid airflow.

16. Preparing for HALT • Prepare the correct personnel for the HALT team. • It is not advisable to test a complex product with a lot of sub assemblies simultaneously. An ideal HALT on a complex product includes testing of all subassemblies and finally the complete product in a final HALT. Hari Mountogianakis

17. The HALT Discovery Process • The philosophy of HALT is to eliminate the responsible failure modes for operating and destruct limits and to push them further and further out. • Maximizing your margins increases your product´s life, robustness and reliability. • The following diagram shows the graphical presentation of these limits.

18. The HALT Discovery Process Operating and Destruction limit of a product before HALT

19. The HALT Discovery Process • The figure helps to understand the HALT technique. For example if a high ripple of the power supply is detected and hundreds of units were tested, the distribution of this failure mode would be as shown on the graph. • By increasing the stress until the failure is uncovered, it will be detected during HALT. If the tail of this distribution falls into the operating specifications, the failure mode exists in some of your delivered products. Hari Mountogianakis

20. The HALT Discovery Process Operating and Destruction limit of a product after HALT Lower Destruct Limit Lower Operating Limit Upper Operating Limit Lower Operating Limit Product Specification Operating margin Destruct margin

21. The HALT Discovery Process • When the tails are well outside the product specifications, the product ages (fatigue process of all components and parts) and the limits drift and begin to creep into the Specification Limits. • Pushing out the stresses until a failure mode occurs, secures a highly accelerated aging, and precipitates failure modes in just a few days, instead of months until they occur in the field.

22. The HALT Discovery Process • A root cause failure analysis ensures that failure modes are understood and the failure distribution will never have a tail inside product specifications and will never shift over a time or fatigue. • There are two stopping points. Either the limit of the test equipment or the fundamental limits of the technology. • After a Root Cause Failure Analysis, you have a clear understanding of the limits and margins of your product and you will know why the failures occur. Hari Mountogianakis

23. Benefits of HALT • Early detection of latent faults • Huge savings in warranty costs • Reduced time to market • Increased reliability • Increased customer satisfaction

24. HASS HASS (Highly Accelerated Stress Screen)

25. HASS • HASS is a production screen test that is used to make sure that the limits of a product determined in HALT were not decreased after the production. • Deliverable units are used. • HASS can catch and uncover these failures and verifies that no new weak links have been introduced during production. • To design a HASS profile, HALT is absolutely recommended. The Operational and Destruct Limits found there are the basis. • During HASS the Combined Environmental Stresses are applied.

26. HASS • Typically HASS limits are set to 50% of the vibration limit and 80% of the temperature limits found in HALT. • Prior to running a HASS program a HASS proof of screen is run. • The HASS proof of screen ensures that no more than 5% of useful life is removed from the product.

27. Benefits of HASS • Assures manufacturing process and workmanship integrity. • Identify and preclude escape of potentially early life product failures. • Detect and correct component variation. • Decrease field service and warranty costs.

28. Summary After a clear understanding of the goals in HALT and HASS, this test technique and philosophy gives you the opportunity to identify possible defects contained in your product, at an early point during the design. If executed in a clear and carefully way, the result will be a robust product with increased lifetime and reliability, reduced warranty issues and delighted and satisfied customers.

29. HALT and HASS Thank you