Advancing HALT & HASS: Moving to Comparative Limit Analysis

by Mr. Kirk Gray, BSEE

This one-day seminar is intended to provide both review of the basic theory and practice of HALT and HASS and then from that foundation students will learn the advanced use of HALT for comparative boundary or limit analysis for building robust designs. The course will include case histories of the benefits of HALT, as well as the significant challenges to adoption of these techniques. The class will cover many of the pitfalls and errors of misapplication of HALT and HASS.

The class will also cover the expansion of HALT from the simple stresses to advanced use of HALT methods for more rapid discovery of the effect of component variations on reliable operation. The course covers the use of comparative stress limits for making a costs/benefit model for increasing margins. You will learn the process of mapping stress boundaries for use with HASS and HASA for more advanced and comprehensive ongoing reliability monitoring.

This course will quickly cover and review the basic HALT and HASS methods for finding weaknesses in products that cause field failures. The course will contrast HALT and HASS with traditional reliability engineering theories on predictions and life calculations. HALT is presented as a qualitative test method that Dr. Gregg Hobbs demonstrated as the most straight forward and efficient approach to rapid reliability development.

The course will cover the application of HALT in development stage and then HASS or HASA in the production phase. Much of the information for HALT and HASS is geared towards teaching the technique, procedures, or way of performing the Highly Accelerated Life Test (HALT) and Highly Accelerated Stress Screen (HASS). But before you are able to apply these processes you will need the understanding and support of management and design engineering to acquire management approval to spend funds for an outside lab, or even better, the purchase of your own HALT/HASS chamber. The process of selling a new approach in testing before you have a chance to actually prove is sometimes daunting. Most of the challenge of using these methods is in educating the skeptics of the benefits others claim and addressing the previous history of invalid theories and perceptions of causes of unreliability and the limited life of microelectronics. The Stress/Strength model of reliability will be used to graphically illustrate the concepts and use of comparative stress limit analysis.

Examples and case histories of HALT and HASS successes will be presented. Either application results in cost savings and reliability improvements that are orders of magnitude better than those attained using the traditional approaches.

The seminar is developed from the basic theories in the book “HALT & HASS, Accelerated Reliability Engineering” by Dr. Gregg K. Hobbs, the inventor of the methods. This is the original and most complete book on the subject, a copy of which is given to each seminar participant. Many leaders in reliability throughout the world are using these methods, but most do not publish their results to maintain their technological and financial lead!

Participants have reported enormous benefits including:
Reduction of product development time and cost by a factor of 2!
Find firmware and software issues faster
Greatly reduced warranty costs and NDF (No Defects Found) issues!
Case history - One company reduced the warranty return rate from 5% to 0.5% with HALT to HASS!
Vast reduction in screening and test equipment costs!
Not all NDF are NDF. Detect the real problems those in field returns!

OVERVIEW AND HISTORY OF RELIABILITY ENGINEERING

The role of HALT and HASS in the reliability process.
The Classical Traditional Reliability Predication Models – why they do not work
Absolute “Life” calculations in electronics versus metrics limits
HALT as the primary tool of rapid reliability development
Physics of Vibration stress.
Physics of Thermal stress.
Can HALT provide a MTBF estimate?

HALT, HASS and HASA

The classic HALT process.
The HALT chambers and alternatives
The HALT process.
The history of HALT
Understanding multi-axial vibration.
Differences in ED and RS shakers vibration
HALT fixtures.
Effects of thermal stress in HALT.
The Dangers of setting a HALT specification.
How to develop a HASS or HASA stress screen.
Precipitation and Detection screens and pneumatic repetitive shock systems.
HASS and HASA fixtures.
Proof of HASS/HASA (Safety of Screen).
Improvement and continued Optimization of the HASS or HASA screen.

Comparative Stress Analysis
Signal Integrity and thermal skewing
A change in perspective from “life” analysis
Data Deluge – component specifications and limits and what they mean
Capitalizing on the inherent strength in electronics for testing
Warranty returns versus margin – a ROI analysis using limit comparison
Developing Stress Boundary Maps
Uses of Stress Boundary Maps for better HASS discriminators
Typical thermal limits on consumer electronics