HALT vs. ALT: when to use which technique?

Highly accelerated life testing (HALT) is a great reliability technique to use for finding predominant failure mechanisms in a hardware product. However, in many cases, the predominant failure mechanism is wear-out. When this is the situation, we must be able to predict or characterize this wear-out mechanism to assure that it occurs outside customer expectations and outside the warranty period. The best technique to use for this is accelerated life testing (ALT). In many cases, it is best to use both because each technique is good at finding different types of failure mechanisms. The proper use of both techniques together will offer a complete picture of the reliability of the product