If you’ve read our introduction to HALT/HASS testing, you know that Highly Accelerated Life Testing stresses products to the point of failure, offering valuable information about tolerances and design weaknesses.
You also know why HALT matters: by forcing your product to fail, you learn its weak points and can improve the design.
Now we want to go into a little more detail about what the process actually looks like.
Types of Stress
HALT stresses products in two general areas: temperature and vibration.
Temperature testing focuses on extreme cold, extreme heat, and ramp rates between the extremes. In other words, it accounts for the fact that a product may be able to function at a high temperature, but not if it’s heated rapidly. Both potential types of failure (temperature extremes and temperature ramping) are important, and tell you slightly different things about your product.
Vibration testing incorporates both 6 degree-of-freedom testing (the object can move on the x, y, and z axes, and can roll,pitch, and yaw about those axes) and repetitive shock testing. It simulates both real-world use vibration and traumatic vibration (caused, for example, by dropping a device). Again, it’s important to simulate both types of vibrational stress that your product might experience.
Finally, HALT tests combinations of these stress types, to illustrate how compromised conditions in one stress type might affect a product’s performance when subjected to other types of stress. Consider a piece of metal that may become more brittle–i.e., more sensitive to repetitive shock–as it becomes colder. Or a plastic that may be easier to deform by repeated vibration when it is hotter. HALT tests both of these scenarios, and many more.
Types of Failure
There are two types of product failure in HALT tests: operational and destruct failures. (These are also known as soft and hard failures, respectively.)
Operational failures help you establish limits of operation for the product. If a hard disc stops spinning at -50C, that’s an operational failure. Presumably the disc will work normally once the unit is back to a normal temperature. Destruct failures are permanent and non-recoverable. If a component of the same hard disc melts at +100C, that product cannot be used even after return to normal temperature.
Operational and destruct limits are both important, and one of the benefits of HALT is the ability to test each separately, or to isolate particular parts of the product.