Highly Accelerated Life Testing Procedures
Speeding up the process of device or circuit failure requires extreme inputs, those that are unlikely to occur during real-world use by customers regardless of the environment. Three common testing inputs are high and low temperatures, rapid cycling of the same and vibration along six-axes. In some cases, a highly accelerated life test (HALT) will incorporate combined temperature and vibration stresses. These inputs can result in component failure in the span of days, hours, or even minutes compared to months or years of typical usage.
Benefits of HALT Testing
While the percentages of failure based on the stress applied to a product can vary significantly, highly accelerated life testing can typically expose weaknesses faster than other means of testing. For example, of the above inputs, roughly two-thirds of failures will only come after the introduction of vibration alone or combined vibration and temperature tests. This means that during the product development process, a significant number of potential flaws would not be identified through testing that did not include these two stresses.
Just as important, many of the failures highlighted during a HALT test arise from design problems that are relatively easy to remedy. With thermal-based malfunctions, engineers may find that the issues come from materials with vastly different rates of thermal expansion, or deficient leads or crimps. Other problems can come from flaws in the design of the printed circuit boards.
Combined vibration and temperature during HALT testing can also identify issues related to poorly soldered joints and leads. However, failures during vibration may also be caused by fretting, as well as occurring from adjacent parts coming into contact. These design flaws are relatively simple to identify, such as wires rubbing against PCBs or other sharp-edged portions of the system, and arise regularly during the vibration phase of a HALT test.
As a result of the HALT test uncovering these issues early in the process, or soon after the prototype phase, there is the ability to make relatively small changes in design or production. Companies can also identify parts that may not last even during the warranty period in the fraction of the time it might take to find out during normal lifetime testing. As a result, some clients have been able to save a great deal on their product development costs by identifying part and component weaknesses long before the production process.
Some Facts and Misconceptions about Highly Accelerated Life Testing
- Producing failures is the goal of HALT testing. The user should not necessarily focus on what level of stress caused the problem, but should focus on improving the weak points in their product.
- By applying a sequence of stepped low-temperature soaks, high-temperature soaks, rapid temperature transitions, high G random vibrations, and combinations of these testing modes, the HALT Operational Limit and HALT Destruct Limit of the products under test can be determined.
- The stress levels in HALT are typically far beyond those experienced by the product in its normal operating environment. These higher-than-normal stresses accelerate the time to failure and precipitate defects more rapidly than under actual service conditions.
- The unit is in operation during the testing program and is continuously monitored for operational failures.
- As stress-induced failures occur, the cause shall be determined, and if possible, the component should be repaired so that the testing program can continue.
- Stresses shall be increased until the practical limits of the test parameters have been reached. Examples of practical limits include the melting temperature of solder joints or excessive softening of plastics.
- One common misconception is that an abundance of failures will occur during every HALT. Numerous failures will typically occur, but a large quantity of failures is not likely unless the product is very different than any manufactured before. Successful companies produce pretty good products; otherwise they would be out of business. However there may be a weakness or two in a new product that could create early failures resulting in large warranty costs. These weaknesses should be found in a properly run HALT test.
- HALT is a qualitative test with the goal being to expose design weaknesses. The HALT will not demonstrate a service life or a mean time between failures (MTBF). Other reliability methods may be a better fit to predict an MTBF or service life.
Delserro Engineering Solutions provides a variety of testing services, not the least of which is highly accelerated life testing (HALT). However, we can also test products in a variety of environments such as vibration, shock, and climatic. We can also design custom reliability test procedures.
If you are looking to find weak points in a design through testing, please contact us for a plan that best suits your needs. Fill out the short contact form at the link above or call us at (610) 253-6637 for a review of your needs. We look forward to working with you to maximize the return on your testing and design investments.