At DES, we have tested many different kinds of products ranging from medical devices to aerospace products. We have performed numerous reliability tests and developed numerous accelerated life test plans. Many times, our customers ask us, “How do we make our products more reliable?” There are analytical methods and processes that can be used to improve product reliability. However, the focus of this article will be How To Make Your Product More Reliable Through Testing.
1. Incorporate HALT in your Product Development Cycle
Highly Accelerated Life Testing (HALT) is a rigorous reliability test method that is used to expose product weaknesses. The goal of HALT is to proactively find weaknesses and fix them, thereby increasing product reliability. Because of its accelerated nature, HALT is typically faster and less expensive than traditional testing techniques.
During product development, HALT can find design weakness when changes are much less costly to fix. By finding weaknesses and making changes early, HALT can lower product development costs and compress time to market. When HALT is used at the time a product is being introduced into the market, it can expose problems caused by new manufacturing processes. When HALT is performed after a product has been introduced into the market, it can be used to audit product reliability caused by changes in components, manufacturing or suppliers etc. The bottom line is that HALT can reduce product development time and cost, reduce warranty costs, improve customer satisfaction, gain market share, and increase profits.
More information about HALT can be found in the following blog articles:
2. Perform Accelerated Life Testing (ALT)
Accelerated Life Testing (ALT) is a method used to simulate the life of a product in a short period of time. The stresses are higher than normal to compress time. The higher the stresses used in the ALT, the shorter the test time. ALT is best applied to components or less complicated products to focus on specific failure modes. Typical ALT models are the Arrhenius Model, the Arrhenius-Peck Model and the Coffin-Manson Model.
Some benefits of ALT include:
- Determining if a product will have wear-out failures
- Estimating a product’s field life using testing. The life determined through ALT can be compared to desired product life goals and analytical predictions and simulations.
- Finding additional weaknesses not found in HALT
Some key differences between HALT and ALT are:
- HALT will not estimate product life whereas ALT will.
- ALT Tests will use one or two different stresses and typically run longer than HALT tests. Therefore, ALT typically produces wear out failures. An example would be an ALT for a product that sees thousands of temperature cycles in its lifetime, but not much vibration other than from shipping. The ALT would be focused on temperature cycling only and would likely expose it to a few hundred cycles or more. The HALT would expose the product to much fewer temperature cycles, but also incorporates vibration stresses. Thus, different types of failures could result from each test. In HALT perhaps a weakness caused by vibration will occur that could show up during shipping and handling in the field. In ALT, perhaps a failure caused solely by thermal fatigue would occur. So if you only perform only one type of test, perhaps a potential field failure mode could be missed.
More information about ALT can be found in the following blog articles:
3. Perform Design Verification Testing (DVT)
Design Verification Testing is a comprehensive process to verify a product will meet all if its design requirements. DVT is also referred to as verification or validation testing. Obviously, this is done in the design phase before final production. Examples of some of the parameters that are checked during DVT are:
- All product functions such as Electrical and Mechanical functions
- Product performance
- Climatic or environmental testing
- Electromagnetic compatibility (EMC)
- Safety testing
- Software validation
For example, a product could be exposed to specific types of climatic stresses such as salt corrosion, solar (UV), temperature-altitude stresses or water ingress. These types of stresses would not commonly be used in a HALT or ALT. Therefore, unique failure modes could be exposed in DVT.
4. Perform Reliability Demonstration Testing (RDT)
The purpose of an RDT is to demonstrate the Mean Time Between Failure (MTBF) of a product. Reliability Demonstration Tests are usually performed at a system level. For example, a computer server that contains many components such as hard drives, fans, etc. is an example of a system level test. RDTs are commonly performed on repairable systems.
RDTs incorporate a reliability percentage R and a confidence level C. They are limited in using only the stresses the product will see in the field. RDTs are focused on demonstrating the MTBF in the steady state portion of the bathtub reliability curve, where ALT’s are focused on wear-out. Some manufacturers are required to show a minimum MTBF on their products before they can sell them to their customers.
5. Incorporate a HASS or ESS Program
HASS stands for Highly Accelerated Stress Screening. ESS stands for Environmental Stress Screening. Both are screening methods used to expose manufacturing defects that would cause a failure in normal field environments including shipping, handling and use. Both HASS and ESS are performed during manufacturing on production products or components.
The types of stresses used for HASS are similar to those used in HALT. HASS uses combined temperature cycling, random vibration and electrical loading/monitoring. HASS screens are performed in the same type of chamber that is used for HALT. The vibration in HASS is randomly applied over a broad frequency range producing energy to 10,000 Hz in 6 degrees of freedom.
ESS originated out of the military to improve the reliability of their complex products. ESS typically uses temperature cycling and random vibration applied separately. Products are normally electrically powered and functional tested during ESS. Random vibration is usually preformed on and electro dynamic shaker. “Environmental Stress Screening of Electronic Equipment”, DOD-HDBK-344, is a military handbook that provides guidelines for developing ESS programs.
Both HASS and ESS are effective screening programs that yield more rugged/reliable products with less field failures and warranty expenses . More information about HASS and ESS can be found in the following pages:
All of these test methods provide different benefits. Not all of them have to be performed to produce a reliable product. Contact DES to help determine what makes sense for your product.