Optimizing Environmental Stress Screening as a Means for Improved Reliability on Commercial Products

Abstract

The implementation of Environmental Stress Screening (ESS) is an integral part of the development and manufacturing processes of commercial and defense industries. By detecting and fixing latent defects of all types of electronic hardware, ESS ensures all products have been tested above their intended use conditions without removing more life from the product than necessary. ESS testing can also be cost effective for hardware that has already been through the manufacturing process but has not been shown to meet new user requirements. Additional screening of post-manufactured hardware at low levels of assembly can demonstrate the design is capable of meeting these new requirements. Take a modern day laptop for example. You as the customer expect the laptop to perform to the standards advertised. If the company performed ESS testing on their laptops, there is a much higher probability that all latent defects have been removed, protecting their product and your investment from infant mortality and more accurately representing the products advertised life. The key to implementing a successful ESS test is to expose the lowest possible level of hardware to thermal and vibrational environments. Hardware becomes more intricate and complex at higher levels of assembly. Therefore, it is easier and more cost effective to expose circuit cards to these heightened environments rather than built-up hardware. The placement and intensity of the thermal and vibrational environments, also known as ESS screens, are other important aspects in optimizing testing. Knowledge of the robustness of the design at each level allows for the use of environments to precipitate the most latent defects from the hardware without driving the item to failure. In addition to the placement and intensity of the environments, the duration at which the hardware is exposed is key. Since the effectiveness of ESS testing can be quantified through accepted equations, the optimal duration for each test can be determined.