Banner Image

Improving Reliability of Product Assembly through ESS Testing

Posted by Laura Austin on Thu, Sep 06, 2012 @ 07:00 AM

There are many factors to consider when deciding on a contract manufacturer to build your electronics or perform your product assembly. The first factor to come to mind is usually price, but there are others that are equally important. You also have to factor in quality control, shipping costs and reliability of the finished product. Unless your manufacturer has thoroughly tested the design and helped to make appropriate modifications, you could end up losing money in warranty repairs or even recalls.

Reliability testing is a particularly important part of the design and manufacturing process, and one of the most valuable tools in the reliability testing toolbox is Environmental Stress Screening (ESS). ESS works by exposing your design to extreme versions of the sorts of environmental stresses it will encounter “in the wild” including rapid temperature cycling, vibration, and power cycling. In this way, any latent defects in the design become apparent before the design is finalized, giving you and your manufacturer the chance to rework the design before moving on to the production run and product assembly.

The ESS process is generally comprised of three steps:product-assembly

1. Planning

The main purpose of the planning stage is to tailor the screening process to the product being tested. Planning will take into consideration cost, time available, and product life-span requirements. In order to plan effectively, planners must determine the number and type of latent defects likely to exist in the design, the maximum number of defects that are acceptable, and what screens will be most effective given those determinations. Remember that the purpose of ESS is not to remove all latent defects from the product, but rather to put the number and type of the defects into a range that is acceptable.

2. Implementation

Your contract manufacturing company will generally be taking care of most of the ESS implementation and will provide you with the resultant data and recommendations. They will use a “failure reporting, analysis, and corrective action system” (FRACAS), which is usually a software application, to track the failure data (remember that the point of ESS is to provoke failure). The types of data points you should expect to see are: 

  • which component failed

  • which test produced the failure

  • the date and time of the failure

  • a description of the failure symptoms

  • the name of the tester

  • any additional information of interest regarding the failure

3. Monitoringmonitoring

Monitoring is performed by generating reports from the implementation data and comparing ESS results with the expectations established in the planning phase. The parameters used vary somewhat depending on the product, assembly, or component being tested but often include:

  • Incoming defects

  • Screen strength

  • Defects remaining

  • Trend analysis 

Key parameters will also change over the course of production as more information enters the ESS program and it evolves to accommodate that information.


There are several benefits to a well designed ESS program, whether applied as early as the product design phase or as late as the product assembly phase. Increased reliability translates into lower warranty costs for a manufacturer, and that saves you money. Insight into what is causing defects and reliability issues in your current product line can also inform future design processes, effectively acting as an investment in research and development. Increased reliability can also help build your brand, thereby increasing sales.

When shopping around for an electronic contract manufacturer, it is vital not to undervalue the importance of a solid ESS system. A manufacturer with such a system in place will be able to help you improve the reliability not just of your current product, assembly or electronics but will provide information that will be applicable to your future product lines as well. Without an ESS system, it will be very difficult for that contractor to provide the consistency you need.

Topics: electronics manufacturing, product assembly, contract manufacturing, contract electronics manufacturing, electronics industry, technical design, ESS testing, reliability testing