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>Environmental Stress Screening (ESS) – Product Reliability Enchancement

Kingfield routinely manufactures pcb assemblies for products which themselves have been designed to operate in very demanding environments. As a result we work with our clients to develop test strategies to serve two main purposes:-

  • to provide evidence for our customers that their designs are robust and manufacturable
  • to ensure the best quality product goes out into the field

To this end we develop test strategies which are designed to maximise test coverage at the lowest possible cost. By doing this we aim to achieve the exacting product reliability standards our clients demand.  This ensures we keep test costs to a minimum for our clients but also reduce the cost of quality for the product over its lifecycle by minimising customer returns and repair costs.

Steve Chappell, Test Engineering Manager states, “We are always looking for ways to ensure products operate effectively for their full lifecycle by developing  test strategies which are appropriate to the product and its ultimate application. This involves working closely with the customer to agree a complimentary test programme where we will use different test processes to examine various parts of the circuit. This may involve using processes such as Automated Optical Inspection, Flying Probe Test and Functional Test.

However it is also very important to identify latent defects such as non-conforming solder joints which may cause permanent or catastrophic failure at a later date.  In order to find these type of potential problems we use a process called Environmental Stress Screening (ESS). This involves using an oven which is capable of ramping in temperature and then cooling over a set amount of thermal cycles. This causes any poorly formed solder joints to expand and then contract identifying any connections where the lead of the component was just ‘sitting’ on the
solder pad thus causing the product to fail at final test.  As a result those assemblies which have been screened can be assumed to have a higher reliability than a similar unscreened batch of assemblies.

We have had two ESS ovens on site for some time but recently invested in an additional oven capable of ramping to 180DegC and cooling  to -40DegC.  This new oven allows us to meet the exacting standards of the aerospace, defence and oil and gas sectors”.