Posted on 09 Jun, 2016 by Russell Poppe
In recent blog posts, we have discussed two test methods for printed circuit board assemblies (PCBAs): in-circuit test (ICT) and flying probe. Continuing with this theme, in this post, we will look at soak testing.
Soak testing is a form of performance testing that is used in electronics manufacturing to find out how a product "survives" in the wild. Function and stability are tested over a long period of time, in order to identify any manufacturing defects that will effectively "kill" the product.
This is a vital process for two main reasons. For one, it ensures that the product actually works; that it will do what is supposed to do. Secondly, it safeguards your reputation as a manufacturer and prevents time and resources being expended rectifying faults that ought to have been spotted earlier.
How will your product work in the field?
Soak testing, sometimes referred to as endurance testing, involves simulating the real-life conditions under which a product will be placed once it reaches the end customer. For example, an OEM or EMS provider making traffic lights might replicate the conditions at the junction they will be placed in over a defined period, to validate their performance.
During a product’s lifecycle, many problems tend to strike either very early on, or towards the end of the product’s life. Therefore, this test method helps to ward off the first potential batch of problems. A product might work very well for the first couple of hours, but then begin to fail or behave erratically. This test method also identifies faulty components that may have passed an earlier test – ICT, for example - but falter under continuous testing.
A thorough soak test will expose a product to a production load that is as realistic as possible. For instance, a product intended for use in a commercial airliner that travels internationally might be placed under a wide range of temperature settings that change quickly and unexpectedly. The product should be able to continually function as the environment changes.
At this point, it is important to differentiate this test method from stress testing. In the former, a product is tested under "normal" conditions, but in the latter, it is tested to breaking point. So, returning to the previous example, the product might be subject to temperatures more extreme than those that a commercial airliner would generally encounter around the globe. A product is not expected to withstand a stress test - but it is expected to come through a soak test.
Implementing soak testing
A soak test is bespoke to the product being tested and so cost and set up time are variable, dependent on the product and the equipment being used. If you are an OEM outsourcing to an EMS provider, you will need to advise your partner about the potential failure points and specify exactly what you are hoping to achieve via the soak test - for instance what the test should look for and what might go wrong.
It sounds obvious, but it’s important to ensure that the product is tested for the appropriate amount of time - whether that's 24 hours or an entire weekend - to achieve the optimum results. And, of course, any peaks and troughs in production load over this time should be accurately reflected.
Soak testing is a highly valuable form of testing that places a product under "real-life" conditions, in order to uncover any manufacturing defects that will prevent it from performing out in the field. As such, you can send your product on to the end customer, certain it has been manufactured to the highest possible standard and that they won’t be in for any unpleasant surprises.
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