Why functional testing should not be your go-to test strategy

As an original equipment manufacturer (OEM), testing is absolutely critical to everything you do. This means that throughout the manufacturing process, you should be seeking to identify product faults before they become real problems that have the potential to damage your reputation and bottom line - and, in the worst case scenario, cause accidents or injuries.  

In previous posts, we have discussed a number of different test methods, including:

However, some OEMs believe there is only one test method worth implementing: functional test.

But we believe this is a misguided viewpoint and this blog post aims to explain why we feel this way.

What is functional testing?

A functional test essentially proves that a product does what it is supposed to do. Unlike the other test methods mentioned above and in previous blog posts, this one is predominantly focused on the design of a product - rather than the manufacturing quality. In other words, it doesn’t prove that a product has been built well.

Therefore, functional test is generally best reserved for a quick "final assembly" check once the thoroughly tested subassemblies have been put together. If the pass rate is not virtually 100 per cent, then the test strategy (or perhaps the product design) needs to be reviewed.

Accordingly, it becomes clear why it is crucial to identify product faults earlier on in the manufacturing process. You want to maximise the chance of your product passing a functional test. Otherwise, you will have to expend precious time and resources attempting to find out what has gone wrong.

Functional testing usually comes at the very end of the manufacturing process, so the next person to power the product up is the customer. It is surprising how much can be wrong at a component level and still pass a functional test - for example, floating pins on ICs, missing and wrong value components etc can all go undetected. That is, until the customer discovers these issues out in the field.

As a result, this test method can provide false confidence unless these potential errors have been covered elsewhere. Therefore, it should be implemented as part of your test strategy; rather than as your entire test strategy. 

Testing in practice

As is generally the case with testing in electronics manufacturing, each functional test is bespoke to the individual product and is usually developed by the product designer. It can be a steep learning curve – and expensive - for an independent developer to learn the product functionality before designing the test equipment. 

A functional test is often quite slow and debug can be difficult, requiring more time and a higher skill level to determine the cause if the product malfunctions. All of this adds cost.

However, while testing requires a financial investment, failing to test could cost your organisation a lot more in the long run. According to DfR Solutions: "Resolving product acceptance or post-deployment problems is an unwelcome item on the daily to-do list. Depending on the industry (e.g. aerospace, defence, medical, telecom, transportation), potential issues include schedule delays, cost impacts, customer complaints, mission impacts, or even loss of life."

The icing on the cake 

When it comes to proving the reliability and viability of your product, functional testing should be the final piece of the jigsaw - and not the entire puzzle. Whether you are implementing your own test strategy or outsourcing to an electronics manufacturing services (EMS) provider, it is important to ensure that all parties fully understand what you expect to achieve. 

If your product passes a functional test after also passing a series of other tests throughout the manufacturing process, you can send it on to the end customer with a large degree of confidence that it will work optimally in the field. 

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Written by Russell Poppe

Russell describes himself as a Manager, Engineer, manufacturer, teambuilder, organiser, strategist, and occasional content writer. Russell loves to help businesses thrive and grow in the best way that he can and has a wealth of experience in the engineering and manufacturing industry, particularly within electronics. Russell’s previous roles have encompassed general management, engineering, development, manufacturing, quality, and marketing, always with a strong focus on customer service.