Why PCBA testing is important...
01 September 2020
From small consumer electronics, such as lamp controllers, to large-scale industrial equipment in the power generation sector, printed circuit board assemblies (PCBAs) are central to the operation of virtually all electronic devices. And while it can be tempting to regard PCBA testing as a necessary evil, when done correctly, the process adds real value to your end-products.
This article was originally featured in EPDT's 2H 2020 Electronics Outsourcing supplement, included in the September 2020 issue of EPDT magazine [read the digital issue]. Sign up to receive your own copy each month.
Here, Steve Marshall, Managing Director at EMS provider, Offshore Electronics explains why they regard PCBA testing as so vital, before outlining some of the more common testing methods available to manufacturers and drawing comparisons between them…
Reliability of PCBAs is a prerequisite for product success and depends on a number of factors, all of which are important. These include the original board design, the specification, the quality of components and materials used, the care with which each assembly is manufactured, the production conditions and skills of machine operators, and the subsequent handling and assembly into the finished products. Reliability can also depend on the manner in which assemblies are tested during and after the manufacturing process, as incorrect test procedures may fail to detect production or component faults.
You can’t guarantee the quality of your product without testing. And when done correctly, testing will save you time and money in the long term. If your testing procedures are inadequate, there is a risk that you could be shipping products of inferior quality to your customers, which can lead to:
• Increased warranty repairs and field failures;
• Negative impact to your brand reputation;
• And even damaging and costly lawsuits.
These issues are all certain to impact your bottom line.
Weighing the options
So then, what options are available to you for PCBA testing? No single testing system or method for PCBAs will meet the requirements of every manufacturing run, and many factors need to be taken into consideration when developing your testing strategy. It is essential to select proper test procedures from the perspective of the product, business case and reliability.
The first step in building any testing strategy involves building a thorough understanding of the testing methods available, in order to best determine which of these is most appropriate for your product.
At Offshore Electronics, our preferred option is to start with automated optical inspection (AOI), and follow it up with either functional testing or in-circuit testing (or sometimes a combination of the two). Each method serves a particular purpose during the manufacture of PCBAs, and it is important to understand the differences between them, if effective quality control procedures are to be implemented.
Automated optical inspection provides a baseline by verifying that each component has been correctly placed and soldered. As its name implies, functional testing is used to ensure that PCBAs function as they should. By contrast, in-circuit testing is used to examine each individual component on a PCBA, to prove that it is correct, has been fitted to the board in the manner specified and that it works as it should. As we can already see, there are significant differences between the two main testing methods.
Although in-circuit testing can include a degree of functional testing, its primary purpose is to validate each individual component. In some respects, it is a far more comprehensive process, as components are tested independently against a program model containing parameters specific to the component and its functionality.
This is performed in a structured manner, unpowered initially, to test for short or open circuits, followed by test of passive components and simple semiconductors. After this, power is applied to facilitate test on the more complex semiconductors. The strength of this progressive approach is that the faulty or missing component is automatically identified and located without needing skilled engineering analysis.
In-circuit testing is performed using automated test equipment (ATE), which requires a ‘bed of nails’ fixture to be built for each project. While this adds cost to the test process, it can usually be justified if the product volumes are high enough. The test program is written by test engineers, designed around the specification for the board design. In-circuit testing is also generally very fast, typically just a few seconds for even a complex PCBA, which results in a lower cost per PCBA tested.
Where in-circuit testing is not cost-efficient, functional testing can be used to examine the complete, finished assembly. Through the process, inputs and power are applied to the PCBA to ensure that it performs its desired function to a certain specification.
Functional test does, however, require each individual assembly to be able to function independently; you cannot, for example, test an interface assembly if it requires a separate control or power assembly to function, unless you test both assemblies simultaneously, or construct a suitable test rig. The test may also depend on additional data regarding the specification of associated boards or of the finished device.
Normally, however, a functional test only proves that the assembly operates and will not usually detect the presence of faults in parts used as protection elements, which are inactive under normal operating conditions. Furthermore, should a PCBA fail a functional test, skilled engineering analysis will usually be required to identify the root cause.
An integrated approach
Both in-circuit and functional test have their place. Ideally, both are used to confirm the complete integrity and functionality of each PCBA produced. But this may not always be cost effective and a decision then has to be made as to which method is most appropriate.
At Offshore Electronics, our preferred option is usually in-circuit testing, since it offers a shorter test time and better faulty part diagnosis. If a fault is detected, the ATE quickly identifies the exact problem and the fault can easily be repaired – whereas for functional test failures, faults need to be diagnosed using engineering resources.
In practice, we offer both options. Our expert production and test engineers work closely with customers to determine the most efficient and cost effective methods of validating and testing their PCBAs to their required specification, backed by a detailed traceability system.
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