The English language contains over 200,000 words. This allows us to express ourselves with virtually any level of exactness we choose. For example, you can walk, amble, stroll, stride or simply just go to the store. Synonyms such as these that have similar, but not the same meaning can be used to provide clarity. However, when words or phrases have the same sound (i.e. homonyms) or the same spelling (i.e. homographs), things can get confusing. This allows you to run to the store to run up a tab. Confusion is never good, but when it persists despite following a given set of instructions, it can leave you wondering what you should do or what has been done.
In PCB development, a similar type of confusion, ambiguity, exists when it comes to board testing. There are numerous types of tests that are performed on circuit boards throughout the development chain and in some cases, afterwards. Development testing targets board design, manufacturing, and functionality. The performance of design and manufacturing testing is well-defined; however, all or part of the functional testing may be performed by the developer and/or the manufacturer. And therein lies the ambiguity. Regardless of who performs the testing or what additional tests may be included, it is commonly referred to as PCB functional testing. Let's try to bring some clarity to this situation and then we can discuss which tests for functionality are performed by your contract manufacturer (CM).
What Exactly is PCB Functional Testing?
In order to accurately define what PCB functional testing is it may be a good idea to first discuss what it is not. The prevalence of circuit boards in electronic devices and systems that extend into virtually every industry has spawned a wide range of verification and validation processes depending upon several factors; such as where the board will be used, its operation, and its degree of potential to cause harm. Therefore, all PCBs are subject to some environmental, performance and safety standards. To ensure that these are met typically means performing quality assurance (QA) evaluations and adhering to quality control (QC) specifications.
Quality testing is done on procedures, processes or products and usually, there are well-defined testing regimens and assessment metrics. For general PCB development for commercial electronics products, there are many specific tests that may be applicable; therefore, specific tests vary from design to design. For some industries, such as aerospace, medical systems and automotive, there are standards that specify a quality management system (QMS) be instituted within which necessary testing requirements are specified. Though critical and mandated, quality testing does not test for board functionality.
In contrast to quality testing, the objective of PCB functional testing is to verify or validate that the board will perform as designed once installed. In order to quantify this objective, the board must be placed in a duplicate or simulation of the installation environment. This includes applying the necessary inputs and power that the board will receive during operation and taking measurements to verify that the proper outputs are created. These tests are performed on the final board or device and may be performed by the developer, the CM and/or a third party. Although there are CMs that perform functional testing as part of their electronics manufacturing services (EMS), it is more common that your CM will perform only certain types of tests based on the facilities and equipment available to create the simulated environment required for your design.
PCB Functional Testing During Board Manufacturing
Testing PCBs for functionality requires much more than a bench and a multimeter or oscilloscope. In fact, CMs and others that routinely perform functional testing are likely to have one or more functional testers. These are systems, typically in a dedicated cabinet, that consists of hardware, cabling, software and monitors that connect to the board under test, provide all inputs and power and generate documentable results that can be passed to the developer. The most sophisticated of these, many of which are custom-built, will allow for testing specific processors and varying states of operation. This degree of testing is usually not available from most CMs.
Although most CMs do not have the facilities and equipment for complicated functional testing, such as processor evaluation, there are other tests that your CM can perform to aid in analyzing your board’s ability to function once deployed. These are and other PCB functional testing types are listed below.
TYPES OF PCB FUNCTIONAL TESTING
|Function(s) or Condition(s) Tested|
In-Circuit Test (ICT)
|Component input/output voltages and currents, resistance, capacitance, continuity, open/shorts||Parameter value|
|Bed of Nails|
In-Circuit Test (ICT)
|Analog/Digital data, IC data, component input/output voltages and currents, resistance, capacitance, continuity, open/shorts||Parameter value|
|Bend Test||Board flexibility or degree of bendability||Value|
For ICTs, the building of a fixture may be required that will extend the turnaround time for manufacturing. One example is the bed-of-nails where multiple pins or probes are arranged to align with test points on the board. This configuration is usually performed during production. A more robust method is the flying probe that can be used on bare boards as well as during production. This test, however, does require software programming.
|Tempo‘s Custom PCB Manufacturing Service|
PCB functional testing is a required activity to verify your board will perform as intended once deployed. Although the responsibility for instituting this validation procedure lies with the developer, your CM can assist you by performing some or all of the necessary testing during manufacturing. At Tempo Automation, we will assist you with functional testing upon request to ensure that your boards meet their functional objectives in addition to our industry-leading custom prototyping and low-volume production manufacturing services.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on PCB functional testing or how to incorporate into the manufacturing stage of your development, contact us.