In recent years, whether its manufacturers, hobbyists or emerging companies, the application of PCBA functional testing has gained widespread attention, perhaps this is due to the increasing emphasis on quality assurance, changes towards smaller batch manufacturing and subsequently the search for efficient testing methods.
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The entire manufacturing process is complicated and is affected by a variety of factors. There may be hundreds of components and thousands of solder connections on a single board, and without adequate verification, the entire process is a hit and miss affair. Therefore, the electronics manufacturing industry and product developers meet this challenge by establishing various inspection and testing procedures to ensure the quality of their products.
Testing can help identify critical errors early on, increase yield and reduce costs, and improve overall quality and safety. PCB functional testing is one of the best and most versatile tools for verifying a board for usage in the real world, but it is just one of many testing methods in a manufacturers arsenal. With each testing method having its advantages and disadvantages, it can be difficult to determine the best test method for your situation and budget. In this article, we will review 7 of the most common PCBA testing methods.
1.Visual Inspection
PCBA inspection can be generally divided into electrical and visual inspection methods. Visual inspection uses a magnifier or the technicians bare eyes to manually find solder defects and other visible defects such as component orientation, missing components and board stains. This is the simplest and most basic inspection method.
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Applications: Ideal for simple designs with larger components and lower quantities.
2. IN-CIRCUIT TESTING (ICT)
PCBA ICT is currently the most robust and popular type of PCBA testing for larger batches and mature products. A form of automated testing, the typical fault coverage is upwards of 90%. During PCBA ICT, electrical probes in a bed of nails format send currents through specific locations on the board at designated test points. These tests can check for shorts and open circuits, possibly due to missing parts, solder defects or incorrect orientation of diode/transistors.
For large or repeat batches, tailor-made test jigs can be made to perform in-circuit quicker and more efficiently.
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Applications: Suited for testing mature products at high-volume.
3. FLYING PROBE TESTINGFPT
A form of in-circuit testing, flying probe or flying needle testing is often seen as an improvement over bed-of-nails ICT. As well as test points, a flying probe machine can also access untented vias or the ends of components themselves to be used as test points, and can be programmed to check the value of passive parts, directly check diode/transistor orientation and perform voltage measurements. There is no need for a tailor-made fixture, and any changes to the components or PCB design only require updating the software.
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Application: Prototypes, small and medium batch production or small boards with high component density.
4. AUTOMATED OPTICAL INSPECTION (AOI)
AOI uses a single (2D) or two (3D) cameras to take high-resolution images of the PCB, and then compares these with images of a template board of the design being tested, or with a database of images of good and bad boards. An AOI machine can be added to the end of the production line directly, serving as the first line of quality assurance and allowing for adjustments to be made to the production process in-situ.
AOI covers all the checks manual visual inspection would identify with greater accuracy and consistency and can identify incorrectly placed components if visibly distinguishable.
The template method is more accurate, however this is time-consuming to set-up and is not suitable for prototype designs subject to changes.
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Application: Suited for testing mature products at high-volume.
5. AUTOMATED X-RAY INSPECTIONAXI
Compared with other inspection methods, AXI testing technology is unique in that x-rays are used. X-rays can penetrate the PCB and body of components to generate 2D or even 3D images of the solder joints. This makes it ideal for hidden joints such as those on Ball Grid Arrays (BGA) and other underside pads. AXI inspection can also detect solder voids and many other optical inspection methods cannot.
When used alongside the production process, AXI can be a useful tool for detecting defects early on, thus allowing engineers to make process adjustments to eliminate the source of the issue. This reduces the number of boards requiring costly repairs. For small batches or prototyping, x-ray inspection of only the chip components with hidden pads is often sufficient.
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Application: Volume production and complex boards with chip components.
6. BURN-IN TESTING
The burn-in testing is very effective and accurate, allowing you to check the performance and find hidden defects before the boards go out into the field. During burn-in testing, boards are subjected to conditions exceeding the rated operating conditions to detect early failures and test load capacity, thereby eliminating premature failures in the field. Unlike many inspection methods, that only check for indicators for potential failure, burn-in testing simulates extreme operating conditions to trigger failures.
The operating conditions tested can include temperature, voltage/current, operating frequency or any other operating conditions relevant to the design. The data collected through this process can in turn help engineers understand the cause of the defects and optimize the design or manufacturing process.
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Applications: Equipment that may operate in extreme environments or where failure is not acceptable, e.g. medical or military equipment.
7. FUNCTIONAL TESTING (FCT)
Functional testing is performed in the last phase of production to serve as the final quality control procedure. In short, it ensures that the device under test (DUT) operates as intended. Depending on the complexity of the design and the specific testing requirements, functional testing can be as simple as an on-off power test, to a comprehensive test with strict protocols and testing software.
Because of this flexibility, functional testing can be employed as a substitute for more costly testing procedures. Functional testing simulates the actual operating environment and therefore can be more direct than other testing methods. However, it may be more difficult to ascertain the cause of any defects and unlike burn-in testing, functional testing will not catch boards that fail early in the products lifecycle.
Complete 100% functional testing is increasingly being used with small-batch manufacturing to ensure every board coming off the production line is operational.
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Applications: Ideal for small-batch manufacturing, or in conjunction with other testing methods.
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The last thing any designer wants is to discover last-minute that their product is faulty. Electronics of all types, even if theyre properly designed and meticulously built, are prone to problems. Many electronics come out of the prototype stage with plenty of bugs and issues for their designers to troubleshoot. However, when something is left unnoticed until the product is out in the field, it can mean huge problems for the company.
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Testing electronics is so important, especially for printed circuit boards (PCBs), because it prevents several problems from occurring. To get a clearer idea of how PCB testing can improve your PCB products, learn more about what PCB testing is and which primary methods are used to evaluate PCBs.
Testing is a crucial part of the manufacturing process for PCBs. When PCB testing is conducted throughout the production cycle, it can help save money and prevent issues when it comes to the final production run.
Some design analysis techniques can be used during the early stages to help minimize major issues during the manufacturing process, but theres also a wide range of PCB testing methods that can be used on physical boards. These tests, run on prototypes or small-scale assemblies, look most closely at potential shorts, solder joint issues and functionality, ensuring that each tested PCB will function as intended.
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Many companies see PCB testing as an absolute must due to the many advantages it provides them. Check out some of the following top advantages of PCB testing:
While thorough testing isnt necessary for all types of PCBs, especially matured products well into their product life cycle, the majority of new PCB designs need robust and frequent testing of the design process. By establishing an appropriate PCB testing procedure for your organizations needs, you can experience the benefits of PCB testing.
PCB testing and inspection cover a wide variety of printed circuit board testing methods that check if a PCB meets standards. Some of these PCB standards revolve around ensuring the PCB functions properly according to a projects specifications and that it doesnt have any defects. Electric board testers and other circuit board testing methods are used to conduct these inspections and PCB tests.
Circuit board testing procedures evaluate several components of PCBs. These components are analyzed in detail to ensure their quality. The primary components tested can be found below:
Most of these factors are analyzed in early materials testing and environmental tests. However, factors like electrical conductivity and general functionality are analyzed with various methods and equipment.
When considering how to test circuit boards, several methods are available, and no single one will catch every problem or meet the requirements of every designer. Each testing method should be considered closely to determine if it meets the specific needs of your manufacturing environment. Some factors to consider include the type of product youre testing, the problems youre testing for and the reliability of the test method. To give you an overview of the testing methods available, weve summarized the main qualities of four popular types of PCB testing methods below:
In-circuit testing is a popular PCB testing method that many PCB manufacturers prefer to employ, and it can find 98% of faults. This testing method uses special PCB testing steps and equipment, including:
Using the ICT method, a manufacturer can test individual components and measure their performance, regardless of the other components attached to them. Generally, this type of testing is best for 3analog circuits since its best at measuring resistance, capacitance and other analog measures. Additionally, the cost of the equipment means that this testing method is best suited for the final testing of stable, high-volume products, not for low-volume productions or early testing stages where the design may change multiple times.
The fixtureless in-circuit test (FICT), also known as the flying probe test, is a type of ICT that operates without the custom fixtures, reducing the overall cost of the test. First introduced in , FICT uses a simple fixture to hold the board while test pins move around and test relevant points on it using a software-controlled program. Since its introduction, FICT has gained widespread use throughout the electronics manufacturing industry for its versatility.
FICT testing is used for the same things as traditional ICT, but because of the way it goes about testing, it offers different advantages and disadvantages. While FICT is able to adapt to new boards quickly, easily and cost-effectively, with a simple programming change, it tends to be slower than the traditional ICT. This quality makes it an ideal testing method for small-production tests and prototype testing but less effective for large-scale production.
A functional circuit test is exactly what it sounds like it tests the function of the circuit. This type of testing always comes at the end of the manufacturing plan, using a functional tester to check whether a finished PCB performs to specifications.
Some answers to common questions about functional circuit tests and how they work can be found below:
The boundary scan test looks at the wire lines on PCBs and is widely used as a way to test integrated circuits when it isnt possible to reach all the nodes of the circuit. In this type of test, cells are placed in the leads from the silicon to the external pins, testing the functionality of the board.
The big differentiating quality of this type of test is its ability to assess a board without reaching all of its nodes. This quality is an important one for evaluating integrated circuits with multiple layers and high density since these types of PCBs have been becoming more common in recent years.
In fact, this testing method is quite versatile and able to be used for several applications, including system-level tests, memory testing, flash programming and central processing unit (CPU) emulation, among other functions. Its commonly used in field service to detect problems in functioning systems.
To better protect your PCB and have it pass an inspection and test, you may want to consider utilizing some of the top design techniques available today. Design for Manufacturing (DFM), Design for Assembly (DFA), Design for Test (DFT) and Design for Supply Chain (DFSC) are all some of the best design techniques used to ensure a PCB is manufactured correctly.
Essentially, designers use these techniques in the schematics and simulation stage to ensure a PCB meets various parameters and standards before its sent to the manufacturing stage. Learn more about DFM, DFA, DFSC and DFT below.
DFM is the process of arranging a PCB topology with the manufacturing process in mind. With this design mentality, the PCB layout topology is intended to mitigate problems that typically occur during the fabrication and assembly processes, including:
DFM tests should be implemented early in a project timeline to reduce overall costs and development time. There are plenty of software programs available that identify issues like those listed above.
For any PCB assembly, its essential to attach components securely to the circuit board. Unfortunately, doing so can be difficult when the design is hard to assemble, which is why DFA is essential. With DFA, the goal is to determine how to design the PCB so that the assembler can complete their job quickly and effectively.
The DFA process includes the following steps:
Like DFM, DFA tests should be implemented early on in a project design process to minimize production costs and product development time. PCB testing software programs are available to help ensure PCB designs meet DFA standards.
DFT is a type of design that helps make testing more thorough and less costly. Essentially, PCBs designed with DFT in mind are designed to make it easy to detect and locate failures. This way, its easier to run tests quickly and accurately, reducing the amount of time needed for testing. For this to work, designers have to know exactly what type of testing methods theyll be using at each stage of production and design the PCB to work optimally with them.
DFT can require a great deal of additional design and engineering effort in the PCB design process, easily making up for the amount of time saved during testing. The amount of time spent, however, is easily made up for with an overall decrease in manufacturing costs. With faults easier to find, its less likely for PCBs with hidden faults to be sent out, reducing the cost of customer dissatisfaction and potential recalls.
One thing that many designers dont consider is the life cycle of a product or component. Often, certain components become obsolete during the product life cycle of a PCB, and it becomes more difficult to source that component in a cost-effective way. Its essential to consider component life cycles when designing new products with DFSC techniques.
Staying aware of life cycles includes talking to an experienced electronics contract manufacturer to determine stock availability and alternate sourcing for the components of a PCB early in the design process. In the long run, this DFSC strategy will help save money by ensuring a long lifespan for a PCB design.
Regardless of the method you use, PCB testing is an essential step in the design process, helping to save your business a great deal of time and money by preventing bugs before they affect your production. However, to successfully run tests on your PCBs, you need a supplier you can trust to ensure that your prototypes are made to order every time. Millennium Circuits Limited can help.
We provide several prototypes and small-scale production services that can help speed up your testing process. With incredible reliability and no hidden fees, we make sure you can trust us to provide you with high-quality prototypes for your next round of PCB testing. Get a quote today!
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