Guideline

Essential Steps for Effective PCB Board Testing

The PCB test

History of PCB testing

In the early days of PCB manufacturing, boards used to be visually inspected by humans for any errors caused during assembly or any of the manufacturing processes. Technicians used to inspect the board with their bare eyes and find abnormalities like defects caused during the soldering of the components, component alignment with the footprint and any physical damages that have happened during any of the process. 

With the development of technology, testing of boards became difficult with bare eyes and needed much more efficient ways for testing. This led to the development of automated testing methods such as Automated optical inspection (AOI) and In-circuit testing (ICT) methods by which the testing process improved drastically both in the accuracy of inspection and the time consumed to test the boards.

As the components have become smaller and denser, the testing methods are also improved and different types of testing methods are introduced over a period of time. In this article, let us get to know a few of the most commonly used PCB test methods in industry in today’s world of electronics.

Introduction to PCB Board Testing

PCB test is one of the crucial aspects of electronic devices to verify the functionality, integrity and reliability of boards after manufacturing. In the olden days manual visual inspection were done to test the boards for any defects caused during manufacturing. As the complexity of the circuit increased over the years, different types of testing methods were introduced to achieve effective PCB testing. In this article, let us learn more about the different types of testing done and the essential steps that need to be followed effectively during PCB testing.

Types of PCB testing

PCB testing is done to analyze the defects in the boards which would result in the overall poor performance under various environmental conditions in real-time. A few of the most common types of testing methods are listed below:

  • Visual Inspection

It is a very simple inspection method carried out by a trained technician without using any instruments with his bare eyes. Boards are inspected against the design files by the technician to find the visual defects of soldering and component misalignment using the naked eye. This method is also used to check the warpages, missing components, tombstoning effect and soldering defects which can be easily identified using the naked eye. In some cases, to be more accurate, the microscope is used to identify these defects.

The PCB AOI test

  • Automated Optical Inspection (AOI)

In this method, testing is done using an optical image captured by a camera of macro-level zoom and inspected against the design files and manufactured board. It compares the captured image with the actual physical board to identify any defects in soldering, open circuit, short circuit, missing components, tombstoning and any scratches on the surface of the board. AOI is done during several stages in manufacturing as it is an intermediate process. 

  • In-circuit testing (ICT)

Circuit testing is a method of testing boards where the components are assembled to verify their functionality and integrity. It consists of probes that test the populated boards for any defects, open circuits, short circuits and missing components. This kind of testing is suitable for mass production.

  • Continuity and isolation testing

Continuity testing is a method of checking if the circuit is closed or open. It checks for any openings present in the conductive path. Measuring is done between two points to check the resistance in a few ohms. If the value of resistance is low, it means the circuit is closed and if the value is high, then it means the circuit is open and the connection is very weak or not connected at all.

On the other hand, isolation testing is the process of verifying the insulation resistance of the conductive path. It ensures that the insulation material is effectively preventing the leakage of current in the conductive medium. It is done at high voltages which typically measure resistance in a few megaohms (MΩ). 

  • Flying probe testing

It is the process of testing the boards using flying probes that move between several test points on the circuit. These flying probes are movable and can easily access the various points on the circuit board without any dedicated fixtures like other testing methods. It consists of multiple probes that move in all three directions (X, Y & Z). The needle at the end of the probe touches the specific test points on the board to perform the electrical testing to identify the open circuit, short circuit and component failure defects. The coordinates for the movement of probes are generated by the software from the engineering team.

  • Functional testing

The process of evaluating the performance and functionality of the board by subjecting them to real-world scenarios is called the functional testing method. This testing is done for boards that are assembled with components and are ready to be shipped to customers. Along with the open/short circuit and soldering defect, functional testing also identifies power issues, signal distortions and voltage fluctuations in the assembled board.

The PCB testing

Steps for effective PCB testing

Let us now understand the essential steps that are required for effective PCB testing other than the test methods mentioned above

  • Design for Testing (DFT)

The concept of testing the board begins right from the design phase. It involves PCB design engineers to provide test points and access to nodes even after assembling the board during the design phase itself. This will ensure the boards undergo the testing process smoothly without any problems. Considering the DFT method helps find whether the circuit is designed perfectly, fabricated without any defects and all the components are operating perfectly without disturbing the neighboring devices or not.

  • Manufacturing Defect analysis

In addition to the above testing methods, it is essential to analyze manufacturing to identify any defects that are caused during the fabrication process. Automated optical inspection (AOI) and X-ray inspection methods are used to detect any issues caused during the intermediate processes that are not visible to the naked eye. Detecting the defects during the fabrication process helps the fabricator avoid any reworks that would result in costly remakes and ensures that the functionality and reliability of the product are good.

  • Environmental Testing

PCB test in harsh environmental conditions such as humidity, temperature, pressure, vibration and electromagnetic interference is known as environmental testing. To perform under such conditions PCBs have to be compliant with environmental testing conducted. The testing may include temperature cycle tests, exposing the boards to humidity, testing under heavy vibration and EMI/EMC testing. Conducting these tests will make the boards durable and reliable in harsh conditions and increase the lifespan of PCB.

 

Conclusion

Overall, testing the PCB is a crucial step to ensure the functionality, reliability and performance of the end product. Following the essential steps that are required to test the boards makes the manufacturer produce the highest quality standard PCBs in the market. It is necessary for the manufacturer to conduct and implement several testing methods as per the customer requirement in order to succeed in today’s electronic world to compete with others in the market.

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