Many tests can be performed on the PCBA during various stages of the manufacturing and assembly process, to increase reliability and ensure the quality of the final product.
PCB X-ray inspection is one of the most important tests performed in the PCB assembly industry today. It is widely used to detect hidden defects that are not visible otherwise, X-ray inspection reveals hidden issues in traces, components, and solder joints that are not accessible using optical inspection methods.
By reading this blog, you will learn the following about PCB X-ray inspection:
- What is PCB X-ray Inspection
- Composition of PCB X-ray Inspection System
- Principle of X-ray Inspection
- Working Principle of PCB X-ray Inspection
- Pros & Cons of PCB X-ray Inspection
- Categories of PCB X-ray Inspection System
- Defects that can be detected by PCB X-ray Inspection
- Best Time to Use PCB X-ray Inspection Machine
- Steps to Implement PCB X-ray Inspection
What is PCB X-ray Inspection?
PCB X-ray inspection is a non-destructive testing (NDT) imaging method used to verify the quality of circuit boards by inspecting their internal structures. In PCB assembly, X-ray circuit inspection is used to capture possible problems at various stages to verify that the correct process is used and make necessary changes.
In fact, the size, density, and complex circuits make it difficult to find PCB or PCBA defects during inspection. Traditional methods such as optical imaging and thermal methods are not effective enough to find PCB defects. The PCB manufacturing industry uses detailed images of components provided by PCB X-ray Inspection machines to find problems such as solder joints, short circuits, and even damaged components.
Pros & Cons of X-ray Circuit Inspection
Compared with traditional inspection methods, electronic X-ray inspection can find all the hidden features of PCB boards that are not visible, solving the shortcomings of Automatic Optical Inspection (AOI). Although electrical test methods such as In-circuit Testing (ICT) can check the conductivity between connections, they cannot detect the quality of solder joints associated with these connections.
PCB X-ray Inspection machines are changing the way electronic equipment is troubleshooted. Many PCB manufacturers use PCB X-ray inspection instead of optical, ultrasonic, and thermal imaging. This method adds an extra layer of protection to PCB board quality inspection, which can predict whether a specific solder joint will fail over time, ensuring that the board will not fail during field operation.
Below are the advantages and disadvantages of PCB X-ray inspection, which will help you understand PCB X-ray inspection better.
Advantages of PCB X-ray Inspection
- Non-destructive Testing
X-ray circuit inspection is classified as a non-destructive testing(NDT) method, no damage affects the boards throughout the test.
- High-resolution imaging for detailed analysis
In addition to high-contrast grayscale X-ray images, high resolution, and high magnification are generated to allow for detailed analysis of the tested circuit board. High resolution means that more complex defects can be visualized and analyzed.
- Real-time Feedback & Reporting Capabilities
PCB X-ray Inspection enables us to navigate complex PCBs easily and to quickly identify defects in real-time.
- Cost Savings
With PCB X-ray Inspection machines, there is no need to produce batches of sample boards for testing and inspection. Inspection can be completed with 2-3 boards, saving costs for PCB and PCBA.
Disadvantages of PCB X-ray Inspection
- Expensive Inspection Cost
The PCB X-ray machines price is expensive, whether for electrical or medical purposes. Implementing 3D X-ray inspection is more expensive and time-consuming than producing simpler 2D X-ray images.
- Skill Requirements
To inspect the circuit board from these images, a specific skill is required, and the machine operator needs a certain level of experience to make reliable judgments.
- Health Damage
The waves emitted by X-ray machines for PCB can damage the skin and cause skin problems, and operating these machines requires a proper environment.
How does PCB X-ray Inspection Work?
X ray inspection machines use a series of components to find PCB problems. To understand this, you need to understand the composition of PCB X-ray inspection machines, the principle of PCB X-ray circuit inspection, and the entire working process.
Compositions of X Ray Inspection System
- X-Ray Tube
The X-ray tube is responsible for creating X-ray waves. The X-ray tube is based on accelerated electrons that hit a target element, generating the X-ray beam.
- X-ray Detector
The detector is an array of sensors placed on the other side of the X-ray source with the X-ray circuit sample in between.
- Operational Platform
The platform is sometimes called a manipulator or a stage. It is responsible for holding the sample to be inspected to generate a two-dimensional high-resolution image (shadow) of the X-ray circuit.
- Processing software
The software controls the inspection process. Images are displayed to visualize defects. Root cause analysis of defects is also performed. Many X-ray inspection software have void analysis tools that are used to flag areas of solder voids and calculate the total percentage.
Principle of X-ray Inspection in PCB Assembly
The principles of X-ray circuit inspection are the same as any other X-ray imaging technology. When X-rays fall on an object, high-density elements absorb more than low-density elements. Therefore, when the X-ray detector detects the X-rays, the high-density materials appear darker than the less dense elements, creating a 2D plane shadow that is then displayed.
PCB X-ray inspection can detect solder joint defects. A solder joint without voids will appear darker than a solder joint with voids.
Workflow of PCB X-ray Inspection
The X-ray tube generates X-ray photons. These photons are emitted onto the X-ray circuit placed on the operating platform. On the other side, a detector is placed to collect the reflections from the platform to generate an image.
Categories of PCB X ray Inspection Systems
2D X-ray
The PCB X-ray machine can scan the PCB board from one direction or axis. Due to this capability, the results are produced in a faster way and have increased throughput. However, with a 2D X-ray, the viewing angle is limited to a single side.
For single or double layers, 2D X-ray is best, while, for a multi-layer, 3D X-ray is the best solution.
3D X-ray
3D X-ray inspection, also known as Computed Tomography(CT), takes multiple X-ray images of the PCB from different directions, rotates the X-ray circuit sample in the X-ray path or rotates the X-ray source and detector around the PCB, and the processing software combines the 2D images to create a complete 3D model.
It can provide a deeper analysis but is slower than the 2D and has lower throughput.
Online X-ray
Online X-ray inspection systems can run automated X-ray inspection programs. By programming the test criteria, setting the correct inspection parameters, automating the process for areas of interest, and adjusting the imaging angle, the root cause of defects can be automatically analyzed.
Online X-ray inspection Systems are used for production lines with high capacity and provide higher detection efficiency than offline X-rays.
Offline X-ray
Offline X-ray Inspection systems can also be called a Manual X-ray Inspection System(MXI). The inspection process is executed by the machine operator by inspecting every solder joint and the evaluation process of defects is done by comparing to predefined standards.
Offline X-ray inspection is more suitable for sample inspection for process failure analysis or process verification.
Types of Defects Detected by PCB X-ray Inspection
X-ray machines for PCB can be used to find a range of defects in PCB boards. The types of defects it can find include
- Solder ball quality
X-ray circuit inspection can evaluate the quality of solder balls under BGA/CSP packages, ensuring that they are fully melted and form a solid connection.
X-ray machines for PCB allow inspectors to see if there are traces that cross other paths. X-rays can also show broken wires on the board even if they are between multiple layers.
X ray inspection machines can detect whether components are aligned correctly, and can also check whether internal components such as chips inside PCB IC packages are faulty.
- Extra components
X-ray machines for PCB can detect whether there is any debris or excess solder on traces or components.
- Connector defects
PCB X-ray machines can detect all defects related to connectors (such as deformed pins).
When is Best to use X ray Inspection Machines?
PCB X-ray Inspection machines are perfect for optimizing troubleshooting techniques. X-ray inspection machines are best when you want to
- Validate, analyze, and qualify the components.
- Detect problems in later batches.
- Find problems such as broken joints, and burnout components in deeper layers.
- Inspect products that belong to the aerospace, automobile, and medical industries.
- Navigate through the process control steps of PCB fabrication.
How to Implement PCB X-ray Inspection
If you want to use the PCB X-ray Inspection machine for X-ray circuit inspection, you need to follow the steps that are mentioned below.
- First, find the use case for this process. For instance, see what type of PCB board (Single layer, Double layer, or multi-layer) is.
- Depending on the board, select the type of X-ray that will be best suited for the process.
- Next is to define the SOP for inspection methods. Using these SOPs will help in efficiently managing the overall inspection process.
- Also, keep in mind to generate steps to prevent radiation poisoning.
- Scan the X-ray circuit and match the findings with other testing methods.
- Generate the results and troubleshoot the problems in the next sample.
- Repeat the process until your PCB is perfect.
Conclusion
In summary, with the trend of miniaturization of electronic components, circuit board inspection and troubleshooting are becoming increasingly difficult. PCB X-ray inspection provides a non-destructive testing method to visualize the hidden features of the circuit board, which can provide a deeper understanding of the circuit board and find defects.
If you want to learn about X-ray inspection or want your PCB to undergo X-ray circuit inspection, please feel free to contact FC PCBA.
