PCB X-ray inspection is a crucial testing method for printed circuit boards, especially complex, high-density types. So, how does it work and what are its benefits? Here is everything there is to know about using X-rays to examine circuit boards.
What is PCB X-Ray Inspection?
PCB X-ray inspection or AXI (automated X-ray Inspection) utilizes X-ray technology to examine printed circuit boards. The rays are similar to the medical types but slightly adapted for electronics.
The inspection offers a comprehensive analysis of the PCB under test, including a detailed cross-sectional view. Modern X-ray machines can even produce colored images, allowing better viewing.
The method provides better results than other techniques, such as manual and automated visual inspection. The above image shows defects that the technology can help detect. Let’s now look at how the machine works.
How X-Ray Inspection Works
The PCB X-ray inspection system includes the X-ray tube, the PCB holder, the detector, and a processing unit. The tube emits the rays, while the detector captures the image. The processor enhances and interprets the image.
X-ray imaging is also available in two options: 2D and 3D. The two choices differ in detail, speed, and cost. They also suit different PCB types and inspection requirements, as explained below.
2D Inspection
This method produces 2-dimensional images of the PCB under inspection. The image is a top view of the sample and is less detailed. Tilting the PCB reveals the structure of hidden sections, or 2.5 imaging.
That said, 2D image inspection checks circuit boards faster and costs less. These qualities make it suitable for simpler circuit boards and smaller budget projects.
3D Inspection
3D inspection provides a 3-dimensional image of the circuit board. It works by combining 2D images, providing a more informative presentation of its structure.
Although slow and pricier, 3D imaging offers more details than 2D – this benefit makes it suitable for complex boards requiring higher reliability levels.
Resource: https://www.mdpi.com
PCB X-Ray Inspection Process
The X-ray inspection process consists of a series of steps. Below, we track the steps and explain what occurs in each stage, from the beginning to the end.
Board Preparation
The PCB requires preparation, including cleaning to remove contaminants. The board then goes to the inspection platform for scanning, ensuring accuracy.
Setting Scan Parameters
The X-ray machine must be configured to match the PCB’s assessment requirements and ensure a quality image. The settings include voltage levels, exposure time, and tilt angle.
Image Capturing andes detection, and the processing unit creates an image. Advanced software makes adjustments to improve clarity. Denser parts and sections absorb more, and vice versa.
Computer logarithms automate defect detection, identifying voids, shorts, and other flaws. Trained workers also view the X-ray image on a screen for human interpretation.
Results Recording
The inspector documents the results or findings. These are crucial in the quality process, both present and future. The information helps engineers identify design and manufacturing flaws that require addressing.
Resource: https://www.researchgate.net
Defects Detected by X-Ray Inspection
The technique helps detect various anomalies in a printed circuit board. The problems it identifies are divided into the following types: soldering errors, component flaws, board structure issues, and foreign objects.
Soldering Errors
Soldering errors result from the component mounting process. They can be of various types. They include the following:
- Opens and shorts
- Solder bridges
- Soldering voids
- excess solder
- insufficient solder
- Cracked solder joints
- Solder quality issues
Component Flaws
Component flaws are design or assembly errors. They affect the board’s functionality and may even shorten its lifespan. Common component errors that the machine identifies are:
- Component damage
- Lifted leads
- Misalignment
- Missing components
Board Structure Issues
The board itself may have design and fabrication mistakes. The process can identify the following PCB structure defects.
- Layer material cracks
- Delamination (layer separation)
- Voids and inclusions
- Via and through-hole problems
- Internal trace problems, such as breakage or misalignment
Foreign Objects
The technique can detect foreign objects in the circuit board’s surface or internal geometries and structures. The objects include metallic debris from fabrication and assembly processes, such as copper fragments.
What are the Advantages of X-Ray PCB Inspection?
X-ray inspection for PCB quality control offers various benefits, making it popular in circuit board manufacturing. They include the following.
It’s Non-Destructive
X-rays are electromagnetic waves. They present a non-destructive test and won’t cause damage. Their non-destructive nature reduces material wastage, saving on product development and manufacturing costs.
Can Detect Hidden Defects
The waves penetrate solid materials without hindrance. That includes seeing beneath SMD parts, such as BGAs (Ball Grid Array packages). The result is a more comprehensive assessment than visual and automated optical inspection.
Fast Detection
It works quickly, compared to other quality control and inspection methods, such as electrical testing. It can even provide real-time images on a display. This feature reduces assessment periods and reduces production time.
Increased Versatility
It offers a broad range of options. For instance, depending on your board type and budget, you can opt for 2D or 3D imaging. Additionally, you can use the method on many PCB types, from low-density to high-density types.
Resource: https://www.youtube.com/watch?v=_DvseE31rqc
Best X-Ray PCB Inspection Practices
Anyone using the method to examine circuit boards must understand how to do so correctly. That means knowing the method’s dos and don’ts. We compiled a list of best practices.
1. Ensure the specific machine’s features suit your PCB’s quality monitoring needs. It should be a high-resolution type and suitable for the job.
2. Implement real-time analysis when using the technique to check circuit boards. It reduces the assessment time in high-production runs.
3. Develop a comprehensive checklist detailing the defects that need checking. It ensures consistency and comprehensiveness.
4. Always document results. Include all the required information, such as the date and identified defects, for future reference.
5. Manufacturers must train workers on proper machine and examination procedures. That includes in-house quality control guidelines.
Conclusion
X-ray inspection is a non-destructive and comprehensive way to test printed circuit boards. It offers many advantages, from safety to penetrating solid materials. PCB manufacturers usually implement it alongside other quality assessment methods, such as visual and optical examination.
