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What is PCB X Ray Inspection and Its Benefits?

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PCB X ray inspection involves the use of x rays to check circuit boards for defects. It’s one of the most effective quality-control methods, especially when it comes to visualizing hidden flaws, and commonly used to supplement visual inspection. So how does it work? This overview explains x ray inspection of PCB features in detail, including its benefits.

What is X Ray PCB Inspection?

PCB X ray inspection means using an x ray machine to examine printed circuit boards. X rays are extremely high-frequency and high-energy electromagnetic waves of very short lengths, shorter than those of visible light. These waves can penetrate solid objects.

In the world of electronics, manufacturers use the penetrability of x rays to view hidden features of printed circuit boards. For example, with X ray inspection, PCB components such as BGA and high-density IC connections can be checked for misalignment and other problems.

More importantly, x ray inspection allows quality control technicians to view solder joints and inspect them for flaws. This helps catch defects that would otherwise go unnoticed due to their hidden nature. Here is how PCB X ray inspection works:

  • Heavy or high-density materials absorb x-rays more than lighter materials.
  • On a PCB, the solder alloy carries heavier materials. These absorb more x-rays than components and other parts of the board.
  • When X rays are shone on a sample PCB, therefore, only a few will go through the soldered parts
  • A detector, with the help of special software, utilizes the varied absorption of the x rays to create a picture of the PCB; much like it does when scanning bones.
  • The soldered areas appear dark, while other parts appear bright. This image is cast on a computer screen.
  • When a defect is present, a discrepancy in the light and dark areas will appear, such as shadows in the pins and pads.
  • The inspecting technician views this image to find defective soldered areas or components, thereby ensuring high-quality production.
X ray PCB machine and its constituent components
X ray PCB machine and its constituent components
Resource: https://www.mdpi.com

PCB X Ray Machine

An X ray machine for PCB inspection is made up of these major parts; the scanning head (also called X ray tube), sample platform, the drive system, and the detection unit, and. The scanning head emits x-rays, while the sample platform holds the PCB that’s being scanned.

The detection unit catches the x rays that pass through the circuit board, using their differential absorption levels, creates a live image of the board and its components. PCB X ray machines can produce a 2D or 3D representation of the board.

2D PCB X Ray Inspection

2D inspection using X rays produces a single-axis live feed of the circuit board. When tilted (by moving the detection unit), angled imaging is achieved. 2D inspection is a quicker method to use. It’s also less expensive. However, for a more detailed analysis, 3D is often a better option.

3D PCB X Ray Inspection

In this mode, a PCB X ray inspection machine combines 2D slices to produce a 3D structure. Although slower and more costly, this method provides a more detailed view of the sample. As a result, the inspecting technician can see the entire PCB stack up at once, and identify defects more easily.

Using BGA x ray inspection equipment
Using BGA x ray inspection equipment
Resource: https://www.researchgate.net

PCB X Ray Inspection

Using an x ray machine for PCB inspection allows a view of features that cannot be seen using conventional means, such as microscopes and AOI (automated visual inspection). With this technique, the PCB is checked for both component and soldering problems.

X Ray Inspection for Electronic Components

SMT devices, such BGAs and QFN or complex ICs, can be difficult to inspect using the visual method, as their connections are always underneath the package and virtually inaccessible. This necessitates the use of x rays. SMT X ray inspection typically helps catch these flaws:

  • Missing components
  • Misaligned components
  • Damaged components
  • Wrong component value
  • Lifted pins or leads

Component defects, such as misalignment, usually appear as a mismatch of pin and pad shadows. Other flaws are similarly detected; by looking at the bright and dark areas and identifying visible discrepancies.

X Ray Solder joint Inspection

X rays are easily absorbed by the heavy materials of the solder alloy. As a result, the solder appears darker than the other portions of the board, including components and the core or substrate. During PCB X ray inspection, the dark hue of solder helps catch the following problems:

  • Solder voids
  • Solder bridges
  • Insufficient solder
  • Excess solder
  • Solder quality
  • Solder shorts

For example, a less darkened (gray) bridge between solder joints can mean a solder short, while a brighter spot inside the soldered part can be a void. Insufficient soldering is also identified as a bright spot of line, among other flaws.

PCB x ray inspection image
PCB x ray inspection image
Resource: https://hackaday.com

PCB X Ray Advantages

In the electronic industry, its standard practice to use an x ray machine for PCB inspection. This is useful when it comes to critical circuits boards, such as those used in medical, military and aerospace applications. PCB x ray inspection, when compared to visual inspection and other examination methods, offers several unique benefits.

  • No Damage: X ray inspection is non-invasive and non-destruction. No parts of the board or its assembled components are damaged or destroyed during the process.
  • Hidden Flaws: unlike the visual method, x ray PCB inspection can help view parts of the board that are hidden from view, such as inner layers or BGA and IC connections.
  • Flexible Examination: with ability to create either 2D or 3D view of the PCB structure, x ray inspection provides the flexibility needed to analyze different type of circuit boards as per the required levels of visualization.
  • Higher Accuracy: X ray PCB inspection offers greater accuracy when compared to other techniques such as the use of magnifying pieces or microscopes and AOI. It gives a clear analysis of the solder joints, component connections, and other important information needed to ensure a thorough inspection.
  • Failure Analysis: using the information of x ray inspection, engineers can analyze defects and effectively find their root causes. That means better quality PCBs based on practical improvements.

Conclusion

PCB X ray inspection is an effective technique that can help visualize hidden defects for easier identification. By integrating it in the production line, PCB manufacturers can ensure the high quality production of printed circuit board assemblies. PCB inspection when using x rays also offers greater flexibility, as the board can be viewed in either 2D or 3D modes, or with the use of different levels of the rays.

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