X-ray Inspection PCB Benefits: What You Need to Know

X-ray inspection PCB quality control has come a long way. Modern AXI machines provide a more comprehensive analysis, enabling thorough examinations. This article explains the benefits of X-ray inspection and how Venture uses the technology.

What is X-ray PCB Inspection?

PCB X-ray inspection involves using penetrating electromagnetic rays to inspect printed circuit boards. The rays provide a detailed view of the PCB and its components, detecting fabrication and assembly errors.

PCB X-ray inspection can be 2D, 2.5D, or 3D. Here’s what each method means and how it works.

• 2D Inspection – it quickly produces a 2D (top-down) view of the PCB but doesn’t provide a detailed picture of the components.
  
• 2.5D Inspection – involves tilting the sample to allow a better (angled) view of the hidden parts than when using 2D imaging.
  
• 3D Inspection – 3D X-ray PCB inspection, also known as computed tomography (CT), produces a 360-degree image, providing detailed information and enhancing defect identification.
  

One of X-ray inspection’s most significant attributes is the ability to see through materials, revealing hidden defects. Manufacturers use them to ensure PCBAS are error-free, especially if the boards are high-specification types.

How X-ray PCB Inspection Works

X-rays are extremely high-frequency electromagnetic waves. The rays can go through solid objects with minimal absorption. The rate depends on the material’s density, with denser materials (like lead-based solder) absorbing more rays than less dense materials (like FR-4).

Scientists utilize the absorption difference to visualize the internal structures of objects. This variation in absorption creates a contrast image. In a typical PCB X-ray, the dense metallic areas of solder joints and traces appear as lighter shapes, while the less dense laminate material appears darker. In a PCB, this variation helps check laminate structures and solder joints.

The typical AXI machine comprises an X-ray tube to generate the rays and a platform to hold the PCB. It also has a detector to sense the image and a processing unit to display the images and identify flaws.

• The operator prepares the sample and places it on the inspection platform
  
• They must also set the test parameters, such as exposure times
  
• The machine scans the board, generating images from various angles
  
• The detection unit processes and analyses the X-ray image, identifying surface and internal faults
  
• The operator documents the findings to help with the quality control process
  

X-ray Inspection PCB Defects

X-ray PCB inspection defects are typically component, soldering, or substrate errors. Each category presents a unique set of flaws to look for based on the specific PCB type and structure.

Component Defects

The AXI machine can detect component flaws that could cause the circuit board to malfunction or fail in the application world. The problems it identifies include the following:

• Improper alignment
  
• Position Shifting
  
• Lifted Ends
  
• Missing components
  
• Internal faults, such as cracks and other forms of damage
  

Soldering defects

Soldering defects are the most prevalent issues in AXI. They also cause the most risks when they go undetected, some of which compromise a circuit board’s safety. The machine identifies these assembly flaws.

• Solder bridges (unwanted connections of solder between two points)
  
• Tin Whiskers (microscopic crystalline growths from tin surfaces that can cause shorts)
  
• Opens (broken connections)
  
• Voids (empty spaces inside solder joints).
  
• Insufficient solder (solder that’s too little to create a reliable connection)
  
• Excess solder
  
• Parts with no solder
  

Substrate Defects

X-rays also penetrate the board to identify damage within the circuit board’s layers. The faults are impossible to visualize with the naked eye or optical cameras. They include those listed below:

• Layer delamination
  
• Internal cracks
  
• Misaligned or warped layers
  
• Broken or improperly formed traces
  
• Plated Through-Hole (PTH) barrel fill issues
  
• Internal voids or other faults like inclusions

Acceptance Criteria for X-ray SMD Component Inspection

X-ray inspection is particularly essential when checking SMD components, such as BGAs and QFNs. These parts mount to the board’s surface, creating hidden joints. The following are acceptance criteria when examining them.

• Assembled parts show correct alignment with their pads and in their correct positions
  
• Minimal component shift remains acceptable, provided the solder balls still make proper contact with their respective pads
  
• The leads and pads should show proper wetting
  
• Qualifying boards should not have solder bridges or lead protrusions
  
• The distance between solder balls must meet the specified electrical clearance
  
• The total area of voids is less than 20%-25% of the solder joint area, depending on the specific PCB
  

X-ray Inspection PCB Benefits

Using X-rays offers a broad range of benefits, making the process one of the most useful in PCB manufacturing. The following are key advantages that make the technology essential in circuit board quality control measures.

Non-destructive

AXI examination doesn’t destroy printed circuit boards and their mounted components, making it a safe testing procedure. This benefit results in reduced wastage and improved production efficiency, particularly when handling costly materials.

Increased Accuracy

AXI detection covers a broad range of defects, including component faults. This coverage makes it one of the most comprehensive tests in PCB manufacturing. It also visualizes tiny microscopic faults that the eyes or AOI wouldn’t recognize.

Hidden Fault Detection

X-rays can see inside materials, allowing a view of the board’s internal layers. They also enable quality control experts to examine the underside of SMD components. That includes inspecting hidden solder ball joints of BGAs and various other device packages.

Inspection Flexibility

You can use 2D or 3D imaging to match defect detection needs and budget. 2D is faster but less detailed in detecting anomalies. On the other hand, 3D is more thorough but slower and more costly.

The manufacturer chooses the technology to use based on various factors. They include circuit board type, possible defect types, assembled parts, and budget constraints.

X-ray PCB Inspection Use Cases

The effectiveness of X-ray inspection makes it crucial for checking High-Density Interconnect (HDI) and multilayer circuit boards. It’s also essential when the boards must meet specific standards, such as those outlined in IPC guidelines.

Circuit boards that require this type of inspection include those used in military, automotive, telecommunication, aerospace, and medical applications. These are high-reliability PCBs for critical applications.

Sometimes, manufacturers use X-ray inspections to inspect consumer electronics PCBAs. The boards are typically high-interconnect types with surface mount devices (SMDs).

The technology is also crucial when troubleshooting failed PCBAs, given the non-destructive and penetrative nature of X-rays. It identifies more defects than most other methods.

Conclusion

PCB X-ray inspection brings precision and accuracy to circuit board manufacturing and quality control processes. The technology can detect hidden flaws, allowing manufacturers to examine entire boards.

Venture is your go-to PCB manufacturer and assembler. We implement x-ray inspection to ensure no defect goes unnoticed, making your PCBs highly reliable.

Get in touch with us for more about our PCBA production process and testing services. We will be more than happy to help you actualize your project.