What is PCB X-Ray Inspection ?
The X-ray inspection is part of the process control in our quality management system, Not only detect issues in SMT, but the analysis of an X-Ray image can help to determine the root cause of a given defect, such as insufficient solder paste, skewed part placement, or improper reflow soldering profile.
Rayming invest 3D Automatic X-Ray Inspection (AXI) machines to detect QFN,FBGA and other lead-less package types components, our BGA x-ray inpection services is now included by default on any Rayming quotations including the assembly of lead-less packages, The X-ray images can help us also to analyse root causes of detective boards, such as excessive solder, lack of solder, mechanical failures of components, cracks, but also to detect hidden problems inside the PCB, such as bad metallisation in the holes or via cracks, This technique contributes greatly to Rayming’s Quality Management strategy for complex components.
X-ray inspection is a non-destructive test method used to reveal internal structure and detect defects in printed circuit board (PCB) assemblies. This article provides an overview of PCB X-ray technology covering:
- How X-ray inspection works
- Defect types detected
- 2D vs 3D X-ray
- Pros and cons of the technology
- X-ray vs other test methods
- When to use X-ray in the process flow
- Implementing X-ray inspection
Understanding X-ray inspection capabilities and limitations is important for quality management in PCB manufacturing and assembly.
How X-ray Inspection Works
2、Print circuit boards fabrication inspection: Welding line offset bridging, open circuit.
3、SMT weldability inspection: Solder joints empty inspection and measurement.
4、Circuit line inspection: Open circuit, short circuit, defective or fault connection.
5、 Integrity inspection of solder ball in array package and chip covering packaging.
X-ray imaging uses short wavelength electromagnetic radiation to penetrate materials and reveal internal structure:
- X-rays produced by bombarding metal anode target
- Small focal spot for high resolution
- Voltages from 30 to 320 kV
- X-rays passing through board converted to visible light
- Captured by sensor and converted to digital data
- Software renders cross section image
- Computer aided detection finds defects
- Non-destructive, no sample preparation
- Reveals insides of packaged boards
- Detects defects other methods may miss
Defect Types Detected by X-ray
X-ray inspection can find various defects on and within PCB assemblies:
- Insufficient or excessive solder
- Solder voids
- Bridging under components
- Misaligned BGA balls
- Missing parts or wrong parts
- Shifted component position
- Skewed parts
- Incorrect insertion depth
- Pad cratering
- Lifted lands
- Plating voids
- Inner layer separation
- Buried broken traces
- Debris lodged within board
- Metallic contamination
2D vs 3D X-ray Inspection
- Single axis inspection
- Fast imaging for high throughput
- Limited to one viewing angle
- CT scan builds 3D model
- Multi-axis composite viewing
- More defect analysis capability
- Slower throughput speed
Pros and Cons of X-ray Inspection
- Detects hidden and subsurface defects
- Non-destructive testing
- Minimal sample preparation
- Analysis of packaged assemblies
- Costly equipment investment
- Safety procedures for radiation
- Lower throughput than optical inspection
- Skill required to interpret complex images
When to Use X-ray in the Process Flow
- Qualify and analyze components
- Detect defects in incoming boards
- Find hidden issues escaping normal testing
- Diagnose field failures
- Sample production assemblies
- Periodic process monitoring
High Value Products
X-ray vs Other PCB Inspection Methods
Vs Optical AOI
- AOI provides higher speed inline inspection
- X-ray reveals subsurface and hidden defects
Vs ICT/Flying Probe
- Electrical testing confirms circuit operation
- X-ray finds physical and structural flaws
- Both reveal internal structure
- X-ray is non-destructive
Implementing X-ray Inspection
Key considerations when applying X-ray inspection:
- Determine appropriate usage within process
- Select system technology – 2D, 3D, computed tomography
- Develop inspection routines for products
- Understand and interpret X-ray images
- Correlate findings with other test methods
- Institute safety procedures for radiation exposure
- Leverage for troubleshooting escapes and field returns
- Apply judiciously based on value vs. cost tradeoffs
X-ray inspection is a highly valuable but selectively used test method for revealing PCB assembly defects invisible to other techniques. When applied appropriately, X-ray provides unique subsurface inspection capabilities to enhance quality and reliability. Understanding the technology, interpreting results and correlating with other test data allows manufacturers to strategically leverage X-ray to improve process control.
Frequently Asked Questions
Here are some common questions about PCB X-ray inspection:
Q: What types of defects are best found by X-ray vs optical AOI?
X-ray is superior at finding subsurface flaws like voids and buried discontinuities while AOI excels at surface mount defects.
Q: Does X-ray inspection replace functional board testing?
Q: Can X-ray inspection be used on boards with BGAs and QFNs?
Yes, X-ray is an ideal technique for inspecting solder joints under BGAs. It can reveal bridging and head-in-pillow.
Q: What safety precautions are required for PCB X-ray inspection?
Radiation shielding, trained operators, safety interlocks, and procedures are necessary to protect staff from X-ray exposure.
Q: What is the difference between 2D and 3D X-ray inspection?
2D X-ray provides a single 2D view while 3D generates a 3D model through computed tomography scanning at multiple angles.