Aug 15, 2019 
1. What is AXI?
AXI is short for automated X-ray inspection, it's one of the most commonly used approaches for defect inspection in PCB Assembly. Not only does AXI check the solder joints under components, but it also reveals many defects in solder joints that may not be visible by the ordinary optical inspection equipment.
2. How Does AXI Work?
In order to effectively inspect the PCB Assembly’s quality, three conditions are required for AXI:
First, X-ray is a must:
Unlike automated optical inspection (AOI), automated X-ray inspection (AXI) uses
X-rays as its light source, instead of visible light, and utilize its penetrating ability.
Second, a PCB of different density or thickness:
The X-ray penetrating ability means that when a beam of X-rays passes through a PCB, different materials of the board absorb different amounts of X-rays according to their density, atomic number and thickness.
Usually, materials made of heavier elements absorb more X-rays and are easier imaged, such as solder paste, while materials made of lighter elements are more transparent to X-rays.
The third thing is imaging.
The remaining X-rays after penetrating the material must undergo the process of "receiving" and "imaging" to form an X-ray image with contrast that can be understood by human eyes.
Now we get a basic knowledge of AXI, but what is it used for?
3. Applicable & Benefits
Applicable
Generally speaking, AXI is used to inspect ICs (integrated circuits) with packages such as BGA, CSP, QFN and flip chips, where the solder joints are hidden.
Benefits
By AXI, PCB assembly providers are able to inspect the internal quality of PCBA non-destructively:
- locate short circuits on BGA, CSP, QFN and flip chip
- detect voids in solder joints (BGA, CSP, QFN, QFP and flip chip)
- determine displacements of components
- examine semiconductors (wire bonds, die alignment)
- check solder joints
A board seeming to be fine actually has the problems of insufficient solder and solder bridge.
Therefore, the customers can enjoy:
- 100% tested boards
- An in-depth inspection in the early stage such as prototype, to avoid expensive production errors
- Decreased risk of returns
- Reduction of a potential recall quantity
4. AXI Working Processes (Offline, by Elecrow)
4.1 Initialize the AXI machine
4.2 Put the boards into the operation platform
4.3 Starts the inspection
4.4 Automatic BGA inspection
4.5 Finish the inspection and take out the board
5. X-Ray Inspection as a Free Service
Above all, AXI is such a powerful tool that utilized in electronics PCB manufacturing/PCB assembly, and Elecrow takes it as a free service for our PCBA customers based on our persistence to quality.
For more about PCB Assembly service:
https://www.elecrow.com/pcb-assembly.html
Or contact us: service@elecrow.com
