What is AOI and AXI ?


Image taken with top-view cameraAOI stands for Automated Optical Inspection and the main principle of the various machines is similar:
A camera system with various illumination modes captures images of the unit under test (UUT, or device under test, DUT). One or more cameras capture these images from the top or from various angles.
Since the field of view (FOV) is limited and typically smaller than the actual UUT, AOI systems need to take a number of images per PCB. Beside the cameras and lenses, proper illumination is a very important part of the system. Based on the inspection task, different illumination types can be applied, such as spot light, diffuse light, side illumination or multi-colored illumination.


Image taken with angled-view camera After the images have been taken and stored, software analyzes the images and comes to an fail/pass result for each component and its features of interest. The result of this analysis is not as final as it would be with functional test or boundary scan test. Rather, the accuracy of the result depends on the state of the test program (how were the limits and thresholds defined, how many reference images are stored, and how accurate was the Teaching process), on manufacturing process quality and stability, and even on the lot size.


G IconVisit our product pages to see a variety of automated optical inspection (AOI) systems offered by GOEPEL.


AXI stands for Automated Optical X-Ray Inspection and the principles are similar to the AOI. In both cases images were taken of the field-of-interest and the software analyzes the results with the help of algorithms and stored images. The difference to AOI is, that in an AXI machine, x-rays emitted from the tube penetrate the PCB, the detector (fixed or moving) absorbs the x-rays and in combination with the software an x-ray image of the PCB can be created.

AXI systems use three different approaches: 2D (two-dimensional), 2.5D (two-and-a-half-dimensional), and 3D (three-dimensional) X-Ray inspection.

2D: The most simple technology is the 2D x-ray inspection, which has low test coverage because it wouldn't be able to inspect areas which are covered by other components. A typical inspection task would be the testing of solder joints of a BGA in case the part is not covered by its neighbors or no disturbing components are mounted on the other side of the PCB.

2D X-Ray Inspection

2.5 D: As a technology between 2D and 3D, 2.5 D helps to see hidden components by inspecting the area from different angles. The board or the detector are moved to accomplish that.

2.5D X-Ray Inspection

3D: Instead of taking only one picture from the top or customized angle-viewed images, a series of 2D projections are recorded. An algorithm reconstruct the layers and creates a result image without disturbing components. This image is now the base of further analysis such as short-, open- and void-inspection.

3D X-Ray Inspection

G IconGet details about GOEPEL's OptiCon X-Line 3D,
a high-speed, inline 3D automated x-ray inspection system
based on Tomosynthesis



What are the main benefits of automated inspection systems?

  • Automated inspection is faster than manual inspection
  • Automated inspection is more accurate than manual inspection
  • Automated inspection makes reliable and objective decisions
  • As a result, automated inspection will reduce cost and time while improving quality


What exactly can be tested with AOI/AXI ?


  • Check for presence, polarity and correct placement
  • Solder joint inspection
  • Lifted leads
  • Optical character recognition (OCR/OCV)
  • Color code reading and color verification
  • Barcode reading
  • Empty space test for lost parts, flux or solder remains
  • Solder paste inspection


  • Check for presence and correct placement
  • Quality of all solder joints
  • Shorts
  • Voids in all solder joints
  • Solder fill in THT solder joints



G IconReview some design-for-test guidelines
related to AOI and AXI.



GOEPEL offers a variety of seminars and training programs covering AOI/AXI and GOEPEL AOI and AXI systems. Both seminars and training classes can be customized to cover specific topics and can be provided on-site for a corporate audience. We also offer web based training through webinars and conference calls.
For a schedule of upcoming webinars, seminars, and training classes, visit our events page.


View this webinar recording to learn more about high-speed automated x-ray inspection combined with automated optical inspection ...

Or contact us to request further information.