Saki's Automated X-ray Inspection (AXI) Technology

True 3D X-ray inspection is another Saki first. Saki has revolutionized AXI with its Planar Computed Tomography (PCT) technology. It consists of a high-resolution detector and a new CT calculation method for printed circuit board assembly (PCBA) inspection. These improvements provide much faster throughput compared with previous X-ray machine models and has set a new standard for PCBA inspection.

True 3D with Image Reconstruction

Planar Computed Tomography (PCT) is a unique technology to reconstruct the plane of an object. It captures multiple diagonal transmission images from various directions using a micro-focus X-ray tube and reconstructs horizontal sectional images by computerized tomography. In Saki's AXI scanning method, the detector moves parallel with the planar object against the X-ray source. There is no rotational axis, so each diagonal image does not rotate around an axis. The machine can always obtain diagonal images from any direction with the same magnification. Therefore, the system is capable of generating high quality sectional images while also maintaining good separation in the Z direction.

Most so-called "3D" X-ray systems have really been 2.5D because they work on the basis of deconstruction, where they capture an image and have to remove the images from the underside of the board. Saki's system works on the basis of reconstruction. Saki's very high resolution PCT technology is an extension of CT scanners used in the medical field and was developed in-house by Saki engineers and scientists. The automated inspection process completely separates the top and bottom-side images of the board so images are not affected by back-side mounting. The technology utilizes a high-resolution image composed from 200 imaging slices acquired through the board, solder joints, and components, whereas other AXI machines use only about five slices for imaging.

Head-in-Pillow Inspection

Detecting poor wetting of solder is an essential function of AOI and SPI machines. However, head-in-pillow defects that occur with BGA solder joints cannot be captured with AOI machines. Even with AXI, head-in-pillow are the most difficult defects to detect. Saki's 3D AXI systems, using Saki's 3D computed planar technology, can detect any head-in-pillow defect, in real time, and in 3D.

Inspection and Measurement

Saki's BF AXI system offers a programmable resolution from 13–30 microns. Reconstruction of images is done on-the-fly, for every solder joint, creating 3D data for the entire sample. Defects are identified and classified, including 100% of head-in-pillow defects, voids, and dry joints. This results in best-in-class Cpk and gage repeatability and reproducibility, which is particularly critical in aerospace, medical, automotive, and other applications where failure is not an option.

Field of View Images

Planar Computed Tomography image processing is based on capturing the entire field of view (FOV). Saki's BF-3D AXI machines automatically create continuous images with 3D data collection. They allow a user to generate and manage inspection data with line scanning technology, the same technology that originated with Saki on its AOI systems. Having one seamless image, even in areas with large ICs and connectors, saves time and provides clearer images, because it's not necessary to perform a separate operation to stitch the images together. The X-Y resolution of Saki's AXI systems is 13 to 30µm, and is programmable in 1µm increments.

In substrate inspection, the boundary lines of each FOV are automatically connected. With Saki's system, even if one component encroaches on 2 viewing areas, programming and automatic inspection can be accomplished without any boundary line influence. This is a key function for easily setting up the FOV.

Stable, Reliable System

One of the keys to Saki's stable, reliable results is the system's one-ton granite base-plate gantry. Saki developed this highly rigid, two-layer gantry structure to maintain precise control of the detector and inspection object in very high-speed environments. Mounting both the sample and detector stages on both sides of the granite maintains straightness, flatness, and parallelism at a high level. Each axis is driven directly by a linear motor to achieve highly defined performance, positioning control, and excellent repeatability, even at high speed. This robust mechanism provides high reliability, with long-term stability, to ensure the integrity of the Planar CT's high-resolution inspection results.

High-Speed Planar Reconstruction Engine

Saki's AXI machines incorporate multiple cores of CPUs and GPUs for its high-speed planar CT reconstruction operation. Parallel processing of CPUs and GPUs has been highly optimized to shorten operation time to meet inline operation requirements.

In pass/fail analysis, the fault point is displayed in 3D in real time, so even an unskilled operator can determine areas with and without defects. Saki can provide this real-time 3D display technology because of Saki's proprietary 3D reconfiguration technology. In addition, images are stored in designated hard disk drives, so the image can be checked after the product is shipped.

X-ray Tube Box Provides Safety and Efficiency

Saki BF 3D AXI machines are built so that the box containing the X-ray tube has lead shielding inside it and the X-ray source mounted in it. The box has a shutter for shielding purposes and conveyor shutters, both at the entrance to the box for transporting the PCB into the chamber and at the exit for removing the inspected PCB. When loading and unloading the PCBs in automatic operation mode, the X-ray tube shutter is closed and the conveyor shutter is opened. During the scanning process, the X-ray tube shutter is opened and the conveyor shutter is closed. This keeps the intensity of the X-ray stable and X-ray source ramp-up time is not necessary. Consequently, this contributes to a stabile inspection environment, a faster process, a safer procedure, and longer life for the X-ray source.

Stable X-ray Source


Saki's high definition X-ray inspection BF-X2 machines use an open-tube type X-ray system that separates a target from the X-ray tube in a way that insulates it and directly measures the electron beams reaching the target. By doing so, the intensity of the X-rays from the X-ray tube can be directly controlled. This approach stabilizes the system and enables the micro-focus to capture high definition X-ray images, even during inline automatic inspection.


The BF-X3 is equipped with a 130kV closed X-ray tube. This 16W high-output tube, with its very small focal point, enables the BF-X3 to acquire the best high-definition images of any machine on the market. High reliability ensures a long operating life of the tubes.

While open X-ray tubes provide the advantage of a small focal spot with a high-resolution image, they are prone to instability of the X-ray intensity. Saki overcomes this issue by using a special target material and by directly controlling the target current, rather than the tube current. These features provide very stable and accurate X-ray intensity with a safe environment, even for prolonged periods of operation.

Zinc Filter Protection

A large X-ray dose can cause damage, not only to the human body, but also to high density electronic devices. There are several physical factors that damage the devices, but the most significant factor is the photoelectric effect. This effect is dominant in the soft X-ray wave range, for example, below a couple of 10kV energy areas. Zinc effectively absorbs these soft X-rays, while at the same time allowing to pass the high-energy X-rays that are less damaging to electrical devices, yet which are necessary for machines to perform CT analysis. Saki's AXI machines are equipped with a zinc filter that absorbs approximately 94% of the X-ray dose and keeps possible damage to electronic devices at a minimum.

Saki's AXI systems meet the highest safety standards

Saki's AXI systems keep X-ray emissions at a stable and safe level. They are able to start inspection quickly, due to the three shutters located at the PCB entrance, PCB exit, and X-ray emission site. These shutters allow quick inspection by eliminating the need to turn off the X-ray source during board transfer in and transfer out of the machine. The X-ray leakage dose is less than 0.5 μSv/h, thereby allowing an operator to work 40 hours per week/2,000 hours per year,* safely and securely. The system meets rigid European (CE) standards.

* The time is calculated according to dosage constraints in public exposure (1 mSv per year) indicated in the 2007 recommendations of the ICRP.