Saki 3Xi Series 3D-CT Automated X-ray Inspection System
Conventional X-ray inspection techniques
There are many x-ray inspection techniques, such as laminography, tomosynthesis, and oblique CT.
All have achieved only limited success in inline volume production, typically imposing a trade-off between cycle time, inspection capabilities, and accuracy. Saki’s Planar CT technology (Fig.1) has high potential to break through this trade-off.
Saki’s planar CT technology
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.
Fig.1 Concept of Planar CT technology
Comparison between Saki’s Planar CT technology and tomosynthesis
The tomogram acquired by Saki’s Planar CT technology shows much higher definition than images acquired through conventional tomosynthesis.
Fig. Comparison between the images taken by Saki’s Planar CT image (Top) and tomosynthesis (Bottom)
Flexible configurations for diverse needs
Our portfolio of X-ray inspection systems caters for diverse market demands and application requirements, and includes:
– High-powered (200 kV) x-ray machine for internal inspection of semiconductors and power modules such as IGBT, MOSFET, or SiC inverters
– Open-tube type x-ray machine for high-definition inspection
– Closed-tube type (130 kV) x-ray machine for PCB inspection
Unique rigid gantry structure maximizes repeatability of high-definition inspection
The platform hardware must have high positioning accuracy and a rigid structure to enable consistently accurate, advanced inline inspection, operating for long periods in high-volume production.The linear motor drives the stage directly to ensure stable positioning accuracy. In addition, a linear scale on the Z axis of X-ray tube ensures high reproducibility even when the resolution is considerably changed according to the field of view.
Full-Memory Technology ensures ease of use and supports advanced functionality
The unique rigid gantry structure and warpage adjustment, which leverage our expertise in 2D-AOI, combine to acquire seamless 3D images of whole substrates, which are then stored in the memory. This 3D full-screen storing function serves also for traceability.
Precision inspection using slices of images recreated by the CT reconstruction operation
S3D inspection is performed using slices of images acquired by CT reconstruction operation for inspection. As mentioned above, the challenge when reconstructing CT images for 3D inspection is the heavy computation required, which typically demands high-speed processing. Our unique solution realizes high-speed 3D inspection suitable for high-volume inline production, producing high-quality images for all types of components. For example, when inspecting the solder joints of gull-wing leads, our system accurately reproduces the fillet shape. To detect defects such as poor wetting, PASS or FAIL can be classified using the back-fillet position, height, and angle information.
Fig. 3D depiction of solder fillet
Evolution of X-ray inspection
High-definition 3D inspection using slices of images is the most reliable way to detect very small voids (Fig.2) that can occur anywhere in the object. Head-in-pillow defects (Fig.3) occurring in solder balls are difficult to detect using conventional 3D inspection, because they have varied defect shapes. However, shape inspection using Saki’s unique algorithm and high-definition 3D images significantly improves inspection capability.
Fig.2 Void in solder balls Fig.3 HiP in solder balls
Compliant with IPC standards
According to IPC standard (Class3), the de facto standard of today’s electronics industry, the height of solder wetting of the gull wing back fillet is defined as the criteria for PASS or FAIL. Demand for back fillet inspection based on the IPC standard is set to increase in the electronics market.
The IPC standard defines many other PASS/FAIL criteria that require accurate assessment of solder shape and volume, such as filling of through-holes (Fig.4) and the characteristics of flip-chip micro-bumps as well as solder joints of Package on Package (PoP) assemblies and power modules.
Fig.4 Through-hole solder
Saki’s X-ray inspection machines for diverse needs
Our proprietary software, closed tube type (130 kV) x-ray machine for PCB inspection, high-powered (200 kV) x-ray machine for semiconductors and power modules, and open-tube type x-ray machine for high definition deliver scalable solutions that fulfil the diverse needs of the X-ray inspection market.