Visual inspection is often insufficient for verifying solder joints of traditional components. X-ray inspection is required as an alternative inspection method.
3D CT X-ray inspection is essential to detect voids and head-in-pillow (HiP) defects in solder joints. There is growing market demand for these capabilities.
In addition, increased global competition has pushed the demands for high-quality products even further, driving the need for full 3D CT X-ray inline inspection.

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.

Planar CT technology requires fewer projections to acquire the high-definition CT images of planar objects that are needed to perform high-precision inspection. The key challenge is to handle the heavy computational workload. BY developing advanced techniques to accelerate arithmetic processing, Saki has become the first manufacturer to deliver an inline Planar CT solution for X-ray inspection of PCBs. The 3Xi series X-ray inspection machine leverages Saki’s original CT computation software to realize high-speed, high-precision inspection.

Fig.1  Concept of Planar CT technology

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)

3D 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

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.

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