SAKI's 3D CT X-ray Technology Enables Full Inspection of Inline Volume Production

By Yasuo Watabe, Saki Corporation


Recent dramatic progress in IT has removed the differences between developed and developing countries, driving manufacturing industry needs to correspond to increased global competition.

In other words, a more global production system has to be developed to manufacture high quality products, with shorter lead-times and low cost, to address the increased diversity in electrical product specifications.

To realize the above, the following are necessary:

  • A smart factory that enables mass customization
  • Maximizing production efficiency within the smart factory
  • Optimizing the global supply chain.

And, to have a smart factory, open innovation with diverse vendors is necessary.

An example of open innovation is an automated SMT line that consists of equipment from several vendors that operate using M2M communication. To achieve this, Saki Corporation, and other AOI machine vendors, are required to:

  • Optimize production equipment with a feed-back or feed-forward function to other equipment, and
  • Deliver high inspection accuracy, especially for solder joints, to ensure high-quality products.

This is necessary because, as can be seen in the smart phone, electronics are getting smaller, thinner, and more sophisticated, driving electrical components and semiconductor packages to be smaller, thinner, and denser.
With these changes in product parameters, 0201 (mm) ceramic capacitors, flip chip ball grid arrays (FCBGAs), package-on-package (PoP), and wafer level packages (WLP) are more prevalent on printed circuit boards (PCBs), requiring more accurate inspection capabilities. X-ray inspection is necessary to see the solder joint. 3D computed tomography (CT) X-ray inspection, in particular, has been successful in detecting voids and head-in-pillow (HiP) defects in solder balls, which have caused concern in the industry.

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.

The BF-X series automated 3D CT X-ray inspection machines

There are many x-ray inspection technologies, such as laminography, tomosynthesis, and oblique CT. Saki takes CT technology further with its Planar Computed Tomography (PCT) (Fig 1) that acquires high-quality CT images of planar objects using fewer projections. However, these methods are very limited for use as inline machines due to the length of inspection time. There is a trade-off between inspection time and accuracy. In CT, the reconstruction of the objects also slows down the process. To overcome this relation, Saki developed the BF-X series (Fig 2) inspection system, which utilizes Saki's proprietary software technology and PCT technology to achieve both high speed and high accuracy inspection.
Saki's BF-X series has machines to fit various market needs:

  • Closed tube type (130kv) x-ray machine for PCB inspection
  • High-powered open tube type (225kv) x-ray machine for IGBT power modules
  • Open tube type x-ray machine with high resolution for semiconductors.
Figure 1 Planner CT method (image)
Figure 2 BF-X Series

Saki's unique hardware realizes high-accuracy inspection

To maintain stable and accurate inspection results throughout the duration of high speed, high volume inline production, very stable and highly accurate positioning control and a highly rigid hardware construction are essential factors. To achieve this, Saki mounts the sample and the detector stages on the granite, so the process is not affected by thermal expansion or aging that can occur from long, continuous machine operation. It enables the machine to maintain straightness, flatness, and parallelism at a high level.

Each axis is driven directly by a linear motor to get high-definition performance of the positioning control and good repeatability at high speed. The z-axis of the x-ray tube has a linear scale that can maintain good repeatability even if the resolution is changed in every field of view (FOV). Also, a new conveyor system was developed that enables a 45% shorter takt time. Saki is improving its technology daily, without sacrificing machine quality.

Saki's unique software technology enables high-speed CT operation and highly accurate inspection

The BF-X 3D x-ray series operates by capturing hundreds of slices of images which are then recreated by the CT reconstruction operation. As mentioned above, the problem with the CT image reconstruction operation in 3D inspection is that it requires high-speed processing due to the large number of images captured during its operation. However, Saki's unique high-speed processing technology fully utilizes its GPU and CPU capabilities to enable high-speed 3D inspection with high image quality of all components.

For example, the BF-X series can reconstruct an accurate image of a fillet shape to inspect the fillet of the gull wing leads. Therefore, poor wetting solders, which are very difficult to detect by optical inspection, can be easily classified as PASS or FAIL, using the information for the back fillet position, height, and angle that was received from the accurately reconstructed image (Fig 3, 4, and 5).

Figure 3  3D image of Solder fillet

Figure 4  Fillet shape(Good)

Figure 5  Poor solder wetting
According to IPC standard (Class3), de facto standard of the electronics industry, the height of solder wetting of the gull wing back fillet is defined as the criteria for PASS or FAIL. Therefore, we believe the need for back fillet inspection based on the IPC standard will increase in the electronics market. In addition, because Saki's 3D automated x-ray machine takes hundreds of slices throughout the solder joint and then inspects them with high definition 3D, it can detect very small voids (Fig 6) that can occur anywhere.

Figure 6 – Void in Solder balls

Figure 7 – HiP in solder ball

Figure 8 – Through-holes in solder

Head-in-pillow defects (Fig 7) occurring in solder balls are the most difficult inspection items to find because they have varied defect shapes. However, Saki's 3D x-ray machine's high inspection capability, unique algorithm, and high definition 3D images identify almost all head-in-pillow defects.

There are many other defects that are defined in the IPC standard that are difficult to detect, such as the ratio of the amount of solder filling the through-holes (Fig 8), micro-bumps in flip chips, solder joints of PoPs, and power modules, such as insulated gate bipolar transistors (IGBT), that require solder inspection. And the need in the market to detect these defects is getting greater.

Saki Corporation's BF-X series lineup consists of both open tube x-ray machines with high resolution for semiconductors and closed-tube type (225kv) x-ray machines for IGBT power modules to accommodate these various market needs, and has developed its own unique software. We believe this will allow for scalability no matter the inspection target.

Future prospects

In 2020, 5G (5th generation mobile communication system) is planned to be serviced in, accelerating IoT with 5G's high capacity and ultra high speed network function. Everything will be connected to each other in real time, and various services, such as self-driving cars, are expected.

At the manufacturing site, automated inspection technology will gather sensor information from all equipment, analyze this large amount of data, give real-time feedback, and optimize production, not just in this one factory, but in factories connected globally.

With an improved communication infrastructure and IoT, IoT devices will be even smaller and reach high functionality quickly. Inspection needs will be more varied and advanced than ever. The role of 3D x-ray inspection will be even greater and more vital.

In response to the industry background outlined above, Saki Corporation established its own factory in Chiba, Japan to expand its x-ray machine production capacity. We will continue to improve our inspection machine capabilities to enhance communication and linkage with peripheral equipment and/or the host system, and provide a total inspection solution with our complete product lineup to correspond to market needs.

We are pleased to contribute to the realization of your smart factory.