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The magic of image reconstruction on-the-fly

3D planar computed X-ray tomography enables full inspection
The magic of image reconstruction on-the-fly

Recent progress in all areas of microelectronics, such as mobile devices or automotive gear, is driving manufacturing industry needs at a fast pace to correspond with the increased global competition. As a result, a global production system is being developed by Saki, which addresses the increased diverse specifications in electrical products. In an advanced manufacturing environment, AXI inspection is going to play an even bigger role for the detection of hidden failures that is currently not visible with the “classical” automated optical inspection.

Yasuo Watabe, Sales Promotion Group Leader, Saki Corporation

To achieve the production objectives of high quality, high reliability, shorter lead-times and lower cost, the following is required:

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

To run a smart factory, it is necessary to open innovation with diverse machine vendors. For example, an automated SMT line that consists of equipment, from several different vendors, that interact with each other by using M2M (machine-to-machine) communication. In such an environment, AOI equipment is an integral part of the process to be able to:

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

This is particularly necessary because, electronics are getting smaller, thinner, and ever more sophisticated, driving electrical components and semiconductor packages to be smaller, thinner, and denser. With changes in device parameters, 0201 ceramic capacitors, flip chip ball grid arrays (FCBGAs), package-on-package (PoP), and wafer level packages (WLP) are prevalent on printed circuit boards (PCBs), requiring a more accurate production technology, and inspection capabilities. For several years now, AOI has practically become a standard requirement in SMT high-volume lines, but this alone is no longer sufficient to ensure production quality and reliability. Therefore, AXI is needed to be able to see within the solder joints or under bottom terminated components (BTCs), such as the widely utilized QFN packages.

True 3D automated X-ray inspection

3D computed tomography (CT) X-ray inspection, in particular, has been successful in detecting defects that cause the most concern in the industry, such as voids under QFNs and head-in-pillow (HiP) defects in solder balls. However, global competition has pushed the demands for high-quality products even further, driving the need for full 3D CT X-ray in-line inspection. This uses X-rays to examine the features of assembled printed circuit boards, semiconductor packages, or power modules that are hidden from visual view and therefore cannot be captured by automated optical inspection, which uses visible light as its source.

Most X-ray systems use deconstruction, where they capture an image and have to then remove the images from the underside of the board. A true 3D X-ray system operates using reconstruction, where a high resolution planar computed tomography (PCT) technology is used. PCT is an extension of CT scanners used in the medical field. This automated AXI process completely separates the top and bottom-side images of the board so images are not affected by back-side mounting. It utilizes a high-resolution image composed of 200 imaging slices acquired from everything: through the board, solder joints, and components. Most other AXI technologies use less than 10 slices for imaging.

A true 3D system uses these slices to accurately reconstruct the shape of solder balls and fillets/meniscus to perform reliable solder inspection. It doesn’t just inspect, it combines the layers, measures components and features, determines placement variance and board or substrate warpage, and analyzes their internal structures for a true volumetric representation of continuous 3D images without joints. 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 HiP defects, voids, and dry joints, resulting in excellent Cpk and gage repeatability and reproducibility, which is particularly critical in aerospace, medical, automotive.

Role of AXI

AXI systems have to meet the needs of three basic market requirements:

1. Usually as part of the PCB assembly process after reflow for:

  • Solder ball joint inspection of BGAs
  • Solder joint inspection on the bottom side of QFNs (voiding)
  • Solder joint inspection for all parts; such as chips, connectors, and insert parts on the PCB

2. Semiconductor for:

  • High resolution inspection (down to 15 μm)
  • Void inspection of laser through-holes (LTH)
  • Flip chip bonding inspection
  • Package-on-package soldering inspection

3. Power modules for:

  • High power X-ray tubes (225 kV)
  • Void inspection inside the solder joints of insulated gate bipolar transistor (IGBT) modules

Automated 3D X-ray inspection limitations

Many X-ray inspection technologies, such as laminography, tomosynthesis, and oblique CT, are limited for in-line use because the time of inspection is too long, and there is a trade-off between inspection time and accuracy. In CT, the reconstruction of the objects slows down the process. PCT captures high-quality CT images of planar objects using fewer projections, and takes CT technology further, but the more slices the system takes, the more time it takes for the inspection process.

Unique hardware enables high-accuracy inspection

To overcome this trade-off, the company developed an AXI system which utilizes proprietary hardware and software, and PCT technology to achieve both high speed and accuracy inspection. To maintain results that are stable throughout the duration of high-speed, high-volume, in-line manufacturing production, it is essential to have a stable and accurate positioning control, as well as, a rigid hardware construction. To achieve this, the sample and detector stages are mounted on a granite base, so the process is not affected by thermal expansion, vibrations, or aging that can occur from long, continuous machine operation. The granite foundation is necessary for the machine to uphold a high level of straightness, flatness, and parallelism.

Each axis is directly driven by a linear motor to get high-definition performance, 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). Cycle time is reduced to maintain the speed, and a specially developed conveyor system enables a 45 % shorter processing time.

Software for high-speed 3D inspection

In some inspection operations, identifying every defect possible is not essential for proper functioning of the end-product. Fewer slices are needed, so the inspection process can be faster. However, for applications where failure is not an option, speeding the process by reducing the number of slices and images is not an option.

A proprietary software was developed with a unique processing technology that fully utilizes its GPU and CPU capabilities. It works in conjunction with PCT, taking images, and reconstructing of up to 200 slices through the solder joints, enabling high-speed, 3D inspection.

For example, an accurate image of a fillet (meniscus) shape can be reconstructed to enable inspection of the fillet of the gull wing leads. According to the IPC standard (Class 3), the de-facto standard of the electronics industry, the criteria to define the joint as ‘Pass’ or ‘Fail’ is the height of solder wetting of the gull wing back fillet. By using the information for the back-fillet position, the height, and angle that is received from the reconstructed image, poor wetting solders can be classified easily by the 3D AXI system, which would be difficult to detect by optical inspection. The company therefore believes that the need for back-fillet inspection will increase. In addition, because 3D automated X-ray takes hundreds of slices throughout the solder joint which are then inspected with high definition 3D, it can detect small voids that can occur anywhere, especially those hidden under QFN packages, later creating bigger issues in the reflow process. HiP defects that occur in solder balls are the most difficult to identify because of their varied defect shapes. With the combination of hardware, software, and special algorithms, almost all HiP defects, as well as, voiding, can be located.

Other defects defined in the IPC standard are the ratio of the amount of solder filling the through-holes (barrels), micro-bumps in flip chips, solder joints of PoPs, and power modules, such as insulated gate bipolar transistors, that require solder inspection. They are also difficult to inspect, but the need in the industry to detect these defects is getting greater.

Future prospects for AXI

In 2020, 5G, the 5th generation mobile communication system, is planned to be released, accelerating the IoT with 5G high capacity and ultra-high-speed 5G network functionality. Devices, reportedly, will be connected to each other in real time, and products, such as self-driving cars, which are already being tested, will probably see more widespread use.

At the manufacturing site, to maintain quality, reliability, and high-volume production, the Smart Factory/Industry 4.0 initiative is going to prevail. Automated inspection equipment will use innovative technology to collect sensor information from other equipment along the assembly line, then analyze this information and give real-time feedback. Not only will this optimize production for one factory, but also for several corporations that have their manufacturing plants connected globally. With an improved communication infrastructure and growth in IoT applications, devices will be even smaller and reach high functionality quicker. Inspection needs will become more advanced and varied. The role of 3D X-ray inspection is expected to grow and become more vital.

In a Smart Factory environment, AXI system capabilities are used to enhance communication and linkage with peripheral equipment and/or the host system. They become part of a total inspection solution that uses a complete lineup of 3D automated solder, 3D AOI, and 3D AXI systems that must correspond to production needs. Inspection and test equipment have to continue to evolve in order to accommodate demanding manufacturing and assembly challenges.

productronica, Booth A2.259

www.sakiglobal.com


Zusammenfassung Résumé Резюме

In der Fertigung der Mikrolektronik steigen die Anforderungen an die Präzision und Zuverlässigkeit stetig. Neben klassischen elektrischen Testprozessen haben sich AOI sowie AXI als wichtige Ergänzungen durchgesetzt. Die meisten AXI-Systeme arbeiten auf Basis von Bild-Dekonstruktion, wobei sie anschließend von den Aufnahmen erst die Board-Unterseite für eine deutlichere Sichtbarkeit entfernen. Echte 3D-AXI-Systeme auf Basis der planaren Computertomographie (PCT) hingegen rekonstruieren aus vielen Bildschnitten eine genaue und hochaufgelöste Abbildung. Saki hat diese Technik in ein global funktionierendes Fertigungssystem implementiert, um hohe Qualität- und Zuverlässigkeitsanforderungen zu erfüllen – und offeriert damit ein effizientes Werkzeug für die Realisierung von Smart-Factory und Industrie 4.0-Konzepten.

Dans la production de la microélectronique, les exigences de précision et de fiabilité augmentent continuellement. En plus des procédures d‘essai électriques classiques, AOI, ainsi qu‘AXI sont devenus des acquisitions importantes. La plupart des systèmes d’AXI fonctionnent sur la base de la déconstruction de l‘image, où les images de la partie inférieure de la carte de circuit imprimé sont retirées pour une visibilité plus claire. Les vrais systèmes 3D AXI basés sur la tomodensitométrie (TDM), cependant, reconstruisent une image à haute résolution et précise à partir de nombreuses tranches d‘imagerie. Saki a mis en œuvre cette technologie dans un système de fabrication mondiale pour répondre aux exigences de haute qualité et de fiabilité, en fournissant un outil efficace pour établir des concepts de Smart Factory et Industrie 4.0.

В сфере производства электроники постоянно повышаются требования к точности и надежности. Наряду с классическими процессами тестирования продукции широкое распространение получили системы оптического (AOI) и рентгенографического (AXI) контроля качества печатных плат. В основе большинства систем рентгенографического контроля лежит принцип деконструкции изображения, при котором со снимка удаляется сначала нижняя сторона платы для обеспечения лучшего обзора. В то же время в настоящих трехмерных системах рентгенографического контроля (3D AXI) применяется метод планарной компьютерной томографии (PCT), при котором на основании множества слоев реконструируется точное изображение в высоком разрешении. Компания Saki внедрила подобную технологию в производственные системы, эксплуатируемые по всему миру, с целью обеспечения высокого качества и надежности продукции – тем самым компания предлагает эффективный инструмент для реализации «умного» производства в рамках концепции Индустрии 4.0.

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Titelbild EPP EUROPE Electronics Production and Test 11
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11.2023
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