Introduced by Ryan Flaherty, SMTA’s director of communications, and with a welcome from Ankan Mitra, president of SMTA’s India Chapter, Keith Bryant, chairman of the SMTA Europe, gave an extremely informative update on recent advances in X-ray inspection technology and its applications in the electronics industry.
Speaking as an engineer with 30 years’ experience in electronics manufacturing, and having spent the last decade as an industry expert in high-technology X-ray and AOI systems, Bryant shared his knowledge of the theoretical and practical aspects of X-ray inspection in a fascinating webinar presented on behalf of his SMTA colleagues in Bangalore, India.
Although X-ray technology had been used in medical diagnosis for over 100 years—and more recently in the inspection of engineering components—it was only since the 1980s that equipment specific to the electronics industry had been developed, although early versions were basically modifications of medical systems. Over the last 10 years, the increasing complexity of electronic components and assemblies—with drivers, such as reduced feature size, bottom-termination packages, and three-dimensional stacking—brought many challenges in inspection and failure analysis that had accelerated the development of the current generation of high-resolution X-ray imaging technologies.
Bryant explained how to select the right configuration of the X-ray tube and detector to suit a particular electronics inspection application. There were two basic types of X-ray tube: the traditional “closed” tube and the more recently available “open” tube. Closed tubes were assembled, evacuated, and sealed for life during manufacturing. The open tube was capable of better resolution and higher magnification, and it was possible to replace the target and filament. A vacuum was maintained in service by a pumping system. There have been recent improvements in filament life and target material, enabling higher power and improved reliability. And software is used to monitor and stabilise tube output and ensure consistent image quality.
Traditional analogue detector systems had been superceded, initially by digital image intensifiers, and more recently by purpose-built, mega-pixel, digital flat-panel detectors with true X-ray intensity control that are capable of producing stable and repeatable real-time images with an increased number of greyscale levels to enable greater detail to be observed. Bryant showed examples illustrating some of the results that could be achieved with current high-end, flat-panel detector technology. There was no distortion, and fine cracks were easily visible, and real-time digital imaging enabled on-the-fly inspection of LEDs.
Further, Bryant discussed the attributes of mega-pixel images on UHD monitor screens and described some of the image-enhancement features currently available, which improved contrast and made it possible to clearly identify features smaller than one micron. In most cases, with good software and automated functions, it no longer required a highly-qualified technician to operate the X-ray inspection system.
Bryant went on to consider developments beyond two-dimensional X-ray systems and addressed advances in computed tomography (CT). He commented that because traditional cone-beam CT could only be used with very small sample sizes, it could not be classed as a non-destructive technique. But a recent development—oblique or inclined CT—was not destructive, so it could be used on large circuit boards and the images fully reconstructed into three-dimensional models. Bryant also showed examples of inclined CT for component-level inspection, where it could rapidly detect microscopic faults in devices at any position on an assembly. Present-day high-end X-ray systems were useful in detecting faults in LED assemblies, such as wire-bonding failures and die-attach voids.
At the other end of the scale, power-semiconductor devices—such as insulated-gate bipolar transistor modules, often housed in heavy X-ray absorbing metal packages—present challenges to X-ray inspection systems. Bryant demonstrated that inclined CT imaging of the die interfaces could reveal die placement issues and be effective in the void-area calculation.
This SMTA webinar provided a straightforward and logical insight into state-of-the-art X-ray inspection technology and capability in the electronics industry. Keith Bryant’s presentation was always clear and understandable, and he obviously enjoyed delivering the basic elements of his extensive knowledge to an appreciative audience.