The selection and acquisition of an X-ray inspection system requires an extensive amount of product research. Each system has ‘value’ within a defined application, ranging from a basic system requiring extensive operator intervention and interpretation of results, to a fully automated system or systems installed in a tier-one electronic manufacturing production line requiring minimal operator support. X-ray inspection confirms that the soldering process was properly executed during assembly. It is used to find solder bridges (shorts), missing or undersized solder joints (voids), misalignments, and open solder joints. To perform these diagnostic tests, the general setup of a microfocus or nanofocus ® system should include a manipulation or sample table and an image collection device such as an image intensifier or digital detector. The sample table (platform)’s platform design and construction must avoid or dampen vibration to eliminate diminished image sharpness and should enable sample positioning at micrometer precision. Systems under evaluation must be configured to limit the radiation exposure and not damage sensitive ICs. Operating systems capable of providing low-dose emission options to reduce the accumulated exposure to the components are of extreme value.The most salient difference in X-ray inspection systems, however, is in the inspection methodology they employ.


Customers have a choice of both 2-D imaging systems, in which the system inspects the target board from a fixed, top-down view, 2-D with Oblique View with Highest Magnification (OVHM), in which an open tube source provides a wider irradiation angle of the board, and 3-D imaging systems, in which the X-ray source and detector move and capture multiple images that are then compiled to create the 3-D image. Both types of systems use similar image and board rotation, providing oblique views of voids and other misshapen solder balls. 3-D magnification, however, is limited to 2 to 10X, whereas the top-down alignment employed by 2-D systems allows for magnification in the 200 to 400X range.


In addition to the dimensional capabilities of an X-ray inspection system’s imaging system, current technology includes digital detectors, which utilize Complementary Metal-Oxide Semiconductors to provide better, less distorted images with far superior contrast resolutions. This capability is especially valuable for imaging low contrast objects, such as those encountered in adhesives inspection. Digital detectors are especially valuable in conducting lead-free analysis, due to their ability to image contrasts between lead-free and eutectic tin-lead solders. Because of the great differential in magnification capability, 2-D imaging systems are sufficient for most types of X-ray inspection. There are exceptions, however. For instance, the inspection of two-sided boards, the configuration of which demand multiple imaging rather then the fixed, top-down image capturing capability of 2-D imaging, requires 3-D imaging. Similarly, open solder joints normally require 3- D (or 2-D with OVHM) imaging to locate gaps in the solder joint and identify irregular solder mass shapes produced by insufficient wetting of the pad. Finally, to accurately inspect smaller solder joints, such as those found in Fine Ball Grid Arrays (FBGAs), μBGA®a, CSPs, and Flip Chips, the sample table must be tilted. To avoid false positives due to the drop in magnification and long distances separating the solder joints from the X-ray source as the platform tilts, 3-D and 2-D with OVHM imaging systems should be used.

Phoenix X-Ray Systems has recently installed a 3-D X-ray Tomography System at the American Competitiveness Institute. The system provides dedicated reconstruction and imaging processing software for small samples down to approximately 100 mm in diameter. Other system features include image resolution down to 1 μm voxel, (short for Volume Pixel, the smallest distinguishable box-shaped part of a 3-dimensional image) 100-fold maximum magnification, precise dimensional measurements of samples, and 3-D visualization in sectional cuts and slices. In addition, system can be run in 2D mode without modification and provides fast and accurate data acquisition. For additional information, or to arrange for a demonstration of the Phoenix 3-D X-ray Tomography System located at ACI, please contact Bob Berta at 610-362-1200 ext 253 or via e-mail at rberta@aciusa.org.