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www.us-tech.com Building Versatility into High-Throughput X-Ray Inspection By Olaf Szarlan, Public Relations, Viscom AG
D inspection at high speed is just as important for automated X-ray inspection (AXI) as it is for automated optical inspection (AOI). With time-optimized image acquisition technologies and efficient handling, in-line X-ray performance is increasing. There is also the potential to automate manual X-ray inspection (MXI) processes. In the inspection of electronic assemblies,
3
especially for components with hidden solder joints such as BGA or QFN packages, AOI is insufficient. Random samples with MXI are another option, but this is not always the best solution. Where product safety plays an especially crucial role, particularly in the automotive area, a fast, thorough inspection of solder joints is needed. This calls for in-line, high-speed AXI. On these systems, throughput is determined by the inspected assembly handling, since a fully protected housing with mechanical gates is required.
Fast, Precise Change Viscom’s new in- and out-feed system
for AXI reduces the time to change assem- blies to less than four seconds. This hard- ware works with several PCBs in the system simultaneously and moves them in overlapping time slices. Because of the shortened paths, the corresponding switching of assemblies from one position to the next is extremely quick and precise. This reduction in handling time shortens the
idle time overhead of changing assemblies. Actual productive time is the pure analysis time, in which the images are captured and evaluated. Optimizing the analysis time can bring addi-
tional significant throughput gains. During pro- gram creation, time-consuming 3D inspection can be restricted to the components for which it is
Viscom offers a wide range of X-ray systems.
acquiring several views for 3D reconstruction. With the right settings, electronic assemblies can also be optimally represented in the 3D image from predefined perspectives. For structures generally arranged on a grid,
such as BGA balls, irregularly arranged acquisi- tion positions are recommended. Because of the resulting suppression of periodic structures, arti- facts can be largely eliminated, significantly improving the 3D results of the planar computed tomography (PCT). During the development and revision of an AXI system, it is best to lay out the overall 3D
absolutely necessary. Everywhere else, faster orthogonal and angled processes are used.
3D AXI Hardware Optimized solutions for fast image acquisi-
tion also have a positive effect on the analysis time. High-value linear motors, which ensure that flat panel detectors on a cross table (x/y table) can be moved quickly to the different positions, sharply cut image acquisition times for variably angled radiation penetration, especially when
inspection area with ample space, giving the user flexibility to select the acquisition angle. In addi- tion to larger penetration angles and different per- spectives, larger PCBs can be inspected. For high throughput, it is important to use a flat panel detector with as large a field of view as possible.
Variety of Options 3D reconstruction processes are central to
determining the quality of the 3D image. Besides simple and fast methods, such as the addition process, Viscom AXIs implement the FDK (Feldkamp, Davis, Kress) process. Dirk Nülle, managing AXI product developer at Viscom responsible for the new X7056-II 3D AXI says, “This special process of fil- tered rear projection delivers better slice image reconstructions, especially for BGAs. However, it does take somewhat more computation time.” For a user-friendly display and for
basic image improvement, there are aids that include contrast filters and grayscale value adaptation (gamma correction). For sagging PCBs, height correction can be
added to the inspection run. This is accomplished by a tool that adapts the individual inspection positions. The calculated sag model of the assem- bly is then applied for each inspection method. The inspection system software should be as
easy to operate as possible. Depending on the task, either inspection quality or cycle time is the priori- ty. “In our experience, at least nine views are neces- sary to realize 3D. Yet sometimes, it turns out more acquisitions are needed, depending on shadowing and on which components are in opposite positions on a PCB assembled on both sides,” says Nülle.
Continued on next page
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