Agilent's x-ray systems take a new direction
Steve Scheiber, Contributing Technical Editor -- Test & Measurement World, 2/22/2008 9:45:00 AM
A staunch proponent of using laminography as a means to diagnose solder-joint defects on printed-circuit boards, Agilent Technologies has adopted a different technique in its newest creation, the Medalist x6000. The new system incorporates digital image reconstruction.
Laminography examines a series of "slices" at various z-values above the board surface. In each slice, the image content in the focal plane remains in focus, while anything above or below it is blurred. Software examines individual slices or constructs a three-dimensional image from the whole series when necessary. Traditionally, a z-axis motor shifts the whole stage containing the board in the z-direction to change the slice location. In contrast, the x6000 mathematically shifts in the z-axis without physically moving the board. I asked Jim Benson, product marketing engineer for the x6000, why the company is making this significant strategic shift.
"We have always believed that laminography has been very successful in delivering the full 3-D x-ray capabilities to meet customer requirements," commented Benson. "There were competing 3-D systems, but they could not match our performance. In many cases, that is still true. Ultimately, however, we decided we had taken that architecture as far as it could go.
"The market uses terms such as 2-D, 2.5-D, and 3-D to describe different x-ray approaches. 2-D can be described as a simple, straight-down x-ray at different magnification levels. 2.5-D incorporates a stage that rotates both source and detector, giving the user an angled view of the entire solder joint. Both of our 3-D solutions show you a slice of the joint, using angled views to generate that slice.
"One of the key reasons for moving to a digital imaging solution was to maximize throughput. We had already improved laminography's performance several times. We increased the rotation speed of the scintillator and the speed of the controllers, improved acceleration and deceleration of the board on the inspection stage, and reduced the time required for image analysis. Nevertheless, we knew that at some point we would reach a practical limit. We needed to make a transition when the component industry could provide effective cost/performance points for computation and detection. We investigated alternative architectures and made a significant investment in the new platform.
"Our new approach eliminates the time required for z-movement and board settling associated with laminography. We also eliminated the laser mapping that tells the laminographic tools the exact location of the board's surface. Laser surface mapping works quite well when it is properly set up, but its performance can be affected by the board's finish, color, slight component variations, and so on. Since the mapping is used for z-height determination and focus, these subtle variations can reduce inspection accuracy.
"We believe that we made the mapping step as reliable as the technology allowed. With the architecture of the x6000, however, we completely eliminated that step, improving test throughput, simplifying test-program development, reducing the system's parts count, improving call performance by ensuring that images are in focus, and improving system reliability. In addition, we brought the scintillating material closer to the detector, greatly improving the x-ray-to-light conversion efficiency, which also improves throughput.
"Overall we believe that the new system architecture addresses present and future inspection needs, just as laminography provided the best solution for printed-circuit-boards' prior generation."
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