By Ron Iscoff, Editor
The makers of x-ray inspection systems are currently faced with a double-edged sword. On the one hand, their tools are finally making it out of pure research and into some production uses. On the other hand, however, the vendors themselves are seeing a future-and perhaps a fairly imminent-need to develop and build more powerful units with greater magnification and higher resolution. Certainly, x-ray imaging is nothing new. It's become commonplace since the 19th century, when Pierre and Marie Curie and Henri Becquerel discovered the amazing "radio-activity" produced by uranium. Now, while uses in medicine (and airport security) seem highly mundane, the semiconductor packaging industry is turning to it for inspection other machines can't offer. The unrestrained growth of new, exotic package types with ICs hardly imagined a decade ago has forced packagers to look for improved methods of failure analysis and fault detection. This is exactly where, x-ray toolmakers hope, their equipment will find a huge market.
Shrinking Microprocessor Feature Sizes Consider that computer microprocessor feature sizes are forecast to reach the 157nm scale for production use by next year, according to Fred Schlieper of Teradyne's Imaging Solutions Group in Poway, Calif. "This will make the use of system-on-chip feasible," he adds. Smaller IC package designs, he notes, "represent substantial testability challenges to the semiconductor and electronics manufacturing industries." Simply put, he explains, this will demand better performance from test and measurement equipment. A few next-generation advancements that will be sought out, Schlieper believes, include improved x-ray source and detector resolutions, advances in digital detector x-ray sensitivity and image acquisition. Increasing package complexity and decreasing chip feature sizes are driving the demand for higher resolution and imaging capability now offered only by open x-ray tubes, says Lance A. Scott, president/CEO of FeinFocus USA, Stamford, Conn. A broad range of package types-some fairly exotic, some rather pedestrian-drives the quest for higher voltage and power, according to Scott. These include, of course, stacked 3D packages, hermetically sealed opto parts and more robust heat sinks. Several other x-ray equipment makers agree with Scott that the higher resolutions demanded by CSPs and flip chips will swing the industry away from closed tubes to the more powerful open tubes. These offer both high resolution and greater magnification, points out Paul Walter, managing director of Dage Precision Industries, Fremont, Calif.
"The current range of open tubes offers sub-micron feature recognition and geometric magnifications up to 1400x-a major advantage over closed-tube configurations," says Walter. Systems will also become more visually flexible, according to several makers, with an enhanced ability to inspect at oblique angles. Oblique Angles "To determine the shape of the soldered ball joint, it is necessary to include inspection of the structure" at oblique angles, notes Nick Hadland, director of X-Tek, Tyngsboro, Mass. With some current systems, Hadland says, the sample can be placed at the point of interest at maximum magnification. The imaging unit then indexes through the oblique angle. Higher magnifications and robust image processors able to perform quick frame averaging and to measure, annotate and quickly save images and data in standard file formats are becoming increasingly useful, says Keith Ward of Glenbrook Tech-nologies, Randolph, N.J. While demand appears to be growing at one extreme for large, powerful systems with higher resolution and increased image magnification, X-Tek's Hadland says there is also a growing need for smaller systems.
Rework houses, researchers and smaller companies offer an expanding market for more compact systems, such as benchtop units, operating in real time in a cost-effective package, adds Hadland. Having said that systems will become more powerful, will they also become more difficult to operate?
Dage's Walter says that because many x-ray systems evolved from FA labs, they are complicated to use. "As x-ray moves from the lab to the production floor, the systems need to become more user-friendly. Produc-tion environments require simple operating systems and consistency of images." What's Next How do x-ray equipment makers determine what's next? Future requirements "tend to be application-driven," says David Lehmann, vice president of sales at Phoenix X-ray Systems, Camarillo, Calif. Lehmann says Phoenix's R&D team evaluates customer requests for possible ways to implement them. "For example," reports Lehmann, "after seeing our BGA analysis module, one device maker wanted to use it to measure the ball pitch and roundness of Tessera's µBGA packages." The company formulated the request into a spec, evaluated it for feasibility and distributed it in the next software release. Scott of FeinFocus says his company belongs to multiple industry groups. "We gather valuable guidance in working groups, steering committees, trade shows and presentations. "Our involvement with industry consortiums, such as APiA and SEMATECH," he says, "also yields excellent insight into future industry needs." Conclusion With x-ray inspection poised to leap from largely an R&D tool to a production-oriented capital-equipment buy, equipment sellers and their customers will face new challenges in keeping abreast of a rapidly expanding learning curve.
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