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May 18th, 2012
Sonoscan’s acoustic microscopes
Sonoscan is well known for its acoustic microimaging technology, which is widely used by the microelectronics industry to nondestructively detect defects within materials and assemblies.
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Socoscan"s Gen6 C-Mode scanning acoustic microscope
Socoscan's Gen6 C-Mode scanning acoustic microscope

Founded in 1974 by Larry Kessler, with headquarters in Elk Grove Village, Illinois, Sonoscan began by building ultrasound devices for the medical research community, but has since transitioned to working primarily with the microelectronics industry using its acoustic microimaging technology to nondestructively detect defects within materials and assemblies. At the hear t of Sonoscan is i ts acoust ic microimaging technology combined with a long history of strong innovation at its R&D labs, which are staffed by physicists.

“As a company, Sonoscan has grown up with the semiconductor industry. To help that growth occur, we focused on the science involved and opened a laboratory,” Kessler says. “Acoustic microscopy was a relatively new field and, at the very early stages, you could even say we were a solution looking for a problem. By the early 1990s our work became almost predominantly semiconductor related. As semiconductor technologies have changed over the years, we’ve transitioned with them—in terms of being able to see inside plastic encapsulated ICs to fi nd delaminations and defects
that could cause parts to fail later on.”

Companies working on the development of new technologies and new semiconductor devices or ICs frequently experience issues or problems of some sort and need to monitor a process. “Acoustic microimaging provides a nondestructive way to monitor a process, and companies often come in and use our labs to get the insight they need to solve their process issues,” says Kessler.

Acoustic microimaging technology

How does the technology work? Simply put: Sonoscan’s C-SAM® C-mode scanning acoustic microscope launches pulses of ultrasound into a material, which produces echoes that are reflected back from interfaces (homogeneous materials don’t echo). Material interfaces produce an echo that, in turn, gives a picture of what’s going on inside and reveals hidden fl aws before they lead to failures. Acoustic microscopes are capable of discovering tiny defects within materials and assemblies that can occur during manufacturing or environmental testing. Defects—including elaminations as thin as 100 Å—can typically be identified and analyzed more effectively using acoustic microimaging than with other nondestructive inspection methods such as x-ray and infrared imaging.
Acoustic microscopy is highly sensitive to the elastic properties of the material it travels through and can be used to isolate material property variations and measure material density, porosity, inclusions, cracks, and voids. And, increasingly important, it can be used to assess thermal, impact, and fatigue damage. There are many applications for Sonoscan’s acoustic microimaging instruments.

The edge of a bonded pair of 12-inch wafers, and the small

disbonds (white spots) acoustic microimaging detected
between the two wafers (Courtesy of Sonoscan)

Applications include LEDs, MEMS, stacked die, fl ip chip, heat sinks, ceramics, single wafers, bonded wafers, power devices, etc.,” points out Thomas Adams, a consultant to Sonoscan. “All of these items have something inside that is desirable to be able to see.
For example, with fl ip chips it’s important to know that the inside doesn’t contain bubbles or anything else that can kill the device.”

Beyond the microelectronics realm, there are plenty of other applications for acoustic microimaging. For medical devices, it can answer questions like: Is a tube inside another tube really bonded, or is there some gas in there? And for jet engine applications, which require defect-free high performance bearing balls, acoustic microimaging can be used to determine if one of the balls used in a jet engine has a little flake or other damage. This is critical to detect, because as Adams explains, if there is a defect the entire bearing ball will disintegrate and cause all of the other balls to also disintegrate—causing catastrophic damage.

Transducer development and adaptation is another area in which Sonoscan specializes. The company can customize or adapt its transducers to customers’ specific applications to, for example, show defects very brightly and suppress all details they don’t want to see. Or, for other customers, produce images that show everything.
“When we customize the transducer in signal processing, the result is a custom fit for our customer’s needs,” explains Kessler. “We like to specialize and focus on the high tech involved, and to solve the difficult problems using ultrasound. At Sonoscan, we aren’t just ‘box builders.’”

What’s ahead?
With the electronics industry gravitating toward building more devices on silicon, and with systemon-chips becoming more common, Kessler expects to see more opportunities for the acoustic microimaging industry.
“Inspections of devices on silicon are a little more difficult than inspections on single devices. There’s a lot of signal and image analysis involved and, at this point, each customer appears to have their own unique problems in their processes. This will create challenges—and opportunities,” he says.
The work being done at Sonoscan’s laboratory often provides the company with a “heads-up” long-range view of what ’s coming next in the semiconductor field, so they can alter, redesign, and adapt their instrumentation, and also work on developing new solutions that the industry will need.

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