Scanning Acoustic Microscopy (SAM) has become a critical non-destructive testing method for confirming high reliability in aerospace and defense applications by detecting hidden flaws and validating material integrity.

In aerospace and defense, the electronics and materials incorporated into satellites, aircraft, and defense platforms are expected to function in conditions that push the limits of materials science and engineering design. Unlike consumer-grade devices, which may tolerate minor faults, aerospace devices cannot afford a single unexpected failure, since mission success and human safety depend on consistent performance.

This principle forms the foundation of a high-reliability approach - an engineering philosophy focused on designing and manufacturing systems, components, and processes that must perform dependably under mission-critical or extreme conditions. Such conditions may include severe temperature fluctuations, intense mechanical shock and vibration, and corrosive environments.

Achieving high reliability in aerospace and defense requires the deliberate selection of specialized materials coupled with durability-focused design practices to ensure structural and electrical integrity when subjected to extreme stress.

To counter continuous vibration and sudden mechanical shocks, components are often housed in metal enclosures, and their materials are selected for their proven resistance to fatigue and cracking under dynamic loads. High-reliability components may also incorporate specialized coatings and corrosion-resistant alloys that protect against moisture, salt, and fuel vapors. To withstand prolonged mechanical and environmental stress, materials are layered and bonded in a way that helps prevent delamination and surface fractures.

However, even with the most advanced designs and high-performance materials, tiny flaws in electronic assemblies or structural components can trigger system-wide failure once in operation. Hidden defects such as microscopic voids in solder joints, delamination within composite structures, or cracks in semiconductor packages may remain undetected during fabrication. When subjected to the extremes of vibration, thermal cycling, or radiation, such flaws can compromise the entire system.

Testing is therefore an essential element of high reliability to ensure potential weaknesses are identified, functionality is verified, and systems demonstrate lasting dependability prior to deployment. This is where nondestructive evaluation methods become indispensable.

Ultrasonic NDT
Ultrasonic non-destructive testing (NDT) has long served as a core inspection method within the aerospace and defense sectors. This technique employs high-frequency sound waves to detect even the smallest defects in components or assemblies without inflicting any damage. By transmitting these sound waves into electronic materials and structures, ultrasonic inspection can expose hidden internal flaws that would not be visible through external examination alone.

Scanning Acoustic Microscopy (SAM) is a more specialized ultrasonic method that uses much higher frequencies, usually between 50 megahertz and several gigahertz.

"SAM extends defect detection to an entirely new scale: scans that were once limited to 500-micron flaws can now reach down to 50 microns, exposing imperfections that previously went undetected," says Hari Polu, President of PVA TePla OKOS, a Virginia-based manufacturer of SAM and industrial ultrasonic non-destructive (UT-NDT) systems.

Unlike conventional ultrasonic NDT, which is used to detect flaws in large components with complex shapes, SAM is designed to generate highly detailed acoustic images of microstructures and stacked flat layers.

"SAM's high-frequency operation delivers exceptional resolution at the micron or sub-micron level, a precision best suited for analyzing thin samples and layered microstructures," says Polu.

SAM Applications in Electronics and Metals
In the semiconductor and electronics industries, the need for non-destructive failure analysis and reliability testing is accelerating. As a result, SAM equipment has evolved and is now being used to detect subsurface flaws, dis-bonds, cracks, and other irregularities in these types of materials that constitute the "packaging" of semiconductor components.

Beyond the semiconductor components themselves, today's electronics products contain various specialty metals, alloys, plastics, and glass components. All semiconductor components need to be enclosed and packaged in consumer usable form factors. As a result, SAM equipment has evolved and is now being used to detect subsurface flaws, dis-bonds, cracks, and other irregularities in these types of materials that constitute the "packaging" of semiconductor components.

Today, the same rigor of quality testing and failure analysis is also being applied to validate the integrity of diffusion bonded metals. When bonding similar materials, bond strength can approach that of the base metal itself. For dissimilar materials, bond performance depends on the type of intermetallic compounds that form, the thickness of the intermetallic layer, and the presence of microscopic defects such as voids at the interface. To ensure the quality of the interface, materials engineers must analyze samples to validate the quality of the bond.

For both electronic and material testing, SAM operates by directing a focused beam of ultra-high-frequency sound from a transducer onto a tiny point on the target object. The sound is either scattered, absorbed, reflected, or transmitted as it passes through the material. By detecting the direction of scattered pulses and measuring their time of flight (TOF), the system determines the presence of a boundary or object and calculates its distance.

Three-dimensional images are created by scanning point by point and line by line on an object. Scan data is digitally captured and processed by special imaging software and filters to resolve a specific area of focus in either single or multiple layers. Specialists can analyze SAM images to detect and characterize device flaws such as cracks, delamination, inclusions and voids in bonding interfaces as well as evaluate soldering and other interface connections on PCBs.

As important as the mechanical aspects are when conducting a scan, the software is critical to improving the resolution and analyzing the information.

Multi-axis scan options enable A, B, and C-scans, contour following, off-line analysis, and virtual rescanning for composites, metals, and alloys, which result in highly accurate internal and external inspection for defects and thickness measurement via the inspection software. Various software modes can be simple and user friendly, advanced for detailed analysis, or automated for production scanning. An off-line analysis mode is also available for virtual scanning.

"PVA TePla OKOS decided early on to deliver a software-driven, ecosystem-based solution," explains Polu. The company's ODIS Acoustic Microscopy software supports a wide range of transducer frequencies from 500 KHz to 230 MHz.

These software capabilities not only expand SAM's functionality, but they also set the stage for tackling one of the industry's toughest demands: combining speed with resolution. A common challenge with other inspection systems is performing scans quickly enough to remove defective materials without sacrificing resolution. Fortunately, recent advancements in SAM technology have significantly improved throughput speeds and defect detectability, while maintaining image quality.

"While a conventional 5 MHz sensor could take 45 minutes to inspect a 10-inch square alloy, an advanced phased array [SAM] reduces that inspection time to five minutes with more granular detection of small impurities or defects," says Polu.

"Every company will eventually move towards this level of failure analysis because of the level of detection and precision required for specialty metals and materials," says Polu. "The cost advantages and time savings of Industrial SAM equipment make this possible."

From semiconductor packages to high-purity metals, SAM extends inspection to the finest details that conventional methods overlook. As aerospace and defense platforms continue to push the limits of performance, this level of testing is no longer optional—it is essential to ensuring reliability under the harshest conditions.

For more information, contact PVA TePla OKOS at ndt@pvatepla.com or visit www.pvatepla-okos.com. OKOS is a wholly owned subsidiary of PVA TePla AG, Germany.