In high-reliability industries such as aerospace, automotive, and aviation, ensuring the structural integrity of electronic components is essential for safe and reliable operation. Interfacial defects such as delamination may significantly compromise device performance and long-term reliability if not properly detected and characterised.

Non-destructive inspection techniques such as Scanning Acoustic Microscopy (C-SAM) are widely used for detecting internal defects. However, their effectiveness may be limited when inspecting devices with complex geometries or irregular internal structures.

This article highlights the importance of Scanning Electron Microscopy (SEM) as a strategic tool for confirming, characterising, and understanding microstructural defects that may remain undetected using acoustic inspection methods. A case study involving the inspection of electronic devices illustrates the complementary role of SEM in high-reliability quality control and failure investigation processes.

Electronic devices used in aerospace systems, automotive electronics, and avionics applications must meet extremely demanding reliability requirements. These systems operate under harsh environmental conditions including:

• Severe thermal cycling
• Mechanical vibration
• Humidity exposure
• Vacuum environments
• Radiation
• Long-term mechanical and thermomechanical stress

Under such conditions, internal structural defects such as delamination between critical interfaces can lead to progressive degradation and eventual device failure.

Potential consequences of undetected delamination include:

• Increased thermal resistance
• Localized stress concentration
• Degradation of the die attach interface
• Accelerated fatigue mechanisms
• Catastrophic electrical failure

For this reason, advanced quality assurance strategies rely on a combination of non-destructive inspection methods and high-resolution microstructural characterization techniques.

Among these techniques, Scanning Electron Microscopy (SEM) plays a key role in providing detailed insights into the integrity of internal interfaces.

Scanning Acoustic Microscopy (C-SAM) is widely used as a primary non-destructive inspection technique for detecting internal defects in semiconductor packages and electronic assemblies.

The technique is particularly effective in identifying:

Scattering of Ultrasonic Waves on Curved Interfaces in Acoustic Inspection

C-SAM reveals no anomalies in the die attach (paddle)

Subsequent destructive analysis using cross-sectioning combined with Scanning Electron Microscopy revealed the presence of a delamination at the interface between the paddle and the anode die attach.

Interestingly, this delamination had not been previously detected during the C-SAM inspection.

The absence of acoustic detection was attributed to the curved geometry of the paddle surface. This geometry causes dispersion of the ultrasonic waves during acoustic inspection, preventing sufficient energy from being reflected back to the transducer.

As a consequence, the acoustic signal did not generate enough contrast to reveal the presence of the interfacial defect.

SEM imaging of the cross-section provided clear confirmation of the delamination and allowed detailed visualisation of the interfacial separation.

This observation highlights an important limitation of acoustic inspection techniques when evaluating devices with non-planar internal structures.

SEM inspection reveals anomalies in the die attach (paddle/die attach).

Scanning Electron Microscopy offers several advantages that make it an essential tool in the quality control and reliability assessment of electronic devices.

In order to determine whether the observed delamination represents an isolated defect or a potential reliability concern affecting additional components, the inspected devices will undergo temperature cycling testing.

Temperature cycling is an environmental stress test commonly used to evaluate the robustness of electronic assemblies under repeated thermal expansion and contraction.

This type of testing is particularly relevant for devices intended for aerospace, automotive, and aviation applications, where components are frequently exposed to significant thermal gradients during operation.

The test will subject the devices to controlled thermal cycling between defined temperature limits, enabling evaluation of possible defect evolution mechanisms such as:

After completion of the temperature cycling test, the components will be re-inspected using C-SAM. When necessary, additional destructive analysis using cross-sectioning and SEM will be performed to evaluate any structural changes.

This approach will allow investigators to determine whether the observed delamination corresponds to:

• A localised manufacturing anomaly affecting only specific devices, or
• A structural weakness that may propagate under thermomechanical stress conditions.

Scanning Electron Microscopy represents a critical tool in the quality control and reliability evaluation of electronic devices designed for high-reliability applications.

The case presented in this article demonstrates that although non-destructive inspection techniques such as C-SAM are highly effective for initial defect screening, their detection capability may be limited in structures featuring complex or curved geometries.

In the investigated device, the dispersion of ultrasonic waves caused by the curved paddle surface prevented the acoustic detection of an interfacial delamination. However, destructive cross-section analysis combined with SEM imaging successfully confirmed the presence of the defect and enabled detailed microstructural characterization.

SEM provides significant advantages in this context, including:

• High spatial resolution for detecting microstructural defects
• Detailed morphological characterization of critical interfaces
• Identification of failure mechanisms
• Support for root cause analysis and reliability investigations

To further evaluate the reliability impact of the detected defect, the components will undergo temperature cycling testing. Post-test inspection using C-SAM and SEM will allow assessment of defect evolution and determination of whether the observed delamination represents an isolated anomaly or a potential reliability concern.

In industries where operational reliability is essential and failure is not an option, the integration of non-destructive inspection techniques with destructive microstructural analysis and environmental stress testing provides a robust and comprehensive strategy for ensuring device integrity and long-term performance.