In high-reliability industries such as aerospace, automotive, and aviation, identifying and evaluating defects in electronic devices is critical to ensure operational reliability. In a previous study, the strategic role of Scanning Electron Microscopy (SEM) was demonstrated for confirming delamination that was not detected using acoustic inspection.

This follow-up study evaluates the stability and evolution of such defects under thermal stress. After subjecting devices to temperature cycling (20 cycles from −55 °C to +125 °C), C-SAM inspection revealed propagation of structural anomalies, including die surface delamination, cracks in the package, and delamination along interfaces. Cross-section and SEM analysis provided detailed characterisation of the defects, confirming their extent, mode of failure, and systematic occurrence across the lot, indicating a manufacturing-originated defect.

Ensuring the reliability of high-performance semiconductor devices requires not only the detection of defects but also understanding their stability under operational stress.

In the previous study, “Electron Microscopy for Ensuring the Integrity of Critical Devices” (Part I), SEM was demonstrated as a critical tool to confirm interfacial delaminations that were not detectable by C-SAM due to paddle geometry.

While Part I confirmed the presence of defects, a key question remained:
Are these defects stable under operational stress, or do they propagate under environmental conditions?

To answer this, the devices were subjected to temperature cycling (TC) and post-stress inspection.

Temperature cycling (−55 °C to +125 °C, 20 cycles) simulates the thermomechanical stresses experienced by electronic components during operation.

This testing exposes materials with mismatched coefficients of thermal expansion (CTE) to repeated expansion and contraction, which can:

• Propagate existing delaminations
• Initiate cracks along interfaces
• Accelerate degradation at the die attach or molding compound layers

Following TC, devices were screened using C-SAM, and representative units were selected for destructive analysis with cross-sectioning and SEM.

The cross-section analysis, combined with Scanning Electron Microscopy (SEM), provided a comprehensive evaluation of the defects detected after temperature cycling and allowed detailed insight into their nature, extent, and origin.

The analysis confirmed the presence of delamination corresponding to a true physical separation at the paddle / die attach (adhesive) interface. SEM observations showed that the separation is nearly complete across the interface, with only a localised bonding point remaining at the paddle transition area (paddle down region). Following temperature cycling, the separation increased, confirming that the defect propagates under thermomechanical stress.

In addition to the primary delamination, cracks and delamination were observed at the interface between the die surface and the molding compound, indicating secondary structural degradation induced by thermal cycling.

No other associated defects were detected:

The affected interfaces and failure modes were clearly identified:

• Adhesive failure at the paddle / die attach interface
• Interfacial separation between die and molding compound
• No cohesive failure within the attach itself

Importantly, inspection of the entire lot revealed that all devices exhibited similar defects, indicating that the delamination is not a localized anomaly but is systematic across the batch. This strongly suggests a manufacturing-related root cause, potentially associated with:

• Inadequate adhesive (attach) curing
• Process contamination
• Assembly or handling errors

The propagation of the defect after temperature cycling confirms that these manufacturing-induced delaminations are structurally significant and compromise reliability under thermomechanical stress.

While C-SAM remains a powerful screening technique for detecting internal anomalies, SEM provides critical insight into the microstructural mechanisms responsible for defect evolution.

In this investigation, SEM enabled:

These capabilities make SEM an indispensable tool in reliability investigations of high-performance electronic components.

As part of the final qualification flow, the devices will be subjected to additional stress testing, including reflow simulation.

This process replicates the thermal excursions experienced during PCB assembly and represents one of the most severe thermomechanical stress conditions in the device lifecycle. Rapid heating above solder reflow temperatures induces high strain rates and significant CTE mismatch between materials, often resulting in maximum stress concentration at critical interfaces such as die attach and molding compound boundaries.

Given the delamination behaviour observed after temperature cycling, reflow simulation is expected to be a critical step in assessing the ultimate robustness of the devices. In particular, it will allow evaluation of whether the previously identified interfacial weaknesses further propagate or lead to complete mechanical separation under assembly-like conditions.

The results of this final qualification stage will complete the reliability assessment, bridging the gap between environmental stress testing and real manufacturing conditions, and providing a definitive evaluation of device structural integrity.

For those interested in the full evolution of this analysis, the outcome of the reflow simulation and final qualification results will determine the ultimate failure behavior and closure of the study.

This study demonstrates a comprehensive failure analysis of delamination in high-reliability electronic devices using C-SAM, temperature cycling, cross-sectioning, and SEM.

Initial inspections identified interfacial delamination not fully captured by acoustic methods. Temperature cycling (−55 °C to +125 °C, 20 cycles) confirmed that these defects are unstable and propagate under thermomechanical stress, leading to additional degradation such as die surface delamination, package cracking, and interface separation.

SEM cross-section analysis confirmed adhesive failure at the paddle / die attach interface, with secondary interfacial damage at the die/molding compound boundary. The absence of voids or material defects indicates a systematic, process-related origin. The recurrence of similar failures across the lot further supports a manufacturing-related root cause.

Planned reflow simulation will provide the final assessment under the most severe assembly-related thermal stress, completing the reliability evaluation.

Overall, the results highlight the importance of combining non-destructive inspection, environmental stress testing, and microstructural analysis to accurately assess defect stability and prevent latent failures in high-reliability applications.