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Potted Assembly Interfacial Reliability Under Inclined 25000g Mechanical Shock
This study investigates the time and temperature-dependent evolution of interfacial fracture toughness in four distinct potting compounds for printed circuit boards (PCBs). The investigation focuses on the evolution of the interfacial fracture toughness at the potting material-PCB interface.
Technical Paper
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Authored By:
Pradeep Lall, Aathi Pandurangan, Padmanava Choudhury
Auburn University
AL, USA
Ken Blecker
US Army CCDC-AC
NJ, USA
Summary
Electronics utilized in military defense applications are increasingly reliant on commercial off-the-shelf electronics. These applications subject electronics to extreme environments, including high temperatures and high g acceleration loads during transportation, storage, or handling. Given the critical nature of these applications, it is crucial to understand the survivability, failure mechanisms, and the effectiveness of supplemental restraints such as potting materials in reducing the likelihood of failure.
Currently, there is a lack of information regarding interfacial damage thresholds needed for predictive modeling and the impact of sustained high temperatures on interfacial potting failure. This study aims to measure potting material interfacial fracture toughness after exposure to high temperatures for up to 1 year, assess the effect of mode mixity using CNF and ENF measurements, and develop and validate high-g mechanical shock models. The potting/PCB interfaces have been exposed to high-temperature exposures at 100C and 150C. A circular printed circuit board assembled with fine-pitch electronic packages and multilayer ceramic chip capacitors has been potted and tested under high G shock loads.
The fracture toughness parameters have been used to calculate the cohesive zone parameters at the interface. Additionally, the effect of shock orientation on failure propensity under 30-degree and 60-degree shock orientation has been examined. To predict interface and interconnect failure, a model has been developed and validated with experimental data acquired from high-speed imaging and digital image correlation for measurement of out-of-plane deformation and strains.
Conclusions
This study investigates the time and temperature-dependent evolution of interfacial fracture toughness in four distinct potting compounds for printed circuit boards (PCBs). The investigation focuses on the evolution of the interfacial fracture toughness at the potting material-PCB interface over a range of aging durations at elevated temperatures at 100°C and 150°C from 30-360 days. This aging profile allows for a detailed assessment of the interfacial properties between the potting material and the PCB over extended time scales.
Potting A and D showcase a gradual decline in interfacial fracture toughness over time, suggesting progressive interfacial degradation. Potting B exhibits a more pronounced decrease in these parameters, indicating a significantly faster degradation process. Delamination due to purely thermal aging was observed solely at the Potting B interface after 180 days, highlighting its vulnerability to high-temperature conditions. Potting C, characterized by its higher compliance, exhibits an ability to dissipate energy from bending loads, effectively protecting the interface from damage.
This attribute makes it a potential candidate for low-temperature applications with high mechanical loading where energy absorption is crucial. However, even Potting C shows signs of interfacial delamination after prolonged aging 180 days at 100°C and 120 days at 150°C, indicating limitations in its long-term stable performance. In contrast, potting D shows the most stable behavior and minimal degradation over aging. The findings highlight the importance of considering both material properties and operating conditions when selecting a potting compound.
Cohesive zone modeling (CZM) has been used to predict interfacial delamination in potting-PCB assemblies under various aging and loading conditions. By determining key cohesive parameters for each testing condition and validating them against experimental data, the model can accurately capture the onset and progression of interfacial failure. The extracted cohesive parameters are unique to each potting-PCB interface.
This study further demonstrates the predictive capabilities of the validated CZM by simulating interfacial fracture in a high-g shock assembly. The inclined high-g shock experiments provided crucial validation data, confirming the model's ability to accurately capture the effects of aging and its influence on delamination behavior. Notably, the model successfully predicted the observed changes in delamination behavior for aged Potting C/PCB assemblies.
Initially Published in the SMTA Proceedings
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