Effect of temperature and humidity conditioning on mold compound/copper interfacial fracture and the associated cohesive zone models

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Kwatra, Abhishek
Sitaraman, Suresh K.
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Microelectronic packages consist of multilayered structures made of dissimilar materials. Interfacial delamination is a common failure mechanism present in microelectronic packages due to the mismatch in the coefficient of thermal expansion (CTE) between different materials. Epoxy Mold Compound (EMC) on a copper leadframe is a common interface found in microelectronic packages. This work analyzes delamination at an EMC/Copper interface and how the interfacial fracture energy is affected by temperature and humidity conditioning. This work employs delamination experiments to determine how the temperature and humidity conditioning will influence the cohesive zone models (CZM). Starting with an EMC/Copper sample with a starter crack, this work uses a Double Cantilever Beam (DCB) test to obtain the critical load for crack propagation at various crack lengths. Using the experimental data in combination with numerical models, this work obtains the interfacial strain energy release rate (SERR) using fracture mechanics techniques. EMC/Copper samples are thermally aged and humidity conditioned for different conditions based on accelerated stress tests for packaged integrated circuits used by industry. DCB tests are run on these samples after conditioning and the SERR of the interface is obtained. Using the SERR, cohesive zone models are developed for as-received, thermally aged and moisture-conditioned samples. Thermal aging has shown to reduce interfacial adhesion at longer exposure times. Humidity conditioning has shown to reduce interfacial adhesion as well. Modified cohesive zone models reflect such changes in the interfacial fracture energy. The effect of a viscoelastic material model for the EMC is also incorporated in the interfacial fracture energy calculation. The modified CZM parameters, as obtained in this work, can be used to study the reliability of SOIC and other microelectronic packages under thermal aging and humidity conditioning.
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