Plastic integrated circuit packages can fail due to delamination between the interfaces of the different materials. The adhesion properties across the interface of the epoxy encapsulant and the substrate are important to package reliability. A series of button shear tests was conducted to evaluate the adhesion properties of Epoxy Molding Compounds (EMCs) on copper substrate. The interface was primarily studied with a range of EMC materials. With finite element analysis, the distortional strain energy density across the interface was calculated. The distortional strain energy density was found to have a linear relationship with the square of the shear force and the EMC's Young's Modulus. The results of the energy densities across the interface at different shear heights and shear angles...[ Read more ]

Plastic integrated circuit packages can fail due to delamination between the interfaces of the different materials. The adhesion properties across the interface of the epoxy encapsulant and the substrate are important to package reliability. A series of button shear tests was conducted to evaluate the adhesion properties of Epoxy Molding Compounds (EMCs) on copper substrate. The interface was primarily studied with a range of EMC materials. With finite element analysis, the distortional strain energy density across the interface was calculated. The distortional strain energy density was found to have a linear relationship with the square of the shear force and the EMC's Young's Modulus. The results of the energy densities across the interface at different shear heights and shear angles were also reviewed. Based on these observations, an adhesion phenomenon was found.

When packages are subjected to significant temperature changes during processing and qualification, the interfacial adhesion is critical to reliability. A btton shear test was conducted in a constant elevated temperature environment. The results showed that the ability of the interface to withstand mechanical and thermal stress was weaker when subjected to higher temperatures, especially for temperatures higher than the glass transition temperature.

The thermal cycling test is commonly applied for reliability qualification to determine the ability of components and interconnects to withstand mechanical stresses induced. However, the interfacial adhesion is not only affected by thermal cycling mechanical stresses, but also by chemical changes. Thermal oxidation of the copper surface, which is a chemical reaction process, is unavoidable. So, the last part of study is to investigate delamination between EMC and copper leadframe using the button shear test and the X-ray Photoelectron Spectroscopy (XPS) technique. The shear test was conducted on the sample after the thermal cycling in accordance with the JEDEC standard. A tiny copper oxide film is formed on the leadframe across the EMC-leadframe interface after molding. The oxide thickness did not play a role of adhesion in this case. However, cuprous oxide at the intact interfacial area is a critical factor of adhesion. The cuprous oxide was obtained by the chemical composition examined by the XPS technique after the shear test. The increase of the cuprous oxide content was found to be the cause of the enhancement of the interfacial adhesion at the initial phase of the thermal cycling test. A linear relationship between the cuprous oxide content and the adhesion force was found. In addition to the decrease of the cuprous oxide content, it is found that the degradation of interfacial adhesion is related to the decrease in modulus of EMC and the increase in PDMS content.

Interfacial adhesion is found to be highly related to the modulus of EMC and the influence of chemical content.