Effects of moisture absorption and temperature on the adhesion strength between Die Attach Film (DAF) and silicon die

Nowadays, Die Attach Film (DAF) has been commonly employed as a bonding media for thin die attach package and it has the tendency of replacing the normal die attach glues. Package miniaturization and die thickness reduction are the main drivers for DAF implementation in electronic packaging industry, especially in applications which require that the die thickness should be less than 100µm. However, there are still some potential reliability problems in the industry over the application of this new material, particularly the package crack issue which is directly related to material properties of DAF, such as the interfacial adhesion strength and the water absorption rate. In this study, die shear test is employed to determine the interfacial adhesion strength between DAF and silicon die. The samples with DAF and die were adhered on a copper leadframe with a load of 100±5g, heated to 100°C then held at 175°C for 5 hours. With this sample preparation method, the failure was found to occur at the DAF/Die interface during the die shear test, so that the adhesion strength between DAF and die can be well characterized. Measurements with different shear speeds were firstly conducted to find out the best conditions for this test. The effects of the moisture absorption and test temperature on the adhesion strength between DAF and Die were thereby studied. The results show that after being soaked at 85°C/85RH for 168 hours, the shear strength between the DAF and silicon die decrease from 110N to 21N. When the test temperature is 250°C, the shear stress is only 8% of that determined at 25°C. To understand these moisture absorption and temperature effects, the material properties of the DAF, including coefficient of thermal expansion, glass transition temperature, dynamic mechanical property, water absorption rate, were characterized. In summary, this study demonstrates the effect of moisture absorption and temperature on the adhesion strength between DAF and silicon die, which would provide useful and practical guidelines for industry for applications of DAF in different packages.