Thermomechanical Stress and Strain Distribution and Thermal Resistivity Correlation to Bondline Thickness of Ag Sinter

Abstract

Stress and strain energy distribution and thermal resistivity of diebonded Si dies were measured and correlated with varying bondline thickness of hybrid Ag sinter to define and optimize workable bondline thickness window. Thermomechanical simulations were done using carrier device with known PPF-plated Cu flange, Si die, epoxy mold compound and Ag sinter material properties. Principal stress, total strain energy density and interfacial stress distribution were obtained to check susceptibility to die crack, cohesive and adhesive failure respectively using Finite Element Analysis. On the other hand, thermal resistivity (Rth) per die section (Final Peak, Final Carrier, Driver Peak, and Driver Carrier) were measured across varying dry bondline thickness of 20, 40 and $60\mu \mathrm{m}$. Results reveal that maximum principal stress, strain energy and interfacial stress experienced on the die, die-attach, and die backside - die-attach interface are inversely proportional to the bondline thickness of Ag sinter which means lower bondline thickness are more susceptible to reliability failures. Moreover, thermal resistivity on all die sections dramatically increases with increasing bondline thickness and should be controlled within 20 to $60\mu \mathrm{m}$ thickness range.