Structural Size Effect on Mechanical Behavior of Intermetallic Material in Solder Joints: Experimental Investigation

Abstract

The elastic and plastic mechanical properties of intermetallic compound (IMC) phases of a leadfree Sn3.5Ag/Cusubstrate soldering system are investigated in different sized joints using nanoindentation. The specimens were prepared using solid–liquid interdiffusion soldering process with joint sizes ranging from 15 to 450 خ¼m. Solder joints were subjected to 360 آ°C soldering temperature for 20 min and then air cooled to room temperature to create testable IMCs thicknesses. Nanoindentation was used to extract the elastic and plastic properties of Cu6Sn5, Cu3Sn, and Ag3Sn IMCs and خ²tin and copper materials. Cu–Sn IMCs formed in specimens with smaller joint size show higher elastic modulus, hardness, and yield strength and lower work hardening exponent. This was attributed to the dimensional constraints associated with decreasing joint size and the local stresses developed during fabrication in joints with different sizes. Local elastic modulus and hardness of single grains of Cu6Sn5 were obtained using a combination of nanoindentation and electron backscatter diffraction (EBSD) techniques. Grains with caxis at a 45 deg angle with respect to the nanoindentation loading direction show higher elastic modulus (∼8.70% higher) and hardness (8.85% higher) compared to the grains that have a caxis that is almost perpendicular to the nanoindentation loading direction.