The objective of the current research was the examination of microstructural features in lead-free solders and solder joints with incorporated particles. To improve the mechanical properties of solder joints the solders microstructures were modified by the addition of particles. Fine, evenly distributed particles can restrict grain growth, dislocation motion and crack propagation so as to strengthen the solder against creep and fatigue. The composite solders were produced by mechanical mixing and in-situ methods. Sn-3.5Ag and Sn-4.0Ag-0.5Cu solders were matrix alloys and Cu, Ni particles as well as Cu-coated glass spheres for reinforcement. The amounts of reinforcements were in the range of 1-15 vol. %. A comparison is made between the composites microstructures when various types, sizes and volume fractions of particles and different matrix alloys were used. The assessment criteria were the chemical reactions between the particles and the matrix, tendency for agglomeration and uniformity of the particles distribution. Simulation of the aging process was carried out to investigate the changes in the interfacial intermetallic layers with aging time.

The microstructures were investigated using SEM with an integrated EDX system and EPMA. Topographic images of the areas at the solder - substrate interface were derived from the AFM examinations. Tensile tests were conducted both for the bulk non-composite and the composite solder joints. The fractography of the tensile tested specimens is presented.