Determination of Mechanical Properties of Differently Oriented Ã\x9f-Tin Crystals in Small Solder Joints and Small Tensile Specimens using EBSD and Nano Hardness Measurements

In modern electronics solder joints are mostly composed of a lead-free solder alloy and interfaces of tin, nickel/gold or copper at the component and the circuit board side. Mostly SAC (SnAgCu) - alloys will be used in electronic products with high tin content. In the course of design and development the volume of these solder joints decreases rapidly. With this the solder joint exists only of some - one to four - single tin crystals with eutectic parts, and the percentage of the intermediate compounds that grow at the interface of the component/circuit board and solder increases rapidly. The orientation of the anisotropic tin crystal and the intermetallic phases plays an important role concerning the reliability of a solder joint. However, very few information about their physical and mechanical properties is known in literature depending on their orientation. The orientation of the tin crystals was determined by EBSD measurements in cross sections of solder joints and tensile specimens. Micro/Nano hardness measurements and tensile tests of differently oriented beta-tin crystals in solder joints and small tensile test specimens were made to get information whether the grain orientation influences the mechanical behaviour as hardness, Yield strength and tensile strength. The nano hardness was determined by Vickers indentation. For example, the Vickers hardness of different oriented tin crystals - between [320] and [001] orientation - ranges between 16 and 28 VHN (0.16-0.28 GPa). The [001] oriented crystals show the highest hardness. A correlation to the other material parameters as Yield strength and tensile strength will be discussed using stress-strain diagrams of different SAC alloys.