Mechanical properties and microstruture of directionally solidified Sn-Ag-Cu solder alloys

• Grant number: 11/09343-2
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2011
• End date: June 30, 2012
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: José Eduardo Spinelli
• Grantee: Pedro Deghaid Pereira
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil

Abstract

The main alternative tin-based alloys, which can be used to replace the traditional Sn-Pb alloys, are Sn-Ag-Cu alloys. Some systems are candidate like Sn-Zn, Sn-Cu, Sn-Bi, Sn-In, etc. The lead is considered a hazardous substance which is enough to be restricted nowadays in markets like U.S. and Europe. The Sn-Ag-Cu alloys are characterized by low melting point and compatible mechanical properties. However, the appreciable Ag contents which are used to manufacture such alloys increase the costs of production of solder joints. In order to preprogram the soldering steps of electronic devices the control of solidification thermal parameters such as cooling rate and growth rate becomes essential. This control is important essentially in terms of some particular level of final mechanical strength which is desired to be achieved. The solidification thermal parameters can affect the as-cast structure regarding several features: size, morphology, distribution of dendrites, cells and intermetallics formation (Cu6Sn5 and Ag3Sn).Little is known about the influence of cooling rate and growth rate in the as-cast structure of Sn-Ag-Cu solder alloys. The unsteady-state directional solidification systems can be very useful in order to determine the development of the thermal solidification parameters along the solidified solder alloy. Such parameters can be correlated with microstructure parameters like cell spacing, dendritic spacing and interphase spacing. The area fractions of the intermetallic compounds (IMC´s) are also possible to be determined along the solidified casting. The aim of this study is to perform solidification experiments with Sn-Ag-Cu alloys in order to determine correlations between solidification parameters and microstructure features. Mechanical parameters such as microhardness profiles (HV), ultimate tensile strength, yield tensile strength and elongation may be determined and further correlated with microstructure.