Microthermomechanical Analysis of Lead-Free SN-3.9AG-0.6CU Alloys; Part I: Viscoplastic Constitutive Properties
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MICROTHERMOMECHANICAL ANALYSIS OF LEAD-FREE SN-3.9AG-0.6CU ALLOYS; PART I : VISCOPLASTIC CONSTITUTIVE PROPERTIES 1 Peter Haswell , Abhijit Dasgupta CALCE Electronic Products and Systems Center University of Maryland, College Park, MD 20742 USA
ABSTRACT This is part I of a two-part paper on the mechanical behavior of lead-free solders. The constitutive properties of Sn3.9Ag0.6Cu lead-free alloy are presented and compared against baseline data from eutectic Sn63Pb37 solder. Monotonic, displacement-controlled and load-controlled tests are performed over various temperatures, strain rates and stresses using the thermo-mechanical-microstructural (TMM) test system. It is shown that the lead-free alloy exhibits creep strain rates that are from one to five orders of magnitude lower than the eutectic SnPb alloy, depending on the stress level and the homologous temperature.
the standard SnPb alloy. Several variations of the SnAgCu system are available, with silver and copper content varying by a few tenths of a percent. It is not believed that these small variations significantly affect measured mechanical properties, considering the variation typically found in constitutive and durability data. The test approach used in this work is presented in Haswell and Dasgupta [1999 and 2000]. Modifications and improvements to the original experimental test setup are presented here. The experimental test matrices for both the lead-free and the SnPb eutectic solder are presented, as well as the results of these tests. Finally, some comparisons between the two alloys are presented.
INTRODUCTION The coming legal restrictions on the use of lead in electronic products in the European Union and Japan have led to a search for a suitable lead-free replacement for the current standard Sn63Pb37 eutectic solder. This task is established with necessary acknowledgement of the continuing research involved in characterizing the Sn63Pb37 alloy, despite decades of dedicated research into its constitutive, durability and microstructural properties. The SnAgCu tertiary alloy system has emerged as a leading lead-free candidate solder for replacing the ubiquitous SnPb eutectic solder. With acceptable cost, availability, manufacturability and toxicity, it is the subject of various research efforts, most prominently the lead-free solder project of the National Electronics Manufacturing Initiative (NEMI). Among the other areas of knowledge required for the implementation of a new solder, besides those mentioned previously, are the material’s constitutive and durability properties. This paper concentrates on the creep constitutive properties of the SnAg3.9Cu0.6 alloy, with a comparison to 1
EXPERIMENTAL APPROACH The test apparatus used in this work is essentially the same as that used in Haswell and Dasgupta [1999, 2000]. Displacement is actuated by a lead-zirconate-titanate (PZT) piezoelectric stack and monitored closed-loop with a linear variable differential transducer (LVDT) with a displacement range of 100 µm and a resolution of ±10 nm. Load is monito
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