Abstract
Eutectic (Sn-3.5wt.%Ag) solder alloy is used in electronic circuits in which the creep property of the solder joints is essential for their applications. The study of creep, structure and thermal properties of three solder alloys (Sn-3.5wt.%Ag,Sn-3.5wt.%Ag-0.27wt.%Ti and Sn-3.5wt.Ag-0.27wt.%Cd) is characterized by the presence of (Ag3Sn-IMC) beside the phase (β-Sn). The microstructure parameters obtained from the X-ray analysis represented by, lattice parameters (a, c), the axial ratio (c/a), the residual strains (Δa/a0, Δc/c0) and peak height intensities (hkl) of some crystallographic planes are given. All parameters were found to be sensitive to the additions of (Ti or Cd), applied stresses and working temperatures in the range (298-373K).The crystallite size of the (211) reflection was found to increase from (61-132nm) with the additions and to decrease from (115-79nm) with the working temperatures. The morphological studies show a remarkable decrease in the size of (β-Sn) grains with the addition of (Cd) content which confirms the X-ray data. The obtained results show a decrease in melting temperature with the additions. The creep properties are notably improved by the addition of either (Ti) or (Cd). In order to reveal the creep characteristics such as stress exponent (n) and activation energy (Q), the tensile creep tests were performed within the temperature range (298-373K) at constant applied stress (17.27MPa). Based on the obtained stress exponents and activation energies, it is explained that the dominant deformation mechanism is dislocation climb over all temperature range.
Highlights
Over the past several decades Pb-Sn systems have been used for conventional solder process owing to combination of material properties and low cost [1,2,3,4]
In order to understand the thermal behaviors of the three original solder alloys (S1, S2, S3), differential thermal analyses (DTA) were carried out at heating rate of (10 oC/min.) in nitrogen flow atmosphere
It is assumed that the deformation is dominant by one creep mechanism in the whole stress range applied; the stress exponent can be taken as a constant at any given temperature
Summary
Over the past several decades Pb-Sn systems have been used for conventional solder process owing to combination of material properties and low cost [1,2,3,4]. SnAg alloys are being considered as one of the most favorable Pb-free solder system In this respect numerous studies have been devoted to the microstructure of SnAg solder alloys [11,12,13,14,15,16]. Since the properties of the binary Pb-free solders cannot fully meet the requirements for applications in electronic, packaging, additional alloying elements were added to improve the performance of these alloys. To provide an excellent performance improving solder microstructure, reducing IMC growth and increasing the drop life time, the coarse -Sn grain in the alloy solder become finer and uniform by the addition of trace Ti element [9]. In order to understand the thermo mechanical performance for electronic applications for the Sn–Ag solder alloys, the present study was developed to investigate the microstructure and mechanical behavior at (different stresses, temperatures and additions). Correlation between the microstructure and mechanical properties due to Cd or Ti additions were discussed
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