الفهرس 
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Abstract
The elimination of radionuclides heavy metals and other poisonous elements besidesinvestigating the microstructure, thermal and mechanical properties lead-free solders that used for the microelectronics industry are a worldwide significant target. In this sense, it is useful to identify the natural radioactive nuclides heavy metal and other poisonous trace elements (Macro and micro element contents) levels at various concentrations such as; Au-196, Th-227, Ag-110M, Fe-59, Zn-65, Rb-89, Rh-106M, Bi-207, Cs-137, Eu-154, Sb-126, Eu-152, Co-56, Co-58, Co-60 and K-40. If this lead-free solder contains high concentrations of natural radioactive nuclides, workers handling them might be exposed to significant levels of radiation. Therefore, it is important to determine the radioactive nuclides in this solder to protect the working, the safety rules and some precautions should be applied for those working in this field.: The natural radionuclides (238U, 232Th and 40K) and their daughter products contents of Sn-6.5Zn solders have been estimated in gamma-ray spectrometry and their levels using 100% Hyper-Pure Germanium (HPGe) detector. The mean activities due to radionuclides, heavy metal and other poisonous elements were measured.The microstructure was examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS). The basic features of thermal properties of the selected solder alloys have been studied by using the differential scanning calorimetry (DSC). Tensile stress-strain test were performed at constant temperatures 25, 70 and 110 °C .
The results of this assessment obtained by the gamma-ray spectroscopic analysis, have indicated the presence of relatively high levels of natural radioactivity, heavy metal and other poisonous elements. This implies that a comprehensive study should be conducted to protect theworking from the high dose in this field.
Microstructural investigation shows that hypoeutectic Sn–6.5Zn alloy composed of β-Sn-rich phase and α-Zn fiber. No intermetallic compounds (IMCs) with various Bi contents were observed in solder matrix. The fiber spacing was remarkably increased and its diameter decreased after 1.0 wt.%Bi addition. Moreover, a small bright Bi precipitates were detected with increasing Bi content to 3.0 wt. The experimental results showed that addition of Bi could effectively reduce both the onset and eutectic temperatures, while the amount of undercooling less than 1.0 °Cwas recorded. A comparison of tensile strength of Sn–6.5Zn with Bi-containing solders indicated that the tensile strength of Bi-containing solders was enhanced to about 200%, although the ductility was slightly decreased. The higher strength was contributed by the solid solution effect and precipitations hardening of Bi atoms or particles, which can remarkably modify the microstructure, blocks the dislocation motion and increases the tensile strength of Bi-containing solders.