• Journal of Welding and Joining
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• v.16 no.3
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• pp.148-156
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• 1998

The purpose of this study is to investigate the characteristics of Pb-Free Sn-2%Ag-Bi solder alloys. The solder alloys used in this study is Sn-2%Ag-(3,5,7,9%) Bi It is examined that their properties such as melting range, wettability, microstructure, microhardness, and tensile property. The addition of Bi(3,5,7,9%) lowered the melting point of the solder and the melting range was 196~203$^{\circ}C$. The wettability of the solder as equal to that of Sn-37% Pb solder. The morphology of structure did not change largely by addition of Bi. But the structure of cellular dendrite of linear type displayed. The tensile strength of the solder was superior to that of Sn-37%Pb solder. But the elongation was inferior to that of Sn-37%Pb solder. The hardness of Sn-2%Ag solder was tow times and that of Sn-2%Ag-Bi solder was three times of that in Sn-37%Pb solder. But the effect of increment of Bi content did not change largely.

• Journal of the Korean institute of surface engineering
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• v.35 no.1
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• pp.11-16
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• 2002

As environmental concerns increasing, the electronics industry is focusing more attention on lead free solder alternatives. In this research, we have researched wettability of intermediate solder of Sn3Ag9Bi5In, which include In and Bi and has similar melting temperature to Sn37Pb eutectic solder. We investigated the wetting property of Sn3Ag9Bi5In. To estimate wettability of Sn3Ag9Bi5In solder on various substrates, the wettability of Sn3Ag9Bi5In solder on high-pure Cu-coupon was measured. Cu-coupon that plated Sn, Ni and Au/Ni and Si-wafer adsorbed Ni/Cu under bump metallurgy on one side. As a result, the wetting property of Sn3Ag9Bi5In solder is a little better than that of Sn37Pb and Sn3.5Ag.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.163-169
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• 2019

Sn-Pb solder alloys in electronics rapidly has been replaced to Pb free solder alloys because of various environmental regulations such as restriction of hazardous substances directive (RoHS), European Union waste electrical, waste electrical and electronic equipment (WEEE), registration evaluation authorization and of chemicals (REACH) etc. Because Sn58%Bi (in wt.%) solder alloy has low melting point and higher mechanical properties than that of Sn-Pb solder, it has been studied to manufacture electronic components. However, the reliability of Sn58%Bi solder could be lowered because of the brittleness of Bi element included in the solder alloy. Therefore, we observed the microstructures of Sn58%Bi composite solders with various contents of Sn-decorated multiwalled carbon nanotube (Sn-MWCNT) particles and evaluated bonding strength of the FR-4 components assembled with Sn58%Bi composite solder. Also, microstructures and bonding strengths of the Sn58%Bi composite solder joints were evaluated with the number of reflows from 1 to 7 times, respectively. Bonding strengths and fracture energies of the Sn58%Bi composite solder joints were measured by die shear test. Microstructures and fracture modes were observed with scanning electron microscope (SEM). Microstructures in the Sn58%Bi composite solder joints were finer than that of only Sn58%Bi solder joint. Bonding strength and fracture energy of Sn58%Bi composite solder including 0.1 wt.% of Sn-decorated MWCNT particles increased up to 20.4% and 15.4% at 5 times in reflow, respectively.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.97-103
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• 2014

Among various lead-free solders, the Sn-58Bi solders have been considered as a highly promising lead-free solders because of its low melting temperature and high tensile strength. However, Sn-58Bi solder has the poor ductility. To enhance the mechanical property of Sn-58Bi solder, epoxy-enhanced Sn-58Bi solders have been studied. This study compared the microstructures and the mechanical properties of Sn-58Bi solder and Sn-58Bi epoxy solder with aging treatment. The solders ball were formed on the printed circuit board (PCB) with organic solderability preservative (OSP) surface finish, and then the joints were aged at 85, 95, 105 and $115^{\circ}C$ for up to 100, 300, 500 and 1000 hours. The shear test was conducted to evaluate the mechanical property of the solder joints. $Cu_6Sn_5$ intermetallic compound (IMC) layer grew with increasing aging time and temperature. The IMC layer for the Sn-58Bi epoxy solder was thicker than that for the Sn-58Bi solder. According to result of shear test, the shear strength of Sn-58Bi epoxy solder was higher than that of Sn-58Bi solder and the shear strength decreased with increasing aging time.

• Journal of Welding and Joining
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• v.16 no.3
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• pp.157-166
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• 1998

Recently as environmental pollution caused by Pb has posed a serious threat to the global environment, the trend to regulate the usage of Pb in electronic industry is one the rise. Currently, the solder alloy with high Pb content, Sn-37%Pb, is utilized in the electronic assembly therefore, the objective of this study is to develop an alternative solder alloy for the existing Sn-37%Pb solder alloy. First thing, this work choosed Sn-5%Pb-1.5%Ag, Sn-5%Pb-1.5%Ag-x%Bi(x=1~5%) for candidate solder alloys, and examined their properties such as melting range, wettability, microhardness, tensile property, oxidation behavior and microstructure. Wettability was on the same level of Sn-37%Pb. Dissolution of Pb ion in Sn-5%Pb solder was 0.46ppm. This solder alloy revealed cellular dendrite microstructure $\beta$-Sn matrix, Pb-rich phase, Ag/Sn, and Cu/Sn Intermetallic compounds. The range of solidification temperature was within 3$0^{\circ}C$. Also these alloy displayed higher tensile strength and lower elongation than Sn-37%Pb. The resistance of oxidation in Sn-5%Pb-1.5%Ag solder alloy was superior to that of Sn-37%Pb solder alloy. But that of Sn-5%Pb-1.5%Ag-5%Bi solder alloy was equal to that of Sn-37%Pb solder alloy.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.2
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• pp.39-43
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• 2002

The eutectic solder Sn-37Pb and the lead free solder alloys with the compositions of Sn-0.7Cu, Sn-3.5Ag, Sn-3.5Ag-0.75Cu, Sn-2.0Ag-0.7Cu-3.0Bi were applied to the 48 BGA packages, and then it was discussed for the shear strength at the solder joints as the hardness and the composition of the small solder ball. As a result of experiments, the high degree of hardness with the displacement of 0.043 mm was obtained in Sn-2.0Ag-0.7Cu-3.0Bi. The shear strength of the lead free solder was higher than that of Sn-37Pb solder, and it can be obtained the maximum value of about 52% in Sn-2.0Ag-0.7Cu-3.0Bi.

• Transactions on Electrical and Electronic Materials
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• v.15 no.3
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• pp.155-158
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• 2014

The phase transformation of Sn-Pb-Bi solder for photovoltaic ribbon during soldering was studied using real-time synchrotron x-ray scattering. At room temperature, Sn and Pb crystal phases in the solder existed separately. By heating to $92^{\circ}C$, a new PbBi alloy crystal phase was formed, which grew further up to $160^{\circ}C$. The Sn crystal phase first started to melt at $160^{\circ}C$, and was mostly melted at $165^{\circ}C$. In contrast, the Pb and PbBi crystal phases started to melt at $165^{\circ}C$, and were mostly melted at $170^{\circ}C$. The useful result was obtained, that the solder's melting temperature decreased from $183^{\circ}C$ to $170^{\circ}C$ by addition of a small amount of Bi atoms to the eutectic Sn62-Pb38 (wt%) solder. Our study first revealed the detailed in-situ phase transformation of Sn-Pb-Bi solder during heating to the eutectic temperature. Considering the results of peel strength and hardness, adding 1 wt% of Bi atoms to the Sn62-Pb38 (wt%) solder produced an appropriate composition.

• Journal of Welding and Joining
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• v.23 no.3
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• pp.61-67
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• 2005

Since lead (Pb)-free solders for electronics have higher melting points than that of eutectic Sn-Pb solder, they need higher soldering temperatures. In order to decrease the soldering temperature we tried to coat Sn-Bi layer on $Sn-3.5\%Ag$ solder by electroplating, which applies the mechanism of transient liquid phase bonding to soldering. During heating Bi will diffuse into the $Sn-3.5\%Ag$ solder and this results in decreasing soldering temperature. As bonding samples, the 1608 capacitor electroplated with Sn, and PCB, its surface was finished with electroless-plated Ni/Au, were selected. The $Sn-95.7\%Bi$ coated Sn-3.5Ag was supplied as a solder between the capacitor and PCB land. The samples were reflowed at $220^{\circ}C$, which was lower than that of normal reflow temperature, $240\~250^{\circ}C$, for the Pb-free. As experimental result, the joint of $Sn-95.7\%Bi$ coated Sn-3.5Ag showed high shear strength. In the as-reflowed state, the shear strength of the coated solder showed 58.8N, whereas those of commercial ones were 37.2N (Sn-37Pb), 31.4N (Sn-3Ag-0.5Cu), and 40.2N (Sn-8Zn-3Bi). After thermal shock of 1000 cycles between $-40^{\circ}C$ and $+125^{\circ}C$, shear strength of the coated solder showed 56.8N, whereas the previous commercial solders were in the range of 32.3N and 45.1N. As the microstructures, in the solder $Ag_3Sn$ intermetallic compound (IMC), and along the bonded interface $Ni_3Sn_4$ IMC were observed.

• Journal of Welding and Joining
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• v.20 no.2
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• pp.77-81
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• 2002

Many kinds of Pb-free solder have been investigated because of the environmental concerns. Sn-Ag-Cu system is well blown as most competitive Pb-free solder. However, since Sn-Ag-Cu system has relatively high melting point compared to Sn-Pb eutectic, it may a limitation, the some application. In this study, Bi and In contained solder of $Sn_3Ag_8Bi_5In$ which has relatively lower melting point, $188~204^{\circ}C$, was investigated. $Sn_3Ag_8Bi_5In$ solder ball of $500\mu\textrm{m}$ diameter was set on the Ni/Cu/Cr-UBM and reflow soldered in the range of $220~240^{\circ}C$ for 5~15s. The maximum shear strength of the solder ball was around 170mN by reflowing at $240^{\circ}C$ for 10s. Intermetallic compound formed on the UBM of Si-wafer was analysed by SEM(scanning electron microscope) and XRD(X-ray diffractometer).

• Journal of Welding and Joining
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• v.18 no.6
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• pp.42-47
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• 2000

The object of this study is to estimate Sn-Ag-Bi-Ga solder alloy as a substitute for Sn-37Pb alloy. For Sn-Ag-Bi-Ga alloys, Ag, Bi and Ga contents are varied. (Ag : 1~5%, Ga : 3%, Bi : 3~6%) Comparing to Sn-37Pb alloy Sn-Ag-Bi-Ga alloys have wider melting temperature range up to max. $18.7^{\circ}C$. With increasing Ag, Bi contents, the wettability of the alloys increased up to max. 6.6 mN. The vickers hardness of the alloys was max. 46.4 Hv. The ultimate tensile stress of the alloys was max. 60.3 MPa and the elongation was max. 1.2%. The joint strength between circuit board and solder was max. 55.5 N and the joint strength between connector and solder was max. 176.1 N. There were no cracks in this alloys after thermal shock test.