• Journal of the Microelectronics and Packaging Society
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• v.8 no.3
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• pp.43-47
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• 2001

Sn-3Ag-8Bi-5In was developed for the intermediate melting point solder. Although In-contained solder is expensive, its melting point is lower than these of Sn-Ag-Cu alloys. Sn-3Ag-8Bi-5In solder used for this research has a melting range of 188~$204^{\circ}C$. On this study wetting characteristics of Sn-3Ag-8Bi-5In were evaluated in order to investigate its availability as a Pb-free solder. Wettabilities of Sn-37Pb and Sn-3.5Ag solders were also studied to compare these of the Sn-3Ag-8Bi-5In. Experimental results showed that the zero-cross-time and wetting time at $240^{\circ}C$ for the Sn-3Ag-8Bi-5In were 1.1 and 2.2 second respectively. These values are a little better than these of Sn-37Pb and Sn-3.5Ag solders. The equilibrium wetting farce of the Sn-3Ag-8Bi-5In was 5.8 mN at $240^{\circ}C$, and it was tuned out to be a little higher than that of Sn-3.5Ag and lower than that of Sn-37Pb.

• 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.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.4
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• pp.505-509
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• 2002

Pb is considered to be eliminated from solder, due to its toxicity. However, melting temperatures of most Pb-free solders are known higher than that of Sn37Pb. Therefore, there is a difficulty to apply Pb-free solders to electronic industry. Since Sn3Ag8Bi5In has relatively lower melting range as $188~200^{\circ}C$, on this study. Wettability and soldering characteristics of Sn3Ag8Bi5In solder in BGA were investigated to solve for what kind of problem. Zero cross time, wetting time, and equilibrium force of Sn3Ag8Bi5In solder for Cu and plated Cu such as Sn, Ni, and Au/Ni-plated on Cu were estimated. Plated Sn on Cu showed best wettability for zero cross time, wetting time and equilibrium farce. Shear strength of the reflowed joint with Sn3Ag8Bi5In ball in BGA was investigated. Diameter of the ball was 0.5mm, UBM(under bump metallurgy) was $Au(0.5\mu\textrm{m})Ni(5\mu\textrm{m})/Cu(18\mu\textrm{m})$ and flux was RMA type. For the reflow soldering, the peak reflow temperature was changed in the range of $220~250^{\circ}C$, and conveyor speed was 0.6m/min.. The shear strength of Sn3Ag8Bi5In ball showed similar level as those of Sn37Pb. The soldered balls are aged at $110^{\circ}C$ for 36days and their shear strengths were evaluated. The shear strength of Sn3Ag8Bi5In ball was increased from 480gf to 580gf by aging for 5 days.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.481-486
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• 2002

We have investigated the effects of plating materials for Cu lead (Sn-lOPb, AwPdJNi, Sn-3.5Ag, Sn-3Bi and Sn-0.7Cu) on properties of QFP joints using a Sn-8Zn-3Bi solder. The results were compared with the joints using Sn-3. 5Ag-0. 7Cu and Sn-37Pb solders. As a result, the joints with the Sn-3.5Ag, Sn-3Bi and Sn-0.7Cu plated Cu lead had the reliability comparable to those of the Sn-3.5Ag-0.7Cu and Sn-37Pb soldered joints with respect to the joint strength after the high temperature holding tests at 348K to 423k. In particular, the joint with the Sn-3.5Ag plated Cu lead had the best reliability. This is caused by the low growth rate of a Cu-Sn interfacial reaction layer that degrades the joint strength of the soldered joints. Consequently, the Sn-3.5Ag plating was found to be most feasible plating for the Sn-8Zn-3Bi soldered joint.

• Proceedings of the KWS Conference
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• 2001.10a
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• pp.168-170
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• 2001

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.128-132
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• 2003

무전해 Ni-P UBM과 3가지 경우의 무연 솔더간의 계면연구를 통해 Bi가 솔더의 합금원소로 들어감에 따라 계면반응에 어떠한 영향을 줄 수 있는 가를 연구했다. 3가지 다른 무연 솔더는 Bi가 각각 $0wt\%,\;4.8wt\%,\;58wt\%$들어간 Sn3.5Ag, Sn3.5Ag4.8Bi, Sn58Bi 이다. reflow를 수행한 후에 세 가지 솔더에서 나타나는 계면에서의 IMC는 $Ni_3Sn_4$로서 어떤 다른 솔더도 Bi를 함유한 IMC가 계면에선 관찰되지 않았다. 다만 SnAgBi 솔더의 경우 특이하게 솔더내에서 침상의 $Ni_3Sn_4$가 reflow후에 관찰되었다. 또한 반응속도의 척도가 되는 Ni-P UBM소모속도를 비교해 보면 reflow후의 SnAg와 SnAgBi의 경우에는 비슷하나 SnBi의 경우에는 알서 두 솔더에 비해 눈에 띠게 느림을 관찰하였다. 이러한 Ni-P UBM의 소모경향을 Bi의 함량, 그에 따른 Sn의 상대적인 함량의 관점에서 고찰하고자 한다.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.919-926
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• 2002

In this study, the numerical prediction of the thermal fatigue lie? of a $\mu$BGA (Micro Ball Grid Array) solder joint was focused. Numerical method was performed using the three-dimensional finite element analysis for various solder alloys such as Sn-37%Pb, Sn-3.5%Ag, Sn-3.5%Ag-0.7%Cu and Sn-3.5%Ag-3%In-0.5%Bi during a given thermal cycling. Strain values obtained by the result of mechanical fatigue tests for solder alloys, were used to predict the solder joint fatigue life using the Coffin-Manson equation. The numerical results showed that Sn-3.5%Ag with the 50-degree ball shape geometry had the longest thermal fatigue life in low cycle fatigue. A practical correlation for the prediction of the thermal fatigue life was also suggested by using the dimensionless variable γ. Additionally Sn-3.5Ag-0.75Cu and Sn-2.0Ag-0.5Cu-2.0Bi were applied to 6$\times$8$\mu$BGA obtained from the 63Sn-37Pb Solder. This 6$\times$8$\mu$BGA were tested at different aging conditions at 130$\^{C}$, 150$\^{C}$, 170$\^{C}$ for 300, 600 and 900 hours. Thickness of the intermetallic compound layer was measured thor each condition and the activation energy thor their growth was computed. The fracture surfaces were analyzed using SEM (Scanning Electron Microscope) with EDS ( Energy Dispersive Spectroscopy).

• Journal of the Microelectronics and Packaging Society
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• v.8 no.3
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• pp.37-42
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• 2001

The concerns of the toxicity and health hazard of lead in solders have demanded the research to find suitable lead-free solder alloys. It was discussed that effect of the intermetallic formation and structure on the reliability of solder joints. In this study, lead-free solder alloys with compositions of Sn/3.5Ag/0.75Cu, Sn/2.0Ag/0.5Cu/2.0Bi were applied to the 48 $\mu$BGA packages. Also, the lead-free solder alloys compared with eutectic Sn/37Pb solder using shear test under various aging temperature. Common $\mu$BGA with solder components was aged at $130^{\circ}C$, $150^{\circ}C$ and $170^{\circ}C$. And the each temperature applied to 300, 600 and 900 hours. The thickness of the intermetallics was measured for each condition and the activation energy for their growth was computed. The fracture surfaces were analyzed using SEM (Scanning Electron Microscope) with EDS (Energy Dispersive Spectroscopy). These results for reliability of lead-free interconnections are discussed.