• Journal of the Microelectronics and Packaging Society
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• v.16 no.4
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• pp.23-28
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• 2009

We investigated the wafer-level MEMS capping process for which cavity formation in Si wafer was not required. Ni caps were formed by electrodeposition on 4" Si wafer and Ni rims of the Ni caps were bonded to the Cu rims of bottom Si wafer by using epoxy. Then, top Si wafer was debonded from the Ni cap structures by using SnBi layer of low melting temperature. As-evaporated SnBi layer was composed of double layers of Bi and Sn due to the large difference in vapor pressures of Bi and Sn. With keeping the as-evaporated SnBi layer at $150^{\circ}C$ for more than 15 sec, SnBi alloy composed of eutectic phase and Bi-rich $\beta$ phase was formed by interdiffusion of Sn and Bi. Debonding between top Si wafer and Ni cap structures was accomplished by melting of the SnBi layer at $150^{\circ}C$.

• 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 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 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 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.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.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.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.133-137
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• 2003

The effect of Bi additions to the eutectic Sn-3.5Ag solder alloy on the growth kinetics of the intermetallic compound (IMC) layers during solid-state aging of Sn-Ag-Bi/Cu solder joints has been Investigated. The Bi additions enhanced the growth rate of the total IMC layer comprising of $Cu_6Sn_5$ and $Cu_3Sn$ sublayers. This enhanced IMC growth rate was primarily due to the rapid increase In the growth rate of $Cu_6Sn_5$ sublayer. The growth rate of $Cu_3Sn$ sublayers was little influenced and appeared to be retarded by the Bi additions. The observed growth behavior of $Cu_6Sn_5$ and $Cu_3Sn$ sublayers could be understood if the interfacial reaction barrier at the $Cu_6Sn_5/solder$ interface were reduced by the segregation of Bi at the interface.

• 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 International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.98-103
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• 2002

BGA(Ball Grid Array) 패키지의 솔더볼 패드 중의 하나인 Au/Ni-Co/Cu 금속층 위에 Bi가 첨가된 Sn-3.5Ag-$\chi$Bi 솔더볼을 리플로우시켰다. 리플로우한 후 130 $^{\circ}C$에서 열처리함에 따른 계면상 및 솔더 내부의 상변화를 관찰하였다. 계면에는 (Ni,Co)$_3$Sn$_4$외에 (Au,Ni,Co,Bi)Sn$_4$가 생성되었음을 관찰할 수 있었고, 솔더 내부에는 (Au,Ni,Co,Bi)SH$_4$, Ag$_3$Sn, Bi 상이 혼재되어 있었다. Nano-indentation에 의한 경도 측정 결과, Bi 함량 증가에 따라 경도는 증가하였으나, 볼전단(Ball Shear) 테스트 결과는 Bi가 증가됨에 따라 오히려 볼전단 강도값이 감소하였다. 이는 파면 검사 결과, 파괴 경로가 주로 계면의 금속간 화합물과 솔더 사이에서 진행함에 기인한 것이다. 솔더 내부의 파괴 경로를 가진 2.5Bi가 가장 우수한 볼전단 강도값을 나타내었는데, 이는 솔더내의 Bi의 고용강화에 기인한 것으로 보인다.