• Journal of the Microelectronics and Packaging Society
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• v.12 no.1 s.34
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• pp.35-40
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• 2005

The oxidation of pure Sn and Sn-0.7Cu, Sn-3.5Ag, Sn-lZn, and Sn-9Zn alloys at $150^{\circ}C$ was investigated. Both the chemical nature and the amount of oxides were characterized using electrochemical reduction analysis by measuring the electrolytic reduction potential and total transferred electrical charges. X-ray photoelectron spectroscopy (XPS) was also conducted to support the results of reduction analysis. The effect of Cu, Ag and Zn addition on surface oxidation of Sn alloys is reported. For Sn, Sn-0.7Cu and Sn-3.5Ag, SnO grew first and then the mixture of SnO and $SnO_2$ was found. $SnO_2$ grew predominantly for a long-time aging. For Zn containing Sn alloys, both ZnO and $SnO_2$ were formed. Zn promotes the formation of $SnO_2$. Sn oxide growth rate of Pb-free solder alloys was also discussed in terms of alloying elements.

• 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.

• Journal of Welding and Joining
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• v.29 no.6
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• pp.65-70
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• 2011

The effect of flip chip bonding parameters on formation of intermetallic compounds (IMCs) between Au stud bumps and Sn-3.5Ag solder was investigated. In this study, flip chip bonding temperature was performed at $260^{\circ}C$ and $300^{\circ}C$ with various bonding times of 5, 10, and 20 sec. AuSn, $AuSn_2$ and $AuSn_4$ IMCs were formed at the interface of joints and (Au, Cu)$_6Sn_5$ IMC was observed near Cu pad side in the joint. At bonding temperature of $260^{\circ}C$, $AuSn_4$ IMC was dominant in the joint compared to other Au-Sn IMCs as bonding time increased. At bonding temperature of $300^{\circ}C$, $AuSn_2$ IMC clusters, which were surrounded by $AuSn_4$ IMC, were observed in the solder joint due to fast diffusivity of Au to molten solder with increased bonding temperature. Bond strength of Au stud bump joined with Sn-3.5Ag solder was about 23 gf/bump and fracture mode of the joint was intergranular fracture between $AuSn_2$ and $AuSn_4$ IMCs regardless bonding conditions.

• 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).

• Transactions of the Korean hydrogen and new energy society
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• v.17 no.1
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• pp.69-74
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• 2006

Thick film $H_2$ sensors were fabricated using $SnO_2$ loaded with $Ag_2O$ and $PtO_x$. The composition that gave the highest sensitivity for $H_2$ was in the weight% ratio of $SnO_2 : PtO_x : Ag_2O$ as 93 : 1 : 6. The nano-crystalline powders of $SnO_2$ synthesized by sol-gel method were screen printed with $Ag_2O$ and $PtO_x$ on alumina substrates. The fabricated sensors were tested against gases like $H_2$, $CH_4$, $C_3H_8$, $C_2H_5OH$ and $SO_2$. The composite material was found sensitive against $H_2$ at the working temperature $130^{\circ}C$, with minor interference of other gases. The $H_2$ gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on $SnO_2-Ag_2O-PtO_x$ system exhibited the high performance, high selectivity and very short response time to $H_2$ at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of $H_2$.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.151-156
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• 2007

In this paper, the creep characteristics of lead and lead-free solder joint were investigated using the QFP(Quad Flat Package) creep test. Two kind of solder pastes(Sn-3Ag-0.5Cu, Sn-0.2Sb-0.4Ag-37.4Pb) were applied to the QFP solder joints and each specimen was checked the external and internal failures(i.e., wetting failure, void, pin hole, poor-heel fillet) by digital microscope and X-ray inspection. The creep test was conducted at the temperatures of $100^{\circ}C$ and $130^{\circ}C$ under the load of 15$\sim$20% of average pull strength in solder joints. The creep characteristics of each solder joints were compared using the creep strain-time curve and creep strain rate-stress curves. Through the comparison, the Sn-3Ag-0.5Cu solder joints have higher creep resistance than that of Sn-0.3Sb-0.4Ag-37.4Pb. Also, the grain boundary sliding in the fracture surface and the necking of solder joint were observed by FE-SEM.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.4 s.37
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• pp.307-313
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• 2005

Electromigration behavior in the Sn96.5Ag3.0Cu0.5 solder lines was investigated and compared Sn96.5Ag3.0Cu0.5 with eutectic SnPb. Measurements were made for relevant parameters for electromigration of the solder, such as drift velocity, threshold current density, activation energy, as well as the product of diffusivity and effective charge number (DZ$\ast$). The threshold current density were measured to be $2.38{\times}10^4A/cm^2$ at $140^{\circ}C$ and the value represented the maximum current density which the SnAgCu solder can carry without electromigration damage at the stressing temperatures. The electromigration energy was measured to 0.56 eV in the temperature range of $110-160^{\circ}C$. The measured products of diffusivity and the effective charge number, DZ$\ast$ were $3.12{\times}10^{-10} cm^2/s$ at $110^{\circ}C$, $4.66{\times}10^{-10} cm^2/s$ at $125^{\circ}C$, $8.76{\times}10^{-10} cm^2/s$ at $140^{\circ}C$, $2.14{\times}10^{-9}cm^2/s$ at $160^{\circ}C$ SnPb solder existed incubation stage, while SnAgCu did not have incubation stage. It was thought that the diffusion mechanism of SnAgCu was different from that of SnPb.

• Korean Journal of Materials Research
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• v.19 no.1
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• pp.13-17
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• 2009

A semi-empirical method to estimate the surface tension of molten alloys at different oxygen partial pressures is suggested in this study. The surface tension of molten Ag-Sn and Ag-Cu alloys were calculated using the Butler equation with the surface tension value of pure substance at a given oxygen partial pressure. The oxygen partial pressure ranges were $2.86{\times}10^{-12}$－$1.24{\times}10^{-9}$ Pa for the Ag-Sn system and $2.27{\times}10^{-11}$－$5.68{\times}10^{-4}$ Pa for the Ag-Cu system. In this calculation, the interactions of the adsorbed oxygen with other metallic constituents were ignored. The calculated results of the Ag-Sn alloys were in reasonable accordance with the experimental data within a difference of 8%. For the Ag-Cu alloy system at a higher oxygen partial pressure, the surface tension initially decreased but showed a minimum at $X_{Ag}$ = 0.05 to increase as the silver content increased. This behavior appears to be related to the oxygen adsorption and the corresponding surface segregation of the constituent with a lower surface tension. Nevertheless, the calculated results of the Ag-Cu alloys with the present model were in good agreement with the experimental data within a difference of 10%.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.1
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• pp.81-88
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• 2010

Thermal annealing and electromigration test were performed at $150^{\circ}C$ and $4{\times}10^3\;A/cm^2$ conditions in order to investigate the effect of PCB surface finishs on the growth kinetics of intermetallic compound (IMC) in Sn-3.0Ag-0.5Cu solder bump. The surface finishes of the electrodes of printed circuit board (PCB) were organic solderability preservation (OSP), immersion Sn, and electroless Ni/immersion gold (ENIG). During thermal annealing, the OSP and immersion Sn show similar IMC growth velocity, while ENIG surface finish had much slower IMC growth velocity. Applying electric current accelerated IMC growth velocity and showed polarity effect due to directional electron flow.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.3
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• pp.9-18
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• 1999

In this study, Metallugical properties between Sn-3.5Ag, Sn-37Pb eutectic solders and Au/Ni/cu substrate according to time span above the melting point were investigated. A conventional reflow soldering machine wert used for this study and time span above the melting point was determined by changing peak soldering temperature and conveyor speed. As results, scallop type intermetallic compounds of $Ni_3Sn_4$ were formed at joint interface and no Cu-Sn compounds were found at all; Ni layer performed as a barrier for Cu diffusion. As the peak soldering temperature increased, thickness of the intermetallic compound layer increased; maximum thickness of the scallop-layer was 2.2$\mu\textrm{m}$. The shape of scallops were transformed from hemi-sphere type to elliptical shape with smaller size. Micro-hardness of the solder joint decreased as the eutectic structure of Sn-3.5Ag and Sn-37Pb increased.