• Journal of the Microelectronics and Packaging Society
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• v.15 no.4
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• pp.51-57
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• 2008

In this paper, wetting and interfacial reaction properties for low Ag containing Sn-Ag-Cu Pb-free solder alloy, i.e., Sn-0.3Ag-0.7Cu were investigated and compared with those of Sn-1.0Ag-0.5Cu and Sn-3.0Ag-0.5Cu. Melting behavior and stress-strain curves of some Sn-xAg-xCu alloys were also measured using a differential scanning calorimeter(DSC) and a tensile test machine, respectively. In order to enhance insufficient wetting properties of Sn-0.3Ag-0.7Cu alloy, the improvement of wetting properties were analyzed by applying fluxes containing higher content of halide or indium adding of 0.2wt.% into the solder alloy. It was concluded that the small addition of indium is more effective for the improvement of wettability in low temperature range of $230{\sim}240^{\circ}C$ than applying flux containing higher content of halide.

• ETRI Journal
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• v.35 no.6
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• pp.1152-1155
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• 2013

A cost-effective and simple solder on pad (SoP) process is proposed for a fine-pitch microbump interconnection. A novel solder bump maker (SBM) material is applied to form a 60-${\mu}m$ pitch SoP. SBM, which is composed of ternary Sn3.0Ag0.5Cu (SAC305) solder powder and a polymer resin, is a paste material used to perform a fine-pitch SoP through a screen printing method. By optimizing the volumetric ratio of the resin, deoxidizing agent, and SAC305 solder powder, the oxide layers on the solder powder and Cu pads are successfully removed during the bumping process without additional treatment or equipment. Test vehicles with a daisy chain pattern are fabricated to develop the fine-pitch SoP process and evaluate the fine-pitch interconnection. The fabricated Si chip has 6,724 bumps with a 45-${\mu}m$ diameter and 60-${\mu}m$ pitch. The chip is flip chip bonded with a Si substrate using an underfill material with fluxing features. Using the fluxing underfill material is advantageous since it eliminates the flux cleaning process and capillary flow process of the underfill. The optimized bonding process is validated through an electrical characterization of the daisy chain pattern. This work is the first report on a successful operation of a fine-pitch SoP and microbump interconnection using a screen printing process.

• Journal of the Korean Society of Safety
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• v.30 no.6
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• pp.7-11
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• 2015

The present study investigates the impact shear strength of thermal aged Sn-3Ag-0.5Cu lead-free solder joints at impact speeds ranging from 0.5 m/s to 2.5 m/s. The specimens were thermal aged for 24, 100, 250 and 1000 hours at $100^{\circ}C$. The experimental results demonstrate that the shear strength of the solder joint decreases with an increase in the load speed and aging time. The shear strength of the solder joint aged averagely decreased by 43% with an increase in the strain rate. For the as-reflowed specimens, the mode II stress intensity factor ($K_{II}$) of interfacial IMC between Sn-3.0Ag-0.5Cu and a copper substrate also was found to decrease from $1.63MPa.m^{0.5}$ to $0.97MPa.m^{0.5}$ in the speed range tested here. The degradations in the shear strength and fracture toughness of the aged solder joints are mainly caused by the growth of IMC layers at the solder/substrate interface.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.1
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• pp.117-123
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• 2015

The need for drop simulations for board-leveled flip chips in micro-system packaging has been increasing. There have been many studies on flip chips with various solder ball compositions. However, studies on flip chips with Sn-1.0Ag-0.5Cu and Sn-3.0Ag-0.5Cu have rarely been attempted because of the unknown material properties. According to recent studies, drop simulations with these solder ball compositions have proven feasible. In this study, predictions of the impact lifetime by drop simulations are performed considering Cu and Cu/Ni UBMs using LS-DYNA to alter the design parameters of the flip chips, such as thickness of the flip chip and size of the solder ball. It was found that a smaller chip thickness, larger solder ball diameter, and using the Cu/Ni UBM can improve the drop lifetime of solder balls.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.1
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• pp.55-62
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• 2023

In this study, Sn-3.0Ag-0.5Cu (wt.%, SAC305) solder dipping process was performed between Ni-foam skeleton with different pore per inch (PPI) to fabricate Ni-foam/SAC305 composite solder, and then applied to the transient liquid phase (TLP) bonding process to evaluate the microstructure and mechanical properties of the bonded joint. The Ni-foam/SAC305 composite solder preform consisted of Ni-foam and SAC305, and an intermetallic compound (IMC) having a (Ni,Cu)₃Sn₄ composition was formed at the Ni-foam interface. During TLP bonding process, the IMC at the Ni-foam interface was converted to (Ni,Cu)₃Sn₄+Au, and as the bonding time increased, the Ni-foam and SAC305 continuously reacted, and the bonded joint was converted into an IMC. And it was confirmed that the 130 PPI Ni-foam/SAC305 composite solder joint was converted into an IMC at the fastest rate. As a result of performing a shear test to confirm the effect of Ni-foam on mechanical properties, solder joints under all conditions exhibited excellent mechanical properties of 50 MPa or more in the early stages of the TLP bonding process, and the shear strength tends to increase as the bonding time increases.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.2 s.35
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• pp.121-128
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• 2005

Solder joints in microelectronic devices are frequently operated at an elevated temperature in service. They also experience plastic deformation caused by temperature excursion and difference in thermal expansion coefficients. Deformed solders can go through a recovery and recrystallization process at an elevated temperature, which would alter their microstructure and mechanical properties. In this study, to predict the changes in mechanical properties of Pb-free solder joints at high temperatures, the high temperature microhardness of several Pb-free and composite solders was measured as a function of temperature, deformation, and annealing condition. Solder alleys investigated include pure Sn, Sn-0.7Cu, Sn-3.5Ag, Sn-3.8Ag-0.7Cu, Sn-2.8Ag-7.0Cu (composite), and Sn-2.7Ag-4.9Cu-2.9Ni (composite). Numbers are all in wt.$\%$ unless specified otherwise. Solder pellets were cast at two cooling rates (0.4 and $7^{\circ}C$/s). The pellets were compressively deformed by $30\%$ and $50\%$ and annealed at $150^{\circ}C$ for 2 days. The microhardness was measured as a function of indentation temperature from 25 to $130^{\circ}C$. Their microstructure was also evaluated to correlate with the changes in microhardness.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.333-337
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• 2008

This study investigates crack propagation behavior of Sn-3.0Ag-0.5Cu solder under pull-push loading conditions. Fatigue Crack Growth (FCG) tests were conducted on Center Cracked Plate (CCP) specimens in fast-fast (pp) strain waveform. The fast-slow (pc), slow-fast (cp) and slow-slow (cc) strain waveforms were also used to study the effect of strain rates. The crack propagation rates for the four strain waveforms were correlated with J-integral range and a scatter band of factor 4 was found. The crack growth rates for the pc waveform was highest, followed by cp, cc and then pp waveforms.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.1
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• pp.77-85
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• 2004

To evaluate the effect of plasma cleaning on the soldering reliability the plasma cleaning using Ar-10vol%$H_2$ gas was applied on a UBM(Under Bump Metallization). The UBM consisted of Au/ Cu/ Ni/ Al layers which were deposited on a Si-wafer with 20 nm/ 4 $\mu\textrm{m}$/ 4 $\mu\textrm{m}$/ 0.4 $\mu\textrm{m}$ thickness respectively. Sn-3.5%Ag, Sn-3.5%Ag-0.7%Cu and Sn-37%Pb solder balls sized of 500 $\mu\textrm{m}$ in diameter were used. Solder balls on the UBM were plasma reflowed under Ar-10%$H_2$ plasma (with or without plasma cleaning). They were compared with air reflowed solder balls with flux. The spreading ratios of plasma reflowed solder with plasma cleaning was 20-40% higher than that of plasma reflowed solder without plasma cleaning. The shear strength of plasma reflowed solder with plasma cleaning was about 58-65MPa. It showed 60-80% higher than that of plasma reflowed solder without plasma cleaning and 15-35% higher than that of air reflowed solder. Thus it was believed that plasma cleaning for the UBM using Ar-10vol%$H_2$ gas was considerably effective for the improvement of the strength of solder ball.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.110-113
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• 2003

여러가지 Sn-Ag-Cu 솔더조성과 솔더링 후의 냉각속도에 따라 솔더링 접합부에서의 계면 미세조직의 다양한 변화를 관찰해 보았다. 현재까지 Sn-Ag-Cu 3원계 공정점에 대한 정확한 연구가 미흡하고, 상용으로 제품화되고 있는 Sn-Ag-Cu 합금계는 3원계 공정조성에서 약간 벗어난 조성들을 선택하고 있다고 할 수 있다. 따라서, 본 연구에서 사용한 Sn-Ag-Cu 합금 조성은 Sn-3.5Ag, Sn-3Ag-0.7Cu, Sn-3Ag-1.5Cu, Sn-3.7Ag-0.9Cu, Sn-6Ag-0.5Cu로 선택하였으며, 각 조성에서 Lap Shear Joint를 제조하였다. 사용한 Solder pad는 Cu pad와 Cu pad 위에 Au/Ni를 plating한 것을 이용하였다. 리플로우 솔더링 조건은 $250^{\circ}C$ 이상의 온도에서 60초 실시하였으며, 리플로우 솔더링 후의 냉각속도를 달리하여 냉각시켰다. 솔더링 후의 냉각속도가 느려질수록 계면 금속간화합물(IMC)의 두께가 더욱 증가하며, 조대화되었다. 또한 솔더 조성의 영향에서 Cu와 Ag의 함량이 높을수록 계면 IMC의 두께가 증가되었으며, 이는 솔더내부에 형성된 IMC 입자들이 조대화되어 계면 IMC층에 결합되어 나타났기 때문이다.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.4
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• pp.27-36
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• 2007

In this study, we investigated the interfacial reactions between various Sn-Ag-Cu(SAC) solder alloys and ENIG(Electroless Ni Immersion Gold) and Cu-OSP(Organic Solderability Preservative) pad finish. In the case of the interfacial reaction between Sb added SAC solder and ENlf thinner P-rich Ni layer was formed at the interface. In the case of the interfacial reaction between Ni added SAC solder and Cu-OSP, the uniform $Cu_6Sn_5$, intermetallic compounds(IMCs) were formed and $Cu_6Sn_5$ grain did not grow after multiple reflows. Thinner $Cu_3Sn$ IMCs were farmed at the interface between $Cu_6Sn_5$ and Cu-OSP after $150^{\circ}C$ thermal aging.