• 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.18 no.3
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• pp.9-17
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• 2011

Nano-composite solders have been studied to improve the properties of Pb-free solder joints. The nanoparticles in the composite solders were carbon nanotubes(CNTs), metals (Ag, Ni, Cr, etc.), ceramics (SiC, $ZrO_2$, $TiB_2$, etc.). To fabricate the nano-composite solders, mechanical mixing methods and in-situ fabrication method has been used for well-dispersed nano phase. The characteristic properties of the nano-composite solders were high creep resistance, low undercooling, low IMC growth rate and fine microstructures. More researches on the nano-composite solders are required to improve the processibility and the reliability of the nano-composite solder joints.

• Journal of Korea Foundry Society
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• v.22 no.1
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• pp.35-41
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• 2002

To improve the reliability of solder joints, a composite solder which consists of solder matrix and intermetallic reinforcements was manufactured by a new method. The cast ingot of Sn-6.9Cu-2.9Ag alloy had primary Cu6Sn5 intermetallics in the form of dendrites. After rolling the ingot, the intermetallic dendrites were crushed into fine particles and distributed uniformly throughout the solder matrix. As the rolled strips became thinner, the average size of the crushed particles reached a critical size which did not decrease any more by further rolling. The critical size was nearly the same as the average width of intermetallic dendrite trunk. The crushed intermetallic particles did not melt and remained in solid state during reflow soldering due to their high meltingterm-perature. The coarsening and gravitational segregation of the particles were observed during reflow soldering.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.3
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• pp.1-6
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• 2019

Wettability is an important factor to decide solderability of solder, flux, other soldering-related materials and soldering conditions. The wettability also affects the reliability of solder joint. Wetting balance test is a good method for quantitatively measuring wettability between solder and substrate. The wetting balance test is easy to reproduce the wetting experiment and to measure the wetting time and force. And this test provides wetting curve to calculate the surface tension of the molten solder. Development of new solder has been continued in accordance with various and harsh environment in the electronics industry. In this paper, the principle of wetting balance test and recent research issues including nano-composite solder are explained.

• Journal of Welding and Joining
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• v.32 no.3
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• pp.68-73
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• 2014

Among through silicon via (TSV) technologies, for replacing Cu filling method, the method of molten solder filling has been proposed to reduce filling cost and filling time. However, because Sn alloy which has a high coefficient of thermal expansion (CTE) than Cu, CTE mismatch between Si and molten solder induced higher thermal stress than Cu filling method. This thermal stress can deteriorate reliability of TSV by forming defects like void, crack and so on. Therefore, we fabricated SiC composite filling material which had a low CTE for reducing thermal stress in TSV. To add SiC nano particles to molten solder, ball-typed SiC clusters, which were formed with Sn powders and SiC nano particles by ball mill process, put into molten Sn and then, nano particle-dispersed SiC composite filling material was produced. In the case of 1 wt.% of SiC particle, the CTE showed a lowest value which was a $14.8ppm/^{\circ}C$ and this value was lower than CTE of Cu. Up to 1 wt.% of SiC particle, Young's modulus increased as wt.% of SiC particle increased. And also, we observed cross-sectioned TSV which was filled with 1 wt.% of SiC particle and we confirmed a possibility of SiC composite material as a TSV filling material.

• 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.28 no.1
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• pp.31-37
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• 2021

Sn-3wt%Ag-0.5wt%Cu (SAC305) solder is most popular solder in electronics industry. However, SAC305 has also drawbacks such as growth of β-Sn phase, intermetallic compounds (IMCs) of Ag3Sn, Cu6Sn5 and Cu3Sn which can result in deterioration of solder joints in terms of metallurgically, mechanically and electrically. Thus, improvement of SAC305 solders have been investigated continuously by addition of alloying elements, nano-particles and etc. In this paper, recent improvements of SAC solders including nano-composite alloys and related solderabilty and metallurgical and mechanical properties are investigated.

• 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 KWS Conference
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• 2009.11a
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• pp.74-74
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• 2009

카본나노튜브(CNT) 복합체는 우수한 기계적 성질을 가지고 있어 다양한 분야에서 연구되고 있다. 본 연구에서는 카본나노튜브(CNT)를 간단한 볼밀공정을 사용하여 Sn3.5Ag solder ball과 SAC305 powder 표면에 혼합하고 이를 통해 접합부 특성을 관찰하였다. 볼밀을 실시하기 전 카본나노튜브(CNT)는 초음파을 이용하여 분산을 실시하였다. Sn3.5Ag solder ball의 직경은 450um이고 SAC305 powder의 직경은 약 30um이었으며 이때 사용한 볼밀볼의 직경은 각각 3mm, 1mm이다. 볼밀 회전속도는 약 300rpm이고 6, 12, 18, 24시간동안 볼밀을 실시하였다. 24시간 볼밀 후에도 solder ball과 solder powder의 모양은 크게 변하지 않았다. SEM을 통해 표면을 관찰한 결과 분산된 카본나노튜브(CNT)는 solder ball과 solder powder의 표면에서 관찰되었다. 카본나노튜브(CNT)가 삽입된 solder ball은 BGA coupon 위에 놓고 Reflow를 실시하여 접합하였고 solder powder은 flux를 첨가하여 paste로 제조하여 2012 chip에 대한 접합특성을 관찰하였다. 카본나노튜브(CNT)는 solder ball 내부의 표면근처에서 관찰되었으며 카본나노튜브(CNT)가 혼합된 solder ball은 Aging 실시 후에 IMC 두께가 카본나노튜브(CNT)가 혼합되지 않은 solder ball에 비해 두께가 작고 접합강도는 약 10% 증가하였다. 또한 카본나노튜브(CNT)가 혼합된 solder paste와 카본나노튜브(CNT)가 혼합되지 않은 solder paste를 비교한 결과 인쇄성은 모두 양호하였으며 카본나노튜브(CNT)가 혼합된 paste를 사용한 chip의 전단강도가 높게 나타났다.

• Journal of the Microelectronics and Packaging Society
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• v.28 no.2
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• pp.95-103
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• 2021

Sn-58Bi-xRu composite solders were prepared by adding Ru nanoparticles to Sn-58Bi, a typical low-temperature solder, and the interfacial reaction and solder joint reliability were analyzed by reacting with Cu/OSP and ENIG surface treated PCB boards. The Cu₆Sn₅ IMC formed by the reaction with Cu/OSP had little change in thickness depending on the Ru content, and ductile fracture occurred inside the solder during the high-speed shear test without any significant change even after 100 hr aging. In reaction with ENIG, the Ni₃Sn₄ IMC thickness tended to decrease as the Ru content increased, and ENIG-specific brittle fracture was found in some specimens. Since Ru element is not found near the interface, it is judged not to be significantly involved in the interfacial reaction, and it is analyzed that it mainly exists together with the Bi phase.