• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.84-87
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• 2003

Since Pb-free solder alloys have been used extensively in microelectronic packaging industry, the interaction between UBM (Under Bump Metallurgy) and solder is a critical issue because IMC (Intermetallic Compound) at the interface is critical for the adhesion of mechanical and the electrical contact for flip chip bonding. IMC growth must be fast during the reflow process to form stable IMC. Too fast IMC growth, however, is undesirable because it causes the dewetting of UBM and the unstable mechanical stability of thick IMC. UP to now. Ni and Cu are the most popular UBMs because electroplating is lower cost process than thin film deposition in vacuum for Al/Ni(V)/Cu or phased Cr-Cu. The consumption rate and the growth rate of IMC on Ni are lower than those of Cu. In contrast, the wetting of solder bumps on Cu is better than Ni. In addition, the residual stress of Cu is lower than that of Ni. Therefore, the alloy of Cu and Ni could be used as optimum UBM with both advantages of Ni and Cu. In this paper, the interfacial reactions of Sn-3.5Ag-0.7Cu solder on Ni-xCu alloy UBMs were investigated. The UBMs of Ni-Cu alloy were made on Si wafer. Thin Cr film and Cu film were used as adhesion layer and electroplating seed layer, respectively. And then, the solderable layer, Ni-Cu alloy, was deposited on the seed layer by electroplating. The UBM consumption rate and intermetallic growth on Ni-Cu alloy were studied as a function of time and Cu contents. And the IMCs between solder and UBM were analyzed with SEM, EDS, and TEM.

• Journal of the Microelectronics and Packaging Society
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• v.16 no.1
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• pp.33-38
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• 2009

The use of portable devices has created the need for new reliability criterion of drop impact tests because of the tendency to accidentally drop in the use of these devices. The effects of different PCB surface finishes (organic solderability preservative (OSP) and electroless nickel immersion gold (ENIG)) and high temperature storage (HTS) test on the drop reliability were studied. Various drop test conditions were used to evaluate a drop reliability of assemblies to endure such impact and shock load. In the case of the as-reflowed samples (no HTS test), the SAC/OSP boards exhibited a better drop impact reliability than that of SAC/ENIG. However, the reverse was true if HTS test is performed. In addition, significant decrease of drop reliability was observed for both SAC/ENIG and SAC/OSP assemblies after HTS test. It was also observed that the thickness of intermetallic compound layer do play an important role in the brittle fracture of drop test.

• International Journal of Korean Welding Society
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• v.5 no.1
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• pp.15-28
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• 2005

The ball shear test was investigated in terms of the effects of test parameters, i.e., shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. Two representative Pb-free solder compositions were examined in this work: Sn-3.5Ag-0.75Cu and In-48Sn. The substrate was a common SMD type with solder bond pad openings of 460 $\mu$m in diameter. The microstructural investigations were carried out using SEM, and the IMCs were identified with EDS. Shear tests were conducted with the two varying test parameters. It could be observed that increasing shear height, at fixed shear speed, has the effect of decreasing shear force for both Sn-3.5Ag-0.75Cu and In-48Sn solder joints, while the shear force increased with increasing shear speed at fixed shear height. Too high shear height could cause some undesirable effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball. The low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces. The shear speed conditions were discussed with the stress analyses of the solder ball, and we cannot find any conspicuous finding which is related to optimum shear speed from the stress analyses.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.76-76
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• 2009

눈부신 전자산업의 발달로 대부분의 전자제품이 다기능/경박단소화 되고 있어, 고밀도 실장 기술인 양면 표면실장과 고집적 패키징 기술인 패키지 적층 공정의 적용이 점차 확대되고 있다. 따라서 양면 표면실장 및 패키지 적층 공정에 사용되는 저온 접합용 무연 솔더 즉, $183^{\circ}C$(Sn-37Pb 공정 솔더 융점) 이하의 융점을 가지는 저온 무연 솔더에 대한 관심이 높아지고 있다. 한편, 미세피치 적용 분야에 있어 ACF/P를 이용한 COG 접속 분야 외에도 최근 저온 접합용 무연 솔더를 이용한 접속 분야가 각광을 받고 있다. 따라서, 접속피치 미세화에 대응하기 위해 스크린 인쇄성을 향상시킬 수 있는 저온 무연 솔더 paste 제조 및 공정 기술의 개발이 필요한 실정이다. 현재 대표적인 저온 무연 솔더 조성은 Sn-Bi계($138^{\circ}C$ 융점)와 Sn-In계($120^{\circ}C$ 융점)이다. 하지만, 이들 조성의 신뢰성 등에 있어 개선의 여지가 있으므로 이를 해결하기 위한 무연솔더 조성의 개발이 필요하다. 이와 같은 관점에서, 본 연구는 $137^{\circ}C$의 융점을 갖는 Sn-57.6Ag-0.4Ag 저온 무연 솔더 paste를 $217^{\circ}C$의 융점을 갖는 Sn-3.0Ag-0.5Cu 솔더 paste와 비교하여 인쇄성, reflow 특성, void inspection, 미세조직 관찰 및 underfill 적용 등의 실험을 실시하였다.

• Journal of the Korean Ceramic Society
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• v.43 no.2 s.285
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• pp.92-97
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• 2006

Dolomite type $BaSn(BO_3)_2$ ceramics with rhombohedral crystal structure has been synthesized via solid state reaction route. Dielectric properties were measured for the samples sintered at $1050\~1200^{\circ}C$ for 2 h in air. Dielectric constant, loss tangent, and temperature coefficient were increased with sintering temperature due to the evolution of $BaSnO_3$, secondary, phase. Optimum dielectric properties were obtained at the $BaSn(BO_3)_2$ ceramics sintered at $1100^{\circ}C.\;CuO/Bi_2O_3$ was added to $BaSn(BO_3)_2$ ceramics to lower the sintering temperature for LTCC application, then Co and Fe-based coloring agents were added for colorizing the LTCC tape. Typical dielectric properties of $BaSn(BO_3)_2$ ceramics with $5 wt\%\;CuO/Bi_2O_3\;and\;3wt\%$ Co-coloring agent that sintered at $900^{\circ}C$ were $\varepsilon_r=9.89,\;tan{\delta}=0.92\times10^{-3},\;and\;TCC=112ppm/^{\circ}C$. Thus obtained LTCC tape was co-fired with Ag paste for compatibility test and revealed no sign of Ag reaction with the ceramics.

• The Journal of Korean Academy of Prosthodontics
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• v.23 no.1
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• pp.39-59
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• 1985

The purpose of this study was to investigate how gap distances of 0.13mm, 0.15mm, 0.20mm, and 0.30mm affects solder joint strength from gold alloys and nickel-chromium base alloys and to examine the composition of solder gold, the solder joint of gold alloys and nickel-chromium base alloys. The tensile test specimens were prepared in the split stainless steel mold with a half dumbbell shape 2.5mm in diameter and l2mm in length. 6 pairs of specimens of each gap distance group of gold alloys and nickel-chromium base alloys were made and 48 pairs of all specimens were soldered with solder gold of 666 fineness. All soldered specimens were machined to a uniform diameter and then a tensile load was applied at a cross-head speed of 0.10mm/min using Instron Universal Testing Machine, Model 1115. The fractured specimens at solder gold of solder joint fracture with each gap distance of 0.13mm, 0.15mm, 0.20mm, and 0.30mm were examined under the Scanning Electron Microscope, JSM-35c and the composition of solder gold, the solder joint of gold alloys and nickel-chromium base alloys was analyzed by Electron Probe Micro Analyzer. The results of this study were obtained as follows: 1. In case of soldering of gold alloys, the tensile strength between gold alloys showed $37.33{\pm}2.52kg/mm^2$ at 0.13, $39.14{\pm}3.35kg/mm^2$ at 0.15mm, $43.76{\pm}2.97kg/mm^2$ at 0.20mm, and $49.18{\pm}4.60kg/mm^2$ at 0.30mm. There was statistically significant difference at each gap distance, and so the greater increase of gap distance showed the greater tensile strength. 2. In case of soldering of nickel-chromium base alloys, the tensile strength between nickel-chromium base alloys showed $34.84{\pm}4.26kg/mm^2$ at 0.13mm, $37.25{\pm}2.49kg/mm^2$ at 0.15mm, $42.91{\pm}4.32kg/mm^2$ at 0.20mm, and $46.93{\pm}4.21kg/mm^2$ at 0.30mm. There was not statistically significant difference only between 0.13mm and 0.15mm and bet ween 0.20 mm and 0.30mm, but generally the greater increase of gap distance showed the greater tensile strength. 3. The greater increase of gap distance shoed less porosities in solder gold at solder joint fracture. 4. In solder gold Au, Cu, Ag, Zn, and Sn were composed and Au and Cu were mostly distributed uniformly. 5. In solder joints of solder gold and gold alloys Au, Cu, Ag, Zn, and Sn were composed in solder gold and Au, Cu, Ag, Pt, and Pd were composed in gold alloys. Au and Cu of solder gold and gold alloys were mostly distributed uniformly and the diffusion of other elements except Pt and Pd around the solder joint was not almost found. In solder joints of solder gold and nickel-chromium base alloys Au, Cu, Ag, Zn, and Sn were composed in solder gold and Ni, Cr, and Al were composed in nickel-chromium base alloys. Au and Cu of solder gold and Ni and Cr of nickel-chromium base alloys were mostly distributed uniformly and the diffusion of other elements except Cr around the solder joint was not almost found.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.3
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• pp.67-74
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• 2011

Keys to high wiring density semiconductor packages include flip-chip bonding and build-up substrate technologies. The current issues are the establishment of a fine pitch flip-chip bonding technology and a low coefficient of thermal expansion (CTE) substrate technology. In particular, electromigration and thermomigration in fine pitch flipchip joints have been recognized as a major reliability issue. In this paper, electromigration and thermomigration in Cu/Sn-3Ag-0.5Cu (SAC305)/Cu flip-chip joints and electromigration in Cu/In/Cu flip chip joints are investigated. In the electromigration test, a large electromigration void nucleation at the cathode, large growth of intermetallic compounds (IMCs) at the anode, a unique solder bump deformation towards the cathode, and the significantly prolonged electromigration lifetime with the underfill were observed in both types of joints. In addition, the effects of crystallographic orientation of Sn on electromigration were observed in the Cu/SAC305/Cu joints. In the thermomigration test, Cu dissolution was accelerated on the hot side, and formation of IMCs was enhanced on the cold side at a thermal gradient of about $60^{\circ}C$/cm, which was lower than previously reported. The rate of Cu atom migration was found comparable to that of electromigration under current conditions.

• Restorative Dentistry and Endodontics
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• v.18 no.2
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• pp.431-445
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• 1993

The purpose of this study was to observe corrosion characteristics of six dental amalgams and was to analyse corrosion products electrochemically. After each amalgam alloy and Hg was triturated as the direction of the manufacturer by using mechanical amalgamator, the triturated mass was inserted into the cylinderical metal mold ($12{\times}10mm$) and was condensed with 160kg/$cm^2$ by using the hydrolic press. The specimen was removed from the mold and was stored at room temperature for 1 week, and was polished with amalgam polishing kit. The anodic and cathodic polarization curve was obtained by using cyclic voltammetric method with 3-electrode potentiostat in saline for each amalgam and Ag, Sn, Cu plate specimen at $37{\pm}0.5^{\circ}C$. The potential sweep range was -1.7V~0. 4V(vs SCE) in working electrode and scan rate was 50mV/s and the exposed surface area of each specimen to the electrolytic solution was $0.79cm^2$. The results were as follows. 1. In anodic-cathodic polarization curve of amalgam specimens, two anodic current rising areas and two cathodic current peaks were obtained at the low Cu amalgam(CF, CS) specimen and three anodic current rising areas and three cathodic current peaks were obtained at the high Cu amalgam (TY, DS, HV) specimen. 2. As this compared with the anodic and cathodic current peak potentials of Sn, Cu and Ag specimen, the first cathodic current peak I c was caused by the reduction of divalent tin salt, second cathodic current peak IIIc results from the reduction of quadravalent tin salt, and third cathodic current peak me results from the reduction of copper salt. 3. As reverse potential sweeping was done repeatedly, anodic current was decreased slightly in all amalgam specimens.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.2
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• pp.17-27
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• 2011

This paper describes an experimental study and finite element analysis (FEA) carried out for investigating thermal deformation behavior of solders, resulting from temperature change in the solder. With such a goal in mind, a shear specimen that was composed of two metal bars having different coefficient of thermal expansion and solder blocks placed between two bars was designed and fabricated. Two different types of solder blocks, eutectic solder (Sn/36Pb/ 2Ag) and lead-free solder (Sn/3.0Ag/0.5Cu) were tested as well. Fringe patterns for several temperature steps were recorded and analyzed for three temperature cycles using a real-time moir$\acute{e}$ setup. The experimental data was verified with FEA and used to evaluate the suitability for numerous solder constitutive models available in literatures. FEA employing Anand material model suggested by Darveaux et al. and Chang et al. were found to be in an excellent agreement with the experimental results for the eutectic solder and the lead-free solder, respectively. In addition, numerical predictions on bending displacement, shear strain and viscoplastic distortion energy are documented and viscoplastic deformation behavior of two types of solder material are compared.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.1 s.34
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• pp.65-71
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• 2005

At present, Electronic industries push ahead to eliminate the Pb(Lead) -a hazardous material-from all products. Especially, we have performed to select the optimum standard composition of lead free alloy for the application to products for about 3 years from 2000. These days, we have the chance for applying to the mass-production. This project constructed the system for applying the lead free solders on consumer electronic products, which is one of the major products of the LG Electronics. To select the lead free solders with corresponding to the product features, we have passed through the test and applied with Sn-3.0Ag-0.5Cu alloy system to our products, and for the application to the high melting temperature composition, we secured the thermal resistance of the many parts and substrate and optimized the processing conditions. We have operated the temperature cycling test and the high temperature storage test under the standards to confirm the reliability of the products. On these samples, we considered the consequence of our decision by the operating test. For the long life time of the product, we have operated the temperature cycling test at $-45^{\circ}C\;-\;+125^{\circ}C$, 1 cycle/hour, 1000 cycles. Also we have tested the tin whisker growth about lead free plating on lead finish. We have analyzed with the SEM, EDS and any other equipment for confirming the failure mode at the joint and the tin whisker growth on lead free finish.