• Proceedings of the KWS Conference
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• 2010.05a
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• pp.82-82
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• 2010

표면실장 공법을 통해 CSP 패키지를 보드에 실장 하는데 있어 무연솔더 접합부의 신뢰성에 영향을 미치는 인자 중 가장 중요한 것은 접합부에 형성되는 IMC (Intermetallic compound, 금속간화합물)인 것으로 알려져 있다. 접합부의 칩 부분에는 솔더와 칩의 UBM (Under bump metalization)이 접합하여 IMC가 형성되나, 보드 부분에는 솔더와 보드의 UBM 뿐만 아니라 그 사이에 솔더 페이스트가 함께 접합되어 IMC가 형성된다. 본 연구에서는 패키지의 신뢰성 연구를 위해 솔더 페이스트의 유무 및 두께에 따른 무연 솔더 접합부의 미세조직의 변화를 분석하였다. 본 실험에서는 Sn-3.0(Wt.%)Ag-0.5Cu 조성과 본 연구진에 의해 개발된 Sn-Ag-Cu-In 조성의 직경 $450{\mu}m$ 솔더 볼을 사용하였으며, 솔더 페이스트는 상용 Sn-3.0Ag-0.5Cu (ALPHA OM-325)를 사용하였다. 칩은 ENIG (Electroless nickel immersion gold) finish pad가 형성된 CSP (Chip scale package)를, 보드는 OSP (Organic solderability preservative)/Cu finish pad가 형성된 것을 사용하였다. 실험 방법은 보드를 솔더 페이스트 없이 플라즈마 처리 한 것, 솔더 페이스트를 $30{\mu}m$ 두께로 인쇄한 것, $120{\mu}m$의 두께로 인쇄한 것, 이렇게 3가지 조건으로 준비한 후, 솔더 볼이 bumping된 칩을 mounting하여, $242^{\circ}C$의 peak 온도 조건의 oven(1809UL, Heller)에서 reflow를 실시하여 패키지를 형성하였다. 이후 시편은 정밀 연마한 후, OM(Optical Microscopic)과 SEM(scanning electron microscope) 및 EDS(energy dispersive spectroscope)를 사용하여 솔더 접합부 IMC의 미세조직을 관찰, 분석하였다.

• Journal of Welding and Joining
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• v.33 no.3
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• pp.19-24
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• 2015

Joint properties of electric control unit (ECU) module using Sn-Cu-(X)Al(Si) lead-free solder alloy were investigated for automotive electronics module. In this study, Sn-0.5Cu-0.01Al(Si) and Sn-0.5Cu-0.03Al(Si) (wt.%) lead-free alloys were fabricated as bar type by doped various weight percentages (0.01 and 0.03 wt.%) of Al(Si) alloy to Sn-0.5Cu. After fabrications of lead-free alloys, the ball-type solder alloys with a diameter of 450 um were made by rolling and punching. The melting temperatures of 0.01Al(Si) and 0.03Al(Si) were 230.2 and $230.8^{\circ}C$, respectively. To evaluation of properties of solder joint, test printed circuit board (PCB) finished with organic solderability perseveration (OSP) on Cu pad. The ball-type solders were attached to test PCB with flux and reflowed for formation of solder joint. The maximum temperature of reflow was $260^{\circ}C$ for 50s above melting temperature. And then, we measured spreadability and shear strength of two Al(Si) solder materials compared to Sn-0.7Cu solder material used in industry. And also, microstructures in solder and intermetallic compounds (IMCs) were observed. Moreover, thickness and grain size of $Cu_6Sn_5$ IMC were measured and then compared with Sn-0.7Cu. With increasing the amounts of Al(Si), the $Cu_6Sn_5$ thickness was decreased. These results show the addition of Al(Si) could suppress IMC growth and improve the reliability of solder joint.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.114-117
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• 2003

본 연구에서는 계산을 통해 나온 Sn-Ag-Cu 삼원계 공정점(Sn-3.7Ag-0.9Cu)을 바탕으로 그 근처의 응고경로가 다른 6가지 조성(Sn-4.6Ag-0.4Cu, Sn-4.9Ag-1.0Cu, Sn-3.9Ag-1.3Cu, Sn-2.2Ag-1.2Cu, Sn-2Ag-0.7Cu, Sn-2.7Ag-0.3Cu)에 대한 솔더합금의 미세조직을 관찰하였다. 응고경로는 $L\;\rightarrow\;L+Primary\;\rightarrow\;L+Primary+Secondary\;\rightarrow\;Ternary\;Eutectic+Primary+Secondary$로 되며 6가지 경우를 예상할 수 있다 솔더합금의 미세조직은 느린 냉각으로 인하여 빠른 냉각, 보통 냉각에 비해 상대적으로 커다란 $\beta-Sn$ dendrite를 보였고 $Ag_3Sn,\;Cu_6Sn_5$과는 다르게 $\beta-Sn$는 약 $30^{\circ}C$의 과냉(DSC분석)이 존재하게 되어 Sn-4.6Ag-0.4Cu의 경우에는 $Ag_3Sn$상이, Sn-2.2Ag-1.2Cu의 경우에는 $Cu_6Sn_5$가 과대성장을 하였다. 솔더의 기계적 특성을 살펴보고자 Cu 기판위에서 각 조성의 솔더볼을 솔더링한 후 다양한 냉각 속도를 적용하여 reflow 솔더링을 하고 솔더/기판 접합에 대한 전단 강도 시험을 실시했다. 냉각 속도가 빠를수록 $\beta-Sn$의 dendrite가 미세해져서 높은 전단 강도를 보였고 6가지 조성의 솔더볼중 공정조직 분율이 낮은 Sn-2Ag-0.7Cu 조성의 경우에서 낮은 전단 강도가 나타났다.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.450-455
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• 2002

Cu-cored Sn-Ag solder balls were fabricated by coating pure Sn and Ag on Cu balls. The melting behavior and the solderability of the BGA joint with the Ni/Au coated Cu pad were investigated and were compared with those of the commercial Sn-Ag and Sn-Ag-Cu balls. DSC analyses clarified the melting of Cu-cored solders to start at a rather low temperature, the eutectic temperature of Sn-Ag-Cu. It was ascribed to the diffusion of Cu and Ag into Sn plating during the heating process. After reflow soldering the microstructures of the solder and of the interfacial layer between the solder and the Cu pad were analyzed with SEM and EPMA. By EDX analysis, formation of a eutectic microstructure composing of $\beta$-Sn, Ag$_3$Sn, ad Cu$_{6}$Sn$_{5}$ phases was confirmed in the solder, and the η'-(Au, Co, Cu, Ni)$_{6}$Sn$_{5}$ reaction layer was found to form at the interface between the solder and the Cu pad. By conducting shear tests, it was found that the BGA joint using Cu-cored solder ball could prevent the degradation of joint strength during aging at 423K because of the slower growth me of η'-(Au, Co, Cu, Ni)$_{6}$Sn$_{5}$ reaction layer formed at the solder, pad interface. Furthermore, Cu-cored multi-component Sn-Ag-Bi balls were fabricated by sequentially coating the binary Sn-Ag and Sn-Bi solders on Cu balls. The reflow property of these solder balls was investigated. Melting of these solder balls was clarified to start at the almost same temperature as that of Sn-2Ag-0.75Cu-3Bi solder. A microstructure composing of (Sn), Ag$_3$Sn, Bi and Cu$_{6}$Sn$_{5}$ phases was found to form in the solder ball, and a reaction layer containing primarily η'-(Au, Co, Cu, Ni)$_{6}$Sn$_{5}$ was found at the interface with Ni/Au coated Cu pad after reflow soldering. By conducting shear test, it was found that the BGA joints using this Cu-core solder balls hardly degraded their joint shear strength during aging at 423K due to the slower growth rate of the η'-(Au, Cu, Ni)$_{6}$Sn$_{5}$ reaction layer at the solder/pad interface.he solder/pad interface.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.80-83
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• 2003

본 연구에서는 고온 솔더 범프와 저온 솔더 패드를 이용하여 $140^{\circ}C$에서 1분간의 리플로 공정을 통해 접합에 성공하였다. 고온 솔더 범프로 Sn-4.0Ag-0.5Cu 솔더 볼을 사용하였고, 저온 솔더는 In-48Sn $(mp:\;117^{\circ}C)$ 솔더를 기판에 evaporation 방법으로 두께 $20\;{\mu}m$의 패드 형태로 증착하였다. $140^{\circ}C$에서 1분간의 리플로 공정을 통해 칩과 기판을 접합하였으며, 접합 단면을 관찰해 본 결과 저온 솔더가 녹아 고온 솔더에 wetting된 것을 관찰하였다. 이 시편을 상온에서 시효처리를 실시한 결과 시간의 경과에 따라 저온 솔더와 고온 솔더가 상호 확산하여 약 $40\;{\mu}m$였던 확산층의 범위가 점차 증가하는 것을 관찰할 수 있었다. 또한, 리플로 공정변수에 따른 솔더의 미세구조 변화 및 ball shear strength등의 기계적 특성에 대해 고찰하였다.

• Journal of Welding and Joining
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• v.12 no.3
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• pp.48-55
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• 1994

In this experiment, to find optimum brazing conditions for Cu/Stainless Steel brazing using filler metals of Ag-Cu-Zn-Cd system, first of all spreading ratio was tested on 304 stainless Steel and low carbon steel. And then shear test of brazed joint was executed. As the result of that, the shear strengths of brazed joints were the range of 60-90 MPa. Through microstructure analysis for brazed interface layer, We found as follows. Firstly interface layer increased as time increased. Secondly continuous layer of Ag-Cd compound was observed along the side of stainless steel. Also by means of EDS analysis for fracture surface, ductile fracture was occurred and precipitates on the fracture surface were found to include Cr, Mn, Si in Ag-rich phase.

• Journal of Welding and Joining
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• v.17 no.5
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• pp.69-76
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• 1999

A copper-tungsten sintered alloy(Cu-W) has been friction welded to a tough pitch copper in order to investigate the effect of upset pressure on friction weldability. Under the condition of friction time 0.8sec, upset pressure 150MPa, the tensile strength and Charpy impact value of the friction welded joint were 336MPa, $400KJ/m^2$ respectively. And highest temperature of the weld measured was below $800^{circ}K$ which is very lower than melting point of Cu($1356^{circ}K$). Under the same conditions, W grains picked up in Cu matrix from Cu-W profitably affected on these mechanical fracture, and were dispersed in Cu by plastic flow during brake time.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.841-842
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• 2013

• Proceedings of the Materials Research Society of Korea Conference
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• 2006.05a
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• pp.25.2-25.2
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• 2006

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.66-66
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• 2009

Various alloy system, such as Cu-Sn-Ti, Cu-Ag-Ti, and Ni-B-Cr-based alloy are used for the brazing of diamond grits. However, the problem of the adhesion strength between the diamond grits and the brazed alloy is presented. The adhesion strength between the diamond grits and the melting filler alloy is predicted by the contact angle, thereby, instead of diamond grit, the study on the wettability between the graphite and the brazing alloy has been indirectly executed. In this study, Cu-13Sn-12Ti filler alloy was manufactured, and the contact angles, the shear strengths and the interfacial area between the graphites(diamond grits) and braze matrix were investigated. The contact angle was decreased on increasing holding time and temperature. The results of shear strength of the graphite joints brazed filler alloys were observed that the joints applied Cu-13Sn-12Ti alloy at brazing temperature 940 $^{\circ}C$ was very sound condition indicating the shear tensile value of 23.8 MPa because of existing the widest carbide(TiC) reaction layers. The micrograph of wettability of the diamond grit brazed filler alloys were observed that the brazement applied Cu-13Sn-12Ti alloy at brazing temperature $990^{\circ}C$ was very sound condition because of existing a few TiC grains in the vicinity of the TiC layers.