• Corrosion Science and Technology
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• 제6권2호
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• pp.50-55
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• 2007

The smaller size and higher integration of advanced electronic package systems result in severe electrochemical reliability issues in microelectronic packaging due to higher electric field under high temperature and humidity conditions. Under these harsh conditions, electronic components respond to applied voltages by electrochemical ionization of metal and the formation of a filament, which leads to short-circuit failure of an electronic component, which is termed electrochemical migration. This work aims to evaluate electrochemical migration susceptibility of the pure Sn, Sn-3.5Ag, Sn-3.0Ag-0.5Cu solder alloys in $Na_{2}SO_{4}$. The water drop test was performed to understand the failure mechanism in a pad patterned solder alloy. The polarization test and anodic dissolution test were performed, and ionic species and concentration were analyzed. Ag and Cu additions increased the time to failure of Pb-free solder in 0.001 wt% $Na_{2}SO_{4}$ solution at room temperature and the dendrite was mainly composed of Sn regardless of the solders. In the case of SnAg solders, when Ag and Cu added to the solders, Ag and Cu improved the passivation behavior and pitting corrosion resistance and formed inert intermetallic compounds and thus the dissolution of Ag and Cu was suppressed; only Sn was dissolved. If ionic species is mainly Sn ion, dissolution content than cathodic deposition efficiency will affect the composition of the dendrite. Therefore, Ag and Cu additions improve the electrochemical migration resistance of SnAg and SnAgCu solders.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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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.

• Journal of Welding and Joining
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• 제21권3호
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• pp.92-98
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• 2003

This paper describes the numerical prediction of the thermal fatigue life of a $\mu$BGA(Micro Ball Grid Array) solder joint. Finite element analysis(FEA) was employed to simulate thermal cycling loading for solder joint reliability. Strain values, along with the result of mechanical fatigue tests for solder alloys were then used to predict the solder joint fatigue life using the Coffin-Manson equation. The results show that Sn-3.5mass%Ag solder had the longest thermal fatigue life in low cycle fatigue. Also a practical correlation for the prediction of the thermal fatigue life was suggested by using the dimensionless variable ${\gamma}$, which was possible to use several lead free solder alloys for prediction of thermal fatigue life. Furthermore, when the contact angle of the ball and chip has 50 degrees, solder joint has longest fatigue life.

• 마이크로전자및패키징학회지
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• 제20권2호
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• pp.59-64
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• 2013

3차원 적층 패키지를 위한 Cu/Ni/Au/Sn-Ag/Cu 미세 범프의 열처리에 따른 금속간 화합물 성장 거동을 분석하기 위하여 in-situ SEM에서 $135^{\circ}C$, $150^{\circ}C$, $170^{\circ}C$의 온도에서 실시간 열처리 실험을 진행하였다. 실험 결과 금속간 화합물의 성장 거동은 열처리시간이 경과함에 따라 시간의 제곱근에 직선 형태로 증가하였고, 확산에 의한 성장이 지배적인 것을 확인 할 수 있었다. Ni/Au 층의 존재로 인해 Au의 확산으로 복잡한 구조의 금속간 화합물이 생성 된 것을 확인할 수 있다. 활성화 에너지는 $Cu_3Sn$의 경우 0.69eV, $(Cu,Ni,Au)_6Sn_5$경우 0.84 eV로 Ni이 포함된 금속간 화합물이 더 높은 것을 확인 하였으며, 확산 방지층 역할을 하는 Ni층에 의해 금속간 화합물 성장이 억제됨에 따라 신뢰성이 향상 될 것으로 사료된다.

• 마이크로전자및패키징학회지
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• 제26권3호
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• pp.81-88
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• 2019

본 연구에서는 그래핀 산화(graphene oxide, GO) 분말 첨가가 ball grid array(BGA) 패키지와 printed circuit board(PCB)간 Sn-3.0Ag-0.5Cu(SAC305) 무연솔더 접합부의 electromigration(EM) 수명에 미치는 영향에 대하여 보고 하였다. 솔더 접합 직후, Ni/Au표면처리된 패키지 접합계면에서는 $(Cu,Ni)_6Sn_5$가 생성되었으며 organic solderability preservative(OSP) 표면처리 된 PCB 접합계면에서는 $Cu_6Sn_5$ 금속간화합물(intermetallic compound, IMC)이 생성되었다. $130^{\circ}C$, $1.0{\times}10^3A/cm^2$ 전류밀도 하에서 EM 수명평가 결과, GO를 첨가하지 않은 솔더 접합부의 평균 파괴 시간은 189.9 hrs으로 도출되었고, GO를 첨가한 솔더 접합부의 평균 파괴 시간은 367.1 hrs으로 도출되었다. EM에 의한 손상은 패키지 접합계면에 비하여 pad 직경이 작은 PCB 접합계면에서 전자 유입에 의한 Cu의 소모로 인하여 발생하였다. 한편, 첨가된 GO는 하부계면의 $Cu_6Sn_5$ IMC와 솔더 사이에 분포하는 것을 확인하였다. 따라서, SAC305 무연솔더에 첨가된 GO가 전류 집중 영역에서 Cu의 빠른 확산을 억제하여 우수한 EM 신뢰성을 갖는 것으로 생각된다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2007년 추계학술발표대회 개요집
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• pp.222-222
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• 2007

• 한국재료학회지
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• 제15권8호
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• pp.536-542
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• 2005

Recently European Council(EU) published the RoHS(restriction of the use of certain hazardous substances in electrical and electronic equipment) which is prohibit the use of Pb, Hg, Cd, $Cr^{+6}$, PBB or PBDE in the electrical and electronic equipments. So EU member States shall ensure that, from 1 July 2006, new electrical and electronic equipment put on the market does not contain 6 hazardous substances. The one of the most important in electronics manufacturing process is soldering. Soldering process use the chemical substances which are applied in fluxing and cleaning processes and it can generate the malfunction of electronics caused by corrosion in the fields conditions. Therefore this study researched on the polarization and Tafel properties of Sn40Pb and Sn3.0Ag0.5Cu(SAC) solder based on the electrochemical theory. We prepared SnPb specimens which was aged in $150^{\circ}C,\;180^{\circ}C$ for 15 minutes ana Sn3.0Ag0.5Cu specimens that was aged in $180^{\circ}C,\;220^{\circ}C$ for 10 minutes. Experimental polarization curves were measured in distilled ionized water and $3.5 wt\%$, 1 mole NaCl electrolyte of $40^{\circ}C$, pH 7.5. Ag/AgCl and graphite were utilized by reference and counter electrode, respectively. To observe the electrochemical reaction, polarization test was conducted from -250 mV to +250 mV. From the polarization curves that were composed of anodic and cathodic curves, we obtained Tafel slop, reversible electrode potential(Ecorr) and exchange current density(Icorr). In these results, corrosion rate for two specimen were compared Sn3.0Ag0.5Cu with SnPb solders

• 마이크로전자및패키징학회지
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• 제17권1호
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• pp.25-31
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• 2010

본 연구에서는 무연 솔더 중 우수한 특성을 보여 실용화된 Sn-3.0Ag-0.5Cu 조성의 솔더를 사용하여 2주 동안의 시효조건에서 W의 함량이 무전해 Ni-W-P 도금층과 솔더와의 계면에서의 IMC 생성에 미치는 영향에 대해서 조사하였다. 도금층내 인의 함량은 8 wt.%로 고정하였고, 텅스텐의 함량은 각각 0, 3, 6 및 9 wt.%로 변화시켰으며, 모든 시료는 $255^{\circ}C$에서 리플로우한 후, $200^{\circ}C$에서 2주 동안 시효처리하였다. 각각의 시료에서 $(Cu,Ni)_6Sn_5$와 $(Ni,Cu)_3Sn_4$의 IMC가 관찰되었으며, 시효처리시간의 증가에 따라 UBM과 무연납의 계면에서 생성된 IMC가 증가함을 보였고, W의 함량이 높을수록 열적 안정성이 증가하여 $Ni(W)_3P$의 생성 속도를 늦춰 그에 따른 영향으로 IMC의 두께가 증가함을 보였다.

• 마이크로전자및패키징학회지
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• 제22권2호
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• pp.47-53
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• 2015

인쇄회로기판 솔더 상부 및 하부 접합부의 서로 다른 표면처리 조건에 따른 Sn-3.0Ag-0.5Cu (SAC305) 접합부의 열처리 및 전류 인가에 따른 금속간 화합물 성장거동을 비교하기 위하여 in-situ 미세구조분석 및 electromigration (EM) 수명평가를 실시하였다. 솔더 접합 직후, 상부 접합부의 electroless nickel immersion gold (ENIG) 표면처리에서는 $(Cu,Ni)_6Sn_5$, 하부 접합부의 organic solderability preservative (OSP) 표면처리에서는$ Cu_6Sn_5$, $Cu_3Sn$ 금속간 화합물이 접합 계면에서 생성되었다. EM 수명평가 결과 온도 $130^{\circ}C$, 전류밀도 $5.0{\times}10^3A/cm^2$ 하에서 평균파괴시간이 약 78.7 hrs으로 도출되었고, 하부 OSP 표면처리에서 전자가 솔더로 빠져나가는 부분에서 Cu의 소모에 의한 단락이 주 손상기구로 확인되었다. In-situ 주사전자현미경을 통해 계면 미세구조 분석 결과 상부 접합부 ENIG 표면처리에서 전자의 방향에 따른 미세구조의 큰 차이가 없고 뚜렷한 손상이 관찰되지 않았으나, 하부 접합부 OSP 표면처리의 경우 전자가 솔더로 유입되는 부분에서 빠른 Cu 소모로 인한 보이드 성장이 관찰되었다. 따라서, SAC305무연솔더 접합부에서 ENIG 표면처리가 OSP 표면처리보다 보다 우수한 EM확산방지막 역할을 하여 금속간 화합물 성장을 억제하고 보다 우수한 EM 신뢰성을 보이는 것으로 판단된다.

• Electronic Materials Letters
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• 제14권6호
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• pp.678-688
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• 2018

The repeated-bending properties of Sn-0.7Cu, Sn-0.3Ag-0.7Cu (SAC0307), and Sn-3.0Ag-0.5Cu (SAC305) solders mounted on flexible substrates were studied using highly accelerated stress testing (HAST), followed by repeated-bending testing. In the Sn-0.7Cu joints, the $Cu_6Sn_5$ intermetallic compound (IMC) coarsened as the HAST time increased. For the SAC0307 and SAC305 joints, the $Ag_3Sn$ and $Cu_6Sn_5$ IMCs coarsened mainly along the grain boundary as the HAST time increased. The Sn-0.7Cu solder had a high contact angle, compared to the SAC0307 and SAC305 solders; consequently, the SAC0307 and SAC305 solder joints displayed smoother fillet shapes than the Sn-0.7Cu solder joint. The repeated-bending for the Sn-0.7Cu solder produced the crack initiated from the interface between the Cu lead wire and the solder, and that for the SAC solders indicated the cracks initiated at the surface, but away from the interface between the Cu lead wire and the solder. Furthermore, the oxide layer was thickest for Sn-0.7Cu and thinnest for SAC305, regardless of the HAST time. For the SAC solders, the crack initiation rate increased as the oxide layer thickened and roughened. $Cu_6Sn_5$ precipitated and grew along the grain and subgrain boundaries as the HAST time increased, embrittling the grain boundary at the crack propagation site.