• Journal of Welding and Joining
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• v.13 no.4
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• pp.1-6
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• 1995

Sn-Pb계 솔더는 용접, 접합성, 가격등과, 작업성이 양호하기 때문에 전자기기 실장에 사용되어 왔고, 모든 실장장치도 Sn-Pb 솔더용으로 만들어져 있다. 그러나 솔더중의 Pb는 사용할 수 없다는 분위기가 점차 확산되고 있다. 이것은 Pb가 인체에 들어가면 중추신경을 손상시킨다고 알고 있기 때문이다. Pb의 사용 규제 조치에 대해 서는 10년전 부터 미국 국회에 몇번이나 상정된 바가 있지만, Pb피해에 대해서 입증 할 수 없다는 이유로 입안이 되지 않았지만, 실제는 대체합금이 없기 때문에 입안이 되지 않은 것으로 알려져 있다. 그러나 앞으로 5년 이내에 유예기간을 두고 2000년 이후 부터 사용을 규제할 것으로 알려져 있다. 또한 북유럽에는 Pb 솔더 금지법이 의회에 제출되어 있는 것으로 알려져 있고, 곧 OECD에서도 상정될 예정이다. 결국 지구상의 환경보호 차원에서 앞으로 Pb사용이 규제될 것임은 틀립이 없다. 따라서 Pb 가 함유되어 있지 않은 솔더의 개발은 각나라 마다 핫 이슈임에 틀림이 없다. 미국 AT&T 등에서 이미 Pb Free 솔더와 공정개발에 들어가 특허화하고 있고, 특히 유럽은 연구 개발이 왕성하여 Pb Free 솔더로서 실장한 핸더폰을 생산하는 실적까지 있다. 일본도 이미 대학, 연구소, 회사로 구성된 Pb Free 솔더 연구회가 구성되어 솔더개발 에 박차를 가하고 있다. 국내에 기업체, 연구소, 학교 등에서는 이러한 긴박감을 느 끼지 못하는 것으로 사료된다. 본 해설에서는 Sn-Pb 공정계 대체 솔더인 Pb Free 솔더 의 개발 방향과 문제점을 정리하여 기술하고자 한다.

• Journal of Welding and Joining
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• v.32 no.3
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• pp.74-80
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• 2014

Due to environmental regulations (RoHS, WEEE and ELV) of the European Union, electronics and automotive electronics have to eliminate toxic substance from their devices and system. Especially, reliability issue of lead-free solder joint is increasing in car electronics due to ELV (End-of-Life Vehicle) banning from 2016. We have prepared engine control unit (ECU) modules soldered with Sn-40Pb and Sn-3.0Ag-0.5Cu (SAC305) solders, respectively. Degradation characteristics of solder joint strength were compared with various conditions of automobile environment such as cabin and engine room. Thermal cycle test (TC, $-40^{\circ}C$ ~ ($85^{\circ}C$ and $125^{\circ}C$), 1500 cycles) were conducted with automotive company standard. To compare shear strength degradation rate with eutectic and Pb-free solder alloy, we measured shear strength of chip components and its size from cabin and engine ECU modules. Based on the TC test results, finally, we have known the difference of degradation level with solder alloys and use environmental conditions. Solder joints degradation rate of engine room ECU is superior to cabin ECU due to large CTE (coefficient of thermal expansion) mismatch in field condition. Degradation rate of engine room ECU is 50~60% larger than cabin room electronics.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.25-27
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• 2005

Sn-9Zn solder balls were bonded to Cu and ENIG (Electroless Nickel/Immersion Gold) pads, and the effect of aging on their joint reliability was investigated. The interfacial products were different from the general reaction layer formed in a Sn-base solder. The intermetallic compounds formed in the solder/Cu joint were $Cu_{5}Zn_{8}$ and $Cu_{6}Sn_{5}$. After aging treatment, voids formed irregularly at the bottom side of the solder because of Sn diffusion into the $Cu_{5}Zn_{8}$ IMC. In the case of the solder/ENIG joint, $AuZn_{3}$ IMCs were formed at the interface. In the case of the Sn-9Zn/ENIG, the shear strength remained nearly constant in spite of aging for 1000 hours at $150^{\circ}C$. On the other hand, in the case of the Sn-9Zn/Cu, the shear strength significantly decreased after aging at $150^{\circ}C$ for 100hours and then remained constant by further prolonged aging. Therefore, the protective plating layer such as ENIG must be used to ensure the mechanical reliability of the Sn-9Zn/Cu joint.

• Journal of the Microelectronics and Packaging Society
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• v.15 no.4
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• pp.65-70
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• 2008

The mechanical shear strength of BGA(Ball Grid Array) solder joints under high impact loading was investigated. The Sn-37Pb solder balls with a diameter of $500{\mu}m$ were placed on the pads of FR-4 substrates with ENIG(Electroless Nickel Immersion Gold) surface treatment and reflowed. For the High Temperature Storage(HTS) test, the samples were aged a constant testing temperature of $120^{\circ}C$ for up to 250h. After the HTS test, high speed shear tests with various shear speed of 0.01, 0.1, 1, 3 m/s were conducted. $Ni_3Sn_4$ intermetallic compound(IMC) layer was observed at the solder/Ni-P interface and thickness of IMC was increased with aging process. The shear strength increased with increasing shear speed. The fracture surfaces of solder joints showed various fracture modes dependent on shear speed and aging time. Fracture mode was changed from ductile fracture to brittle fracture with increasing shear speed.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.3
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• pp.81-88
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• 2019

In this study, the effects of graphene oxide (GO) addition on electromigration (EM) lifetime of Sn-3.0Ag-0.5Cu Pb-free solder joint between a ball grid array (BGA) package and printed circuit board (PCB) were investigated. After as-bonded, $(Cu,Ni)_6Sn_5$ intermetallic compound (IMC) was formed at the interface of package side finished with electroplated Ni/Au, while $Cu_6Sn_5$ IMC was formed at the interface of OSP-treated PCB side. Mean time to failure of solder joint without GO solder joint under $130^{\circ}C$ with a current density of $1.0{\times}10^3A/cm^2$ was 189.9 hrs and that with GO was 367.1 hrs. EM open failure was occurred at the interface of PCB side with smaller pad diameter than that of package side due to Cu consumption by electrons flow. Meanwhile, we observed that the added GO was distributed at the interface between $Cu_6Sn_5$ IMC and solder. Therefore, we assumed that EM reliability of solder joint with GO was superior to that of without GO by suppressing the Cu diffusion at current crowding regions.

• Journal of Welding and Joining
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• v.25 no.3
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• pp.57-63
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• 2007

Electrochemical migration characteristics of Pb-free solder alloys are quantitatively correlated with corrosion characteristics in harsh environment conditions. In-situ water drop test and corrosion resistance test for Sn-3.0Ag-0.5Cu solder alloys were carried out in NaBr and NaF solutions to obtain the electrochemical migration lifetime and pitting potential, respectively. Sn-3.0Ag-0.5Cu solder alloy shows similar ionization and electrochemical migration behavior with pure Sn because of Ag and Cu do not migrate due to the formation of resistant intermetallic compounds inside solder itself. Electrochemical migration lifetime in NaBr is longer than in NaF, which seems to be closely related to higher pitting potential in NaBr than NaF solution. Therefore, it was revealed that electrochemical migration lifetime of Sn-3.0Ag-0.5Cu solder alloys showed good correlation to the corrosion resistance, and also the initial ionization step at anode side is believed to be the rate-determining step during electrochemical migration of Pb-free solders in these environments.

• 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.

• Journal of the Korean Society of Industry Convergence
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• v.12 no.4
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• pp.215-219
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• 2009

A packaging technology based on flip-chip bonding and Pb-free solder for silicon pressure sensors on printed circuit board (PCB) is presented. First, the bump formation process was conducted by Pb-free solder. Ag-Sn-Cu solder and the pressed-screen printing method were used to fabricate solder bumps. The fabricated solder bumps had $189-223{\mu}m$ width, $120-160{\mu}m$ thickness, and 5.4-6.9 standard deviation. Also, shear tests was conducted to measure the bump shear strength by a Dage 2400 PC shear tester; the average shear strength was 74 g at 0.125 mm/s of test speed and $5{\mu}m$ shear height. Then, silicon pressure sensor packaging was implemented using the Pb-free solder and bump formation process. The characteristics of the pressure sensor were analogous to the results obtained when the pressure sensor dice are assembled and packaged using the standard wire-bonding technique.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.3
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• pp.55-61
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• 2000

Sn-37Pb and Sn-3.5Ag-0.7Cu solder balls of 0.3 mm diameter were reflow soldered with the variation of soldering peak temperature and conveyer speed of reflow machine. The peak temperatures far soldering were changed in the range of 220~$240^{\circ}C$ for Sn-37Pb and 230~$260^{\circ}C$ for Sn-3.5Ag-0.7Cu. As the results of experiments, optimum soldering condition for Sn-37Pb was $230^{\circ}C$ of soldering temp., 0.7~0.8 m/min of conveyer speed. The optimum condition for the Sn-3.5Ag-0.7Cu was $250^{\circ}C$ and 0.6 m/min. The maximum shear strength for the soldered joints of Sn-37Pb was 555 gf and of Sn-3.5Ag-0.7Cu was 617 gf. Thickness of the intermetallic compound Cu6Sn5 on the soldered interface was 1.13~1.45 $\mu\textrm{m}$ for Sn-37Pb and 2.5~4.3 $\mu\textrm{m}$ for Sn-3.5Ag-0.7Cu.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.09a
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• pp.147-163
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• 2003

European Union bans the usage of Pb in electronics from July 1 st, 2006. The Near-eutectic Sn-Ag-Cu alloys are the leading candidate Pb-free solders (for SMT card assembly). .The microstructure of Sn-Ag-Cu alloys is discussed in terms of solidification, composition and cooling rate. Methods of controlling Ag3Sn plates are discussed. .Thermo-mechanical fatigue behaviors of Sn-Ag-Cu solder joints are reviewed. Tin pest, whisker growth, electromigration of Pb-free solders are discussed.