• Journal of the Korean institute of surface engineering
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• v.36 no.5
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• pp.373-378
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• 2003

With increasing environmental concerns, application of lead-free solder and fluxless soldering process have been taken attention from the electronic packaging industry. Plasma treatment is one of the soldering methods for the fluxless soldering, and it can prevent environmental pollution cased by flux. On this study fluxless soldering process under $Ar-H_2$plasma using lead free solders such as Sn-3.5 wt%Ag, Sn-3.5 wt%Ag-0.7 wt%Cu and Sn-37%Pb for a reference was investigated. As the plasma reflow has higher soldering temperature than normal air reflow, the effects of UBM(Under Bump Metallization) thickness on the interfacial reaction and bonding strength can be critical. Experimental results showed in case of the thin UBM, Au(20 nm)/Cu(0.3 $\mu\textrm{m}$)/Ni(0.4 $\mu\textrm{m}$)/Al(0.4 $\mu\textrm{m}$), shear strength of the soldered joint was relatively low as 19-27㎫, and it's caused by the crack observed along the bonded interface. The crack was believed to be produced by the exhaustion of the thin UBM-layer due to the excessive reaction with solder under plasma. However, in case of thick UBM, Au(20 nm)/Cu(4 $\mu\textrm{m}$)/Ni(4 $\mu\textrm{m}$)/Al(0.4 $\mu\textrm{m}$), the bonded interface was sound without any crack and shear strength gives 32∼42㎫. Thus, by increasing UBM thickness in this study the shear strength can be improved to 50∼70%. Fluxed reflow soldering under hot air was also carried out for a reference, and the shear strength was 48∼52㎫. Consequently the fluxless soldering with plasma showed around 65∼80% as those of fluxed air reflow, and the possibility of the $Ar-H_2$ plasma reflow was evaluated.

• Proceedings of the KWS Conference
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• 2000.10a
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• pp.284-286
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• 2000

• Journal of Welding and Joining
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• v.19 no.3
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• pp.305-310
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• 2001

UBM-coated Si-wafer was fluxlessly soldered with glass substrate in $N_2$ atmosphere using plasma cleaning method. The bulk Sn-37wt.%Pb solder was rolled to the sheet of $100\mu\textrm{m}$ thickness in order to bond a solder disk by fluxless 1st reflow process. The oxide layer on the solder surface was analysed by AES(Auger Electron Spectroscopy). Through rolling, the oxide layer on the solder surface became thin, and it was possible to bond a solder disk on the Si-wafer with fluxless process in $N_2$ gas. The Si-wafer with a solder disk was plasma-cleaned in order to remove oxide layer formed during 1st reflow and soldered to glass by 2nd reflow process without flux in $N_2$ atmosphere. The thickness of oxide layer decreased with increasing plasma power and cleaning time. The optimum plasma cleaning condition for soldering was 500W 12min. The joint was sound and the thicknesses of intermetallic compounds were less than $1\mu\textrm{m}$.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2000.11a
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• pp.75-78
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• 2000

• Journal of the Microelectronics and Packaging Society
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• v.11 no.1
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• pp.77-85
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• 2004

To evaluate the effect of plasma cleaning on the soldering reliability the plasma cleaning using Ar-10vol%$H_2$ gas was applied on a UBM(Under Bump Metallization). The UBM consisted of Au/ Cu/ Ni/ Al layers which were deposited on a Si-wafer with 20 nm/ 4 $\mu\textrm{m}$/ 4 $\mu\textrm{m}$/ 0.4 $\mu\textrm{m}$ thickness respectively. Sn-3.5%Ag, Sn-3.5%Ag-0.7%Cu and Sn-37%Pb solder balls sized of 500 $\mu\textrm{m}$ in diameter were used. Solder balls on the UBM were plasma reflowed under Ar-10%$H_2$ plasma (with or without plasma cleaning). They were compared with air reflowed solder balls with flux. The spreading ratios of plasma reflowed solder with plasma cleaning was 20-40% higher than that of plasma reflowed solder without plasma cleaning. The shear strength of plasma reflowed solder with plasma cleaning was about 58-65MPa. It showed 60-80% higher than that of plasma reflowed solder without plasma cleaning and 15-35% higher than that of air reflowed solder. Thus it was believed that plasma cleaning for the UBM using Ar-10vol%$H_2$ gas was considerably effective for the improvement of the strength of solder ball.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.11a
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• pp.105-108
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• 2002

환경에 관한 관심이 증대되면서 Sn37Pb 솔더를 대체하기 위한 새로운 무연솔더의 개발이 진행되고 있다1). 또한 연구의 초점이 되고 있는 것이 플럭스의 사용에 관한 것이다. 플럭스는 솔더의 산화막을 제거하는데 필수적이지만, 플럭스 세정제의 독성 문제로 무플럭스 솔더링에 대한 관심이 크게 증대되고 있다2),3). 무플럭스 솔더링의 방법에는 여러 가지가 있으며, 그 중 한가지가 플라즈마를 이용한 방법이다4). 본 연구에서는 솔더표면의 이물질과 산화막을 제거하기 위한 플라즈마 처리가 접합 후, 접합부에 미치는 영향에 대해서 알아보았다. 기판은 Evaporator를 이용하여 Au/Cu/Ni/Al UBM을 증착한 Si-wafer를 사용하였다. 사용된 솔더는 Sn37Pb, Sn3.5Ag와 Sn3.5Ag0.7Cu 솔더볼이며, 열중 및 적외선 겸용 리플로 머신과 Ar＋H$_2$를 이용한 플라즈마 에쳐를 사용하여 범프를 형성하였다. 플라즈마 처리가 계면의 미세조직과 기계적 강도에 끼치는 영향을 알아보기 위하여 플라즈마 처리된 시편과 리플로 한 후의 시편을 비교 분석하였다. 전단시험기로 계면의 강도를 측정하였으며, 주사전자현미경으로 범프의 표면과 계면 및 전단파면을 관찰하고 이에 대하여 고찰하였다. 산화막제거를 위한 플라즈마 처리가 저음점인 솔더의 미세조직을 기존의 솔더링 접합부와는 다르게 변화시킴으로써 솔더부의 전체적인 특성에 영향을 끼치는 것을 알 수 있었다.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.99-106
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• 2011

Joint strength between a solder ball and a pad on a substrate is one of the major factors which have effects on electronic device reliability. The effort to improve solder joint strength via surface cleaning, heat treatment and solder composition change have been in progress. This paper will discuss the method of solder ball joint strength improvement using LF hydrogen radical cleaning treatment and focus on the effects of surface treatment condition on the solder ball shear strength and interfacial reactions. In the joint without radical cleaning, voids were observed at the interface. However, the specimens cleaned by hydrogen-radical didn't have voids at the interface regardless of cleaning time. The shear strength between the solder ball and the pad was increased over 120%(about 800gf) when compared to that without the radical treatment (680gf) under the same reflow condition. Especially, at the specimen treated for 5minutes, ball shear strength was considerably increased over 150%(1150gf). Through the observation of fracture surface and cross-section microstructure, the increase of joint strength resulted from the change of fracture mode, that is, from the solder ball fracture to IMC/Ni(P) interfacial fracture. The other cases like radical treated specimen for 1, 3, 7, 9min. showed IMC/solder interfacial fracture rather than fracture in the solder ball.