• Journal of Welding and Joining
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• v.16 no.5
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• pp.100-107
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• 1998

This paper describes fluxless soldering of reflow soldering process using solder foil instead of solder pastes. There is an increasing demand for the reliable solder connection in the recent high density microelectronic components technologies. And also, it is problem fracture of an Ozone layer due to freon as which is used to removal of remained flux on the substrate. This paper discussed joining phenomena, boudability and joining processes of microelectronics devices, such as between outer lead of VLSI package and copper pad on a substrate without flux. The shear strength of joints is 8 to 13 N using Sn/Pb (63/37 wt.%) solder foil with optimum joining conditions, meanwhile, in case of using Sn/In (52/48 wt.%) solder foil, it is possible to bond with low heating temperature of 550 K, and accomplish to high bonding strength of 25N in condition heating temperature of 650K. Finally, this paper experimentally shows fluxless soldering using solder foil, and accomplishes key technology of microsoldering processes.

• 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 $1\mu\textrm{m}$.

• 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.

• Journal of Welding and Joining
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• v.20 no.4
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• pp.498-504
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• 2002

Fluxless flip chip bonding process using plasma treatment instead of flux was investigated. The effect of plasma process parameters on tin-oxide etching characteristics were estimated with Auger depth profile analysis. The die shear test was performed to evaluate the adhesion strength of the flip chip bonded after plasma treatment. The thickness of oxide layer on tin surface was reduced after Ar+H2 plasma treatment. The addition of H2 improved the oxide etching characteristics by plasma. The die shear strength of the plasma-treated Sn-Pb solder flip chip was higher than that of non-treated one but lower than that of fluxed one. The difference of the strength between plasma-treated specimen and non-treated one increased with increase in bonding temperature. The plasma-treated flip chip fractured at solder/TSM interface at low bonding temperature while the fracture occurred at solder/UBM interface at higher bonding temperature.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.439-449
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• 2002

This paper reviews our recent research works on the interconnection technologies in electronic packaging and assembly. At the aspect of advanced joining methods, laser-ultrasonic fluxless soldering technology was proposed. The characteristic of this technology is that the oxide film was removed through the vibration excitated by high frequency laser change in the molten solder droplet. Application researches of laser soldering technology on solder bumping of BGA packages were carried out. Furthermore, interfacial reaction between SnPb eutectic solder and Au/Ni/Cu pad during laser reflow was analyzed. At the aspect of soldered joints' reliability, the system for predicting and analyzing SMT solder joint shape and reliability(PSAR) has been designed. Optimization design method of soldered joints' structure was brought forward after the investigation of fatigue failure of RC chip devices and BGA packages under temperature cyclic conditions with FEM analysis and experimental study. At the aspect of solder alloy design, alloy design method based on quantum was proposed. The macroproperties such as melting point, wettability and strength were described by the electron parameters. In this way, a great deal of the experimental investigations was replaced, so as to realize the design and research of any kinds of solder alloys with low cost and high efficiency.

• Journal of Welding and Joining
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• v.18 no.6
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• pp.74-82
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• 2000

The fluxless wetting properties of UBM-coated Si-wafer to the binary lead-free solders(Sn-Ag, Sn-Sb, Sjn-In, Sn0Bi) were estimated by wetting balance method. With the new wettability indices from the wetting curves of one side coated specimen, the wetting property estimation of UBM-coated Si-wafer was possible. For UBM of Si-chip, Au/Cu/Cr UBm was better than au/Ni/TI in the point of wetting time/ At general reflow process temperature, the wettability of high melting point solders(Sn-Sb, Sn-Ag) was better than that of low melting point one(Sn-Bi, Sn-In). The contact angle of the one side coated Si-plate to the solder could be calculated from the force balance equation by measuring the static state force and the tilt angle.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2001.11a
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• pp.138-140
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• 2001

Fluxless flip chip bonding using plasma & ultrasonic wave was investigated in order to evaluate the effect of plasma & ultrasonic treatment on the bondability of the Sn-3.5wt%Ag solder bumped die to TSM-coated glass substrate. The $Ar+10%H_2plasma$ was effective in removing tin oxide on solder surface. The die shear strength of the plasma-treated Si-chip is higher than that of non-treated specimen but lower than that of specimen bonded with flux. The die shear strength with the bonding load at 25W ultrasonic power increased to 0.8N/bump for all bonding temperature but decreased above 1.0N/bump.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.2 s.31
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• pp.23-28
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• 2004

We utilized Ag capping layer for fluxless bonding. To investigate the effect of Ag capping layer, two sets of sample were used. One set was bare In and Sn solders. The other set was In and Sn solders with Ag capping layer. In ($10{\mu}m$) and Sn ($10{\mu}m$) solders were deposited on Cu/Ti/Si substrate using thermal-evaporation, and Ag ($0.1{\mu}m$) capping layers were deposited on In and Sn solders. Solder joints were made by joining two In and Sn deposited specimens at $130^{\circ}C$ for 30 s under 0.8, 1.6, 3.2 MPa using thermal compression bonder. The contact resistance was measured using four-point probe method. The shear strength of the solder joints was measured by the shear test of cross-bar sample in the direction. The microstructure of the solder joints was characterized with SEM and EDS. In and Sn solders without Ag capping layers were only bonded at $130^{\circ}C$ under high bonding pressure. Also the shear strength of the In-Sn solder joints under was lower than that of the Ag/In-Ag/Sn solder joints. The resistance of the solder joints was $2-4\;m{\Omega}$ The solder joints consisted of In-rich phase and Sn-rich phase and the intermixed compounds were found at the interface. As bonding pressure increased, the intermixed compounds formed more.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.221.2-221.2
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• 2005

• Journal of the Microelectronics and Packaging Society
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• v.14 no.2 s.43
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• pp.49-57
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• 2007

Au-Sn solder alloy were deposited in multilayer and co-sputtered film by rf-magnetron sputter and the composition control and analysis were studied. For the alloy deposition condition, each components of Au or Sn were deposited separately. On the basis of pure Sn and Au deposition, the deposition condition for Au-Sn solder alloy were set up. As variables, the substrate temperature, the rf-power, and the thickness ratio were used for the optimum composition. For multilayer solder alloy, the roughness and the composition of solder alloy were controlled more accurately at the higher substrate temperature. In contrast, for co-sputtered solder, the substrate temperature influenced little to the composition, but the composition could be controlled easily by rf-power. In addition, the co-sputtered solder film mostly consisted of intermetallic compound, which formed during deposition. The compound were confirmed by XRD. Without flux during bonding of solder alloy film on leadframe, the adhesion strength were measured. The maximum shear stress was $330(N/mm^2)$ for multilayer solder with Au 10wt% and $460(N/mm^2)$ for co-sputtered solder with Au 5wt%.