• Proceedings of the KWS Conference
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• 2003.11a
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• pp.86-88
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• 2003

The characteristic of induction heating solder bump(solder ball: Sn-37Pb, Sn-3.5Ag, Sn-3.0Ag-0.5Cu) has analyzed in this paper. The initial condition of induction heating depends on the time and current. The shape of lead-free solder bump is better than lead solder. The shear strength of lead solder bump has decreased with aging time. The average of shear strength of solder bump is about 10N, 11N, and 11N respectively. The lead-free solder bump's shear strength is better than lead solder and varies irregularly with aging time.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.2
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• pp.157-162
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• 2010

This paper describes the thermal fatigue life prediction models for 95.5Sn-4.0Ag-0.5Cu solder joints of Flip chip package considering Under Bump Metallurgy(UBM). A 3D Finite element slice model was used to simulate the viscoplastic behavior of the solder. For two types of solder bump pitches, simulations were analyzed and the effects of underfill packages were studied. Consequently, it was found out that solder joints with underfill had much better fatigue life than solder joints without underfill, and solder joints with $300{\mu}m$ bump pitch had a longer thermal fatigue life than solder joints with $150{\mu}m$ bump pitch. Through the simulations, flip chip with lead-free solder joints should be designed with underfill and a longer bump pitch.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.11
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• pp.874-878
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• 2001

Solder bump was electroplated on wafer for flip chip application. The process is as follows. Ti/Cu were sputtered and thick PR was formed by several coating PR layer. Fine pitch vias were opened using via mask and then Cu stud and solder bump were electroplated. Finally solder bump was formed by reflow process. In this paper, we opened 40㎛ vias on 57㎛ thick PR layer and electroplated solder bump with 70㎛ height and 40㎛ diameter. After reflow process, we could form solder bump with 53㎛ height and 43㎛ diameter. In plating process, we improved the plating uniformity within 3% by using ring contact instead of conventional multi-point contact.

• Korean Journal of Metals and Materials
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• v.46 no.5
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• pp.310-314
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• 2008

Electromigration test of flip chip solder bump is performed at $140^{\circ}C$ C and $4.6{\times}10^4A/cm^2$ conditions in order to compare electromigration with thermomigration behaviors by using electroplated Sn-3.5Ag solder bump with Cu under-bump-metallurgy. As a result of measuring resistance with stressing time, failure mechanism of solder bump was evaluated to have four steps by the fail time. Discrete steps of resistance change during electromigration test are directly compared with microstructural evolution of cross-sectioned solder bump at each step. Thermal gradient in solder bump is very high and the contribution of thermomigration to atomic flux is comparable with pure electromigration effect.

• Journal of Welding and Joining
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• v.20 no.5
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• pp.72-77
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• 2002

Flip-chip interconnection that uses solder bump is an essential technology to improve the performance of microelectronics which require higher working speed, higher density, and smaller size. In this paper, the shear strength of Cr/Cr-Cu/Cu UBM structure of the high-melting solder b01p and that of low-melting solder bump after aging is evaluated. Observe intermetallic compound and bump joint condition at the interface between solder and UBM by SEM and TEM. And analyze the shear load concentrated to bump applying finite element analysis. As a result of experiment, the maximum shear strength of Sn-97wt%Pb which was treated 900 hrs aging has been decreased as 25% and Sn-37wt%Pb sample has been decreased as 20%. By the aging process, the growth of $Cu_6Sn_5$ and $Cu_3Sn$ is ascertained. And the tendency of crack path movement that is interior of a solder to intermetallic compound interface is found.

• Journal of Welding and Joining
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• v.31 no.3
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• pp.4-10
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• 2013

In electronic industry, the trend of future electronics will be flexible, bendable, wearable electronics. Until now, there is few study on bonding technology and reliability of bonding joint between chip with micro solder bump and flexible substrate. In this study, we investigated joint properties of Si chip with eutectic Sn-58Bi solder bump on Cu pillar bump bonded on flexible substrate finished with ENIG by flip chip process. After flip chip bonding, we observed microstructure of bump joint by SEM and then evaluated properties of bump joint by die shear test, thermal shock test, and bending test. After thermal shock test, we observed that crack initiated between $Cu_6Sn_5IMC$ and Sn-Bi solder and then propagated within Sn-Bi solder and/or interface between IMC and solder. On the other hands, We observed that fracture propated at interface between Ni3Sn4 IMC and solder and/or in solder matrix after bending test.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.469-474
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• 2002

Laser and hot air reflow soldering of PBGA solder ball was investigated. Experimental results showed that surface quality and shear strength of solder bumps reflowed by laser was superior than the solder bumps reflowed by hot air, and the microstructure inside the solder bumps reflowed by laser was much finer. Analysis on interfacial reaction showed that eutectic solder reacted with Au/Ni/Cu pad shortly after the solder was melted. Interface of solder bump reflowed by laser consists of a continuous AuSn$_4$ layer and remnant Au element. Needle-like AuSn$_4$ grew sidewise from interface, and then spread out to the entire interface region. A thin layer of Ni$_3$Sn$_4$ intermetallic compound was found at the interface of solder bump reflowed by hot air, AuSn$_4$ particles distributed inside the whole solder bump randomly. It is the combination effect of the continuous AuSn$_4$ layer and finer eutectic microstructure inside the solder bump reflowed by laser that resulted in higher shear strength.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.4
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• pp.23-29
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• 2000

We demonstrate the fabrication method of high-density and high-quality solder bump solving a copper (Cu) cross-contamination in Si-LSI laboratory. The Cu cross-contamination is solved by separating solder-bump process by two steps. Former is via-formation process excluding Cu/Ti under ball metallurgy (UBM) layer sputtering in Si-LSI laboratory. Latter is electroplating process including Ti-adhesion and Cu-seed layers sputtering out of Si-LSI laboratory. Thick photoresist (PR) is achieved by a multiple coating method. After TiW/Al-electrode sputtering for electroplating and via formation in Si-LSI laboratory, Cu/Ti UBM layer is sputtered on sample. The Cu-seed layer on the PR is etched during Cu-electroplating with low-electroplating rate due to a difference in resistance of UBM layer between via bottom and PR. Therefore Cu-buffer layer can be electroplated selectively at the via bottom. After etching the Ti-adhesion layer on the PR, Sn/Pb solder layer with a composition of 60/40 is electroplated using a tin-lead electroplating bath with a metal stoichiometry of 60/40 (weight percent ratio). Scanning electron microscope image shows that the fabricated solder bump is high-uniformity and high-quality as well as symmetric mushroom shape. The solder bumps with even 40/60 $\mu\textrm{m}$ in diameter/pitch do not touch during electroplating and reflow procedures. The solder-bump process of high-uniformity and high-density with the Cu cross-contamination free in Si-LSI laboratory will be effective for electronic microwave application.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.181-183
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• 2006

This paper studies the mechanical behaviors of Sn-3.5Ag solder joint against substrate(such as Au/Ni/Cu, Au/cu, Ni/Cu and Cu pad) after induction heating, a new soldering method. It was found that the solder bump formation depends on the time and current of the induction heating system. Also the heating value of the solder bump were found to vary with respect to the thermal conductivity of the pads on the substrate. In case of Au/Ni/Cu pad and Au/Cu pad, solder bump's shear strength were high for the heating time of $1.5{\sim}2sec$. For Ni/Cu pad, solder bump's shear strength were found to increase with time increment.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.11a
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• pp.49-53
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• 2002

The Sn-Cu eutectic solder bump formation ($140{\mu}{\textrm}{m}$ diameter, $250{\mu}{\textrm}{m}$ pitch) by electroplating was studied for flip chip package fabrication. The effect of current density and plating time on Sn-Cu deposit was investigated. The morphology and composition of plated solder surface was examined by scanning electron microscopy. The plating thickness increased with increasing time. The plating rate increased generally according to current density. After the characteristics of Sn-Cu plating were investigated, Sn-Cu solder bumps were fabricated on optimal condition of 5A/dm$^2$, 2hrs. Ball shear test after reflow was performed to measure adhesion strength between solder bump and UBM (Under Bump Metallization). The shear strength of Sn-Cu bump after reflow was higher than that of before reflow.