• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.100-103
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• 2007

A microlens array has been required to improve light conversion efficiency in image sensors. A microlens array can be usually fabricated by photoresist reflow, hot-embossing, micro injection molding, and UV-imprinting. Among these processes, a UV-imprinting, which is operated at room temperature with relatively low applied pressure, can be a desirable process to integrate microlens array on image sensors, because this process provides the components with low thermal expansion, enhanced stability, and low birefringence, furthermore, it is more suitable for mass production of high quality microlens array. In this study, to analyze the optical properties of the wafer scale microlens array integrated image sensor, another wafer scale simulated image sensor chip array was designed and fabricated. An aspherical square microlens was designed and integrated on a simulated image sensor chip array using a UV-imprinting process. Finally, the optical performances were measured and analyzed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.6
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• pp.575-579
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• 2004

Package reliability test was conducted to investigate the effect of solder paste composition at BGA Package. It was found that the shape and size of the phase form are affected by the processing parameters. The material have used to fill in the via was Sn/36Pb/2Ag and Sn/0.75Cu type solder paste. Sn/36Pb/2Ag and Sn/0.75Cu paste were fabricated on Tape-BGA substrates by screen printing process, and via ball mount data were characterized with variations of dwell time of 85 seconds at reflow peak temperature at 22$0^{\circ}C$ or 24$0^{\circ}C$. The test condition was MRT 30 $^{\circ}C$/60 %RH/96 HR. Failures formed of a ball-off in solder paste process were observed by using a Optical Microscope and SEM(Scanning Electron Microscope). It was concluded that intermetallic layer growth played important roles in increasing solder fatigue strength for addition of Ag composition. The degradation of shear strength of solder composition is discussed.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.1
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• pp.69-74
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• 2015

With difficulties during the cleaning of reflow flux residues due to the decrease of the part size and interconnection pitch in the advanced electronic devices, the need for the no-clean solder paste is increasing. In this study, an epoxy curable solder paste was made with SAC305 solder powder and the curable flux of which the main ingredient is epoxy resin and its reflow solderability, flux residue corrosivity and solder joint mechanical properties was investigated with comparison to the commercial rosin type solder paste. The fillet shape of the cured product around the reflowed solder joint revealed that the curing reaction occurred following the fluxing reaction and solder joint formation. The copper plate solderability test result also revealed that the wettability of the epoxy curable solder paste was comparable to those of the commercial rosin type solder pastes. In the highly accelerated temperature and humidity test, the cured product residue of the curable solder paste showed no corrosion of copper plate. From FT-IR analysis, it was considered to be resulted from the formation of tight bond through epoxy curing reaction. Ball shear, ball pull and die shear tests revealed that the adhesive bonding was formed with the solder surface and the increase of die shear strength of about 15~40% was achieved. It was considered that the epoxy curable solder paste could contribute to the improvement of the package reliability as well as the removal of the flux residue cleaning process.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.3
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• pp.89-93
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• 2020

Complex warpage behavior of the electronic packages causes internal stress so many kinds of mechanical failure occur such as delamination or crack. Efforts to predict the warpage behavior accurately in order to prevent the decrease in yield have been approached from various aspects. For warpage prediction, silicon is generally treated as a homogeneous material, therefore it is described as showing no warpage behavior due to thermal loading. However, it was reported that warpage is actually caused by residual stress accumulated during grinding and polishing in order to make silicon wafer thinner, which make silicon wafer inhomogeneous through thickness direction. In this paper, warpage behavior of the single-side polished wafer at solder reflow temperature, the highest temperature in packaging processes, was measured using 3D digital image correlation (DIC) method. Mechanism was verified by measuring coefficient of thermal expansion (CTE) of both mirror-polished surface and rough surface.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.3
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• pp.9-18
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• 1999

In this study, Metallugical properties between Sn-3.5Ag, Sn-37Pb eutectic solders and Au/Ni/cu substrate according to time span above the melting point were investigated. A conventional reflow soldering machine wert used for this study and time span above the melting point was determined by changing peak soldering temperature and conveyor speed. As results, scallop type intermetallic compounds of $Ni_3Sn_4$ were formed at joint interface and no Cu-Sn compounds were found at all; Ni layer performed as a barrier for Cu diffusion. As the peak soldering temperature increased, thickness of the intermetallic compound layer increased; maximum thickness of the scallop-layer was 2.2$\mu\textrm{m}$. The shape of scallops were transformed from hemi-sphere type to elliptical shape with smaller size. Micro-hardness of the solder joint decreased as the eutectic structure of Sn-3.5Ag and Sn-37Pb increased.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.1
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• pp.1-6
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• 2014

Flip chip bonded LED packages possess lower thermal resistance than wire bonded LED packages because of short thermal path. In this study, thermal and bonding properties of flip chip bonded high brightness LED were evaluated for Au-Sn thermo-compression bonded LEDs and Sn-Ag-Cu reflow bonded LEDs. For the Au-Sn thermo-compression bonding, bonding pressure and bonding temperature were 50 N and 300oC, respectively. For the SAC solder reflow bonding, peak temperature was $255^{\circ}C$ for 30 sec. The shear strength of the Au-Sn thermo-compression joint was $3508.5gf/mm^2$ and that of the SAC reflow joint was 5798.5 gf/mm. After the shear test, the fracture occurred at the isolation layer in the LED chip for both Au-Sn and SAC joints. Thermal resistance of Au-Sn sample was lower than that of SAC bonded sample due to the void formation in the SAC solder.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2001.07a
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• pp.119-126
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• 2001

Chip-on-glass(COG) mounting of area array electronic packages was attempted by heating the rear surface of a contact pad film deposited on a glass substrate. The pads consisted of an adhesion(i.e. Cr or Ti) and a top coating layer(i.e. Ni or Cu) was heated by an UV laser beam transmitted through the glass substrate. The laser energy absorbed on the pad raised the temperature of a solder ball which is in physical contact with the pad, forming a reflowed solder bump. The effects of the adhesion and top coating layer on the laser reflow soldering were studied by measuring temperature profile of the ball during the laser heating process. The results were discussed based on the measurement of reflectivity of the adhesion layer. In addition, the microstructures of solder bumps and their mechanical properties were examined.

• Transactions of Materials Processing
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• v.13 no.3
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• pp.290-295
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• 2004

Mircolens and microlens V-groove are realized using a novel fabrication technology based on the exposure of a resist, usually PMMA, to deep X-rays and subsequent thermal treatment and inclined deep X-ray lithography, respectively. The fabrication technology is very simple and produces microlenses and microlens V-groove with good surface roughness of several nm. The molecular weight and glass transition temperature of PMMA is reduced when it is irradiated with deep X-rays. The microlenses were produced through the effects of volume change, surface tension, and reflow during thermal treatment of irradiated PMMA. Microlenses were produced with diameters ranging from 30 to $1500\mu\textrm{m}$. The surface X-ray mask is also fabricated to realize microlens arrays on PMMA sheet with a large area. The size of the micro V-groove is fabricated in the range of 12~$60\mu\textrm{m}$.

• Journal of Welding and Joining
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• v.15 no.2
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• pp.36-42
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• 1997

In this paper, stability of initial strength at solder joint with lead free solders, such as Sn-In (52-48%) and Sn-Ag (96.5-3.5wt%) was studied. To obtain at solder joint with high quality, it is very important to control the temperature at the interface of solder joints. It is found that the thermal EMF (electro motive force) occurs betwee lead frame and copper pad on a substrate during reflow soldering process using heated tip. As a result of control the temperature at interface of solder joints, variation of initial strength at solder joint decreases from about $\pm40%$ to $\pm20%$, and it is realized Pb free soldering process using Sn/In and Sn-Ag solder paste.

• 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.