• Journal of Sensor Science and Technology
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• v.16 no.5
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• pp.325-330
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• 2007

For the application to optic devices, wafer level package including spacer with particular thickness according to optical design could be required. In these cases, the uniformity of spacer thickness is important for bonding strength and optical performance. Packaging process has to be performed at low temperature in order to prevent damage to devices fabricated before packaging. And if photosensitive material is used as spacer layer, size and shape of pattern and thickness of spacer can be easily controlled. This paper presents polymer bonding using thick, uniform and patterned spacing layer of SU-8 2100 photoresist for wafer level package. SU-8, negative photoresist, can be coated uniformly by spin coater and it is cured at $95^{\circ}C$ and bonded well near the temperature. It can be bonded to silicon well, patterned with high aspect ratio and easy to form thick layer due to its high viscosity. It is also mechanically strong, chemically resistive and thermally stable. But adhesion of SU-8 to glass is poor, and in the case of forming thick layer, SU-8 layer leans from the perpendicular due to imbalance to gravity. To solve leaning problem, the wafer rotating system was introduced. Imbalance to gravity of thick layer was cancelled out through rotating wafer during curing time. And depositing additional layer of gold onto glass could improve adhesion strength of SU-8 to glass. Conclusively, we established the coating condition for forming patterned SU-8 layer with $400{\mu}m$ of thickness and 3.25 % of uniformity through single coating. Also we improved tensile strength from hundreds kPa to maximum 9.43 MPa through depositing gold layer onto glass substrate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.8
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• pp.1388-1397
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• 2003

Since the reliability of adhesively bonded joints for composite structures is dependent on many parameters such as the shape and dimensions of joints, type of applied load, and environment, so an accurate estimation of the fatigue life of adhesively bonded joints is seldom possible, which necessitates an in-situ reliability monitoring of the joints during the operation of structures. In this study, a self-sensor method for adhesively bonded joints was devised, in which the adhesive used works as a piezoelectric material to send changing signals depending on the integrity of the joint. From the investigation, it was found that the electric charge increased gradually as cracks initiated and propagated in the adhesive layer, and had its maximum value when the adhesively bonded joint failed. So it is feasible to monitor the integrity of the joint during its lifetime. Finally, a relationship between the piezoelectric property of the adhesive and crack propagation was obtained from the experimental results.

• Proceedings of the Optical Society of Korea Conference
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• 2002.07a
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• pp.254-255
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• 2002

Optical elements such as small glass lenses or optical fibers can be permanently bonded to substrates using Al inter-layer by applying Pressure and heating. As an example aspherical lens was bonded on a silicon V-groove. The bonding has high shear strength and good thermal cycling stability.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.3
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• pp.217-222
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• 1981

The stress analysis of two-orthotropic layer, adhesively bonded structures is considered. An orthotropic plate has a through-crack of finite length and is adhesively bounded by a sound orthotropic plate. The problem is resuced to a pair of Fredholm integral equations ofthe second kind. Using a numerical integration scheme to evaluate the intgrals, The integral equations are reduced to a system of algebraic equations. By solving these equations some numerical results for stress intensity factors are presented for various crack lengths.

• Journal of the Korean Society for Heat Treatment
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• v.16 no.5
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• pp.260-266
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• 2003

In order to study the interfacial reaction between Nb thin sheet and Fe-C-(Si) alloy with different Chemical compositions, they were cast-bonded. The growth of carbide layer formed at the interface after isothermal heat treatment at 1173K, 1223K, 1273K and 1323K for various times was investigated. The carbide formed at the interface was NbC and the thickness of NbC layer was increased linearly in proportional to the heat treating time. Therefore, It was found that the growth of NbC layer was controlled by the interfacial reaction. The growth rate constant of NbC layer was slightly increased with increase of carbon content when the silicon content is similar in the cast irons. However, as silicon content increases with no great difference in carbon content, the growth of NbC layer was greatly retarded. The calculated activation energy for the growth of NbC layer was varied in the range of 447.4~549.3 kJ/moI with the compositions of cast irons.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.5
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• pp.81-88
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• 2002

An interface crack of a piezoelectric medium bonded between an elastic layer and a half-space is analyzed using the theory of linear piezoelectricity. Both out-of-plane mechanical and in-plane electrical loads are applied to the piezoelectric laminate. By the use of courier transforms, the mixed boundary value problem is reduced to a singular integral equation which is solved numerically to determine the stress intensity factors. Numerical analyses for various material combinations are performed and the results are discussed.

• Transactions on Electrical and Electronic Materials
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• v.15 no.4
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• pp.221-225
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• 2014

Although gold wire bonding techniques have already matured in semiconductor manufacturing, weakly bonded wires in semiconductor chip assembly can jeopardize the reliability of the final product. In this paper, weakly bonded or failed aluminum bonding pads are analyzed using X-ray photoelectron spectroscopy (XPS), Auger electron Spectroscopy (AES), and energy dispersive X-ray analysis (EDX) to investigate potential contaminants on the bond pad. We found the source of contaminants is related to the dry etching process in the previous manufacturing step, and fluorocarbon plasma etching of a passivation layer showed meaningful evidence of the formation of fluorinated by-products of $AlF_x$ on the bond pads. Surface analysis of the contaminated aluminum layer revealed the presence of fluorinated compounds $AlOF_x$, $Al(OF)_x$, $Al(OH)_x$, and $CF_x$.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.150-153
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• 2003

Longitudinal strains({$varepsilon}_x$) of the core and skin layers in glass fiber reinforced plastic(GFRP) cross-ply composite laminates have been studied using the embedded optical fiber sensor of totally-reflected extrinsic Fabry-Perot interferometer(TR-EFPI). Foil-type strain gauges bonded on both the upper and lower surfaces were used for the measurement of the surface strains. Both TR-EFPI sensor and strain gauge bonded on the specimen surface showed excellent agreement within -0.0086 ~ +0.0302% strain. It was shown that values of {$varepsilon}_x$ in the interior of the surface layer and the core layer measured by embedded TR-EFPI sensor was significantly higher than that of the specimen surface measured by strain gauges. The experimental results were ascertained with finite element analysis. Embedded TR-EFPI optical fiber sensor could measure accurately the internal strains which were different from the surface.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.22-26
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• 2001

In this paper, we examine the steady state dynamic electromechanical behavior of an eccentric Yoffe crack in a piezoelectric ceramic layer bonded between two orthotropic elastic layers under the combined anti-plane mechanical shear and in-plane electrical loadings. We adopted permeable crack face condition. Numerical values on the dynamic energy release rate are obtained. The initial crack propagation orientation for PZT-5H piezoceramic is also predicted by maximum energy release rate criterion.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.129-134
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• 1996

Bonding strength of reinforcing material has been recognized to be the most important factor which determines the strengthening effect and the durability of repair work. The properties of bonding layers affects the stress distribution at the end of the plate, therefore the behavior of bonding layer has to be investigated. In this study, the stress distribution at the end of the bonded plate has been tested and compared with Roberts' analysis. Shear stress and vertical normal stress at the end of strengtening plate are analysized and the effedts of bonding layer thickness, plate thickness and plate length on the bonding behavior are tested. The test results showed that thickness is one of the most important factor, which is the thinner the thickness, the smaller the maximum stress.