• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.8 s.227
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• pp.1087-1092
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• 2004

Adhesion and friction forces influence adversely on performance and durability of MEMS. It has been reported that the adhesion and friction forces can be reduced with the introduction of micro surface bumps into the contacting interfaces. In this study experiments were conducted to investigate comparatively the effect of hemispherical and torus micro bumps on the adhesion and friction forces. It is confirmed that micro bumps reduce the adhesion and friction forces, and their effect is more pronounced with the bumps of smaller outer boundary radius. Moreover, the results shows that the torus bumps exhibit more rapid decrease of the adhesion and friction forces with the decrease in the outer boundary radius of bump than the hemispherical bumps. When the magnitude of adhesion force is same, the torus bumps generate smaller friction force than the hemispherical bumps. The usage of hemispherical and torus bumps to reduce the adhesion and friction forces in MEMS is discussed.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.3
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• pp.1-10
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• 2023

Recently, as the demand for high-performance computers and mobile products increases, semiconductor packages are becoming high-integration and high-density. Therefore, in order to transmit a large amount of data at once, micro bumps such as flip-chip and Cu pillar that can reduce bump size and pitch and increase I/O density are used. However, when the size of the bumps is smaller than 70 ㎛, the brittleness increases and electrical properties decrease due to the rapid increase of the IMC volume fraction in the solder joint, which deteriorates the reliability of the solder joint. Therefore, in order to improve these issues, a layer that serves to prevent diffusion is inserted between the UBM (Under Bump Metallization) or pillar and the solder cap. In this review paper, various studies to improve bonding properties by suppressing excessive IMC growth of micro-bumps through additional layer insertion were compared and analyzed.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.3
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• pp.408-414
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• 2012

Screen printing is a printing method that uses a woven mesh to support an ink-blocking stencil by transferring ink or other printable materials in order to form an image onto a substrate. Recently, the screen printing method has applied to micro-electronic packaging by using solder paste as a printable material. For the screen printing of solder paste, metal masks containing a number of micro-holes are used as a stencil material. The metal mask undergoes deformation when it is installed in the screen printing machine, which results in the deformation of micro-holes. In the present study, finite element (FE) analysis was performed to predict the amount of deformation of a metal mask. For an efficient calculation of the micro-holes of the metal mask, the sub-domain analysis method was applied to perform FE analyses connecting the global domain (the metal mask) and the local domain (micro-holes). The FE analyses were then performed to evaluate the effects of slot designs on the deformation characteristics, from which more uniform and adjustable deformation of the metal mask can be obtained.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.1
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• pp.26-32
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• 2012

In the present study, the stencil printing process using solder paste are numerically analyzed. The key design parameters in the stencil printing process are the printing conditions, stencil design, and solder paste properties. Among these parameters, the effects of printing conditions including the squeegee angle and squeegee pressure are investigated through finite element (FE) analysis. However, the FE analysis for the stencil printing process requires tremendous computational loads and time because this process carries micro-filling through thousands of micro-apertures in stencil. To overcome this difficulty in simulation, the present study proposes a two-step approach to sequentially perform the global domain analysis and the local domain analysis. That is, the pressure development under the squeegee are firstly calculated in the full analysis domain through the global analysis. The filling stage of the solder paste into a micro-aperture is then analyzed in the local analysis domain based on the results of the preceding global analysis.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.235-237
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• 2007

In this paper, fabrication of Sn-3.0Ag-0.5Cu solder bumping having accurate composition and behavior of intermetallic compounds(IMCs) growth at interface between Sn-Ag-Cu bumps and Cu substrate were studied. The ternary alloy of the Sn-3.0Ag-0.5Cu solder was made by two binary(Sn-Cu, Sn-Ag) electroplating on Cu pad. For the manufacturing of the micro-bumps, photo-lithography and reflow process were carried out. After reflow process, the micro-bumps were aged at $150^{\circ}C$ during 1 hr to 500 hrs to observe behavior of IMCs growth at interface. As a different of Cu contents(0.5 or 2wt%) at Sn-Cu layer, behavior of IMCs was estimated. The interface were observed by FE-SEM and TEM for estimating of their each IMCs volume ratio and crystallographic-structure, respectively. From the results, it was found that the thickness of $Cu_3Sn$ layer formed at Sn-2.0Cu was thinner than the thickness of that layer be formed Sn-0.5Cu. After aging treatment $Cu_3Sn$ was formed at Sn-0.5Cu layer far thinner.

• Korean Journal of Materials Research
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• v.18 no.3
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• pp.117-122
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• 2008

Micro-sized bumps on a multi-layered build-up PCB were fabricated by pulse-reverse copper electroplating. The values of the current density and brightener content for the electroplating were optimized for suitable performance with maximum efficiency. The micro-bumps thus electroplated were characterized using a range of analytical tools that included an optical microscope, a scanning electron microscope, an atomic force microscope and a hydraulic bulge tester. The optical microscope and scanning electron microscope analyses results showed that the uniformity of the electroplating was viable in the current density range of $2-4\;A/dm^2$; however, the uniformity was slightly degraded as the current density increased. To study the effect of the brightener concentration, the concentration was varied from zero to 1.2 ml/L. The optimum concentration for micro-bump electroplating was found to be 0.6 ml/L based on an examination of the electroplating properties, including the roughness, yield strength and grain size.

• Tribology and Lubricants
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• v.19 no.2
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• pp.102-108
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• 2003

The height of laser bumps has been considered as the limit of the minimum flying height in the contact start-stop (CSS) of hard disk drives. In this paper, tribological interactions at flying height under laser bumps are investigated in a spin stand for development of ultra-low flying head-disk interface. With the reduction of the spinning speed in a spin stand, the flying height is decreased under the height of laser bumps and, then, head-disk interactions are investigated using AE and stiction/friction signals. During seek tests and 20000 cycle-sweep tests, AE and stiction/friction signals are not significantly changed and there are no catastrophic failures of head-disk interface. Bearing analysis and AFM analysis show that there are signs of wear and plastic deformation on the disks. It is suggested that flying height could be as low as and, sometimes, lower than laser bump height.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.842-845
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• 2000

It is essential to reduce stiction between the slider and the disk for super-smooth media such as glass disk for high density recording. We developed a stiction-reduced slider by fabricating mechanical bumps on the air bearing surface of the slider by indentation technique. This paper presents a possibility and concept of Stiction-Free-Slider which can operate on the data zone of a magnetic disk. The slider hat many bumps and their heights are in the tens of nm range. The SFS shows good performance on the data zone. Moreover, little wear of the bumps was observed when the preload was small.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.122-126
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• 2001

Magnetic hard disk drive is continually being pushed to reduce head-disk spacing for higher recording densities. The current minimum spacing between the air-bearing slider and disk has been reduced to under 15 nm. In this work, it was investigated if flying height could be lowered under the height of laser bumps. With the reduction of the spinning speed, the flying height was decreased under the height of laser bumps. When a head swept between landing zone and data zone, the head-disk impact was monitored using AE and friction signals. It is demonstrated that magnetic hard disk drive could be operated without tribological failures under the height of laser bumps.

• Korean Journal of Metals and Materials
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• v.49 no.5
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• pp.411-418
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• 2011

The current study investigates the electroplating characteristics of Sn-Cu eutectic micro-bumps electroplated on a Si chip for flip chip application. Under bump metallization (UBM) layers consisting of Cr, Cu, Ni and Au sequentially from bottom to top with the aim of achieving Sn-Cu bumps $10\times10\times6$ ${\mu}m$ in size, with 20${\mu}m$ pitch. In order to determine optimal plating parameters, the polarization curve, current density and plating time were analyzed. Experimental results showed the equilibrium potential from the Sn-Cu polarization curve is -0.465 V, which is attained when Sn-Cu electro-deposition occurred. The thickness of the electroplated bumps increased with rising current density and plating time up to 20 mA/$cm^2$ and 30 min respectively. The near eutectic composition of the Sn-0.72wt%Cu bump was obtained by plating at 10 mA/$cm^2$ for 20 min, and the bump size at these conditions was $10\times10\times6$ ${\mu}m$. The shear strength of the eutectic Sn-Cu bump was 9.0 gf when the shearing tip height was 50% of the bump height.