• Journal of the Korean Electrochemical Society
• /
• v.2 no.3
• /
• pp.138-143
• /
• 1999

Recently, miniaturization of large scale integrated circuits (LSI) and printed circuit board (PCB) have become essential with the downsizing of electronic devices. Gold electroplating is applied of conductivity wiring or terminals for improvement of conductivity and corrosion resistance. However, electroplating is not applicable since the circuits are becoming finer and denser. Accordingly, electroless plating is recently highly attractive method because of the simplicity of the operation requiring no external source of current and no elaborate equipment. In this work, we tried to develop a plating technique on electroless Ni/Au plating. First, the electroless Ni plating was deposited on the PCB with agitation in the bath at $85^{\circ}C$. Then the Au layer was deposited on the Ni layer surface by same method at $90^{\circ}C$. The bonderability were tested in order to evaluate the stability of the electroless Ni/Au by gold wire or solder ball test.

• Korean Journal of Applied Biomechanics
• /
• v.21 no.3
• /
• pp.361-368
• /
• 2011

The purpose of this study was to investigate the effect of isometric hip adduction and abduction on the muscle activities of vastus medialis oblique(VMO) and vastus lateralis(VL) during leg squat exercises. This study consisted of 21 healthy subjects who had no medical history of anterior knee pain or lower extremity disorders. The ball and belt were used to isometrically adduct and abduct the hip joint during the leg squat exercise, respectively. The surface electromyograms of VMO and VL were analyzed, and the findings were used to calculate the VMO:VL ratio during 3 different quadriceps-strengthening exercises(leg squat, LS leg squat with isometric hip adduction, LSHD leg squat with isometric hip abduction, LSHB). The muscle activities of VMO and VL and the VMO:VL ratios were compared using the paired t-test with Bonferroni adjustment. The results showed that the muscle activities of VMO and VL during LSHD were greater than those during LSHB. The VMO:VL ratio was the highest during LSHD. This finding suggests that LSHD using a ball is more effective than LS and LSHB in selectively increasing the muscle activities of VMO. Therefore, we suggest that leg squat exercise with isometric hip adduction using a ball would be useful for maintaining correct patella tracking and for selectively strengthening VMO.

• Journal of the Microelectronics and Packaging Society
• /
• v.19 no.4
• /
• pp.45-50
• /
• 2012

A family of multi-die DRAM packages was developed that incorporate the full functionality of an SODIMM into a single package. Using a common ball assignment analogous to the edge connector of an SODIMM, a broad range of memory types and assembly structures are supported in this new package. In particular DDR3U, LPDDR3 and DDR4RS are all supported. The center-bonded DRAM use face-down wirebond assembly, while the peripherybonded LPDDR3 use the face-up configuration. Flip chip assembly as well as TSV stacked memory is also supported in this new technology. For the center-bonded devices (DDR3, DDR4 and LPDDR3 ${\times}16$ die) and for the face up wirebonded ${\times}32$ LPDDR3 devices, a simple manufacturing flow is used: all die are placed on the strip in a single machine insertion and are sourced from a single wafer. Wirebonding is also a single insertion operation: all die on a strip are wirebonded at the same time. Because the locations of the power signals is unchanged for these different types of memories, a single consolidated set of test hardware can be used for testing and burn-in for all three memory types.

• Applied Chemistry for Engineering
• /
• v.29 no.4
• /
• pp.405-412
• /
• 2018

Three types of bis[3-(dialkyloxylphosphorothionyl) thio-2-methylpropanyloxy]alkane (BAPA) drived from alkane diol were synthesized. The principal chain of each BAPA had a different carbon number, i.e., 6, 9, and 11. The three types of synthesized BAPA were compared to zinc dialkyl dithiophosphates (ZDDPs) in terms of abrasion resistance. A four-ball test was conducted to evaluate the anti-abrasion performance of the synthesized BAPA according to the length of the principal carbon chain. Each product was added to an additive at a concentration of 1% of the base oil weight, and the wear scar diameter (WSD) was measured as 0.472, 0.459, and 0.480 mm, respectively. Among the BAPA compounds, dialkyl dithiophosphoric acid (DDP), which is the side chain of bis[methacryloyloxy] nonane (BMOO9), was synthesized by varying the carbon number, i.e., 4, 8, and 12, and subsequently the 4-ball test was carried out. The WSD was determined as 0.537, 0.459, and 0.531 mm, respectively. As a result, it was found that when a side chain is short, a thin film is formed. In contrast, a long side chain hindered the formation of a film, and hence the best result was achieved when the carbon number was 8. As for the ZDDPs, the WSD was determined to be 0.563 mm, when measured under the same conditions. The measurements confirm that the synthesized BAPA compounds are superior to the ZDDPs as abrasion resistance additives.

• Journal of the Microelectronics and Packaging Society
• /
• v.15 no.4
• /
• pp.65-70
• /
• 2008

The mechanical shear strength of BGA(Ball Grid Array) solder joints under high impact loading was investigated. The Sn-37Pb solder balls with a diameter of $500{\mu}m$ were placed on the pads of FR-4 substrates with ENIG(Electroless Nickel Immersion Gold) surface treatment and reflowed. For the High Temperature Storage(HTS) test, the samples were aged a constant testing temperature of $120^{\circ}C$ for up to 250h. After the HTS test, high speed shear tests with various shear speed of 0.01, 0.1, 1, 3 m/s were conducted. $Ni_3Sn_4$ intermetallic compound(IMC) layer was observed at the solder/Ni-P interface and thickness of IMC was increased with aging process. The shear strength increased with increasing shear speed. The fracture surfaces of solder joints showed various fracture modes dependent on shear speed and aging time. Fracture mode was changed from ductile fracture to brittle fracture with increasing shear speed.

• Proceedings of the KSME Conference
• /
• 2001.11a
• /
• pp.174-179
• /
• 2001

In order to investigate the fracture behaviors(perforation modes) and resistance to perforation during ballistic impact of aluminum alloy plate, ballistic tests were conducted. Depth of penetration experiments with 5.56mm-diameter ball projectile launched into 25mm-thickness Al 5052-H34 targets were conducted. A powder gun launched the 3.55g projectiles at striking velocities between 0.6 and 1.0 km/s. radiography of the damaged targets showed different penetration modes as striking velocities increased. Resistance to perforation is determined by the protection ballistic limit($V_{50}$), a statistical velocity with 50% probability for complete perforation. Fracture behaviors and ballistic tolerance, described by perforation modes, are respectfully observed at and above ballistic limit velocities, as a result of $V_{50}$ test and Projectile Through Plates (PTP) test methods. PTP tests were conducted with $0^{\circ}$ obliquity at room temperature using 5.56mm ball projectile. $V_{50}$ tests with $0^{\circ}$ obliquity at room temperature were conducted with projectiles that were able to achieve near or complete perforation during PTP tests. The effect of various impact velocity are studied with depth of penetration.

• Journal of Fashion Business
• /
• v.27 no.2
• /
• pp.39-51
• /
• 2023

The purpose of this study was to effectively improve the thigh muscles of adult women working from home due to COVID-19. In this study, ten adult women working from home performed 1) an electromyography test, 2) a static balance test on a balance board, and a 3) dynamic balance test by squatting on a Bosu ball four times: before electric muscle stimulation (EMS), after EMS, after high-intensity circuit training (HICT), and after EMS plus HICT. For this test, EMS was attached to a medical knee support to manufacture an EMS knee band that could be easily worn regardless of the location. For the experiment, EMS(electric muscle stimulation) was attached to the medical knee protector to manufacture an EMS knee band that can be easily worn regardless of location, and was measured based on the right foot. The study results confirmed that in all tests (electromyography test, static balance test on the balance board, and dynamic balance test by squatting on a Bosu ball), thigh strength improved in the order of treatment before EMS, after EMS, after HICT, and after EMS plus HICT. The study showed that people working from home or with activity restrictions due to COVID-19 had better exercise effects when wearing the EMS knee band and performing HICT, even in a small space.

• Journal of the Microelectronics and Packaging Society
• /
• v.20 no.3
• /
• pp.59-62
• /
• 2013

Experimental analyses on the solder joint reliability of plastic ball grid array under harsh random vibration were presented. The chips were assembled on the daisy chained circuit boards for the test samples preparation, half of which were processed for underfill to investigate the underfill effects on the solder failures. Acceptance and qualification levels were applied for the solder failure tests, and the overall controlled RMS of the power spectrum densities of the steps were 22.7 Grms and 32.1 Grms, respectively. It was found that the samples survived without any solder failure during the tests, demonstrating the robustness of the packaging structure for potential avionics and space applications.

• Tribology and Lubricants
• /
• v.39 no.3
• /
• pp.111-117
• /
• 2023

This paper presents an experimental investigation of the tribological characteristics of PTFE composites filled with nano CuO particles under low sliding speed and load. All the specimens were prepared by sintering. Before sintering, the mixture of PTFE powder and CuO particles were mixed by a high-speed mixer using CuO volume fractions of 0.2 vol. % and 5 vol. %. Each mixture was sintered at 350 ℃ for 30 min on the steel disk. We conducted ball-on-disk sliding test an hour using a steel ball against PTFE composites, including pure PTFE. The load and sliding speed used was 2 N and 0.01 m/s, respectively. Adding nano CuO particles increases the friction coefficient because of the abrasiveness of hard nano CuO particles. The highest coefficient of frictions was obtained from 5 vol. % CuO. Conversely, the lowest wear of the composites was obtained from the 5 vol. % CuO nanocomposite. This study reveals that the addition of nano CuO particles can lower the wear of PTFE, despite an increase in the coefficient of friction. However, the coefficient friction is still moderate compared to other engineering polymers. In addition, the amount of CuO nano particles has to be optimized to reduce friction and wear at the same time.

• Journal of the Microelectronics and Packaging Society
• /
• v.12 no.4 s.37
• /
• pp.289-299
• /
• 2005

The ball shear force was investigated in terms of test parameters, i.e. displacement rate and probe height, with an experimental and non-linear finite element analysis for evaluation of the solder joint integrity in area array packages. The increase in the displacement rate and the decrease in the probe height led to the increase in the shear force. Excessive probe height could cause some detrimental effects on the test results such as unexpected high standard deviation and probe sliding from the solder ball surface. The low shear height conditions were favorable for assessing the mechanical integrity of the solder joints. The mechanical and electrical properties of the Sn-37Pb/Cu and Sn-3.5Ag/Cu BGA solder joints were also investigated with the number of reflows. The total thickness of the intermetallic compound (IMC) layers, consisting of Cu6Sn5 and Cu3Sn, was increased as a function of cubic root of reflow time. The shear force was increased up to 3 or 4 reflows, and then was decreased with the number of reflows. The fracture occurred along the bulk solder, in irrespective of the number of reflows. The electrical resistivity was increased with increasing the number of reflows.