• Korean Journal of Materials Research
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• v.21 no.12
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• pp.650-654
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• 2011

In this paper, the effects of conventional and newly developed elastomer modified underfill materials on the mechanical shock reliability of BGA board assembly were studied for application in mobile electronics. The mechanical shock reliability was evaluated through a three point dynamic bending test proposed by Motorola. The thermal properties of the underfills were measured by a DSC machine. Through the DSC results, the curing condition of the underfills was selected. Two types of underfills showed similar curing behavior. During the dynamic bending reliability test, the strain of the PCB was step increased from 0.2% to 1.5% until the failure circuit was detected at a 50 kHz sampling rate. The dynamic bending reliability of BGA board assembly using elastomer modified underfill was found to be superior to that of conventional underfill. From mechanical and microstructure analyses, the disturbance of crack propagation by the presence of submicron elastomer particles was considered to be mainly responsible for that result rather than the shear strength or elastic modulus of underfill joint.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.2
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• pp.87-93
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• 2022

The demand for metal-polymer joining technology have been increasing, especially in the industrial fields of automotive and aerospace, which require the manufacturing of various lightweight parts. Conventional joining processes have technical hurdles on aspects such as thermal degradation, need for chemical surface treatment, or complicated process settings. These issues can be alleviated by employing interlocking structures for the metal-polymer joined interface. In this study, we joined 3D-printed metal and polymer parts, which were featured with 3D-printed interlocking structures at their interface. By using high frequency induction heating, the joined region could be locally heated to reduce the thermal degradation and distortion of polymer parts. In addition, through the adjustment of interface morphologies and compression conditions, the polymer flow could be optimized to completely fill the interlocking grooves on metal parts, thereby achieving high joining strength. This suggests feasible guidelines for manufacturing metal-polymer joined structures involving 3D-printed architectures.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.372-377
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• 2002

Residual stress by welding should be reduced because that decreases the reliability on strength of welded structure. The reason is that the total stiffness of structure decreases by non-linear behavior of weldment under external load. The release of residual stress by mechanical loading and unloading is often performed in the fabrication of box structure for steel bridge. The proper degree of loading and unloading is significant at release method of residual stress by mechanical loading because that degree is changed by material and geometric shape of welded structure. Therefore, the simulation model that could exactly analyze the release of residual stress by mechanical loading is to be necessary. This simulation model should be established on the based of variable and accurate measurement data. In this study, the non-linear behavior of weldments under external loading and unloading, such as the decrease and increase of structure stiffness, was investigated by monitoring of nominal stress and strain. Tensile loading and unloading test under variable load was performed and the proper degree of stress relaxation was measured by sectioning technique using strain gauge.

• Journal of Welding and Joining
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• v.30 no.5
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• pp.34-39
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• 2012

This study was conducted to investigate the microstructure and mechanical properties of friction stir lap joints. Invar 42 and SS 400 were selected as the experimental materials, and friction stir welding was carried out at a tool rotation speed of 200 rpm and welding speed of 100 mm/min. The application of friction stir welding to Invar 42 effectively reduced the grain size in the stir zone; the average grain size of Invar 42 was reduced from $11.5{\mu}m$ in the base material to $6.4{\mu}m$ in the stir zone, which resulted in an improvement in the mechanical properties of the stir zone. The joint interface between Invar 42 and SS 400 showed a relatively sound weld without voids and cracks, and the intermetallic compounds with $L1_2$ type in lap jointed interface were partially formed with size of 100 nm. Moreover, the hook in the advancing side of Invar 42 was formed from SS 400, which contributed to maintenance of the tensile strength. The evolution of microstructures and mechanical properties of friction stir lap jointed Invar 42 and SS 400 are also discussed herein.

• Journal of Welding and Joining
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• v.17 no.6
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• pp.53-61
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• 1999

The use of thick plate in increasing in recent years due to the rapid expansion of chemical plants, nuclear plants, ships and other industrial plants. Welding is the most popular joining techniques employed in manufacturing industrial machineries and structures. Normally, Groove shapes are prepared according to appropriate rules and regulations such as KS, JIS, AWS, LR, DNV and etc. for various thicknesses of plate. However those groove angles tend to be too large. As a result of large groove angle, residual stress, deformation of material and strength reduction is obtained. Therefore, the reliability and safety of structures and machinery tend to be decreasing. Therefore, in this paper, theoretical as well as experimental study are carried out to find optimum groove shapes for T-welded joint of mild steel. The test specimen are made in same condition with simulation model. Welding residual stresses measurement by sectional cutting method. ⅰ) The mechanical difference for change the thickness of plate and groove angle are not appeared. ⅱ) In a mechanical point of view minimum preparation angle(40°) is more suitable than maximum groove angle(60℃). ⅲ) The measurement value and distribution of welding residual stresses are not effected largely by groove angle. It is mechanical restraint that mainly affect welding residual stresses distribution. In mechanical point of view minimum groove angle is more suitable than maximum groove angle. Therefore, it is appropriate to minimize the size of groove shape in strength and safety.

• International Journal of Korean Welding Society
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• v.2 no.1
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• pp.40-44
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• 2002

Residual stress by welding should be reduced because that decreases the reliability on strength of welded structure. The reason is that the total stiffness of structure decreases by non-linear behavior of weldment under external load. The release of residual stress by mechanical loading and unloading is often performed in the fabrication of box structure for steel bridge. The proper degree of loading and unloading is significant at release method of residual stress by mechanical loading because that degree is changed by material and geometric shape of welded structure. Therefore, the simulation model that could exactly analyze the release of residual stress by mechanical loading is to be necessary. This simulation model should be established on the based of variable and accurate measurement data. In this study, the non-linear behavior of weldments under external loading and unloading, such as the decrease and increase of structure stiffness, was investigated by monitoring of nominal stress and strain. Tensile loading and unloading test under variable load was performed and the proper degree of stress relaxation was measured by sectioning technique using strain gauge.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.1
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• pp.118-125
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• 1992

Joining of thermoplastics is an area of growing importance in the automotive, aerospace, electronics medical and other domestic appliance industries. While adhesive Bonding or mechanical fastening could be used to join thermoplastics, welding is very effective because of its speed and low cost. This study investgated the ultrasonic joining of thermoplastics. Four kinds of thermoplastics such as Acrylonitrile Butadiene Styrene, Polystyrene, Polyethylene and Polypropylene were used, ultilizing all possible joining combinations. In each combination of thermoplastics, the weldability of the joint was evaluated as a function of weld time, amplitude of vibration and pressure. It was generally found that joining of amorphous thermoplastics with semicrystalline thermopastics resulted in poor joints due to its different crystalline structure. Joining of the amorphous thermoplastics together and joining of the semicrystalline thermoplastics together produced the best joints owing to its same crystalline structure.

• Ceramist
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• v.9 no.6
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• pp.30-36
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• 2006

Joining ceramics to metals has a variety of applications both in the structural and the electronics fields. One of the great benefits of the adoption of joining into the structural applications is to provide reliability to the ceramic components by backing up with metal components. In joining ceramics and metals, two key factors, i.e., establishing chemical bonding at interfaces and dissipation of thermal stress across interfaces, should be paid for attention. Many joining methods have been already established such as adhesive and mechanical joining, brazing and soldering, and solid state bonding. Each has its own benefits with some drawbacks. One can select a suitable process and materials following the requirements of the application. This report focuses on the current status of joining technology for ceramics/metal system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.917-923
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• 2014

Subminiature joining bolts are required for the electronic parts of gadgets such as mobile phones and watch phones. During the miniaturization of bolt heads, it is difficult to obtain sufficient joining force owing to the risk of shear fracture of the bolt head or severe plastic deformation on the bit region. In this study, the maximum joining torque for the bit depth was predicted using finite element analysis. A shear fracture test was conducted on a wire used in bolt forming. The results of this test were subjected to finite element analysis and a fracture criterion was obtained by comparing the experimental and analysis results. The shear fracture of the bolt head during joining was predicted based on the obtained criterion. Furthermore, the maximum joining torque was predicted for various bit depths. Fracture on the boundary between the bolt head and thread was found to occur in lower joining torque as bit depth increases.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1056-1063
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• 2010

We present a new joining method for Pd-Cu membrane foils used as permeation tubes to collect $CO_2$. Since foils have poor mechanical strength, joining should be done at low temperatures to reduce residual stresses and without joining pressure. This contradicts the well known conditions for good contact between base materials that determines joint qualities. We selected Sn-Ag-Cu alloys that are highly reactive with Pd and Cu as a filler metal. As the filler melts at joining temperatures as low as $220{\sim}280^{\circ}C$, Pd and Cu are dissolved into the melt and react with the filler elements, which raises the melting temperature of the filler based on eutectic structures among the elements. Then, isothermal solidification progresses for the rest of the joining time. Intermetallic compounds (IMC) in the joints, one of the main factors for brittle joints, are inevitably formed. However, by optimizing both joining time and temperature, we balanced the wettability with IMC. Sealing test results confirmed that the joints are mechanically reliable during operation.