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In this study, we investigated the phenomenon of electrochemical migration (ECM) on a silicon (Si) substrate with a silver pattern directly printed using the screen-printing method. The microstructure and electrical characteristics of the directly printed Ag pattern under different sintering conditions were examined. In addition, the ECM characteristics of a directly patterned Ag circuit on a Si substrate were evaluated and compared with those of an immersion Ag circuit. Clusters were formed by interparticle necking during the sintering process; the cluster size in the patterns increased with increasing sintering temperature. The granular Ag films sintered at high temperatures had excellent electrical characteristics as a result of the formation of interparticle necking with sufficient size, despite the presence of porosity and large voids. The directly printed Ag pattern had lower resistance to ECM than the immersion Ag electrode.

This study examined the ternary Ni2SnP layer in Sn–3.5Ag–0.7Cu/electroless Ni (P) solder joints using in situ transmission electron microscopy (TEM). TEM confirmed the formation of an Ni2P phase underneath the ternary Ni2SnP after reflowing. We can directly observe the Sn diffused into Ni2P to form Ni2SnP during annealing in TEM. These results suggested that the ternary Ni2SnP forms through the diffusion of Sn into Ni2P. In addition, small Kirkendall voids were newly formed in the ternary Ni2SnP layer after annealing in TEM.

The adhesion strength of a Cu/Ni-Cr/polyimide flexible copper clad laminate (FCCL), which was manufactured via a roll-to-roll process, was evaluated according to the thickness of the Ni-Cr seed layer using a 90° peel test. The changes in the morphology, chemical bonding, and adhesion properties were characterized using a scanning electron microscopy (SEM), an atomic force microscopy (AFM), and an X-ray photoelectron spectroscopy (XPS). The thickness of the Ni-Cr (Ni:Cr = 80:20) seed layer in which the maximum peel strength of the FCCL was observed was 200A. The higher FCCL peel strength was attributed to the lower proportion of C-N bonds and higher proportion of C-O and carbonyl (C = O) bonds in the polyimide surface compared with the FCCL with a lower adhesion strength. The FCCL with a higher peel strength had a fractured polyimide surface with a higher surface roughness. The adhesion strength between the metal and polyimide was pirmarily attributed to the chemical interaction between the metal layer and the functional groups of the polyimide.

In this study, the effect of various seed layers (95Ni–5Cr, 80Ni–20Cr and Cr) on the adhesion strength of flexible copper clad laminate (FCCL), which was manufactured by the roll-to-roll process, was evaluated after heat treatment. The changes in the morphology, chemical bonding, and adhesion properties were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and a 90° peel test. The results showed that both the peel strength and thermal resistance of the FCCL increased as the Cr ratio of the seed layer increased. The roughness of the fracture surface decreased as the heat treatment temperature and holding time increased. The heat treatment of the FCCL increased the proportion of C–N bonds and reduced that of the C–O and carbonyl (C=O) bonds in the polyimide. The chemical function and roughness of the fracture surface were affected by the composition and ratio of the seed layer. Therefore, the adhesion strength between the metal and polyimide was mostly attributed to the chemical interaction between the metal layer and the functional groups of the polyimide.

In this study, we investigated the effect of the Cu content on the interfacial reactions between the Sn–Ag– x Cu solders and Cu substrate. In addition, we evaluated the effects of adding Cu or Ni to Sn–Ag solder on the interfacial reactions of the Sn–Ag–Cu (or Ni)/ENIG joints. The formation and growth of interfacial intermetallic compounds (IMCs) between the Ni-containing Sn–Ag–Ni solder and ENIG substrate were studied and the results were compared to the Sn–Ag–Cu/ENIG system. Increasing the amount of Cu added to the Sn–Ag solder significantly reduced the thickness of the Cu 3 Sn IMC, while increasing that of the total Cu–Sn and Cu 6 Sn 5 IMCs. (Ni,Cu) 3 Sn 4 and Ni 3 Sn 4 IMCs formed at the Sn–3.0Ag–0.5Cu/ENIG and Sn–3.0Ag–0.5Ni/ENIG interfaces, respectively. These two IMCs grew during isothermal aging and similar interfacial microstructures were found in the Sn–3.0Ag–0.5Cu (or Ni)/ENIG joints. Comparing the Sn–3.0Ag–0.5Cu/Cu and Sn–3.0Ag–0.5Cu/ENIG joints, the growth rate of the IMC layer for the Cu substrate was about 3.3 times faster than that for the ENIG substrate.

The LED chips, packages and related materials have been already key issue on electronic applications and substitution of conventional lights. It is easily expected that the development trend of LED products is nearly the same as that of electronic products with higher performance, higher integration, lower energy and lower cost. And then we also prospect that the dissipated heat from LED chip is to be big problem for a reliability of products, as likely that electronic packages contain heat sink or heat spreader for controlling heat dissipation. In fact, the heat from an LED package with 1~3W LED chip shows a nearly 60~150°C, which affects thermal damage related to performance, joint failure, crack, etc. The thermal via was fabricated with 16 segments of via sizes ranged 0.2~1.2mm and via pitches ranged 0.5~3mm using 1~3W LED, respectively. The thermal resistivity was analyzed by the thermal transient tester with the variation of via sizes and pitches, which was also compared with the temperature difference of the top and bottom side of LED package. As a results, we convincingly proved the relationships between the design of thermal via and the heat dissipation of LED module, which were directly applicable to LED industry.

The PET-ITO substrate has been usually applied to many flexible applications such as selectively conducting films, flexible printed circuit, display panels, interconnections, terminals, etc., where the PET-ITO substrate has a main role to enhance the performance in the components of touch screen panels, solar cell panels and so on. Today’s flexible technology is issued on forming fine pattern, pattern alignment and mass-productivity on PET-ITO substrates, which is strongly related to thermal shrinkage and expansion of the substrate[1~5]. We investigated in this study the thermo-mechanical behavior of PET-ITO substrate using a thermo-mechanical analyzer (TMA) in order to analyze thermal strain with varying temperature.

This study evaluated the reliability of fine-pitch, flip-chip bonding with ultrasonic energy and non-conductive film (NCF). The surface treatment was carried out with H2SO4 before flip-chip bonding (FCB). The electro-plated Cu bumps on the Si wafer and Cu-coated glass substrate were prepared for chip on glass (COG). The ultrasonic bonding was carried out, with and without NCF, under optimum bonding pressure and time. The mechanical properties were tested by die shear testing. The reliabilities of COG with and without NCF were evaluated with thermal shock testing, humidity and temperature (HT) testing, and high temperature storage (HTS) testing after FCB. The contact resistances of COG were evaluated for electrical reliability. To determine the variation in the initial value of the contact resistance of the flip-chip bumps according to the bonding method, the bonded interface of each sample was analyzed with scanning electron microscopy (SEM).

Light emitting diode (LED) has been largely used in industry of consumer electronics such as cell-phones, PDAs, and computers. Since all light sources convert electric power into radiant energy and heat, LED also does the same with an increase of its power. Generally, it only converts 15~25% of electric power into visible light; the rest of the power, 75~85%, is converted into heat. This excess heat should be conducted away from the LED die to circuit boards or heat sinks since heat affects directly performance of the LED. The piled heat in LED products brings color shift and reduces light output very rapidly. Furthermore, the lifecycle of LED products shorten if the heat problem continues. In order to prevent LED products from these negative effects, effective thermal resistance paths need to be achieved so that LED products let the heat conduct from the LED to the outside such as printed circuit board. In this research, optimization studies on thermal-via is to be performed. The 1W and 3W LED assembled printed circuit board with 16 different via designs is set up to measure its temperature for 4 hours in a real time. It was obtained by this work that the optimized thermal via was very effective to dissipate the heat from the LED.

We investigated the effects of adding small amounts of cerium (Ce) to low Ag content Sn solder (Sn–1.0 wt.%Ag) on melting temperature, microstructure, wettability and mechanical properties using differential scanning calorimeter, optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy, wetting balance tester, Vickers hardness tester and tensile tester assays. The addition of Ce had little influence on the melting behavior of Sn–1.0Ag solder, but improved its wettability, mechanical properties, and microstructure.

Dissimilar friction stir welding between steels with different carbon contents was carried out by placing the parent materials at two different fixed locations: the advancing side (AS) and the retreating side (RS). The phase transformation and the depth and width of the weld were affected by the fixed location. A smaller weld nugget was formed, and more martensite transformation occurred when the stronger SK5 steel was fixed at AS, compared to that at RS. This variation was attributed to the difference of temperature and materials flow between AS and RS.

We investigated the effects of sintering temperature on microstructural evolution and electrical characteristics of screen printed Ag patterns. A commercial conducting paste containing Ag nanoparticles was screen printed onto a Si substrate passivated with SiO"2 and sintered under a sintering temperature range from 150^oC to 300^oC. Four point probe method was used to measure the DC resistance, while a network analyzer and Cascade's probe system in the frequency range from 10MHz to 30GHz were employed to measure the S-parameters of the sintered Ag conducting patterns. The resistivity under the application of a DC decreased from 398@m@Wcm to 9@m@Wcm with increasing sintering temperature from 150^oC to 300^oC. From the measured S-parameters, the electrical losses in high frequencies also decreased with increasing sintering temperature (about 1.2dB at 30GHz) due to the formation of an interparticle neck after heat treatment at high temperatures.

The solid-state interfacial reactions of Pb-free solders (Sn-3.5Ag, Sn-3.5Ag-0.7Cu, and Sn-0.7Cu) with electroless nickel-immersion gold (ENIG)-plated Cu substrate, and the growth of interfacial intermetallic compound (IMC) layers were investigated and compared during aging at 200°C for up to 1000 h. The Sn-3.5Ag-0.7Cu solder exhibited a higher IMC growth rate and a higher consumption rate of the Ni(P) layer than the other two Pb-free solders. The interfacial reaction of the Sn-0.7Cu/ENIG-plated Cu system during aging was the slowest among the three kinds of solder joint. The thickness of the interfacial IMCs were ranked in the order Sn-3.5Ag-0.7Cu > Sn-3.5Ag > Sn-0.7Cu. The higher melting temperature of the Sn-0.7Cu solder and the presence of Cu element within the solder suppressed the growth of the interfacial IMC layer and the consumption of the Ni(P) layer, resulting in the superior interfacial stability of the solder joint at high temperature of 200°C.

The effect of displacement rate and intermetallic compound (IMC) growth on the shear strength of electroplated Sn-2.5Ag (in wt.%) flip chip solder with Cu under-bump metallization (UBM) were investigated after multiple reflows. Cu"6Sn"5 IMC was formed at the interface after one reflow. After five reflows, two different IMC layers, consisting of a scallop-shaped Cu"6Sn"5 phase and a planar Cu"3Sn phase, and their thicknesses increased with increasing reflow number up to 10. The shear strengths peaked after four reflows, and then decreased with increasing reflow number. Increasing displacement rate increased the shear force. The tendency toward brittle fracture characteristics was intensified with increasing displacement rate and reflow number.

The mechanical reliability of Sn-3.5 wt.%Ag solder joints with four different electroless Ni plating layers [Ni-1B, Ni-3B, Ni-7P, and Ni-10P (in wt.%)] was investigated as a function of aging time up to 60 days at 150° C. The ultimate shear stresses for fracture were higher in the ball shear tests when using Ni-B samples than those with Ni-P metallization if the aging treatment at 150° C was shorter than 15 days, and vice versa when the aging time was higher than 45 days. In all the joints, Ni3Sn4 intermetallic compounds (IMCs) were formed at the interfaces. The thickness of the IMC layer increased with decreasing B or P content, i.e., increasing Ni content. The reaction rate between the Sn-Ag solder and Ni-P was slower than that between the Sn-Ag solder and Ni-B. In the shear test, the failure mode switched from a bulk-related failure (ductile fracture) to an interface-related failure (brittle fracture), depending on the aging time. After prolonged aging treatment, weak solder/Ni3Sn4 interfaces led to a failure mode of brittle fracture for all the solder joints, due to the formation of thick Ni3Sn4 IMCs. The failure for the Sn-Ag/Ni-B joints was more abrupt and brittle due to the formation of the thick, interfacial Ni3Sn4 IMC. The results demonstrated that the Sn-Ag/Ni-P joint was more reliable than the Sn-Ag/Ni-B joint from the viewpoints of interfacial IMC thickness and long-term mechanical reliability.

Low carbon steel plates were joined by friction stir spot welding (FSSW) with lap configuration. The tool penetration depth exerted a strong effect on the failure mode of the joined samples and a weak effect on the joint shear strength. With increasing tool penetration depth, and consequently with increasing depth of the tool shoulder pressing into the top sample, the failure mode in a lap-shear test changed from brittle to ductile and concentrated near the pinhole located away from the weld towards the base metal. No mechanically mixed layer was formed between the top and bottom plates at the weld nugget due to the limited tool penetration and the fact that the pin height of the welding tool was less than the steel plate thickness. The region under the pin exhibited a fully recrystallized microstructure, with grain growth and a different texture.

A new bumping process on a Si die by electroplating without a photo-resist-mold (PRM) was assessed for the three dimensional (3D) stacking of Si dice. In this process, solder bumps were deposited selectively onto the surface of a Cu plugged-through silicon-via (TSV) in a Si die. Since lithography related processes to make a PRM for solder bumping were omitted, it can reduce the production time and cost for bumping. The substrate was a Si wafer, and TSVs were produced by deep-ion-reactive-etching (DRIE). As an insulation layer, SiO2 was formed by high-density-plasma-chemical-vapor-deposition (HDPCVD) or wet oxidation method. A Ti adhesion and an Au seed layers were deposited by sputtering. Cu was plugged into the vias by pulsed direct-current (DC) electroplating. The backside of the Si wafer was ground by chemicalmechanical-polishing (CMP). Sn bumps were electroplated on the Cu plugged vias by a current supplied through a Cu-overplated layer (COL) on the vias surface. As experimental results, wet oxidation provided a uniform SiO2 thickness through the via depth, whereas the SiO2 thickness by HDPCVD decreased with the via depth. The Ti and Au thicknesses also decreased along the via depth. In electroplating for Cu plugging

Joints of galvanized steel were obtained by friction stir spot welding (FSSW) with lap configuration using CPS design tool. No mechanically mixed layer was formed between the top and bottom plates at the weld nugget due to the limited tool penetration and the lower pin height of the welding tool than the steel plate thickness. A deformed region, in which ZnO particles were detected, was observed in the joint. The formation of this deformed region was attributed to the explosion of the Zn coating layer due to friction heating and tool compression. With increasing tool penetration depth, the tensile shear strength of the joint increased to a maximum value of 3.07 kN at a tool penetration depth of 0.52 mm. [doi:10.2320/matertrans.M2009337]

In this study, the effect of two laminating parameters, laminating pressure and holding time, on the adhesion strength of flexible copper clad laminate (FCCL) with an epoxy-type adhesive layer was evaluated. The changes in the adhesion property, fracture surface, morphology, and chemical bonding state were characterized by 90° peel test, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The results showed that the adhesion strength of the FCCL was decreased as the laminating pressure was increased beyond the suitable level. Laminating pressure exerted the greatest influence over the FCCL adhesion strength. On the other hand, the holding time did not significantly affect the peel strength of the FCCL. The fracture of FCCL occurred at the interface between the rolled Cu and the adhesive layer. In addition, the FCCL with high adhesion strength was stable with the variation of adhesion strength after temperature and humidity test.

The adhesion strength of a Cu/Cr/polyimide (PI) flexible copper clad laminate (FCCL), which was manufactured by the roll-to-roll process, was evaluated according to the thickness of the Cr seed layer using the 90° peel test. The changes in the morphology, chemical bonding and adhesion properties were characterized by scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The peel strength of the FCCL decreased with increasing Cr layer thickness. The higher FCCL peel strength was attributed to the lower proportion of C-N bonds and higher proportion of C-O or carbonyl (C=O) bonds on the PI surface compared to the FCCL with the lower adhesion strength. The FCCL with the higher peel strength had a fractured PI surface with a higher surface roughness. The adhesion strength between the metal and PI was mostly attributed to the chemical interaction between the metal layer and the functional groups of the PI.

The joint strength of friction stir spot welded 5J32 Al alloy was investigated according to the tool shape (threaded pin tool: TPT; cylindrical tool: CT; cylindrical tool with projection: CTP) and tool penetration depth. With increasing tool penetration depth, the vertical joint deformation increased in TPT and CT, whereas the joint diameter increased in TPT. The tensile shear load of the joint using TPT and CT did not vary with tool penetration depth, because the decreased upper plate thickness impeded the increase of the tensile shear load. That of CTP, however, rapidly increased with increasing tool penetration depth to produce a maximum tensile shear load of 4.6 kN. CTP, with its shoulder comprising a slight, broad projection, retarded the vertical joint deformation and produced good mechanical properties.

In this study, the interfacial reaction and joint reliability of immersion Ag-plated Cu substrate with the Sn–0·7Cu (wt-%) ball–grid array (BGA) solder was investigated. During reflow, the Ag plating layer was dissolved completely into the molten Sn–Cu solder and some of the Cu layer was also dissolved into the molten solder. The dissolved Ag and Cu were precipitated as Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) in the solder matrix. Upon reflow, the Sn–Cu solder exhibits an off-eutectic reaction to produce the eutectic phase and precipitate (Cu6Sn5 and Ag3Sn). The Cu–Sn IMC layer was formed at the solder/Cu interface after reflow, and the IMC layer grew during aging treatment. During the shear tests, the failure mode switched from a bulk-related failure to an interface-related failure. After aging for 250 h, the joint failed partially at the solder/Cu6Sn5 interface. The brittle fracture was linked to the formation of thick Cu–Sn IMC layer.

The effects of Cu and Ni additions on the wettability and interfacial reaction of Sn–Ag solder with Cu substrate were investigated. The wettability of the Sn–3.0Ag–0.5Cu (or Ni) solder alloy was firstly measured by a wetting balance test. The formation and growth of intermetallic compounds (IMCs) between the Sn–Ag–Ni solder and Cu substrate were evaluated, and compared the results to the Sn–Ag–Cu/Cu system. In the wetting test, the Cu and Ni additions exerted positive and negative effects, respectively, on the wettability of the Sn–Ag solder. In the solid-state reaction of the Sn–Ag–Cu/Cu solder joint, two IMC layers, Cu 6 Sn 5 and Cu 3 Sn, grew with increasing aging temperature and time. The growth rate of the Cu 3 Sn IMC was higher than that of the Cu 6 Sn 5 IMC at the high aging temperatures of 150 and 170 °C. On the other hand, in the case of the Sn–Ag–Ni/Cu solder joint, thick (Cu,Ni) 6 Sn 5 and thin Cu 3 Sn IMCs formed and grew at the interface during isothermal aging. The addition of Ni to the Sn–Ag solder effectively suppressed the growth of the Cu 3 Sn IMC but increased the amount of the (Cu,Ni) 6 Sn 5 IMC at the interface.

Tool wear is a key issue for the friction stir spot welding (FSSW) of steel plates, especially in the automobile industry. In this study, steel plates were welded 500× using FSSW with WC–Co alloy tools of two different compositions. The effect of the weld number on the joint strength and the tool wear characteristics were analyzed by using a non-contact, 3D measurement system, scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). The experimental results indicated that the tool suffered extreme wear and that the joint strength was affected by the worn tool shape after welding. This tool wear was attributed to the formation of a ternary W–Fe–O compound, oxidative wear of WC and fatigue of the Co binder.

The traditional ball shear test is not suitable for evaluating joint reliability under drop loading, since the applied test speeds, usually lower than 5 mm/s, are well below the impact velocity applied to the solder joint in a drop test. The present study expands recently reported research by investigating the effect of thermal aging on the joint strength and fracture mode of Sn-3.0Ag-0.5Cu ball grid arrays during high-speed shear testing, with a shear height of 50 μm and a shear speed ranging from 0.01 m/s to 3 m/s. The test specimens were aged at 393 K for 1000 h. After reflow, a (Ni,Cu)3Sn4 intermetallic compound (IMC) layer was observed at the solder/Ni-P interface and the thickness of the IMC layer was increased through the aging process. The shear strength increased with increasing shear speed. The fracture surface of the solder joints showed three different fracture modes according to the shear speed and aging time. The fracture mode changed from ductile fracture to brittle fracture with increasing shear speed.

This study investigated the microstructural evolution and evaluated the thermo-mechanical reliability of a Sn-3.0Ag-0.5Cu (in wt.%) flip chip package during a thermal shock test. The reliability of the flip chip bonded packages was evaluated by means of the thermal shock in the temperature range of 233 K to 398 K. After 250 thermal shock cycles, cracks finally occurred at the corner solder bump joint on the chip side interfacial regions. In that, the crack initiated at the solder region near the intermetallic compound (IMC) layers. For the interpretation of the failure mechanism of the package, finite element analyses were conducted. From the finite element analysis or computational simulation result, the distribution of the plastic work in the corner solder bump was found to be most considerable. This means that the corner solder bump has the highest potential for first crack initiation and growth, because the thermo-mechanical failure of the solder joints is mainly caused by the accumulation of the plastic work. This matched well with the experimental results.

Flexible copper clad laminates(FCCLs) were fabricated using the electro-plating process and the combined effect of the current density and plating time on their surface morphology, texture, hardness, electrical resistivity and folding behavior was evaluated. To achieve Cu layers with similar thicknesses, the current density was varied in the range of 0.2−3 A/dm 2 and the plating time was controlled in the range of 0.5−7.5 h to compensate for the variation of the current density. The surface morphology, hardness, and folding behavior were characterized by atomic force microscopy, nanoindentation technique and Massachusett Institute of Technology folding endurance test, respectively. The X-ray diffraction patterns indicated that the Cu phase was formed without any secondary phases; however, the preferred orientation changed from (220) to (111) as the current density increased over 1 A/dm 2 . In addition, it was observed that the root-mean-square and hardness values decreased when the current density increased and the plating time decreased simultaneously. The electrical resistivity was as low as approximately 21 nΩ·m and the number of cycles without failure in the folding test was over 15 000, which were comparable to those of commercial FCCLs.

특히, 한국에서는 매년 칩의 집적도를 두 배 향상시킨다는 독자적인 황의 법칙(Hwang’s Law)을 제창하기도 하였다. 그러나 지금까지 이루어져 온 2차원 공정 기술에서의 회로 선폭의 감소는 약 30nm급 공정에서 한계에 이르러 더 이상 황의 법칙과 무어의 법칙을 달성 할 수 없는 실정에 이르렀다. 회로의 선폭이 약 30nm에 이르면 칩 크기가 작아지면서 게이트 크기 및 구동 전압의 감소로 인하여 칩 성능은 향상시키지만, 신호 배선 단면적의 감소로 인하여 저항 증가 및 좁아진 배선 거리로 인한 간섭의 발생으로 신호 지연이 발생하게 된다. 궁극적으로 약 30nm급 공정에서는 칩 성능 향상의 효과보다 저항 증가 및 신호 지연효과로 인한 마이너스적 요소가 더 크게 작용하게 된다. 뿐만 아니라, 한계로 여겨지는 30nm급 기술을 적용하여 제품을 제조하기 위해서는 보다 정교한 공정기술이 요구되기 때문에 제조비용 상승과 더불어 제품 가격의 상승은 불가피해진다. 따라서 현재 이러한 한계를 극복하고 집적도를 높일 수 있는 기술로 각광받고 있는 기술 중 하나가 3차원 칩 실장 기술이다. 3차원 칩 실장 기술은 실리콘 웨이퍼에 비아(via) 홀을 형성하고, 형성 된 비아를 전도체로 충진시켜 다이를 수직적으로 접속시켜주는 기술이다. 이러한 3차원 칩 실장 의 구조로 인해 칩 간 접속 거리가 짧아짐에 따라 전기적 신호의 전송 속도를 증가 시키고 소비 전력을 획기적으로 감소시킬 뿐만 아니라 기계적, 전기적 신뢰성을 보다 향상시킬 수 있는 장점이 있다. 게다가 3차원 칩 실장 기술을 적용할 경우 2차원 실장기술의 공간적 제약에서 벗어나, 다이를 수직으로 쌓아 올림으로서 메모리 용량을 손쉽게 두 배, 세 배 이상 늘릴 수 있게 된다. 뿐만 아니라 로직(logic), 수동소자, 광소자, 메모리, 중앙처리장치 등 시스템 구성을 위해 필요한 여러 소자들을 수직적으로 쌓아 올림으로써 작은 패키지 하나로 완성 된 시스템을 구현 할 수 있다는 장점도 지니고 있다

Carbon nanotube (CNT) doped MgB1.9 - 0.1 at% CNT bulk superconductors were fabricated using an in-situ technique to improve the critical current density (Jc) in a high magnetic field. The effects of doping and the sintering temperature on the phase formation, microstructure, and critical properties were evaluated. Two types of the CNT were used as dopants: the conventional CNT (CCNT) with a mixture of large and small diameter (5 and 20 nm) and the small CNT (SCNT) with 5 nm diameters. For both CNT-doped samples, the a-axis lattice parameter decreased but its reduction was more significant at 900degC than at 800degC. The decrease in Tc was consistent with the change in the a-axis lattice parameter, which is probably due to the effect of C substitution for the B sites in MgB2. The Jc of the doped samples decreased more slowly with increasing magnetic field than that of the undoped samples. In addition, the SCNT-doped sample exhibited superior Jc(B) behavior than the CCNT-doped sample. This was partly attributed to the higher doping level and the presence of finer CNTs, which acts as an effective pinning center.

This study investigated the feasibility of ultrasonic bonding of a rigid printed circuit board (RPCB) to a flexible printed circuit board (FPCB) with a non-conductive film (NCF) for improving the long-term reliability and lowering the manufacturing cost. Peel tests of the joints were carried out with increasing bonding time to optimize the bonding condition. High-temperature storage and thermal cycling tests were carried out to evaluate the reliability. The RPCB was successfully bonded to the FPCB with NCF using a transverse ultrasonic bonding. The optimum time taken for bonding was 3 sec. The joints with NCF showed a good reliability after the high-temperature storage test at 125°C for 1,000 h and the thermal cycling test for 1,000 cycles.

The failure behaviors of flip chip solder joints under various loading conditions of the high-speed shear test (H-SST) were investigated with an experimental and non-linear 3-dimensional finite element modeling study. The solder composition used in this study was Sn -3.0 Ag -0.5 Cu ( in wt .%). The shear forces were far greater by H-SST than by low-speed shear test (L-SST). The shear force further increased with increasing shear speed, mainly due to the high strain-rate sensitivity of the solder alloy. Brittle interfacial fractures were more easily achieved by H-SST, especially at the higher shear speed. This was discussed in terms of the relationship between the strain-rate and work-hardening effect and the resulting stress concentration at the interfacial regions

This study investigated the influence of three parameters, the distance between electrodes, bias voltage, and surface finish material, on the electrochemical migration (ECM) in flexible printed circuit boards (FPCBs) during water drop testing. The ECM rate increased when the distance between electrodes of opposite polarity was decreased and the bias voltage was increased. Irrespective of the distance between the electrodes and the bias voltage, the growth rate of dendrites from the cathode to the anode decreased with the following order of surface finish material: Cu, electroless Ni, and electroless nickel-immersion gold. The order of the corrosion rate in distilled water with pH 6.5 was the same. Therefore, the ECM rate on the FPCB increased with increasing corrosion rate of the FPCB surface finish material.

The microstructural evolution and interfacial reactions of fluxless-bonded, Au–20 wt.%Sn/electroless nickel-immersion gold (ENIG) solder joint were investigated during reflow and aging. After the reflow process, only (Au,Ni)Sn intermetallic compound (IMC) was formed at the interface. After prolonged reflow reaction, the (Au,Ni)Sn IMCs that had been formed in the initial reflow stage grew into the solder and a (Ni,Au) 3 Sn 2 IMC was formed at the interface. In the aging treatment, the solid-state interfacial reaction was much faster at 250 °C than at 150 °C. After aging at 250 °C for 100 h, a thick (Au,Ni)Sn IMC layer was formed at the interface. With increasing aging temperature and time, the δ(AuSn)-phase adjacent to the interfacial layer was gradually replaced by the ζ(Au 5 Sn)-phase. The interfacial (Au,Ni)Sn IMC grew with the preferential consumption of the available δ-phase in the solder. The Ni 3 P layer formed from the Ni(P) layer in the initial 500 h of aging was subsequently further transformed into a Ni 5 P 4 layer during further aging treatment between 500 and 1000 h. The original electroless Ni(P) plating layer lost its initial role of a diffusion barrier due to its crystallization. After aging for 1000 h, the Ni 5 P 4 layer was partially destroyed, and the Au–Cu IMCs were formed below the P-rich Ni layer.

This study investigated a method for controlling the interfacial reaction between a Sn–3.5Ag–0.7Cu (wt.%) solder and an electroless nickel-immersion gold-plated Cu substrate through heat treatment. The interfacial reaction layer was controlled by heat treating of the electroless Ni–P plated layer. By applying a heat treatment, the thickness of the reaction layer (intermetallic compounds, P-rich Ni layer) was observed to be reduced. The formation of Ni2SnP, which significantly affects the mechanical reliability of solder joints, was suppressed.

PurposeThis study seeks to investigate the electrochemical migration (ECM) behaviour of printed circuit boards (PCBs) with Sn‐37Pb and Sn‐3.0Ag‐0.5Cu (wt.%) solders under various factors such as the distance between the electrodes and bias voltage.Design/methodology/approachThis study investigated the ECM phenomena with different surface finishes of Sn‐37Pb and Sn‐3.0Ag‐0.5Cu solders using water drop (WD) and temperature and humidity bias (THB) tests. After the WD and THB tests, the dendrite phase was identified using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).FindingsThe ECM resistance of the conventional Sn‐37Pb alloy was lower than that of the Pb‐free Sn‐3.0Ag‐0.5Cu alloy. The dendrites grew at the cathode electrodes on the PCB and expanded to the anode electrode. The main elements in the dendrites on the Sn‐37Pb and Sn‐3.0Ag‐0.5Cu finished PCBs were tin and lead, respectively.Originality/valueThis study evaluates the ECM phenomena of representative solder alloys on PCBs.

In this study, we evaluated the mechanical reliability of Sn-rich, Au–Sn/Ni flip chip solder bumps by using a sequential electroplating method with Sn and Au. After reflowing, the average diameter of the solder bump was approximately 80 μm and only a (Ni,Au) 3 Sn 4 intermetallic compound (IMC) layer was formed at the interface. Due to the preferential consumption of Sn atoms within the solder matrix during aging, the solder matrix was transformed sequentially in the following order: β -Sn and η -phase, η -phase, and η -phase and e -phase. In the bump shear test, the shear force was not significantly changed despite aging at 150 °C for 1000 h and most of the fractures occurred at the interfaces. The interfacial fracture was significantly related to the formation of brittle IMCs at the interface. The Sn-rich, Au–Sn/Ni flip chip joint was mechanically much weaker than the Au-rich, Au–Sn/Ni flip chip joint. The study results demonstrated that the combination of Sn-rich, Au–Sn solder and Ni under bump metallization (UBM) is not a viable option for the replacement of the conventional, Au-rich, Au–20Sn solder.

High-speed ball shear test was investigated in terms of the effects of two test parameters, shear speed and shear height, with an experimental and computational simulation utilizing 3-dimensional non-linear finite element modeling for evaluating the solder joint integrity of ball grid array (BGA) packages. A representative Pb-free solder alloy, Sn–0.7Cu, was employed in this study. Far greater shear forces were measured by high-speed shear test than by low-speed shear test. The shear force further increased with shear speed mainly due to the high strain-rate sensitivity of the solder alloy. Brittle interfacial fractures can be more easily achieved by high-speed shear test, especially in higher shear speed. These were discussed with the strengthening mechanism of the solder materials by density and mobility of dislocations. Shear force decreased with shear height, and it could be found that excessively high shear heights unfavorably affected the test results leading to unexpectedly high standard deviation values or shear tip sliding from the solder ball surface.

This study examined the effects of isothermal aging and temperature–humidity (TH) treatment of substrate on the joint reliability of a Sn–3.0Ag–0.5Cu (wt.%)/organic solderability preservative (OSP)-finished Cu solder joint. Two types of OSP-finished chip-scale-package (CSP) substrates were used, those subjected and not subjected to the TH test. This study revealed an association between the interfacial reaction behaviors, void formation and mechanical reliability of the solder joint. Many voids were formed at the interface of the OSP-finished Cu joint subjected to the TH test. These voids were caused by the oxidation of the OSP-finished Cu substrate during the TH test. In the shear tests, the shear force of the joint with the substrate not subjected to the TH test was slightly higher than that with the TH test. The mechanical reliability of the solder joint was degraded by voids at the interface.

The adhesion strength of Cu/Ni–Cr/polyimide flexible copper clad laminate (FCCL) was evaluated according to the composition ratio of the Ni–Cr layer and the thickness of the Cu electroplating layer, by using a 90° peel test. The changes in the morphology, chemical bond and adhesion property were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The peel strength of the FCCL increased with increasing Cr content and increasing Cu electroplating layer thickness. This increasing FCCL peel strength was attributed to a lower C–N bond and higher C–O and carbonyl (C=O) bonds in the polyimide surface compared to the FCCL with a lower adhesion strength. The adhesion property of the FCCLs was significantly affected by the Ni:Cr ratio.

The electromigration of conventional Sn-37Pb and Pb-free Sn-3.0Ag-0.5Cu (in wt.%) solder bumps was investigated with a high current density of 2.5 × 104 A/cm2 at 423 K using flip-chip specimens comprised of an upper Si chip and a lower bismaleimide triazine (BT) substrate. Electromigration failure of the Sn-37Pb and Sn-3.0Ag-0.5Cu solder bumps occurred with complete consumption of electroless Ni immersion Au (ENIG) underbump metallization (UBM) and void formation at the cathode side of the solder bump. Finite element analysis and computational simulations indicated high current crowding of electrons in the patterned Cu on the Si chip side, whereas the solder bumps and Cu line of the BT substrate had a relatively low density of flowing electrons. These findings were confirmed by the experimental results. The electromigration reliability of the Sn-3.0Ag-0.5Cu solder joint was superior to that of Sn-37Pb.

The surface morphology, electrical property, solderability and interfacial reaction with Sn–3.5 wt.%Ag solder of two electroless nickel–boron (EN–B) deposits (Ni–1 wt.%B and Ni–3 wt.%B) were investigated. The B content of the EN–B layer decreased with increasing pH value. The crystallinity and solderability of the EN–B plating layer decreased with increasing B content, while the electrical resistivity increased. Reaction layers of Ni 3 Sn 4 and Ni 3 B were formed at the interfaces between the Sn–3.5Ag solder and the two EN–B deposit layers. The thickness of the interfacial Ni 3 Sn 4 intermetallic compound (IMC) layer decreased with increasing B content, i.e., decreasing Ni content. These study results confirmed that the interfacial reaction between solder and the EN–B layer is significantly affected by the B content of the EN–B layer.

In this study, the effect of a Ni-Cr layer on the adhesion strength of flexible copper clad laminate (FCCL) was evaluated after thermal treatment. The changes in the chemical composition, morphology, and adhesion properties were characterized by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and 90 deg peel test. The results showed that both the peel strength and thermal resistance of the FCCL increased with increasing Cr ratio. The thermal treatment of the FCCL increased the proportion of C-N bonds and reduced that of the C-O and carbonyl (C=O) bonds in the polyimide. The roughness of the fracture surface decreased with increasing thermal treatment temperature and holding time. The chemical function and roughness of the fracture surface were affected by the Ni-to-Cr ratio.

Thermo-mechanical reliability of the anisotropic conductive film (ACF) joints in relation with flip chip bonding forces was evaluated by thermal shock testing. Two kinds of main failure modes were detected after thermal shock testing: formation of a conduction gap between conductive particles and Au bump or Ni/Au-plated Cu pad, and delamination of the adhesive matrix from the plated Cu pad on the flexible substrate. The determination of the failure mode was mainly affected by the variation of the bonding force. The main failure mode of the thermally shocked ACF joints was conduction gap for the joints with low bonding forces and adhesive matrix delamination for the joints with high bonding forces. Finite element analysis was also performed to determine the stress distributions within the two kinds of flip chip packages having different bonding gaps when it was stressed by the temperature rising.

Analytical electron microscopy (AEM) was used to examine the initial interfacial reaction layers between a eutectic Sn–3.5Ag solder and an electroless nickel-immersion gold-plated (ENIG) Cu substrate during reflow at 255 °C for 1 s. AEM confirmed that a thick upper (Au,Ni)Sn2 layer and a thin Ni3Sn4 layer had formed through the reaction between the solder and ENIG. The amorphous electroless Ni(P) plated layer transformed into two P-rich Ni layers. One is a crystallized P-rich Ni layer, and the other is an intermediate state P-rich Ni layer before the crystallization. The crystallized P-rich layer consisted of Ni2P and Ni12P5. A thin Ni2P layer had formed underneath the Ni3Sn4 layer and is believed to be a predecessor of the Ni2SnP ternary phase. A Ni12P5 phase was observed beneath the Ni2P thin layer. In addition, nanocrystalline Ni was found to coexist with the amorphous Ni(P) phase in the intermediate state P-rich Ni layer.

This paper presents an investigation on the conduction behaviors of the anisotropic conductive film (ACF) interconnections bonded at various bonding forces. The connection resistance of the ACF joints decreased with increasing bonding force up to 70 N, but subsequently converged to a value of 10 mΩ at bonding forces above 70N. This convergence of the connection resistance in the ACF joints was due to two opposing factors: decreased resistance due to increased contact area and increased resistance due to decreased currentflow path that may have been affected by the delamination of the metal film from the polymeric cores at high bonding forces. During thermal shock testing of the adhesive joints, two different conduction behaviors were observed: increasing connection resistance and the termination of Ohmic behavior. The former was due to decreased contact areas caused by warpage of the package, whereas the latter was caused by delamination at the interface.

The electrochemical migration (ECM) with flexible printed circuit board (PCB) was affected by factors such as distance between the electrodes and bias voltage using water drop (WD) test. The rate of migration was increased by decreasing the distance between electrodes of the opposite polarity and increasing the bias voltage.