Change In Contact Resistance Research Articles

A study on thermal cycling (T/C) reliability of anisotropic conductive film (ACF) flip chip assembly for thin chip-on-board (COB) packages

In this work, thermal cycling (T/C) reliability of anisotropic conductive film (ACF) flip chip assemblies having various chip and substrate thicknesses for thin chip-on-board (COB) packages were investigated. In order to analyze T/C reliability, shear strains of six flip chip assemblies were calculated using Suhir’s model. In addition, correlation of shear strain with die warpage was attempted.The thicknesses of the chips used were 180μm and 480μm. The thicknesses of the substrates were 120, 550, and 980μm. Thus, six combinations of flip chip assemblies were prepared for the T/C reliability test. During the T/C reliability test, the 180μm thick chip assemblies showed more stable contact resistance changes than the 480μm thick chip assemblies did for all three substrates. The 550μm thick substrate assemblies, which had the lowest CTE among three substrates, showed the best T/C reliability performance for a given chip thickness.In order to investigate what the T/C reliability performance results from, die warpages of six assemblies were measured using Twyman–Green interferometry. In addition, shear strains of the flip chip assemblies were calculated using measured material properties of ACF and substrates through Suhir’s 2-D model. T/C reliability of the flip chip assemblies was independent of die warpages; it was, however, in proportion to calculated shear strain. The result was closely related with material properties of the substrates. The T/C reliability of the ACF flip chip assemblies was concluded to be dominatingly dependent on the induced shear strains of ACF layers.

312 工具・被削材間接触電気抵抗変化を利用したフライスエ具摩耗の推定(トライボロジー1)

312 工具・被削材間接触電気抵抗変化を利用したフライスエ具摩耗の推定(トライボロジー1)

Tactile Sensing Using Contact Resistance in MWNT/PDMS Composites

ABSTRACTA carbon nanotube polymer composite has been used to develop a flexible multi-touch tactile sensor device. Rather than employing the inherent bulk piezoresistive properties of the composite, the contact resistance between polymer and electrode was exploited to achieve finger pressure measurement with fast response. We have synthesized a series of multi-walled nanotube (MWNT) silicone composites to test the feasibility of a force sensor based on the change in surface contact resistance as a function of applied force. A single layer MWNT/polydimethyl-siloxane (PDMS) composite in the range of 1.5-3.0 % w/w nanotubes was employed as a force sensor material in an array of electrodes. It was determined that sensors based on these materials are viable as tactile sensing systems for finger-touch forces in the range of 1-100 N.

Localized insulator-conductor transformation of graphene oxide thin films via focused laser beam irradiation

By scanning a focused laser beam over graphene oxide (GO) film deposited on SiO2/Si substrates, conductive strips as small as 1 μm can be patterned directly either as a channel in the insulating matrix, or as a stand-alone micro belt. The conductivity was increased by at least two orders of magnitude with the mobility estimated in the range of 1–10 cm2/V s. Raman mapping and X-ray photoelectron spectroscopy studies demonstrated the reduction of GO in the laser-irradiated area. The conductance of the patterned channel was independent of the change in oxide-electrode contact resistance of the graphene, and increased linearly with increasing channel width. Increasing irradiation power by repeated scanning initially increased the conductivity of the irradiated area and saturated at a conductivity of ∼36 S/cm. Partial oxidative burning combined with photothermal reduction was identified as the underlying mechanism for the enhancement of the conductivity after laser irradiation on the GO film. Oxidative burning can be controlled by varying the film thickness and laser power.

Independently driven four-probe method for local electrical characteristics in organic thin-film transistors under controlled channel potential

We describe an independently driven four-probe method to investigate local channel mobility in organic field-effect transistors (OFETs). In OFET devices, probe-organic contact resistance affects device characteristics even in four-probe measurement because a change in contact resistance at the source probe induces a change in channel potential, resulting in different local carrier density. To overcome this problem, we introduced a feedback circuit between the source probe and a channel voltage probe to keep the channel potential constant. We demonstrate four-probe I-V measurement on a pentacene thin film (50 nm thick) under controlled channel potential. The feedback successfully enables us to separate contact resistance and channel resistance even under different contact conditions. We also measured four-probe resistance as a function of gate bias and channel probe position. The present results were in good agreement with two-dimensional model calculation by arranging four probes in a defect-free area; the mobility of the pentacene single grain was evaluated to be 0.25 cm(2)/(V s).

Research on Wearable Sensors Based on Knitted Fabrics with Silver Plating Fiber

Two kinds of plain fabrics, made of silver plating yarn, were tested on conductivity under weft extension to investigate the relationships between tensile property and resistance. The results are following: the resistances of two kinds of fabrics have a linear relationship with strain within a definite range; the strain sensitivity of the inelastic plain fabric is smaller than that of the elastic plain fabric; the changes of contact resistance of the overlapped yarns cause the inelastic plain fabric sensitive to strain; when two kinds of fabrics were stretched repeatedly to simulate heartbeat signals, their resistance remained stable at a value. So they satisfy stability requirement.

Suppression of bias stress-induced degradation of pentacene-TFT using MoO x interlayer

The bias stress effect in pentacene thin-film transistors (TFTs) with and without MoO x interlayer was characterized. The device without MoO x interlayer showed a large threshold voltage shift of 5.1 V after stressing with a constant gate-source voltage of −40 V for 10000 s, while at the same condition, the device with MoO x interlayer showed a low threshold voltage shift of 1.9 V. The results can be attributed to the stable interface between MoO x/pentacene and small contact resistance change for the device with MoO x/Cu electrode. Pentacene-TFTs with MoO x interlayer showed a high field-effect mobility of 0.61 cm 2/V s and excellent bias stability, which could be a significant step toward the commercialization of OTFT technology.

Scaling limits of resistive memories

This paper is intended to provide an expository, physics-based, framework for theestimation of the performance potential and physical scaling limits of resistive memory.The approach taken seeks to provide physical insights into those parameters and physicaleffects that define device performance and scaling properties. The mechanisms of resistiveswitching are based on atomic rearrangements in a material. The three model cases are: (1)formation of a continuous conductive path between two electrodes within an insulatingmatrix, (2) formation of a discontinuous path of conductive atoms between two electrodeswithin an insulating matrix and (3) rearrangement of charged defects/impurities near theinterface between the semiconductor matrix and an electrode, resulting in contactresistance changes. The authors argue that these three model mechanisms or theircombinations are representative of the operation of all known resistive memories.The central question addressed in this paper is: what is the smallest volume of matterneeded for resistive memory? The two related tasks explored in this paper are: (i)resistance changes due to addition or removal of a few atoms and (ii) stability of afew-atom system.

Influence of Voltage on Arc Characteristics and Electrode Mass Change of AgNi Contacts for Electromagnetic Contactors

Recently, photovoltaic power systems and electric vehicles have been commonly used. Therefore, the importance of DC (direct current) switching is expected to increase in the near future. The authors have been examining a method of evaluating the electrode loss of AgNi contacts for an electromagnetic contactor with a medium DC load current at a resistive circuit. In this study, the arc energy and electrode mass changes were investigated in more detail. We carried out experiments of 100,000 operations for an electromagnetic contactor at a load current of 5A constant with a source voltage change from 100 to 160V. The arc duration, contact resistance, arc energy, and electrode mass changes were measured. As a result, the arc duration was found out increase with the source voltage. In addition, the stationary cathode mass change (loss) increased proportion only to the total arc energy. However, the stationary cathode loss per unit arc energy decreased at the highest source voltage.

Properties of silver-tin alloys obtained from pyrophosphate-cyanide electrolytes containing EDTA salts

Silver-tin alloy coatings are electrodeposited from a newly developed EDTA containing cyanide-pyrophosphate electrolyte and some properties of the obtained coatings, such as microhardness, internal stress, abrasion resistance, plug-in forces and electrical contact resistance depending upon the applied current density or the tin content of the alloy, respectively, are investigated. The co-deposition of tin leads to the change of the tensile stress of pure silver coatings to compressive stress in the formed solid solution of the alloy and to almost stress free coatings at high current densities. The microhardness runs over a maximum at current densities, where the silver lattice is saturated with tin and the deposition of phase heterogeneous coatings starts. The abrasion resistance diminishes at increased tin content, and the changes of the electrical contact resistance are in the opposite direction. The measured plug-in forces show the lubricating properties of the alloy coatings.

Conduction degradation by fretting corrosion phenomena for contact samples made of high-copper alloys

The main cause of electrical contact resistance degradation by corrosion is the vibration of contact interfaces. The purpose of this paper is to analyse the change of contact resistance by means of a vibration test for uncoated sphere/plane contact made of new high-copper alloys. The influence of electrical and mechanical properties of materials, and mainly hardness, on contact resistance has been studied in this work. During the fretting test, a contact point was submitted to 16,000 vibration cycles under fretting amplitude of 50 μm and 1 Hz frequency. The sphere part was fixed, while the plane part was submitted to relative motion. At the end of the test, the fretted surfaces and the wear debris were analyzed by scanning electron microscope and energy dispersive X-ray spectroscopy to evaluate damage, oxidation and elemental composition present in the wear surfaces. In addition, the measurement of the wear track profile using a 3D surface scanning system was introduced. Increases in contact resistance and contact temperature were examined during the fretting test. The results showed that the contact resistance for the harder alloy was higher than that obtained for the other materials. In addition, topographic measurements showed that the small wear track corresponds to the harder material.

Effect of water content on the piezoresistivity of MWNT/cement composites

The piezoresistive behaviors of multi-walled carbon nanotube (MWNT)/cement composites with different water contents under uniaxial compression are investigated. Experimental results indicate that the piezoresistive sensitivities of MWNT/cement composites with 0.1, 1.3, 3.3, 5.7, 7.6, and 9.9% of water content are 0.60, 0.61, 0.73, 0.68, 0.34, and 0.06 kΩ/MPa, respectively. These findings indicate that piezoresistive sensitivities of MWNT/cement composites strongly depend on the water content in the composites. The mechanism behind the non-linear relationship between piezoresistivity and water content is also studied via the changes of contact resistance induced by field emission effect of MWNTs in the composites.

Effect of aluminium sheet surface conditions on feasibility and quality of resistance spot welding

A study investigating the effect of sheet surface condition on resistance spot welding (RSW) of aluminium has been carried out. This concentrates on two automotive aluminium alloys; AA5754 and AA6111, used for structural and closure applications respectively. The results show the marked effect that surface condition can have on the RSW process. For AA5754 sheet incomplete removal of a ‘disrupted surface layer’ prior to surface pretreatment is shown to have a detrimental effect on the RSW process. The solid wax lubricant used to assist metal forming leads to unpredictable changes in contact resistance, and consequently affects the process stability. For AA6111 closures the final surface topography can influence the RSW process. Standard ‘mill’ and electro-discharge textured (EDT) finish sheet surfaces were examined and preliminary results suggest that both are suitable for welding. The successful application of RSW of aluminium sheet requires careful consideration of the sheet surface condition. This requires close collaboration between material suppliers and automotive manufacturers.

Research Regarding Heat Exchange Through Nanometric Polysynthetic Thermal Compound to Cooler–CPU Interface

This article documents some of the factors that influence the heat transfer through polysynthetic thermal compounds at the central processing unit (CPU)/heat sink interface. First, special attention is paid to assessing the effect of mechanical and thermal properties of the contacting bodies, applied contact pressures, and surface roughness characteristics, as well as the use of different thermal interface materials on the maximum temperature experienced by the CPU. Second, it can be appreciated that good wetting of the mating surfaces and the retention of asperity micro-contacts can become critical elements in effectively removing the heat generated by the CPU. This study uses the Holman model for calculating the heat transfer, indicating the role of thermal contact resistance. The mathematical results clearly indicate that any strain in the interface material leads to a change in thermal contact resistance, with an effect on CPU overheating. Experimentally obtained images with an atomic force microscope clearly revealed that eliminating micro-gaps using thermal interface materials can facilitate the heat transfer by significantly lowering the thermal contact resistance of the CPU/heat sink assembly. This effect is amplified by the plastic deformation of micro-contacts due to high contact pressures and lower micro-hardness levels.

Gradation of mechanical properties in gas-diffusion electrode. Part 2: Heterogeneous carbon fiber and damage evolution in cell layers

In PEM fuel cell, gas-diffusion electrode (GDE) plays very significant role in force transmission from bipolar plate to the membrane. This paper investigates the effects of geometrical heterogeneities of gas-diffusion electrode layer (gas-diffusion layer (GDL) and catalyst layer (CL)) on mechanical damage evolution and propagation. We present a structural integrity principle of membrane electrode assembly (MEA) based on the interlayer stress transfer capacity and corresponding cell layer material response. Commonly observable damages such as rupture of hydrophobic coating and breakage of carbon fiber in gas-diffusion layer are attributed to the ductile to brittle phase transition within a single carbon fiber. Effect of material inhomogeneity on change in modulus, hardness, contact stiffness, and electrical contact resistance is also discussed. Fracture statistics of carbon fiber and variations in flexural strength of GDL are studied. The damage propagation in CL is perceived to be influenced by the type of gradation and the vicinity from which crack originates. Cohesive zone model has been proposed based on the traction–separation law to investigate the damage propagation throughout the two interfaces (carbon fiber/CL and CL/membrane).

Pressure Effect on the Homogeneity of Spark Plasma‐Sintered Tungsten Carbide Powder

A combined experimental/numerical methodology was developed to aid full densification of pure ultrafine tungsten carbide powder by means of Spark Plasma Sintering (SPS) operating in Current Control mode. Applied pressure ranged from 5 to 80 MPa while the current intensity was set and held constant at 1400 A. The developed SPS model used a moving‐mesh technique to account for the electrothermal contact resistance change during both shrinkage and punch sliding follow‐up. The pressure dependence on the electrothermal contact resistance was also taken into account by the model. The experimental and numerical results showed the effects of pressure on grain growth, residual porosity, and hardness observed along the sample radius. Upon increasing sintering pressure, complete densification was obtained by reducing the peak temperature measured at the die surface. By combining experimental and modeling results, a direct correlation between compact microstructure homogeneity and sintering parameters (i.e., temperature and applied pressure) was established.

산화물 박막 트랜지스터 동작에 대한 접촉 저항의 영향

The TFTs have been fabricated with 3 different geometry SID electrodes which have the same channel W/L ratio (W/L = 5) due to constant channel resistance, The 3 samples have different channel widths (350, 150, and 25 <TEX>${\mu}m$</TEX>) and channel lengths (70, 30, and 5 <TEX>${\mu}m$</TEX>) by fixed channel W/L ratio simultaneously on one chip for reliable comparisons. Resultant on-current and field effect mobility are proportional to the channel width, while the subthreshold swing is inversely proportional to the channel width mainly due to the change of contact resistance. These results show that the contact resistance strongly affects the device performances and should be considered in the applications.

Origin of the abnormal behavior of contact resistance in Ohmic contacts to laser-irradiated n-type GaN

Abnormal behavior of contact resistance with annealing in Ohmic contacts to laser-irradiated n-GaN is investigated. Ti/Al contacts on as-grown n-GaN shows no change in contact resistivity with annealing at the temperature range of 100–400 °C. However, the annealing results in the significant increase in contact resistivity in the contacts on laser-irradiated n-GaN. Synchrotron radiation photoemission study reveals the reduction of the concentration of donor-like N vacancies near the surface by the annealing. These results suggest that preventing the annihilation of N vacancies in the laser-irradiated n-GaN is important in improving the performance of vertical-structure GaN-based light-emitting diodes fabricated by laser lift-off.

Effects of Anisotropic Conductive Film Viscosity on ACF Fillet Formation and Chip-On-Board Packages

In this paper, the effects of anisotropic conductive film (ACF) viscosity on ACF fillet formation and, ultimately, on the pressure cooker test (PCT) reliability of ACF flip chip assemblies were investigated. The ACF viscosity was controlled by varying the molecular weight of the epoxy materials. It was found that the ACF viscosity increased as the increase of molecular weight of the epoxy materials. However, there was little variation of the thermomechanical properties among the evaluated ACFs with different viscosites. Also, the results showed that the ACFs have no differences in moisture absorption rate, die adhesion strength, and degree-of-cure. In scanning electron microscopy images, the lower ACF viscosity resulted in the smoother ACF fillet shape and the higher fillet height. From the results of PCT, the ACF flip chip assembly with the smoother fillet shape showed better reliability in terms of contact resistance changes. After 130 h of PCT, the flip chip assembly with lower ACF viscosity also showed a lesser degree of delamination at the ACF/chip interface.

Influence of Fretting Wear on Lifetime of Tin Plated Connectors

Due to the recent increase in electronic devices mounted on automobiles, a large number of connectors, especially low-cost tin plated connectors are being used. As a result, their contact reliability has become problematic. Furthermore, for the connectors which are subjected to fretting wear caused by heat cycle and vibrations, the contact resistance increases because of wear of tin and deposition of oxides, which generates problems of poor contact. This study is intended to analyze the change in contact resistance of tin plated connectors from the start of fretting wear to the end of their lifetime from the viewpoint of practical reliability, and to observe the trace and the characteristics of fretting wear microscopically. This study found that wear and oxidation of tin plated connectors start immediately with fretting wear, and thus accumulation of abrasion powder on fretting areas causes connectors to reach to the end of their useful lifetime quickly. Especially, it was demonstrated that amplitude of fretting has a considerable influence on a connector's lifetime. It is made clear that air-tightness, so-called “gas-tight” of tin in a fretting area influences fretting wear considerably.