The effect of solder wetting on nonconductive adhesive (NCA) trapping in NCA applied flip-chip bonding

Flip-chip bonding using a nonconductive adhesive (NCA) and the effect of solder wetting on NCA trapping were studied. Three different solder materials with different melting point were used for the bonding process: In–48Sn, Bi–42Sn, and Sn–3.5Ag. Additionally, the bonding process was performed at various temperatures. We measured the amount of NCA trapping as functions of the solder material and bonding temperature. The fillers and NCA were easily trapped between the solder and Cu pads. The amount of trapped fillers and NCA increased with softer solder materials. These trapped fillers and NCA could be reduced if the solder melted and reacted to Cu pads during the bonding process. However, if the solder melted after fully curing NCA, the trapped NCA was not reduced due to the low mobility of cured NCA. Therefore, in order to reduce NCA trapping, the solder should be melted before curing NCA. The electrical test results showed that the contact resistance increased with increasing amount of trapped fillers and NCA.     

The effect of annealing temperature on the fracture performance of isotactic polypropylene

The influence of annealing temperature on the fracture behaviour of a commercial extrusion-grade isotactic polypropylene was studied. Fracture mechanics analysis was carried out at room temperature and at a low crosshead speed underJ-controlled conditions. Parameters characterizing fracture initiation,J _IC, and crack propagation,T _M, were determined. Some thermal treatments induced “ductile instability” after a certain amount of crack extension while others strongly enhanced the fracture toughness parameters and promoted completely stable behaviour. Aiming to correlate mechanical properties with the supermolecular structure, the different morphologies induced by thermal treatments were studied by differential thermal analysis. In addition, a qualitative fracture surface analysis was carried out by SEM. Craze formation appeared to be the principal plastic deformation mechanism present. The degree of crystallinity and the degree of interconnection related to the thermal treatment the sample had undergone, are the main structural factors controlling fracture performance.     

Effect of bonding temperature on microstructure and intermetallic compound formation of diffusion bonded magnesium/aluminum joints

The diffusion bonding of two dissimilar alloys Aluminum 5083 and Magnesium AZ31 was carried out at 420 °C, 430 °C,440 °C and 450 °C for bonding time of 60 min. In order to characterize the microstructure evolution in the joint zone, scanning electron microscopy, energy dispersive spectroscopy and x-ray diffraction were applied. The results show that joint formation is attributed to the solid-state diffusion of magnesium and aluminum into Aluminum 5083 and Magnesium AZ31 alloys followed by eutectic formation and constitutional liquation along the interface. At bonding temperature of 430 °C diffusion induced grain coarsening was observed at the interface. With increase in bonding temperature, the atomic diffusivity increases, results in easier and speeder chemical bonding. In bonding temperature of 440 °C the weld had an irregular shaped region in the weld center, having a different microstructure from the two base materials. The irregular shaped region contained a large volume of intermetallic compound Al₁₂Mg₁₇ and showed significantly higher hardness in the weld center. The present study suggests that constitutional liquation resulted in the intermetallic compound Al₁₂Mg₁₇ in the weld center.     

The effect of aluminium on the electrical and mechanical properties of BaTiO3 ceramics as a function of sintering temperature

The effect of aluminium additions on the mechanical behaviour of BaTiO₃ positive temperature coefficient of resistance ceramics sintered in air at temperatures ranging between 1220 and 1400° C has been investigated. Tensile strength has been measured indirectly by the diametral compression of lapped discs using concave loading anvils. Values of ∼ 85 and ∼ 110 MPa for samples fired near their optimum sintering temperature were determined for two batches of material, the latter of which contained additions of Al₂O₃ (0.55 mol%). Strength did not vary systematically with grain size and appeared to be controlled by near surface defects. The size of these cavities, which were generally crescent shaped, was consistent with the material having a bulk fracture toughness of ∼1.3 MPam^1/2. The higher mechanical strength of samples which contained Al₂O₃ additions was attributed to the enhanced “healing up” of these cavities by the liquid phase giving a smaller inherent critical defect size rather than by increasing the bulk toughness of the ceramic.     

The effect of substrate and post annealing temperature on the electrical properties of polycrystalline InSe thin films

The correlation between the electrical properties of vacuum evaporated InSe thin films and the growth conditions as well as post depositional annealing has been investigated. The electrical properties of the deposited films have been studied in the temperature range of 50–320 K. The donor levels present in the InSe films have been analysed by applying the single donor-single acceptor model to the electrical data.     

The effect of an electrical double layer on the voltammetric performance of nanoscale interdigitated electrodes: a simulation study

Finite-element based computational simulation is performed to investigate the effect of an electrical double layer (EDL) on the electrochemical processes of nanometer-scale interdigitated electrodes (nano-IDEs). Results show that the EDL structure will alter the voltammetric current response of nano-IDEs due to the expansion of the diffuse layer into the diffusion layer at the electrode surfaces and the overlap of the electrical fields of the neighboring electrodes. The EDL induced change in the voltammetric current response is more severe for nano-IDEs with a smaller electrode size and gap spacing, and the EDL effect is influenced by the compact layer thickness, the charge valence of the redox species, the electron transfer rate, and the absence of the supporting electrolyte.     

Rate of heating and sintering temperature effect on the electrical properties of Nd ferrite

The real part of the dielectric constant () and the dielectric loss angle (tan ) as well as the ac conductivity of ferrite Mg_1+x Ti _x Nd _y Fe_2–2x–y O₄ 0.1 x 0.9 at fixed Nd concentration of 0.025 were measured at different temperatures as a function of frequencies. The variation of activation energy as a function of the applied frequency was reported. The obtained data were discussed on the basis of the valence exchange between (Fe³⁺, Fe²⁺), (Fe²⁺, Nd³⁺) and (Fe²⁺, Ti⁴⁺). Also the effect of sintering temperature and heating rate of preparation were discussed.     

Hybrid plasma bonding of germanium and glass wafers at low temperature

Hybrid plasma bonding (i.e., sequentially plasma activation followed by anodic bonding) has been demonstrated for germanium and glass wafers for the first time. Void-free interface with high bonding strength has been observed at 200 °C. This improved quality is attributed to reduced surface roughness and increased hydrophilicity of sequentially activated germanium and glass. Three layers caused by reactions of OH molecules between the highly reactive surfaces after plasma activation and opposite migration of cations and anions are observed across the interface.     

The effect of substrate temperature,deposition rate and annealing on the electrical resistivity of thin yttrium films

The effect of substrate temperature, deposition rate and annealing on the electrical resistivity of thin yttrium films in the thickness range 10 to 80 nm is reported. The resistivity of films decreases at higher deposition rates and substrate temperatures. These experimental results are analysed using the Fuchs—Sondheimer and Mayadas—Shatzkes theories. The annealing behaviour of yttrium films is in agreement with the Vand theory.     

The longitudinal electrical conductivity of metal-matrix composites at cryogenic temperature in the presence of a longitudinal magnetic field

We solve the Boltzmann equation in the relaxation time approximation with parallel E and B fields parallel to the continuous fibres reinforcing a metal matrix. It is shown that this solution is identical to that described by us elsewhere, except for the addition of the cyclotron frequency. The addition of the cyclotron frequency term shows that the electrons follow helical paths as they drift down the composite. The boundary considered is either the external or the internal surface of a cylinder representing the fibre. To apply this solution to metal-matrix composite materials we assumed that the cylindrical fibres are non-conducting cylinders in a matrix of pure crystalline metal. The electron mean free path is never greater than half the fibre separation distance. In a companion paper we discuss the application of this solution to metal-matrix composites.     

The effect of joint size on the creep properties of microscale lead-free solder joints at elevated temperatures

Solder joints in electronic packaging systems are becoming smaller and smaller to meet the miniaturization requirements of electronic products and high density interconnect technology. Furthermore, many properties of the real solder joints at the microscale level are obviously different from that of bulk solder materials. Creep, as one of the key mechanical properties at elevated temperatures, can impair the reliability of miniature solder joints in electronic devices. However, there is a lack of knowledge about the comparative creep properties of microscale solder joints of different sizes. Most previous studies have focused on the creep properties of bulk solder materials or solder joints of the same size. In this research, to determine whether a size effect exists for creep properties of solder joints or not, we characterized the creep behaviors of Sn–3.0Ag–0.5Cu lead-free solder joints under tensile loading modes using microscale butt-joint specimens with a copper-wire/solder/copper-wire sandwich structure with two different sizes. Also, the creep failure mechanisms were investigated. Experimental results show that the creep activation energy and creep stress exponent are very similar for both sizes of solder joint. However, under the same testing conditions, the joints with a larger size exhibit a much higher steady-state creep rate and a shorter creep lifetime than the smaller joints.     

Effect of high temperature annealing on the electrical performance of titanium/platinum thin films

In this study, the influence of post deposition annealing steps (PDA) on the electrical resistivity of evaporated titanium/platinum thin films on thermally oxidised silicon is investigated. Varying parameters are the impact of thermal loading with maximum temperatures up to T_PDA = 700 °C and the platinum top layer thickness ranging from 24 nm to 105 nm. The titanium based adhesive film thickness is fixed to 10 nm. Up to post deposition annealing temperatures of T_PDA = 450 °C, the film resistivity is linearly correlated with the reciprocal value of the platinum film thickness according to the size effect. Modifications in the intrinsic film stress strongly influence the electrical material parameter in this temperature regime. At T_PDA > 600 °C, diffusion of titanium into the platinum top layer and its plastic deformation dominate the electrical behaviour, both causing an increase in film resistivity above average.     

The effect of substrate temperature on the structural,optical and electrical properties of vacuum deposited ZnTe thin films

The present paper reports the effect of substrate temperature on the structural, optical and electrical properties of vacuum deposited zinc telluride (ZnTe) thin films. X-ray diffraction (XRD) analysis of the films, deposited on glass substrates, revealed that they have cubic structure with strong (111) texture. Room temperature deposits are tellurium rich and an increase in the substrate temperature up to 553 °K results in stoichiometric films. Electrical conductivity has been observed to increase with the increase in substrate temperature, accompanied by increase in the carrier concentration and the mobility of the carriers. The optical bandgap energy and the thermal activation energy of the films have also been evaluated.     

The effect of substrate temperature on the structural, optical and electrical properties of vacuum deposited ZnTe thin films

The present paper reports the effect of substrate temperature on the structural, optical and electrical properties of vacuum deposited zinc telluride (ZnTe) thin films. X-ray diffraction (XRD) analysis of the films, deposited on glass substrates, revealed that they have cubic structure with strong (111) texture. Room temperature deposits are tellurium rich and an increase in the substrate temperature up to 553 °K results in stoichiometric films. Electrical conductivity has been observed to increase with the increase in substrate temperature, accompanied by increase in the carrier concentration and the mobility of the carriers. The optical bandgap energy and the thermal activation energy of the films have also been evaluated.     

The effect of damping and force application point on the non-linear dynamic behavior of a cracked beam at sub-and superresonance vibrations

The finite element model of an elastic body with a closing crack is presented. Using this model, we show that the non-linear distortions of vibrations at superharmonic and subharmonic resonances are the high sensitive indicators of crack presence. The intensity of these indicators manifestation substantially depends on the level of damping in the system and on the load application point. __________ Translated from Problemy Prochnosti, No. 5, pp. 61–67, September–October, 2006. Report on International Conference “Dynamics, Strength, and Life of Machines and Structures” (1–4 November 2006, Kiev, Ukraine).     

The structural and electrical properties of Zn-Sn-O buffer layers and their effect on CdTe solar cell performance

Thin films of zinc-tin-oxide (ZTO) have been deposited on SnO₂:F coated glass substrates by co-sputtering of SnO₂ and ZnO. The deposition conditions for ZTO were controlled in order to vary film stoichiometry. The electro-optical and structural properties of ZTO have been studied as a function of their stoichiometric ratio and post-deposition annealing conditions. The same films were subsequently utilized as part of a bi-layer transparent front contact for the fabrication of CdTe solar cells: glass/SnO₂:F/ZTO. The performance of these devices suggested that the ZTO deposition and cell processing conditions can be optimized for enhanced device performance in particular for devices with thin CdS. Specifically, high blue spectral response (> 70% at 450 nm), accompanied by high open-circuit voltages (830 mV), and fill factors (70⁺%) have been demonstrated. Best solar cell performance was obtained for multi-phase ZTO films deposited at substrate temperatures of 400°C and a Zn/Sn ratio of 2.0, and which contained the binary phase of ZnO₂.     

Quantitative effects of electrical and vibrational stresses on reliability

This article presents some details on how electrical and vibrational stresses exacerbate failures. This is one of a series of articles on similar subjects by this author. One electrical defect type is pin-holes in oxide layers in ICs. Electrical leakage current through a low insulation pin-hole could cause temperature rise and ultimately, when electrons of sufficient energy causing an avalanche, a thermal runaway condition could develop and maintain an electrical short. On the other hand electromigration could cause conductor opens. Aircraft data indicated that vibration related failures constituted more than 14 per cent of the total number of field failures. Fatigue failures can be directly related to S/N curves of stress to number of cycles to failure. Some measurements indicated that for a particular piece of equipment tested the time to failure varied inversely as the fourth power of vibrational acceleration; and failures of specific groups of component part types were sensitive to particular vibrational acceleration levels. Much information exists that gives quantitative measures on how stresses exacerbate failures. However, there is still a big gap in the relationship between the engineering fundamentals and the failures experienced. The author urges the readers to join force to develop a new reliability engineering foundation based on relationships of defects, failure mechanisms and stresses from which future reliability predictions and reliability analyses can be conducted.