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Protection against lead-free solder in wave-soldering by Ti/TiC coatings prepared by filtered cathodic arc deposition
Abstract
Lead-free solder is increasingly used in the wave soldering but corrosion of the stainless steel holders frequently occurs and produces deleterious effects. To enhance the service life, a Ti/TiC coating is deposited by filtered cathodic vacuum arc (FCVA) on the stainless steel holders. The morphology, structure, composition, microhardness, wear resistance, electron chemical corrosion, and wetting properties against solder are investigated. The results show that not only good frictional properties and corrosion resistance are achieved by the Ti/TiC coatings, but also good tin repelling and hydrophobic characteristics are observed. The Ti/TiC coating provides excellent protection against corrosion of lead-free solder in wave soldering.
... As shown in Fig. 18, the residual solder harmed the structure and performance of SS holders. Xiao et al. [91] used Ti/TiC coating to prevent corrosion. Ti/TiC coating was proven to have excellent performance, such as tin repelling, hydrophobic characteristics, frictional Y. Li et al. properties, and corrosion resistance, which could protect SS holders from the corrosion of lead-free solder. ...
... Lead-free solder on the wave soldering holders[91]. ...
The bonding of dissimilar materials can make the joint possess the select performances of two materials. Suitable brazing/soldering methods can be adopted for different materials and joint structures to achieve high strength bonding. By comparison with other joining technologies, the special brazing/soldering joints have better bonding performances, greater rigidity of the brazing/soldering structure, and good integrity. The best advantage of the brazing/soldering process is that the variety of brazing types. This paper classifies these special brazing/soldering processes to infrared brazing, wave soldering, laser brazing, ultrasonic brazing, and plasma arc brazing process according to their different heat sources and other aspects. The applications of these special brazing/soldering processes in material joining are introduced in this paper. The characteristics and functions of these heat sources and ultrasound in brazing are introduced in this paper. The applicable occasions of these special brazing/soldering processes are sorted out and summarized. Most importantly, the merits and demerits of special brazing/soldering processes are analyzed, and suggestions of the further research are mentioned.
... With the mandatory utilization of lead-free alloys, both technologies face new challenges. ese challenges include, for example, the corrosion susceptibility of the stainless-steel components in wave soldering, as was discussed by Xiao et al. [16], or an uneven temperature distribution in the reflow oven, which may result in various defects of the final product as reported by Deng et al. [17]. ...
In the present work, one near-eutectic and three hypoeutectic Sn-Ag-Cu alloys have been employed for soldering by induction heating. The alloys were produced by induction melting of high purity Ag, Cu, and Sn lumps. The melting behavior of the alloys was investigated by differential scanning calorimetry. The solder alloys were subsequently applied for soldering by conventional hot-plate heating as well as induction heating and both soldering times and peak temperatures were recorded during soldering. Solder joints of two copper sheets were produced. The electrical resistance, tensile strength, and microstructure were analyzed on each soldered joint. The results indicate that the physical and mechanical properties of solder joints are determined by their chemical composition and soldering technology. Induction soldered joints not only have a slightly higher electrical resistivity but also higher mechanical strength, except of the 0.3 wt.% Ag hypoeutectic solder. The highest increase in ultimate tensile strength (28%) was observed for induction soldered joints with 1 wt.% Ag hypoeutectic solder. This effect is ascribed to the homogenous distribution of the intermetallic compounds within the eutectic in the alloy microstructure. The homogenous distribution is aided by rotation of liquid solder due to eddy currents and high-frequency magnetic field generated during induction heating.
... When connecting components in industry, soldering method is popularly used [1][2][3][4][5]. It's a traditional technique to build metallurgic bonds [6][7][8]. ...
Soldering technology is popularly used as a traditional connecting technology in electronics industry. But this technology often hurts components more or less due to its high temperature processing. Electrical conductive adhesive as a substitute for solder in connecting technology, can reduce harm to components. When preparing curable conductive adhesive, curing agent is necessary for curing process. But conductive adhesives with different types of curing agents have different curing temperatures, curing time and electric conductivity. In this paper, three types of conductive adhesives with different curing agents named dicyandiamide, p-hydroxyphenylacetic acid (HPA), tetraethylenepentamine are being compared. Through resistivity test and differential thermal analysis (DTA), it is found that the conductive adhesive sample using tetraethylenepentamine has the lowest curing temperature and resistivity. Therefore, using tetraethylenepentamine to prepare curable conductive adhesive will be a better choice compared with other two curing agents.
... Compared with other coating preparation technology, the coatings deposited by arc ion plating have higher density and better adhesive strength with substrates [8][9][10] . In this paper, TiC coatings deposited by arc ion plating technology using Ti target in the Ar/CH4 mixed atmosphere. ...
TiC coatings were deposited on the AISI304 sheets by cathodic arc ion plating using pure Ti target in Ar/CH4 atmosphere. The surface morphology, hardness and tribological properties were investigated by scanning electron microscope(SEM), micro-hardness tester and ball-on-disc rotating tribometer. The results show that the thickness of the coatings was about 6μm. The hardness was 2000Hv0.05. The tribological tests were carried out at RT, 200°C, 400°C and RT-400°C against alumina balls. The friction coefficient was stable at 0.57 at RT, while the coefficient fluctuated largely at 200°C and RT-400°C due to the lower relative humidity.
The increasing operation temperature of electronic devices significantly accelerates the growth of Cu-Sn intermetallic compounds (IMCs) at the interfaces of Sn-Ag solder/Cu substrate which deteriorates the device reliability. A robust diffusion barrier is thus required to suppress the interfacial reactions between solders and substrates. In this work, electroless Ni-Fe-P coatings with three different internal microstructure were prepared to compare their interfacial reactions and diffusion barrier properties in Sn-Ag solder interconnects. Ni-Fe-P coatings can effectively suppress the excessive growth of interfacial IMCs in Sn-Ag solder interconnects during reflow process. It has been found that the Ni-Fe-P coatings with crystalline structure had great influence on IMCs formation and morphology at Sn-Ag/Ni-Fe-P interfaces. Among three types of Ni-Fe-P coatings, the crystalline Ni-Fe-P exhibited the optimal diffusion barrier property owing to the presence of a uniform and thinnest FeSn2 layer at the interface, while the amorphous Ni-Fe-P coating was less effective due to the irregular and thickest Ni3Sn4 IMCs formed at the interface.
Elastic strain energy under some conditions provides the major contribution to the total energy of a film growing on a substrate from condensing vapour. Polycrystalline films grown with intrinsic stress induced by energetic bombardment are expected to show orientations which minimize total energy. Even for a cubic crystal in a non-hydrostatic stress field the energy is a function of the relative orientation of the stress field and the crystallographic axes. The Gibbs free energy is minimized under constant stress and temperature conditions at thermal equilibrium. In this paper we derive expressions for the Gibbs free energy of a cubic crystal in uniaxial and biaxial stress fields and find the conditions under which it is a minimum. The sign of the expression is the quantity which determines the behaviour of a cubic crystal and if negative, predicts that the [111] direction of the crystal will align with the principal stress of a uniaxial stress field and will lie normal to the plane of principal stresses in a biaxial stress field. Experimental evidence is presented which shows that titanium nitride, TiN, which has a negative value of , obeys these predictions. If is positive, then the [100] direction of the crystal obeys the above rules rather than the [111] direction.
Recently, Diamond like carbon (DLC)-based functionally gradient coatings have been used in a variety of engineering applications
as useful films with appropriate tribological properties verified in many tests. However, due to their inherent residual stresses,
they have a tendency to peel off, thereby limiting their applications (involving high contact stresses) and deposition thickness.
Their brittleness and low adhesion may stem from either a faulty layer design or the wrong choice of material and deposition
method. Therefore, using both a suitable interleaving material and an appropriate deposition technology will create an inclusive
vision to accommodate better film properties. In this study, Ti-a:C and Ti-TiC-a:C films on AISI M2 steel substrates were
deposited by Closed Field Unbalanced Magnetron Sputtering (CFUBMS) method using pulsed-dc biasing, and the mechanical, the
structural, and the tribological properties for both films were investigated. It was seen that the incorporation of a TiC
buffer layer between the Ti interlayer and the a:C matrix played a positive role in terms of hardness, wear rate, and adhesion
properties.
Keywordsfunctionally graded materials (FGM)-vapor deposition-wear-scanning electron microscopy (SEM)-TiC
This paper presents the synthesis and application of 5-(p-aminobenzylidene) -thiorhodanine (ABTR) as a new chromogenic reagent for the determination of mercury. Based on the rapid reaction of mercury(II) with ABTR and the solid phase extraction of the coloured chelate with a C18 disk, a highly sensitive, selective and rapid method for the determination of mercury has been developed. In the presence of pH 3.5 sodium acetate-acetic acid buffer solution and emulsifier-OP medium, ABTR reacted with mercury(II) to form a red chelate in a molar ratio 1:2 (mercury to ABTR). This chelate was enriched by solid phase extraction with a C18 disk and eluted from the disk with dimethyl formamide (DMF). An enrichment factor of 50 was achieved. The molar absorptivity of the chelate in DMF was found to be 1.21 x 105 L mol-1 cm-1 at 555 nm. Beer's law was obeyed in the range of 0.01 ∼ 3 μg mL-1. The relative standard deviation for eleven replicates with a concentration of 0.01 μg mL-1 was 1.98%. This method was applied with good results to the determination of mercury in water and biological samples.
The FetO activity (aFetO) of BF slag containing alkali was determined by the zirconia solid electrolyte battery using gas-slag-metal balance technique so as to understand the relationship between aFetO, potassium capacity(CK), sulfide capacity(CS) and the composition. The results show that the aFetO and CS increase with the binary basicity, while CK decreases. As the MgO content and Al2O3 content increase, the aFetO decreases and CK increases, and the CS increases first and then decreases. When the alkali load of BF is high, the aFetO of slag should be maintained in the range of 0.074-0.078 by controlling composition, thus the slag has suitable desulphurization capacity and large capacity of removing alkali, which is helpful to reduce the alkali metal hazards to BF.
This paper deals with microstructures and properties of SAC305 lead-free solder reinforced with graphene nanosheets (GNS) decorated with Ni nanoparticles (Ni-GNS). These Ni-coated GNS nanosheets were synthesized by an in-situ chemical reduction method. After morphological and chemical characterization, Ni-GNS were successfully integrated into SAC305 lead-free solder alloy with different weight fractions (0, 0.05, 0.1 and 0.2wt %) through a powder metallurgy route. The obtained composite solders were then studied extensively with regard to their microstructures, wettability, thermal, electrical and mechanical properties. After addition of Ni-GNSs, cauliflower-like (Cu, Ni)6 Sn5 intermetallic compounds (IMCs) were formed at the interface between composite solder joint and copper substrate. Additionally, blocky Ni-Sn IMC-GNS hybrids were also observed homogenously distributed in the composite solder matrices. Composite solder alloys incorporating Ni-decorated GNSs nanosheets showed slightly reduced electrical resistivity compared to the unreinforced SAC305 solder alloy. With an increase in the amount of Ni-GNS, the composite solders showed an improvement in wettability with an insignificant change in their melting temperature. Mechanical tests demonstrated that addition of 0.2 wt% Ni-GNS would result in 19.7% and 16.9% improvements in microhardness and shear strength, respectively, in comparison to the unreinforced solders. Finally, the added Ni-GNS reinforcements in the solder matrix were assessed with energy-dispersive X-ray spectroscopy, scanning electron microscopy and Raman spectroscopy.
TiAlC nanostructured hard coatings have been deposited on Si(100) substrates by four-cathode reactive pulsed direct current unbalanced magnetron sputtering at various process conditions. The effects of Al and C on the compositional, mechanical and micro-structural properties of TiAlC coatings have been investigated using X-ray diffraction (XRD), micro-Raman spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, atomic force microscopy and nanoindentation hardness tester. Furthermore, the effect of substrate bias on the surface morphology, micro-structure and mechanical properties of TiAlC coatings is examined in detail. Formation of Ti3AlC(111) phase along with inclusion of TiC and amorphous carbon phases has been confirmed by XRD and micro-Raman spectroscopy studies. The optimized TiAlC coating exhibited a maximum hardness of ~ 30 GPa and elastic modulus of 288 GPa. Analysis of the nanoindentation data indicated that the resistance to plastic deformation (H3/E*2) and elastic strain to failure (H/E*) decrease with C and Al contents in the TiAlC coatings, whereas, these properties increase with an increase in the substrate bias due to grain size refinement. Lastly, fracture toughness of TiAlC coating has also been calculated using a cube corner indenter and the optimized coating exhibited a maximum toughness of ~ 1.38 MPa m1/2 at a load of 50 mN.
The wetting behavior and the interfacial reactions between TiCx
substrate and molten Ti-Al alloys with different Al contents were studied using the Sessile Drop method at 1758 K (1485 °C) in argon atmosphere. It is found that the wettability and interface reaction products depend on Al content in the molten alloy. The initial contact angles between the molten Ti-Al alloy and TiC0.78 surface reduces from 110 to 80 deg when Al content in the alloy changes from 40 to 80 wt pct. The reduction in the initial contact angle is due to the decrease of surface tension of the molten Ti-Al alloys with increasing Al contents. The segregation of Al atoms to the surface occurred at all bulk concentrations of Ti-Al alloys. Al with lower surface tension tends to segregate on the surface of liquid Ti-Al alloy. In the spreading stage, the interfacial reaction led to the decrease in the contact angle. The adhesion in Ti-Al/TiCx
system can be interpreted in terms of strong chemical interactions, which is greatly affected by the diffusion of C. The equilibrium contact angle was measured less than 10 deg. Finally, the reaction sequence at the Ti-Al melt and TiCx
substrate interface is proposed.
Currently, accompanying the development of microelectronic joining and packaging, the integrated level of integrated circuit among the electronic devices has been substantially improved, which means the number of the soldered joints on a device is becoming more and more while the size of the micro-joint turns to be smaller and smaller. Given that soldered joints do play an important role in electronic packaging, serving as both mechanical bridges and electrical interconnections between the components and the bonding pads, to investigate the sensitivity of reliability of lead-free solders to various severe conditions deserves considerable concerns. This paper introduces the recent reliability research of lead-free solders under several specific conditions (e.g., isothermal aging, corrosive environment, drop impact, radiation) comprehensively, producing a fundamental summarization for the further reliability research.
The aim of the current study was the evaluation of the bias voltage influence on the structural and tribological properties of titanium carbide dispersed in diamond-like carbon (TiC-DLC) coatings. To this end, TiC-DLC was deposited on 440C stainless steel substrate by physical vapour deposition method with titanium target and acetylene gas sources. The coating process was performed at the constant chamber pressure of 5 mbar and the bias voltage in the range of 100 to 400 V. The coatings were characterised by means of field emission SEM, X-ray diffraction and Raman spectroscopy. Pin on disc test was used for studying the wear behaviour of the coatings. The best tribological properties of coatings were reached at the bias voltage of 200 V. Overall, raising the bias voltage up to 200 V led to the decrease in the wear and friction initially, while getting the higher voltage (up to 400 V) reversed the process.
The singular perturbation problem for reaction diffusion time delay equation with boundary perturbation is considered. Firstly, the outer solution for the initial boundary value problem is constructed. Then, the initial and boundary layer correction terms are obtained using the stretched variables transforms. Finally, the asymptotic behavior of solution for the initial boundary value problem is studied.
TiC–DLC coatings were in situ synthesized on Ti target surface in acetylene ambient by cathodic arc evaporation. In this process, TiC–DLC composite phases were formed by chemical reaction between Ti target surface and ionized C ions. Different acetylene (C2H2) flow rate and synthetic time were designed as two independent variables to synthesize two series of coatings to study the effects of different synthetic parameters on structure of the coatings. Surface morphology, composition and structure of the coatings were investigated by SEM, EDS, XRD and Raman spectroscopy, respectively. The result showed that the structure and composition of the coatings on the titanium metal target surface could be controlled by changing the C2H2 flow rate. The uniform TiC-DLC composite phases were observed in the coatings, while both C2H2 flow rate and synthetic time could significantly affect the thickness and bonding state of the coatings.
In the present work, a TiC/TiB2 composite coating was produced onto a TC2 Ti alloy by laser cladding with Ti/TiC/TiB2 powders. The cladding surface microstructure, phase components and compositions was characterized with methods of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometry (XRD), and energy dispersive spectrometry (EDS). The cladding layer is consisted of Ti, TiC and TiB2. And the surface microhardness was measured. After laser cladding, a maximum hardness of 1100 HV was achieved in the laser cladding surface layer, which is more three times higher than that of the TC2 substrate (∼300 HV). Due to the formation of TiC and TiB2 intermetallic compounds in the alloyed region and grain refinement the microhardness of coating is higher than TC2 Ti alloy. In this paper, the corrosion property of matrix material and treated samples were both measured in NaCl(3.5 wt%) aqueous solution. From the result we can see that the laser cladding speciments’ corrosion property is clearly becoming better than the substrate.
The high stress of diamond-like carbon (DLC) film limits its thickness and adhesion on substrate. Multilayer structure is one approach to overcome this disadvantage. In this paper, the DLC/TiC multilayer films with different modulation periods (80 nm, 106 nm or 160 nm) at same modulation ratio of 1:1 were deposited on Si(1 0 0) wafer and Ti-6Al-4V substrate by filtered cathodic vacuum arc (FCVA) technology. X-ray diffraction (XRD), transmission electron microscopy (TEM), nanoindention and wear test were employed to investigate the effect of modulation periods on the microstructure and mechanical properties of the multilayer films. The results showed that the residual stress of the DLC/TiC multilayer films could be effectively reduced and the residual stress decreased with the modulation periods decreasing. The hardness of the DLC/TiC multilayer films increased with modulation periods decreasing. The DLC/TiC multilayer film with modulation period of 106 nm had the best wear resistance due to the good combination of hardness, ductility and low compressive stress.
The interfacial properties of �-Ti(0 0 0 1)/TiC(1 1 1) interface, such as adhesion, interface energy, interfa-cial fracture toughness, bonding nature, are investigated using first-principles calculations. Six interface
models with different TiC(1 1 1) termination and stacking sites are investigated to clarify their influence
on the interfacial stability and adhesion strength. C-terminated-hollow-site and Ti-terminated-center-site models exhibit identical epitaxial stacking style after fully relaxation, and can be regarded as the
Ti and TiC sides of the most stable and strongest interface. The possible negative interface energy indi-cates the interfacial diffusion, and even new phase formation, is likely to happen across the interface.
The largest interfacial fracture toughness is estimated about 4.8 MPa m
1/2
. The valence electron density
and partial density of states (PDOS) indicate that its interfacial bonding is mainly contributed from C-Ti
covalent bonds and Ti-Ti metallic interaction.
The titanium carbide/amorphous carbon nanocomposite films have been deposited on silicon substrate by filtered cathodic vacuum arc (FCVA) technology, the effects of substrate bias on composition, structures and mechanical properties of the films are studied by scanning electron spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy and nano-indentation. The results show that the Ti content, deposition rate and hardness at first increase and then decrease with increasing the substrate bias. Maximum hardness of the titanium carbide/amorphous carbon nanocomposite film is 51 Gpa prepared at −400 V. The hardness enhancement may be attributed to the compressive stress and the fraction of crystalline TiC phase due to ion bombardment.
Exenatide, a glucagon-like peptide-1 (GLP-1) receptor agonist, is effective in inducing weight loss. The exact mechanisms are not fully understood. Reduced appetite and food intake may play important roles. Sweet taste contributes to food palatability, which promotes appetite. Interestingly, GLP-1 and its receptor are expressed in the taste buds of rodents and their interaction has an effect on mediating sweet taste sensitivity. Our aim was to investigate whether sweet taste will be changed after long term treatment with exenatide. The results showed that high-fat diet induced obese rats (HF-C) presented metabolic disorders in food intake, body weight, blood glucose and lipid metabolism compared with long term exenatide treated obese rats (EX) and normal chow fed control rats (NC). Meanwhile, greater preference for sweet taste was observed in HF-C rats but not in EX rats. Compared with NC rats, brain activities induced by sweet taste stimulation were stronger in HF-C rats, however these stronger activities were not found in EX rats. We further found reduced sweet taste receptor T1R3 in circumvallte taste buds of HF-C rats, while GLP-1 was increased. Besides, serum leptin was evaluated in HF-C rats with decreased leptin receptor expressed in taste buds. These changes were not observed in EX rats, which suggest them to be the underlying hormone and molecular mechanisms responsible for alterations in sweet taste of HF-C rats and EX rats. In summary, our results suggest that long term treatment with exenatide could benefit dietary obese rats partially by reversing sweet taste changes.
Titanium carbide (TiC) films were deposited employing high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) in an Ar–C2H2 atmosphere of various compositions. Analysis of the structural, bonding and compositional characteristics revealed that the deposited films are either TiC and hydrogenated amorphous carbon (a-C:H) nanocomposites, nanocrystalline TiC, or Ti/TiC, depending on the C/Ti ratio. It was found that Ti-C films grown by HiPIMS show a C/Ti ratio of close to 1 for a wide C2H2 flow range (4–15sccm), with free C ranging from 0 to 20%. Thus, films ranging from near stoichiometric single phase TiC to TiC/a-C:H nanocomposites can be synthesized. This was not the case for DCMS, where films grown using similar deposition rates as for HiPIMS formed larger fractions of amorphous C matrix, thus being nanocomposites in the same C2H2 (above 4sccm) flow range. For a C/Ti ratio of 1 the resistivity is low (4–8×102μΩcm) for the HiPIMS films, and high (>100×102μΩcm) for the DCMS films. The hardness also shows a big difference with 20–27 and 6–10GPa for HiPIMS and DCMS grown films, respectively.
Development of optimized hard coatings requires a multilayer, functionally gradient approach, where adhesion, load support and low friction regions must be elements of the design architecture. Each of these functional regions should be joined through appropriate transition regions to reach desired coating performance. The design of coatings with hard and lubricious diamond-like carbon (DLC) surfaces requires a study of transitions between adhesive metal, load supporting carbide, and wear-resistant DLC materials. These transitions were investigated on the Ti–C system prepared by a hybrid of magnetron sputtering and pulsed laser deposition. Crystalline α-Ti, TiC and amorphous DLC films were formed at 100 °C substrate temperature by varying film chemical composition. Phase transitions between Ti–TiC–DLC were analyzed with XPS, XRD and Raman spectroscopy. A gradual replacement of hcp α-Ti with fcc TiC, and a two-phase region consisting of crystalline TiC and amorphous carbon (a-C) in transitions from Ti to TiC and from TiC to DLC were found. These transitions were reflected in mechanical properties investigated with nanoindentation. A hardness maximum in the two-phase TiC/a-C region was found. The resulting composition-property maps were used to design a wear-resistant coating with Ti/TiC/DLC transitions and a gradual increase in hardness from a steel substrate to a super-hard (60–70 GPa) self-lubricating DLC layer on the surface. This provided a hard coating with a low friction surface, which also resisted brittle failure in tests with high contact loads. © 1997 Elsevier Science S.A. All rights reserved.
The effects of substrate temperature and incident power flux on weakly magnetized TiN ion plating using a spatial array of permanent magnets were studied. The time-dependent rises of temperature for a silicon wafer with various biased voltages and for HSS tools with two kinds of thickness were measured. Incident power flux defined by the variation of Si substrate temperature was calculated for various biased voltages. Using scanning electron microscopy, a surface morphology was taken to study the effect of temperature on the time-dependent microstructual and crystallographic changes of the TiN film. Some X-ray diffraction patterns for phase and orientation of the TiN film were analyzed.
Purpose
To determine the endurance of stainless steels used for wave soldering container materials in molten lead‐free solders.
Design/methodology/approach
A dissolution test on stainless steel wires in molten lead‐free solders was performed. The effects of the composition of the stainless steel, test period, and composition of the lead‐free solder on the dissolution rate were investigated. Dissolution was measured by cross‐sectioning the wires and measuring the reduction in radius.
Findings
The Sn‐Ag lead‐free solder showed faster dissolution than did the conventional Sn‐Pb eutectic. A severe dissolution rate was also observed for the Sn‐Zn system.
Practical implications
Quantitative data for the reaction rate between stainless steels and molten lead‐free solder is useful for the design of soldering machines and in planning their maintainance.
Originality/value
This paper shows the effect of basic factors on the dissolution rate of stainless steels in molten solder. It can give a basic understanding to engineers of the effect of lead free solders on wave soldering process equipment.
The wetting of titanium carbide (TiC0.7) by liquid Al was studied using an improved sessile drop method at 1123–1323K. The initial contact angles were 77–79°, almost independent of temperature, and the final equilibrium contact angles between 17° and 12°, slightly decreasing with increasing temperature. The interfacial reaction yielded Al4C3 and dissolved [Ti] in the early stage of the wetting, and then the formation of the Al4C3 phase was halted by excess Ti accumulated at the interface. As a result, the wetting is essentially improved initially by the formation of the Al4C3 phase and then by the adsorption of Ti at the solid–liquid interface. The role of the Ti adsorption was further demonstrated by the wetting of TiC0.7 by an Al–1at.% Ti alloy.
Solder is widely used to connect chips to their packaging substrates in flip chip technology as well as in surface mount technology. At present, the electronic packaging industry is actively searching for Pb-free solders due to environmental concern of Pb-based solders. Concerning the reliability of Pb-free solders, some electronic companies are reluctant to adopt them into their high-end products. Hence, a review of the reliability behavior of Pb-free solders is timely. We use the format of “case study” to review six reliability problems of Pb-free solders in electronic packaging technology. We conducted analysis of these cases on the basis of thermodynamic driving force, time-dependent kinetic processes, and morphology and microstructure changes. We made a direct comparison to the similar problem in SnPb solder whenever it is available. Specifically, we reviewed: (1) interfacial reactions between Pb-free solder and thick metalliztion of bond-pad on the substrate-side, (2) interfacial reactions between Pb-free solder and thin-film under-bump metallization on the chip-side, (3) the growth of a layered intermetallic compound (IMC) by ripening in solid state aging of solder joints, (4) a long range interaction between chip-side and substrate-side metallizations across a solder joint, (5) electromigration in flip chip solder joints, and finally (6) Sn whisker growth on Pb-free finish on Cu leadframe. Perhaps, these cases may serve as helpful references to the understanding of other reliability behaviors of Pb-free solders.
Though lead-free replacements for SnPb eutectic alloys for reflow, wave, and hand soldering have been developed, relatively little has been reported on practical experience of lead-free wave soldering processes. In wave soldering, the interaction between the PCB, flux, solder alloy and processing equipment makes it desirable to develop the consumables and the wave soldering machine concurrently. A crossfunctional project team was formed and a lead-free wave soldering process developed and validated through nine months of industrial use in production of broad-band communications technology products.
The effects of strain energy on the preferred orientation of TiN thin films were investigated. In the TiN film deposited by plasma‐enhanced chemical‐vapor deposition with a power of 50 W, the overall energy of the film mainly depended on the surface energy because its strain energy was relatively small. The preferred orientation of the film corresponded to the plane with the lowest surface energy, i.e., (200). However, in the TiN film deposited by rf sputtering with a power of 200 W, the overall energy of the film was largely controlled by strain energy due to its large strain energy, and its growth orientation corresponded to the plane with the lowest strain energy, i.e., (111). Furthermore, the preferred orientation of the TiN film was changed from (200) to (111) with the film thickness. It is considered that this phenomenon is due to the increase of strain energy with its thickness.
Sputter-deposited TiN thin films on glass substrate were investigated by X-ray diffraction analysis. The lattice parameter determined on the basis of (200) and (220) peaks is smaller than that determined on the basis of (111) peaks. A decrease in lattice parameter with increasing temperature was observed on annealing. The films exhibited preferred orientation. The tendency towards a specific preferred orientation is discussed on the basis of strain and surface energies. At low substrate temperatures and/or at small film thicknesses surface energy controls growth and a (100) preferred orientation is expected. At large film thicknesses and at high substrate temperatures the strain energy predominates and the (111) orientation is expected.
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