Interconnect Materials Research Articles

The Coating Effect on Interconnect Materials After >10 Years of Furnace Exposures

One of the key components in the SOFC stack is the interconnect which requires versatile material properties for a proper functioning, e.g., high temperature corrosion stability, low ASR degradation and low chromium evaporation. At the same time, a high production capacity needs to be reached in order to fulfil the supply demand required for GW levels. The high production capacity is realized through Alleima AB’s production line with coil-coil physical vapor deposition of coated interconnects for SOFC and SOEC applications [1].More specifically, Sanergy HT 441 is the standard material intended to be used as an SOC interconnect. The substrate is a ferritic stainless steel (ASTM 441) which is coated with thin layers of Ce and Co (<1 µm). The material can be coated on both sides using the same coating or with a different coating. At elevated temperatures the Co coating forms a protective (CoMn)3O4 spinel layer which drastically reduces Cr evaporation while the Ce layer improves the corrosion resistance by reducing the chromia scale growth at the coating/substrate interface and thereby maintaining a low and stable ASR over time.Since long-term stability is a critical property for interconnects, Alleima has over the years gathered data from furnace samples and can thus present results where some samples have been exposed at elevated temperatures during >10 years. The main results include the effect of Ce thickness or choice of substrate on mass gain and subsequent chromia growth. Selected samples with coating elements different than Co have also been investigated. Samples have been further investigated using scanning electron microscopy for cross-sections, x-ray diffraction for characterization of phases and residual stresses as well as glow discharge optical emission spectroscopy for elemental analysis.

Analysis of Structural Degradation Effects in a Solid Oxide Fuel Cell after Long-Term Operation

The sustainable production of hydrogen as well as its re-conversion into electricity will be a key aspect in a future green energy environment that is depending on regenerative resources. In order to ensure the eminent position of solid oxide cells (SOC) in this future hydrogen economy their reliability and long-term performance still needs to be improved. Having this in mind, we performed detailed investigations on samples from cells that were operated for 100,000h to get a profound understanding of structural degradation effects after long-term operation.The investigated samples originate from a two layer stack of fuel electrode supported solid oxide cells that were operated at 700°C and 0.5 A/cm2 in fuel cell mode. The cells consist of a Ni/Y-stabilized ZrO2 (YSZ) fuel electrode, a dense YSZ electrolyte layer, a Gd doped CeO2 (GDC) barrier layer and a La0.58Sr0.4Co0.2Fe0.8O3-d (LSCF) air electrode. Furthermore, an additional contact layer of La0.97Mn0.4Co0.3Cu0.3O3-d was applied on the air electrode surface and, in order to inhibit Cr-poisoning the interconnector material was coated with a manganese oxide layer by wet powder spraying. The stack represents the usual material status from 2009 when the stack operation has been starting.In the post-test analysis the microstructure and chemical composition was investigated by scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDS). The EDS analysis revealed localized, correlated enrichments of Sr and Cr in the bulk of the LSCF air electrode as well as at the LSCF / GDC interface. Moreover, non-correlated, localized Co enrichments could also be detected at the LSCF / GDC interface. In order to get an insight into localized structural changes and to identify impurity phases after long-term operation Raman spectroscopy measurements were performed. Hereby, it was for example possible to visualize, in accordance with the EDS analysis, the formation of a SrCrO4 impurity phase on the LSCF air electrode surface as well as inside the bulk of the LSCF by running Raman measurements on the air electrode surface as well as on embedded and polished cross-section samples. To study the structural degradation in detail with high spatial resolution, additional µ-beam Laue diffraction measurements were performed at the CRG-IF BM32 beamline at European Synchrotron Radiation Facility (ESRF).

Model Based Comparative Analysis of GDC and YSZ Based Solid Oxide Fuel Cells

Designing solid oxide fuel cell (SOFCs) stacks for transportation applications places new challenges on SOFC architecture and operation with respect to power density, dynamic response, and thermal management. Recent developments in SOFCs with either thin-film yttria stabilized zirconia (YSZ) electrolytes (thickness ≤ 5 μm) or highly conductive, gadolinia-doped ceria (GDC) electrolytes (thicknesses ≥10 μm) enable thigh-power-density stack operation at inlet temperatures well below 700ºC with the potential for using compliant seals and lower cost ferrous interconnect materials. Applications, such as hybridized aircraft engines, can use such SOFC stacks if they meet strict requirements with respect to specific power and thermal management. Highly conductive GDC-based electrolytes offer pathways to high power-density SOFCs at operating temperatures below 650ºC, but the rise in mixed ionic electronic conductivity (MIEC) above 650ºC reduces open circuit voltages and thus fuel cell efficiency [1,2]. This necessitates thermal management to maintain operating temperatures and mitigate thermo-mechanical stresses within an SOFC. Thin-film YSZ electrolytes offer lower power densities below 650ºC, but avoid the penalties associated with MIEC behavior at higher temperatures and therefore reduce the challenges associated with thermal management at high power densities. In this work, a model-based approach is used to compare SOFC stack operation with thin-film YSZ electrolytes and with GDC-based electrolytes for operation on hydrogen and reformate fuels at high-power densities relevant for transportation applications.To calibrate models to experimental cell performance, polarization curves of a commercially available YSZ-based cell operating between 600-750ºC and of a high-power-density GDC cell operating between 500-650ºC are used to fit electrochemical model parameters for both electrolytes. Modeling of the YSZ based cell can neglect electronic charge transfer through the membrane electrolyte, but GDC-cell modeling must account for the multiple charge carriers (ceria polarons and oxygen vacancies) in the electrolyte [3]. Electrochemical parameters for ionic conductivities and electrochemical reaction rate parameters for oxide cathodes and nickel-electrolyte-composite anodes are fit to the experimental polarization data over the broad range of operating temperatures. Global rate expressions to account for internal reforming on the active nickel surfaces of anode are adopted from literature [4,5]. The calibrated cell model for each cell type is adopted to a down-the-channel discretized cell simulation to predict heat loss and temperature gradients at high current densities.This presentation compares GDC- and YSZ-based SOFCs in high power-density applications from fundamental and practical perspectives. The open-circuit voltages for GDC-based cells drops with increasing temperature to about 0.85 V/cell at 650°C which is lower than the Nernst open-circuit voltage of YSZ-based cells (≥ 1.05 V/cell) at similar conditions. Both types of cells can sustain power densities around 1.0 W/cm2 with high excess cathode air ratios ≥ 5 to keep temperature gradients near 10°C/cm. These results show that GDC-based cells support higher power densities at lower cell flow inlet temperatures < 600°C, whereas thin-film YSZ cells provide superior performance at flow inlets that drive cell temperatures > 600°C. Higher stack power densities > 1.0 W/cm2 must be supported by stack designs that alleviate high thermal stresses and allow steeper gradients of temperature. A summary of stack design and operational strategies that meet the stringent requirements of high power-density operation will be presented in the light of the modeling resuls..

High temperature electromigration behavior of cobalt lines observed by in situ transmission electron microscopy

As industrial practices shift away from Cu as the initial back-end-of-line interconnect material due to size limitations, new candidate metals are being tested and characterized. Electromigration resistance is particularly important in ultra-narrow lines and an in situ study provides unique insight into the formation and progression of electromigration damage. This, in turn, helps to inform device design so that electromigration resistant circuits can be produced efficiently. In this work, the authors demonstrate an in situ transmission electron microscopy technique for electromigration analysis of Cu replacement metals in microelectronic interconnects. Using this method, candidate metal lines can be tested at high current densities, ∼5×106 A/cm2, at controllable temperatures over the range of 300–1000 °C. In this work, cobalt lines are tested in the range of the effective valence inversion temperature. The analysis examines void nucleation, growth, and migration as a function of temperature and line geometry. We find that there is a relative insensitivity of failure time to operating temperature, with samples tested between approximately 600 and 900 °C having roughly equivalent failure times. We ascribe this result to a combination of linewidth effects and a decrease in the magnitude of the effective valence approaching the inversion temperature. Failure mechanism is also not affected by temperature in this range, with the primary determining factor being the linewidth and corresponding availability of grain boundaries for diffusive mass transport. We also observe increased lifetimes of devices with uniform temperatures compared to those in which large thermal gradients exist.

Novel Cu@Ag Micro/Nanoparticle Hybrid Paste and Its Rapid Sintering Technique via Electromagnetic Induction for High-Power Electronics.

Due to the harsh working environments up to 600 °C, the exploration of high-temperature interconnection materials is significantly important for high-power devices. In this study, a hybrid paste including Cu@Ag core-shell microparticles (MPs) and Ag nanoparticles (NPs) was designed to achieve Cu-Cu bonding. The Cu@Ag MPs exhibited excellent oxidation stability in an air atmosphere with the Ag layer coating on the Cu core. Ag NPs fill the pores among the Cu@Ag MPs and reduce the sintering temperature of the hybrid paste. The Cu-hybrid paste-Cu joints were formed via electromagnetic induction heating within approximately 15 s. When sintered at 26 kW, the shear strength of the joint reached 48 MPa, the porosity decreased to 0.73%, and the resistivity was down to 13.25 μΩ·cm. Furthermore, a possible interconnection mechanism at the contact interface between the Cu substrate and the sintered hybrid paste was proposed, which is related to the melting point of metal particles and the effect of magnetic eddy currents. This fast bonding technology inspires a new approach to interconnection for high-power devices under high operation temperatures.

Controlled and Uniform Wet Etching of Molybdenum Nanowires

We achieved the controlled recess of molybdenum (Mo), which is alternative interconnect material for copper (Cu), by wet chemical etching. This wet etching process includes two main steps which are chemical oxidation of Mo and its subsequent dissolution, respectively. Firstly, Mo nanowires (NWs) are uniformly oxidized with potassium permanganate (KMnO4) solution in acetone. Secondly, the Mo oxide is dissolved using an aqueous solution of HCl. Mo NWs are characterized through transmission electron microscopy (TEM) imaging after each of the above steps. Cyclic etching experiments including oxidation and dissolution of Mo showed that Mo recess is linear and can be controlled for each cycle, where the etching produced the smooth Mo surface. This controlled Mo recess is crucial for the fabrication of next-generation metal interconnects.

Investigation on Rheological Characterization of Isotropic Conductive Adhesives

In the field of microelectronic packaging technology, isotropic conductive adhesives (ICAs) have been used widely as interconnection materials between chips and substrates. ICAs are composed of silver powder particles and adhesive matrix. The paper analysed the rheological properties of ICAs at different temperatures in order to better apply ICAs in dispensing and jet printing processes. The viscosity, viscoelasticity, and thixotropic behaviours of ICAs were studied using various experimental methods such as oscillatory stress shear, and rotational rheology. The rheological behaviours of ICAs conforms to the Cross Model. In SAOS flow field, the ICAs has G”>G’ in LVR region, which shows the viscous component is dominant and ICAs represent viscoelastic fluid characteristics.

Development of high thermal conductivity of Ag/diamond composite sintering paste and its thermal shock reliability evaluation in SiC power modules

Diamond has the highest thermal conductivity among naturally occurring materials and a relatively low coefficient of thermal expansion (CTE), making it a promising interconnected material for next-generation semiconductor power devices. In this study, Ag/diamond composite sintering paste was developed. The agglomerated diamond particles were uniformly dispersed in the sintered Ag porous structure, and the thermal conductivity was increased from 171.4 W/(m·k) for pure Ag sintering to 288 W/(m·k) for an Ag@2%diamond (2% of the total weight of Ag) specimen. The interfacial microstructure evolution and fracture behavior were investigated in detail for a SiC/Direct Bond Copper (DBC) joint structure during an extreme thermal shock test (TST) in the range of −50 °C–250 °C. Importantly, with a moderate amount of diamond additive, the microstructural degradation and severe deformation of the DBC substrate were effectively suppressed. This is mainly attributed to the diamond addition, which can block the migration pathways of Ag atoms toward long-term thermal shock and adjust the thermo-mechanical performance of the sintered layer. This detailed study about Ag/diamond composite paste can provide new guidance for strengthening sintered Ag interconnections for SiC power modules.

Revolution of next-generation interconnect materials and key processes for advanced chips in post-moore era

Revolution of next-generation interconnect materials and key processes for advanced chips in post-moore era

A protocol for fabrication of polymer monolithic capillary columns and tuning the morphology targeting high-resolution bioanalysis in gradient-elution liquid chromatography.

Polymer monolithic stationary phases are designed as a continuous interconnected globular material perfused by macropores. Like packed column, where separation efficiency is related to particle diameter, the efficiency of monoliths can be enhanced by tuning the size of both the microglobules and macropores. This protocol described the synthesis of poly(styrene-co-divinylbenzene) monolithic stationary phases in capillary column formats. Moreover, guidelines are provided to tune the macropore structure targeting high-throughput and high-resolution monolith chromatography. The versatility of these columns is exemplified by their ability to separate tryptic digests, intact proteins, and oligonucleotides under a variety of chromatographic conditions. The repeatability of the presented column fabrication process is demonstrated by the successful creation of 12 columns in three different column batches, as evidenced by the consistency of retention times (coefficients of variance [c.v.]=0.9%), peak widths (c.v.=4.7%), and column pressures (c.v.=3.1%) across the batches.

Unraveling SEI formation and cycling behavior of commercial Ni-rich NMC Li-ion pouch cells through operando optical characterization

Lithium-ion batteries, relying on Ni-rich NMC (LiNixMnyCo1−x−yO2) phases, are widely used in various applications due to their high energy density and extended cycle life. However, further improvements are possible with a deeper understanding of their internal chemistry in real-world conditions. Here, using optical fiber Bragg grating sensors placed inside commercial pouch cells, we demonstrate the feasibility of monitoring the heat release during the formation cycles and real-driving cycling. By collecting temperature data for Li-ion cells using different types of NMCs, we were able to extract the contribution of the anode and the impact of additives on overall heat generation. We also present a comparison of the heat generation of NMC-based batteries under varying power and voltage levels, which provides insights into battery safety in dynamic, real-world environments. Our study reveals the importance of continuously monitoring batteries heat release throughout its lifespan to enhance our understanding of the interconnected materials surfaces and electrolyte reactions.

CoMn2O4 and Cu0.5Co0.5Mn2O4 spinels as efficient protective coating layers on SUS430 for SOFC interconnect

In this study, CoMn2O4 and Cu0.5Co0.5Mn2O4 spinels are examined as protective coatings for chromium diffusion in metallic interconnect of solid oxide fuel cell. Both spinels are prepared by co-precipitation technique in order to obtain high temperature conducting spinels. The spinels obtained after 4 h of calcinations in air at 500 °C exhibit tetragonal crystal structure with average grain size between 90 and 100 nm. Cu0.5Co0.5Mn2O4 spinel exhibits superior electrical conductivity over CoMn2O4 and both display NTCR (negative temperature co-efficient of resistance) behavior illustrating their use as a protective layer on interconnects for fuel cells operating at higher temperatures. Doctor-blade employed spinel coating over SUS430 alloy exhibits good adhesion between protective spinel layer and metallic alloy. Cross section micrographs reveal presence of nanosized and highly dense grains capable to resist the outflow of chromium ions present in SUS430. Mass gain and diffusion rate constant (Kp) was high for CoMn2O4 coated SUS430 illustrating Cu0.5Co0.5Mn2O4 spinel as a better protective coating layer for interconnect application. Chromium outflow is restricted and the same is evident from all cross-section micrographs of spinel coated SUS430 specimens subjected for oxidation up to 1000 h. Estimated thickness of Cr2O3 layer was ∼15 nm for CoMn2O4 whereas Cu0.5Co0.5Mn2O4 coated SUS430 specimen had ∼12.5 μm thickness at the SUS430/spinel interface demonstrating superior resistance to chromium outflow. The area specific resistance was lowest for Cu0.5Co0.5Mn2O4 coated specimen (between 14 mΩcm2 – 15 mΩcm2) followed by CoMn2O4 coated specimen reiterating Cu0.5Co0.5Mn2O4 as efficient protective coating material for SUS430 SOFC interconnect.

Copper-Based Nanomaterials for Fine-Pitch Interconnects in Microelectronics.

ConspectusNanostructured copper-based materials have emerged as a new generation of robust architectures for realizing high-performing and reliable interconnection in modern electronic packaging. As opposed to traditional interconnects, nanostructured materials offer better compliance during the packaging assembly process. Due to the high surface area-to-volume ratio of nanomaterials, they also enable joint formation by sintering through thermal compression at much lower temperatures compared to bulk counterparts. Nanoporous Cu (np-Cu) films have been employed in electronic packaging as materials that facilitate a chip-to-substrate interconnection, realized by a Cu-on-Cu bonding after sintering.In this Account, we discuss the use of self-supported np-Cu films for low-temperature joint formation. The novelty of this work comes from the incorporation of tin (Sn) into the np-Cu structure, thus ensuring lower sintering temperatures with a goal of producing Cu-Sn intermetallic alloy-based joints between two Cu substrates. The incorporation of Sn is done using an all-electrochemical bottom-up approach that involves the conformal coating of fine-structured np-Cu (initially formed by dealloying of Cu-Zn alloys) with a thin layer of Sn.This Account provides insight on existing technologies for using nanostructured films as materials for interconnects as well as the optimization studies for the Sn-coating processes as a new alternative approach. The applicability of the synthesized Cu-Sn nanomaterials for low-temperature joint formation is also discussed. To realize this new approach, the Sn-coating process is administered by a galvanic pulse plating technique, which is optimized to preserve the porosity in the structure with a Cu/Sn atomic ratio that allows for the formation of the Cu6Sn5 intermetallic compound (IMC). Nanomaterials obtained using this approach are subjected to joint formation by sintering at temperatures between 300 and 200 °C under 20 MPa pressure in forming gas atmosphere. Cross-section characterization of the formed joints postsintering reveals densified bonds with minimal porosity that consist predominantly of the Cu3Sn IMC. Furthermore, these joints are less prone to structural inconsistencies compared to existing joints formed using purely np-Cu. The results presented in this Account provide a glimpse into a facile and cost-effective approach for synthesizing nanostructured Cu-Sn films and illustrate their applicability as new interconnect materials.

An investigation of Cr vaporization from SUS430 metallic interconnect and deposition on (La,Sr)MnO3 cathode of intermediate temperature solid oxide fuel cells

In solid oxide fuel cells (SOFCs), chromium deposition and poisoning of metallic interconnect is one of the most important issues in the electrochemical activity and stability of the cathode for the oxygen reduction reaction (ORR). In this paper, the chromium evaporation characteristics, oxide scale growth, and deposition of chromium on the ORR on (La,Sr)MnO3 (LSM) cathode are studied at 700–800 °C for SUS430 alloy interconnect material in the intermediate-temperature solid oxide fuel cells. The chromium vaporization rate is measured using the transpiration technique and the surface morphologies, and cross-sections of oxide scales are examined by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The results indicate that chromium volatilization is correlated with the composition and morphology of the oxide scale, the Cr volatilization process presents two stages according to the structural evolution of the oxide scale. In addition, deposition and poisoning of Cr species released from metallic interconnect on the LSM cathode are studied and the formation of MnCr2O4 phase on the LSM backbone degrades the ORR electrochemical activity, causing the increase of overpotential of the cathode. The results obtained give insight into the mechanism of the Cr poisoning effect in intermediate-temperature.

Study on preparation and sintering properties of nano-silver-coated tin slurry

A nano-sized silver-coated tin (Sn@Ag) slurry was prepared by heterogeneous flocculation method by adjusting the pH value of solution and selecting different dispersants. The slurry improved the oxidation resistance of tin and its dispersibility in silver matrix. The sintering strength of nanometre Sn@Ag slurry increases with the increase of Sn content. When the Sn content reaches 5%, the shear strength of the joint reaches the highest 50 MPa, which is more than 10 MPa higher than that of the pure nanometre silver slurry sintered joint. The increase of shear strength is due to the fact that the equilibrium phase formed after sintering is Ag–Sn replacement solid solution and intermetallic compound Ag 3 Sn, which have the effect of replacement solution strengthening and dispersion strengthening, respectively. It is proved by experiments and analysis that the application of nano-silver paste in chip interconnection is feasible. The research of this subject provides experimental reference and theoretical basis for the application of new generation interconnect materials in power devices and promotes the development of microelectronics packaging technology.

Adsorption and Surface Diffusion of Atomic Ru on TiN and SiO2: A First-Principles Study

Ruthenium (Ru) has been suggested as one of the promising materials for nanoscale interconnects to substitute copper (Cu) that is currently used in the semiconductor industry. Through density functional theory (DFT) calculations, we present the rationales for varying deposition behavior of Ru on different types of substrates. For the SiO2 and TiN substrates, with and without adsorbed hydrogen, our calculation results reveal the adsorption sites and their adsorption energy, the surface diffusion paths and their activation energy, and the surface diffusion coefficients. We confirm that the adsorption of Ru is more stable on TiN than on SiO2 substrates, and that the surface diffusion of Ru adatom is faster on TiN than on SiO2 surface.

Novel favorably interconnected N-doped porous carbon hybrid electrode materials for high energy density supercapacitors

A strategy to prepare facile electrode materials for electrochemical capacitors with high conductivity, high surface area and hierarchical pore structure along with nitrogen functional groups to enhance the electrochemical performance, is presented in this work. Partially unravelled carbon nanotubes (PURNTs) are interconnected to the wrinkled few layered graphene nanosheets (WfG), which act as quick ion and charge transportation channels. Here, PURNTs acts as a spacer to the WfG to avoid the restacking. Though WfG-PURNTs exhibit good results, to further improve the electrochemical performance we developed an electrode material by designing nitrogen-doped porous carbon covered favorably interconnected WfG-PURNTs with interconnected pore structure. The WfG-PURNTs serve as the conductive matrix, which plays a key role in enhancing the N-PC (WfG-PURNTs) electrode material's electrochemical performance. And the nitrogen functional groups, through faradaic red-ox reactions, contribute to the pseudocapacitance in addition to the electric double layer capacitance, thereby enhancing overall supercapacitive performance. The developed N-PC (WfG-PURNTs)-700 shows a high nitrogen amount of 6.8 at %, with a high active surface area of 2418 m2 g−1. The synergistic effect of the WfG-PURNTs and N-doped porous carbon results in high supercapacitive performance and better cyclic stability. It shows an excellent specific capacitance (Cp) of 954 F g−1 at high current density of 2 A g−1. Also, the assembled symmetric supercapacitors show high energy densities of 61.1, 119.4, and 195.4 Wh kg−1 in acidic, neutral and ionic liquid electrolytes, respectively. We also designed asymmetric solid-state flexible supercapacitor which exhibits a high specific capacitance of 209.4 F g−1 at 2 A g−1 and an excellent energy density of 29.15 Wh kg−1. Furthermore, the assembled three such flexible supercapacitors in series connection, could able to light up red colored LED for 30 min once charged for 60 s.

Fabrication of Nanocomposite PDMS/Graphene as Flexible Substrate at Different Graphene Volume

Conductive and flexible electronics have attracted great demands and attention in the field of stretchable and wearable electronic devices. In this work, polydimethylsiloxane (PDMS) was composited with different drops of graphene solution to produce flexible, conductive and optically transparent PDMS/Graphene composite using the drop-cast method. The dielectric constants of PDMS and PDMS/Graphene composite were measured using Agilent dielectric probe. I-V characterization was used to measure the conductivity of the flexible substrate in flat and bending conditions. The UV-VIS was used to measure the transmittance properties of the substrate. Comparing the electrical properties of the pristine PDMS substrate with graphene composited PDMS substrates, the current shows a slight decrease due to the physical morphology of PDMS/Graphene composite that creates a small hole on the surface. No significant changes can be found between 1 drop, 2 drops, 3 drops and 4 drops of graphene in PDMS solution. For the dielectric measurement, the result of composited PDMS/Graphene sample had shown a lower value of dielectric constant (1.1 F/m) compared to pure PDMS (2.33 F/m). This shows that the existence of graphene in PDMS reduces the dielectric constant of pristine PDMS. The result of UV-VIS shows the samples with 4 drops of graphene having the lowest visible transmittance. The PDMS/Graphene composite can be concluded as a dielectric material with a lower dielectric constant. It has the potential to be used as a conductive substrate for further flexible interconnect materials since it has a unique electrical feature and robust mechanical strength.

Neural-fuzzy machine learning approach for the fatigue-creep reliability modeling of SAC305 solder joints

The accuracy of reliability models is one of the most problematic issues that must be considered for the life of electronic assemblies, particularly those used for critical applications. The reliability of electronics is limited by the fatigue life of interconnected solder materials, which is influenced by many factors. This paper provides a method to build a robust machine-learning reliability model to predict the life of solder joints in common applications. The impacts of combined fatigue and creep stresses on solder joints are also investigated in this paper. The common alloy used in solder joint fabrication is SAC305 (Sn–Ag–Cu). The test vehicle includes individual solder joints of SAC305 alloy assembled on a printed circuit board. The effects of testing temperature, stress amplitude, and creep dwell time on the life of solder joints were considered. A two-parameter Weibull distribution was utilized to analyze the fatigue life. Inelastic work and plastic strain were extracted from the stress–strain curves. Then, Artificial Neural Networks (ANNs) were used to build a machine learning model to predict characteristic life obtained from the Weibull analysis. The inelastic work and plastic stains were also considered in the ANN model. Fuzzy logic was used to combine the process parameters and fatigue properties and to construct the final life prediction model. Then a relationship equation between the comprehensive output measure obtained from the fuzzy system and the life was determined using a nonlinear optimizer. The results indicated that increasing the stress level, testing temperature, and creep dwell time decreases reliability. The case of long creep dwell time at elevated temperatures is worst in terms of impact on reliability. Finally, a single robust reliability model was computed as a function of the fatigue properties and process parameters. A significant enhancement of the prediction model was achieved compared to the stress–life equations.

The Coating Effect on Interconnect Materials After >10 Years of Furnace Exposures

The present work has studied the effect of subjecting an AISI 441 ferritic stainless steel in a box furnace exposure in air at 800 °C for up to 10 years. During operation, the mass gain was repeatedly measured at selected time intervals. The results show that there are only small differences in spinel composition when a sample exposed for ~5 years is compared to a sample exposed for 10 years, with the main difference being a growth of the chromia scale from ~10 to ~14 µm. In addition, the chromium content is 12.3 wt-% after 5 years whereafter it is further reduced to 10.5 wt-% during the following exposure time. Despite a relatively low chromium content already after 5 years, there are no visible signs of material failure, e.g, neither spallation nor a a large increase in mass gain during the 10 years in the furnace.