Enhanced Corrosion Protection of Printed Circuit Board Electronics using Cold Atmospheric Plasma-Assisted SiOx Coatings.

The miniaturization and widespread deployment of electronic devices across diverse environments have heightened their vulnerability to corrosion, particularly affecting copper traces within printed circuit boards (PCBs). Conventional protective methods, such as conformal coatings, face challenges including the necessity for a critical thickness to ensure effective barrier properties and the requirement for multiple steps of drying and curing to eliminate solvent entrapment within polymer coatings. This study investigates cold atmospheric plasma (CAP) as an innovative technique for directly depositing ultrathin silicon oxide (SiOx) coatings onto copper surfaces to enhance corrosion protection in PCBs. A systematic investigation was undertaken to examine how the scanning speed of the CAP deposition head impacts the film quality and corrosion resistance. The research aims to determine the optimal scanning speed of the CAP deposition head that achieves complete surface coverage while promoting effective cross-linking and minimizing unreacted precursor entrapment, resulting in superior electrical barrier and mechanical properties. The CAP coating process demonstrated the capability of depositing SiOx onto copper surfaces at various thicknesses ranging from 70 to 1110 nm through a single deposition process by simply adjusting the scanning speed of the plasma head (5-75 mm/s). Evaluation of material corrosion barrier characteristics revealed that scanning speeds of 45 mm/s of the plasma deposition head provided an effective coating thickness of 140 nm, exhibiting superior corrosion resistance (30-fold) compared to that of uncoated copper. As a proof of concept, the efficacy of CAP-deposited SiOx coatings was demonstrated by protecting an LED circuit in saltwater and by coating printed circuits for potential agricultural sensor applications. These CAP-deposited coatings offer performance comparable to or superior to traditional conformal polymeric coatings. This research presents CAP-deposited SiOx coatings as a promising approach for effective and scalable corrosion protection in miniaturized electronics.

Improving the Long-Term Stability of PbTe-Based Thermoelectric Modules: From Nanostructures to Packaged Module Architecture.

Nanostructured lead telluride PbTe is among the best-performing thermoelectric materials, for both p- and n-types, for intermediate temperature applications. However, the fabrication of power-generating modules based on nanostructured PbTe still faces challenges related to the stability of the materials, especially nanoprecipitates, and the bonding of electric contacts. In this study, in situ high-temperature transmission electron microscopy observation confirmed the stability of nanoprecipitates in p-type Pb0.973Na0.02Ge0.007Te up to at least ∼786 K. Then, a new architecture for a packaged module was developed for improving durability, preventing unwanted interaction between thermoelectric materials and electrodes, and for reducing thermal stress-induced crack formation. Finite element method simulations of thermal stresses and power generation characteristics were utilized to optimize the new module architecture. Legs of nanostructured p-type Pb0.973Na0.02Ge0.007Te (maximum zT ∼ 2.2 at 795 K) and nanostructured n-type Pb0.98Ga0.02Te (maximum zT ∼ 1.5 at 748 K) were stacked with flexible Fe-foil diffusion barrier layers and Ag-foil-interconnecting electrodes forming stable interfaces between electrodes and PbTe in the packaged module. For the bare module, a maximum conversion efficiency of ∼6.8% was obtained for a temperature difference of ∼480 K. Only ∼3% reduction in output power and efficiency was found after long-term operation of the bare module for ∼740 h (∼31 days) at a hot-side temperature of ∼673 K, demonstrating good long-term stability.

Co contamination of Si: Plating & aging.

Cobalt has emerged as a vital material in 10 nm technology for localized interconnect layers, potentially offering a compelling alternative to Cu-based interconnects. In this study, we subjected the contamination arising from the presence of cobalt atoms in silicon to comprehensive investigation, employing electron transmission electron microscopy (TEM) observations in conjunction with first-principles calculations. The results show that a dense CoSi layer with a thickness of a few nanometers is formed at the interface of cobalt and Si. The CoSi layer blocks the diffusion of Co atoms into Si. This is due to the semiconducting nature of the covalent bond formed between Co and Si, leading to the emergence of a forbidden zone at the Co/CoSi interface. The diffusion of Co into CoSi is governed by the atomic exchange mechanism, however, the local distortion of the periodic atomic potential due to the presence of the forbidden zone at the Co/CoSi interface hinders the diffusion of Co into Si. Therefore, the deposition of a Co metal layer on a Si chip does not require an additional barrier layer.

Solid-phase transient soldering method based on Au/Ni-W multilayer thin-film-modified copper-based structures.

The copper crystal cone-shaped micro-nanostructure is used as the substrate, and the Ni-W alloy layer and Au nanolayer are plated sequentially. Instantaneous soldering with lead-free solder is realized under ultrasonic assistance at room temperature. This solves the residual stress and thermal damage caused by high melting point lead-free solder on thin chips and thermal components, and ensures the safety and reliability of electronic components. Copper-based microstructures are deposited by electrochemical methods. An amorphous Ni-W alloy layer with a thickness of 180 nm is deposited on the Cu-based microstructures by adjusting the atomic ratio of the plating solution. The Ni-W layer is further coated with a 50 nm Au layer to prevent oxidation. Solid-phase transient soldering is realized by combining the Au/Ni-W multilayer thin-film-modified Cu substructures with commercial solder (SAC305) for a holding time of 3 s at a soldering pressure of 10,000 gf (20 MPa) while ultrasonically assisted. The soldered samples are aged at 180 °C for 10 min, 30 min, and 60 min, respectively. Copper substructures with different surface modifications are subjected to destructive shear experiments with solder balls. Scanning electron microscope and X-ray fluorescence thickness gauge are used to study the microstructure, intermetallic compound (IMC) composition thickness and properties of the soldered interface and section. The cone height of the Cu-based structure is 2-4 µm, and the diameter of the bottom is 800 nm-1200 nm, which has a sharp tip and an excellent L/D ratio. The interface between the Au/Ni-W modified Cu substructure and the solder ball is almost free of holes. The average shear strength at the soldering interface is about 43.06 MPa. The fracture surface after the shear experiment basically occurs inside the solder ball matrix, which belongs to the pure toughness fracture. The interface between the Au/Ni-W-modified Cu-based structure and the solder ball is subjected to long aging treatment at 180 °C. The soldering interface showed a "bright layer". New phases are generated on the solder side above the "bright layer", while no new phases appear on the Cu substructure side below the "bright layer". The copper-based microstructure is inserted into the inside of the solder ball to form an inlay and produce mechanical interlocking. Au/Ni-W alloy modification layer can effectively improve the surface hardness of copper-based structures. This creates a large hardness difference with soft solder and enables the formation of fewer holes in the insertion solder. Amorphous Ni-W alloys are prone to form dense oxide films during ultrasonication. The Au film modification prevents oxide generation and increases the average shear strength of the soldering interface. The Ni-W alloy layer retards the interdiffusion between Cu-Sn, blocks the excessive growth of Cu-Sn IMCs, and reduces the reliability problems caused by interface failure.

Thermal Fatigue Failure of Micro-Solder Joints in Electronic Packaging Devices: A Review.

In electronic packaging products in the service process, the solder joints experience thermal fatigue due to temperature cycles, which have a significant influence on the performance of electronic products and the reliability of solder joints. In this paper, the thermal fatigue failure mechanism of solder joints in microelectronic packages, the microstructure changes of the thermal fatigue process, the influence factors on the joint fatigue life, and the simulation analysis and forecasting of thermal fatigue life are reviewed. The results show that the solder joints are heterogeneously coarsened, and this leads to fatigue cracks occurring under the elevated high-temperature phase of alternating temperature cycles. However, the thickness of the solder and the hold time in the high-temperature phase do not significantly influence the thermal fatigue. The coarsened region and the IMC layer thicken with the number of cycles, and the cracks initiate and propagate along the interface between the intermetallic compound (IMC) layer and coarsened region, eventually leading to solder joint failure. For lead-containing and lead-free solders, the lead-containing solder shows a faster fatigue crack growth rate and propagates by transgranular mode. Temperature and frequency affect the thermal fatigue life of solder joints to different degrees, and the fatigue lifetime of solder joints can be predicted through a variety of methods and simulated crack trajectories, but also through the use of a unified constitutive model and finite element analysis for prediction.

Low temperature soldering technology based on superhydrophobic copper microlayer.

Cu-Cu soldering is realized under certain pressure and low temperature conditions by using a surface silver film to modify the copper microlayer structure, thus solving the problems of high thermal stress and signal delay aggravation caused by high temperature in the traditional reflow soldering process. The copper microlayer modified with silver film is obtained by electrodeposition. The surface substructure of the Cu microlayer is a nano cone-shaped protrusion. The diameter of the bottom of the cone is 500 nm∼1 µm, and the height of the cone is 1∼2 µm. The thickness of the silver film is about 320 nm, and the modification of the copper layer with silver film can effectively prevent the oxidation of the copper layer. Two silver-modified copper microlayers are placed in face-to-face contact as a soldering couple. A certain pressure and low temperature are applied to the contact area to realize the soldering and interconnection. The morphology of the soldered interface and the average shear strength of the soldered joints are analyzed by scanning electron microscopy, transmission electron microscopy and solder joint tester. It is found that under the optimal soldering parameters of soldering temperature 220 °C, soldering pressure 20 MPa and soldering time 20 min, the nano-conical projections of the Cu micrometer layer are inserted into each other to produce a physical blocking effect. The highly surface-meltable silver film effectively connects the surrounding copper layer as an intermediate buffer layer. The average shear strength of soldering joints is significantly increased. Heat treatment experiments have shown that the average shear strength can be effectively increased by heat treatment for an appropriate period of time. Prolonged exposure to heat has little effect on the average shear strength. With the special morphology of the copper microlayer structure and the nano-size effect of the silver layer, soldering can be done at low temperatures. The quality of the soldering interface is good and small soldering dimensions can be obtained.

Preparation and performance of alumina/epoxy-siloxane composites: A comparative study on thermal- and photo-curing process.

Although epoxy-based composites that consist of inorganic fillers and matrixes are widely used in "conventional" electronic packaging applications due to their excellent insulation and robust properties, they limit their uses in "advanced electronic packaging" which requires enhanced thermal conductivity. However, conventional thermal curing methods for fabrication of epoxy-based composites do not fulfill sufficient thermal conductivity. Herein, we apply photo-induced curing strategy for fabricating alumina-incorporated epoxy-siloxane composites that consist of sol-gel derived siloxane matrix and bimodal sized alumina particles as a thermally conductive filler. We investigate how curing mechanism (thermal- or UV-curing) and varying the ratios of the alumina particles of two different sizes affect the various physical properties. It is found that photo-curing process makes greatly enhanced thermal conductivity, low thermal expansion, and high mechanical robustness compared to thermally-cured composites. As the results, we can achieve significantly enhanced thermal conductivity (>11 W/m K) with high thermal stability and mechanical robustness.

MXene-Layered Double Hydroxide Reinforced Epoxy Nanocomposite with Enhanced Electromagnetic Wave Absorption, Thermal Conductivity, and Flame Retardancy in Electronic Packaging.

Due to the increased integration and miniaturization of electronic devices, traditional electronic packaging materials, such as epoxy resin (EP), cannot solve electromagnetic interference (EMI) in electronic devices. Thus, the development of multifunctional electronic packaging materials with superior electromagnetic wave absorption (EMA), high heat dissipation, and flame retardancy is critical for current demand. This study employs an in-situ growth method to load layered double hydroxides (LDH) onto transition metal carbides (MXene), synthesizing a novel composite material (MXene@LDH). MXene@LDH possesses a sandwich structure and exhibits excellent EMA performance, thermal conductivity, and flame retardancy. By adjusting the load of LDH, under the synergistic effect of multiple factors, such as dielectric and polarization losses, this work achieves an EMA material with a remarkable minimum reflection loss (RL) of -52.064 dB and a maximum effective absorption bandwidth (EAB) of 4.5 GHz. Furthermore, MXene@LDH emerges a bridging effect in EP, namely MXene@LDH/EP, leading to a 118.75% increase in thermal conductivity compared to EP. Simultaneously, MXene@LDH/EP contributes to the enhanced flame retardancy compared to EP, resulting in a 46.5% reduction in the total heat release (THR). In summary, this work provides a promising candidate advanced electronic packaging material for high-power density electronic packaging.

Effect of Ball Milling Time on the Microstructure and Properties of High-Silicon-Aluminum Composite.

The duration of ball milling greatly influences the characteristics of high-silicon-aluminum composite during the ball milling process. This study examines how the microstructure, thermal conductivity, and hardness of a high-silicon-aluminum composite are affected by different ball milling times. We exposed the powder to various durations of ball milling and employed different pellet ratios. Following this treatment, the powder underwent consolidation via discharge plasma sintering. Our findings show that with a pellet ratio of 10:1 and a milling duration of 8 h, the powder particles were refined, resulting in a more uniform and dense material composition. This refined material boasted a thermal conductivity of 111.6 W/m·K, a Brinell hardness of 136.8 HBW, and a density of 2.304 g/cm3. This method facilitates the creation of a uniform composite powder composition. It encourages the development of a fine-grain structure, which enables the production of particle-reinforced composites with superior properties.

Advancements in SiC-Reinforced Metal Matrix Composites for High-Performance Electronic Packaging: A Review of Thermo-Mechanical Properties and Future Trends.

With the advancement of semiconductor technology, chip cooling has become a major obstacle to enhancing the capabilities of power electronic systems. Traditional electronic packaging materials are no longer able to meet the heat dissipation requirements of high-performance chips. High thermal conductivity (TC), low coefficient of thermal expansion (CTE), good mechanical properties, and a rich foundation in microfabrication techniques are the fundamental requirements for the next generation of electronic packaging materials. Currently, metal matrix composites (MMCs) composed of high TC matrix metals and reinforcing phase materials have become the mainstream direction for the development and application of high-performance packaging materials. Silicon carbide (SiC) is the optimal choice for the reinforcing phase due to its high TC, low CTE, and high hardness. This paper reviews the research status of SiC-reinforced aluminum (Al) and copper (Cu) electronic packaging materials, along with the factors influencing their thermo-mechanical properties and improvement measures. Finally, the current research status and limitations of conventional manufacturing methods for SiC-reinforced MMCs are summarized, and an outlook on the future development trends of electronic packaging materials is provided.