Electronic Packaging Research Articles

Flexible zinc-ion hybrid micro-supercapacitors with polymeric current collector for integrated energy storage in wearable devices

The ubiquity of conventional micro-fabrication techniques has encountered impediments in constructing cost-effective micro-devices, thereby constraining their broad deployment. Concurrently, the suboptimal energy density inherent to supercapacitors exacerbates this challenge. This study presents a straightforward assembly methodology for the fabrication of a mechano-electrochemically efficient micro-zinc ion hybrid supercapacitor (M−ZSC), alongside the introduction of an innovative polymeric current collector. The M−ZSC is fabricated through a process involving masked spray deposition of a novel adhesive current collector and the electrode materials, and electroplating of zinc nanosheets onto the anode finger, creating an electrochemically performant and mechanically robust device. The resulting M−ZSC exhibits a notable areal capacitance of 52.2 mF/cm2 and an energy density of 18.5 µWh/cm2 for the normal mass-loading of 3.6 mg/cm2, which is amongst the highest reported values for energy storage. The masked spray deposition/hot pressing technique enabled us to fabricate free-standing thick electrodes with a loading density of up to 56.1 mg/cm2, facilitating the achievement of an ultrahigh areal capacitance of 227 mF/cm2 and an energy density of 80.5 µWh/cm2. Furthermore, the M−ZSC exhibits a robust retention of 95 % capacitance at 1 mA/cm2. Critical to its flexibility, the device is constructed using purely additive deposition methods on flexible substrates and is therefore well-tailored for deployment in flexible electronics and on-chip applications. These micro-devices are well-poised for seamless integration within a singular electronics package or chip architecture.

Facile synthesis of Cu-Sn nanoparticle film and its bonding mechanism for power electronic packaging

The Cu-Sn full intermetallic compound is a promising high-temperature electronic packaging material, while its preparation is usually time-consuming. In this work, a novel dual-beam laser co-deposition method was proposed to prepare Cu-Sn nanoparticle film for power electronic packaging with high bonding efficiency. Various Cu-Sn contents were prepared to reveal the bonding mechanism of the full intermetallic compound structure. The results show that joints with a Cu content ranging from 20 wt% to 80 wt% could form full intermetallic compounds within 2 min with the shear strength reaching 120 MPa. Specifically, Cu6Sn5, 'island-like' Cu3Sn, and sintered Cu generated successively in the bondline center with the increasing Cu content. All failures occurred within the bondline indicating a higher interface bonding quality, while the 'island-like' Cu3Sn enhanced the shear strength. This die attach process is compatible with current commercial SiC die attach process with lower material cost as well as high efficiency, enabling the Cu-Sn nanoparticle film to be a promising material for high-reliability power electronic packaging.

Effect of Sb Content on the Microstructure and Mechanical Properties of Eutectic SnPb Solder.

SnPb solder was widely used in electronic packaging for aerospace devices due to its high reliability. However, its creep resistance is poor and can be improved by adding alloying elements. The effects of Sb content on the microstructure, tensile, and creep properties of eutectic SnPb solder were investigated. Sb addition effectively improved the mechanical properties of the SnPb solder. When Sb content exceeds 1.7 wt.%, SbSn intermetallic compounds (IMCs) occurred. And increasing the Sb content increased the tensile strength. Furthermore, Sb addition decreased the steady-state creep rate and increased the stress exponent n, suggesting that the creep resistance had been enhanced, which may be attributed to the hindrance of dislocation movement by SbSn IMCs, as well as the reduction in phase boundaries, which consequently reduced grain boundary sliding.

Thermoplastic polyimide with good comprehensive performance based on carbazole groups and short flexible linkages

AbstractThermoplastic polyimides (TPIs) can meet the requirements of advanced electronic packaging such as flexible copper clad laminate (FCCL) applied under extreme conditions, attributed to their excellent thermal stability, mechanical properties, electrical insulation and chemical resistance. With the increasing demands for electronic devices, such as applications in high‐frequency communication, it is highly desirable to develop high‐performance TPI with good thermoplasticity, thermal stability, mechanical properties and dielectric properties. However, there is a trade‐off between thermoplasticity and other properties. Herein, we introduce an effective strategy to afford TPIs with good performance by copolymerization of a diamine monomer consisted of a coplanar aromatic carbazole group and a short flexible linkage methylene group. On the one hand, short flexible linkages help improve the flexibility of polymer chains and are not too much to enable small‐scale molecular motions below Tg. On the other hand, coplanar aromatic donor groups benefit to strong charge transfer complex (CTC) interaction and π‐π stacking interaction. Based on this strategy, the resultant TPI possesses good thermoplasticity with a proper Tg of 348 °C. Meanwhile, it preserves a low coefficient thermal expansion of 48 ppm K−1, low dielectric constant/dielectric loss factor of 3.27/0.0073 at 10 GHz, and tensile strength of ca. 78 MPa.

Interface microstructures in the wetting of Cu by equiatomic GaInSnBiZn high-entropy alloy

This study investigates the wetting characteristics, interface microstructure evolution of equiatomic GaInSnBiZn HEA on Cu under high vacuum with sessile drop method to extend its electronic packaging applications. Optimal conditions involve a 350 °C temperature maintained for ∼20 min to prevent Bi loss, resulting in a contact angle inversely proportional to temperature and reaching a minimum of ∼15.6°. A dual-layer of Cu9Ga4 and CuGa2 forms at the HEA/Cu interface, consistent with thermodynamic predictions, featuring lower activation energy and growth driven by bulk alloy diffusion. Base on the interface microstructures, Cu9Ga4 and CuGa2 act as diffusion barriers, restricting the movement of other elements while promoting the accumulation of Zn at the interface. The wetting mechanism may be determined by the oxide (Cu2O) removal reaction (i.e., reaction between Ga and Cu2O).

Vertically aligned and conformal BN-coated carbon fiber to achieve enhanced thermal conductivity and electrical insulation of a thermal interface material

Due to excellent thermal conductivity, high aspect ratio, and low density, mesophase pitch-based carbon fibers (MPCFs) are highly desired in electronic packaging. However, their thermal conductivity is hard to present in the polymer matrix because of the disordered stacking and low filling. Moreover, few researches are focused on the enhancement of the electrical insulation performance for MPCFs. Herein, we report vertically aligned and insulating boron nitride (BN) coated carbon fiber (CF) powders as significant fillers for polymer composites, endowing markedly improved thermal conductivity and electrical insulation. The high-quality BN coating layer on the surface of the CF is produced by a cooling precipitation method and high-temperature treatment with ingenious use of solubility properties, exhibiting a conformal, dense, and highly crystalline structure. This preparation method overcomes the limitations of coating thickness and particle agglomeration, resulting in a 31-fold enhancement of the electrical resistivity of the CF powders. After orientation treatment in a silicone rubber matrix, such CF@BN-filled pads exhibit good thermal conductivity, significantly improved insulation performance, and excellent mechanical properties. Among them, the optimized pad achieves a thermal conductivity of 12.06 W m−1 K−1, a volume resistivity of 50 × 108 Ω cm and a breakdown voltage of 3100 V mm−1, exceptional flexibility, and a favorable compression ratio (@45 psi) of 41.7 %. This work provides unique insights into constructing carbon fiber fillers as well as the preparation of high thermal conductivity composites, thereby expanding the application scenarios of carbon fiber powder in electronic packaging.

Effect of polymer infiltration and pyrolysis (PIP) on microstructure and properties of high volume fraction SiC/Al composites prepared by a novel hybrid additive manufacturing

High-volume-fraction SiC/Al (HVF-SiC/Al) composites have a wide range of applications in aerospace, optics, automotive and electronic packaging. However, because the hardness, brittleness and wear resistance increase with the increase in the volume fraction, it is difficult for traditional methods such as machining, to process HVF-SiC/Al composites to complex components. Therefore, in this paper, a novel method of the hybrid additive manufacturing is proposed to fabricate complex-structures SiC/Al composite parts. The effect of polymer infiltration and pyrolysis (PIP) on microstructure and properties of HVF-SiC/Al composites is investigated. The results show that the mechanical properties of the SiC preforms can be effctively enhanced by the PIP process, and this enhancement makes the SiC preforms meet the conditions for subsequent vacuum-pressure infiltration. The mechanical property of HVF-SiC/Al composites show a huge increase when in creasing the volume fraction of SiC. In particular, the flexural strength of HVF-SiC/Al composites increased from 202.28 MPa to 380.87 MPa, and the coefficient of thermal expansion (CTE) has also been reduced from 11.80 to 6.28 × 10−6/K, when the volume fraction of SiC increases from 42 to 80 vol%. For optimise the PIP process in the future, three theoretical models are used to predict the relationship between the CTE and the volume fraction of SiC. The results show that the experimental data are more consistent with the predicted values based on the Kerner's model, but deviate from the Rule-of-mixture (ROM) and Turner's models. Importantly, the complex-structures SiC/Al composite parts was successfully fabricated by this hybrid additive manufacturing.

Prediction of mechanical properties and fatigue life of nanosilver slurry in chip interconnection

This article investigates the failure mode and mechanism of copper pillar solder joints in temperature cycling experiments, focusing on a Cu/nano Ag/Cu solder joint structure. The hot pressing bonding condition at 300 °C with insulation for 10 s is chosen for the experiments. Based on the life test results, the thermal cycling fatigue life of the nanosilver solder joint is determined to be 2050 cycles. To gain further insights, finite element software ANSYS is employed to simulate nanosilver solder joints in flip chips, revealing the stress–strain distribution within the solder joints. The simulation utilizes the Anand viscoplastic constitutive model for the solder joint, providing a reasonable representation of the stress–strain behavior under thermal cycling load. Notably, the simulation highlights that the maximum stress and strain occur in the contact area between the solder joint and the copper column. To enhance accuracy, the calculation equation is refined using relevant experience, resulting in a prediction of the thermal fatigue life of nanosilver solder joints. This prediction aligns closely with the experimental results. The research outcomes not only contribute valuable insights into the behavior of nanosilver solder but also serve as a reference for its application in electronic packaging.

Construction of 3D BN network with high-density thermal conductive paths

Efficient heat dissipation is essential to further improve the integration of high-power electronic packaging devices. Three-dimensional BN networks with high-density thermal conductive paths were designed as the heat transfer skeleton of thermal interface materials. 3D networks with high-density thermal conductive paths inlaid between oriented BN paths were constructed using precursor self-assembly and freeze-drying to improve the thermal conductivity of polymeric materials. The results show that high-density thermally conductive paths have stronger polymer-enhanced thermal conductivity than directional thermal paths and compared with pure TPU, the thermal conductivity of TPU/BN-2 under low BN filling content (10%wt) is increased by 250 % and 286.5 % in the through surface and flat surface respectively. This work provides new ideas for the preparation of polymer composites for thermal interface materials in electronic packaging and integrated circuits with excellent thermal management properties.

Microstructure evolution and micromechanical behavior of solvent-modified Cu–Ag composite sintered joints for power electronics packaging at high temperatures

With the increased deployment of power modules in demanding conditions, sintering materials, especially composite sintering materials, have raised growing interest due to their cost-effectiveness and suitability. Therefore, this study explores the viability of Cu–Ag composite sintering material, focusing on solvent influence through microstructure and mechanical behavior analysis. Micron-sized particle-based Cu–Ag composite pastes were designed and compared using eight solvents (four epoxy-free and four epoxy-added) based on fluidity and thermal stability. The sintered joints' performance, assessed through shear strength analysis, showed comparable values to pure silver sintering for both epoxy-free and epoxy-added samples. Optimized samples from each solvent system underwent reliability analysis, demonstrating that Cu–Ag joints with epoxy resin exhibited significantly higher shear strength after high-temperature storage and thermal cycling tests. Micromorphology and elemental composition analysis revealed differences in aging mechanisms, primarily attributed to variations in porosity due to oxide formation and pore filling by epoxy resin under different solvent systems. Further nanoindentation characterization of micromechanical properties, including hardness, modulus, and creep properties, during high-temperature aging, established constitutive models for insights into reliability evolution. In conclusion, the optimized epoxy-added Cu–Ag sintered joints proposed in this study demonstrated exceptional reliability and acceptable micromechanical properties, presenting a promising option for high-temperature power packaging.

An innovative high-entropy alloy solder for high-reliability low-temperature bonding in 3D electronic packaging–based on nano InSnBiZnAg particles

To address the demand for multilevel package, a low-melting-point high entropy alloy (HEA) solder was developed. It consists of 43In28Sn14Bi9Zn6Ag micro- and nano-particles with a melting point of about 62.80 °C. We obtained 43In28Sn14Bi9Zn6Ag nanoparticles by combining ultrasonic heating interaction with a "hot shock" process. Upon reflowing at 115 °C for 5 min, a Cu/Zn/Ag ternary intermetallic compound (IMC) formed at the interface between the solder and the copper substrate, leading to a shear strength of 40 MPa. The microstructure of this joint exhibits a complex composition with at least three phases, including Bi3In5 phase, Ag5Zn8 phase, and In0.2Sn0.8 solid solution. The stable Ag5Zn8 phase not only enhances the overall strength of the alloy matrix but also impedes the diffusion of In and Bi atoms, thereby preventing the segregation of the Bi3In5 phase. The high mixing entropy and pronounced lattice distortion in this high entropy alloy hinder the diffusion of elements within the solder matrix, mitigating the issue of excessive interfacial IMC growth. Consequently, the solder joints exhibit little degradation even after a high-temperature aging test. This high-entropy alloy solder has promising potential for multi-level chip stacking in 3D packaging.

Foreword: Special Section on Multiphysics Aspects of Power Electronics Packaging—Power Die, Power Module, and Converter Level—Part 1

Foreword: Special Section on Multiphysics Aspects of Power Electronics Packaging—Power Die, Power Module, and Converter Level—Part 1

Thermal-structural Modeling of power electronic package: effects of deposition geometry and dry spot on the stress distributions

A Power Electronics package is a heterogeneous system made of semiconductor devices (dies), metallic-ceramic substrate, baseplate and encapsulating material.The electronic devices can be MOSFETs (Metal Oxide Semiconductors Field Effect Transistors), diodes, IGBTs (Insulated Gate Bipolar Transistors) and passive components such as capacitors, resistors and sensors integrated on support circuit; the complete set of semiconductor devices installed on a package form the so-called “power modulus”.These devices play an important role in the transmission and conversion of energy in electric and hybrid vehicles. Due to the elevated currents and, consequently, the elevated temperatures at which these systems work, and due to the mismatch of the thermal-mechanical properties of the materials from which they are made, stresses and strains develop within the devices.Such stresses can be locally concentrated and amplified, depending on the deposition geometry of the various layers constituting the semiconductor device. Edge termination structures are essential to decrease the electric field at die’s edges, and, including brittle compounds in their composition, like Si3N4 or SiO, they are quite sensitive to mechanical stress.Another reason that may cause the stresses concentrations is the presence of dry spots. Dry spots are areas of various size, located at the interface between die or leadframe and the encapsulating resin, where there is a total or partial lack of adhesion.The aims of this work are, mainly, two. At first, four linear finite element analyses have been performed in order to evaluate the stresses concentrations at the corners of edge termination structure.The first case concerns sharp corners and the other cases concern differently filleted corners. In the second part of this work, it has been analysed the dry spot effect on stress distributions. Due to the small size of the defect with respect to the whole package, a Global-Local FEM approach has been used, creating a local subdomain where the mesh is denser than the global domain and a running a further separate numerical analysis which takes its boundary conditions from the global analysis, so delivering reliable small-scale stress and strain gradients. This approach permits to achieve accurate analyses focused on zones of interest of the global domain, limiting the increase of the computational cost of the modelling.

A combined experimental and numerical approach for heat transfer enhancement in a minichannel using half rectified pulsating flows

The miniaturization of electronic packages and their associated high-power density circuits requires more innovative cooling solutions. Single phase pulsating flows offer a promising solution due to their disruption of the thermal boundary layer. This study aims to bridge the knowledge gap by using experimental and computational methods to investigate the complex flow characteristics of laminar pulsating flows in a heated rectangular minichannel and couple that analysis with an investigation of thermal-hydraulic performance. Experimental analysis involves a uniformly heated thin foil approximating a constant heat flux bottom wall. Wall temperature measurements are recorded using an infrared thermography system. Analogous to the experimental conditions, a three-dimensional conjugate heat transfer computational model is developed with a volumetric heat generation source. Positive and negative half rectified sinusoidal pulsating flow waveforms are studied for dimensionless pulsation frequencies or Womersley numbers of Wo = 2.5 and 5.1 at a fixed flow rate amplitude A 0 = 3. For the positive half rectified waveform, a marginal enhancement in heat transfer of 2.2% for Wo = 2.5, A 0 = 3 was obtained. Whereas the negative half rectified case leads to a heat transfer enhancement of 9% and 6% for Wo = 2.5 and Wo = 5.1 respectively, with a high thermal performance of η = 2.4 over corresponding steady flow.

Construction of three-dimensional network using boron nitride microspheres and the thermal conductivity/stability of epoxy resin composites

Efficient heat dissipation has become the focus of electronic packaging materials, constructing three-dimensional thermally conductive filler networks to prepare composites can realize efficient heat transfer. However, there are few studies comparing the effects of different ways of constructing three-dimensional networks on the thermal conductivity enhancement of polymers. In this study, BNMS self-assembled from BNNSs was used as a thermally conductive filler, and the three-dimensional skeleton was constructed by both the powder mixing pressing method and the ice template method, and scanned to analyze the morphological and structural characteristics. At the same time, the epoxy composites were prepared, and the advantages and disadvantages of the thermal conductivity of the composites prepared in different ways were analyzed by combining the SEM structures. In the powder mixing pressing method, the in-plane and through-plane thermal conductivity of the epoxy composites with the BNMS additive amount of 53.92 wt% reached 10.961 W·m−1·K−1 and 9.955 W·m−1·K−1, respectively, which was increased by 58 and 52 times. The thermal stability has been improved significantly that the T60 was in creased by 60.89°C compared to pure epoxy. Using the ice template method with 7.67 wt% of BNMS addition, the through-plane thermal conductivity of the epoxy composites reaches 0.977 W·m−1·K−1, which is an improvement of 428.1 % compared with pure EP. In addition, both composites maintain low dielectric constants and dielectric losses. It is instructive for the preparation method of subsequent construction of three-dimensional thermally conductive filler networks.

Dielectric, electrical and thermal properties of Sodium Molybdate-hexagonal Boron Nitride composites enabled by cold sintering

Advances in 5G and 6G communication technologies and their applications are in part limited by the capabilities of current electronic packaging materials, as expanded bandwidth is a pressing need for novel dielectric substrates capable of co-firing into packages and devices, characterized by low dielectric loss and enhanced thermal conductivity. This investigation provides further characterization in the dielectric, electrical and thermal conductivity properties over previously reported cold sintered composite of Sodium Molybdate Na2Mo2O7 (NMO) with hexagonal Boron Nitride (hBN), such as relative permittivity (εr) and dielectric loss (tan δ) values at high frequencies of 75–110 GHz, electrical resistivity (ρ) fitting to percolation theory, Weibull statistical analysis of electrical breakdown strength (Eb) and its anisotropic thermal conductivity (κ) influenced by the filler's crystal structure. The cold sintered composites were systematically characterized with respect to filler volume fraction, temperature, and frequency. The findings in this analysis position engineered composites as a promising alternative for microwave substrate materials, with using a densification method that limits interactions and maximizes densification, hence the demonstration with cold sintering.

Reactive diffusion at the interface between Cu and Sn–Ag alloys

This study investigates the microstructural evolution and growth behavior of intermetallic compound (IMC) layers in the Cu/(Sn-yAg, y = 0.29–2.00 wt%) system during isothermal aging within the temperature range of 433–473 K. Through systematic variations in Ag content, aging temperature, and time, the fundamental mechanisms governing IMC formation and growth in Cu/(Sn–Ag) solder joints are elucidated. The results demonstrate that IMC growth kinetics follow a power-law relationship, with IMC layer thickness increasing systematically with annealing time. The addition of Ag significantly influences IMC nucleation and growth, with higher Ag content correlating with faster growth rates. Furthermore, the temperature dependence of IMC growth rates is investigated, revealing higher temperatures leading to increased growth rates, indicative of boundary diffusion-controlled growth. By calculating activation enthalpies, values of 36.4 kJ/mol for Sn-2.00Ag and 30.2 kJ/mol for Sn-0.50Ag were obtained, providing quantitative insights into the faster growth rate of intermetallic compound thickness in the Cu/(Sn-2.00Ag) diffusion couple within the experimental temperature range. These findings offer valuable insights into factors affecting the reliability and performance of solder joints in electronic packaging applications.

Highly efficient fiber to Si waveguide free-form coupler for foundry-scale silicon photonics

As silicon photonics transitions from research to commercial deployment, packaging solutions that efficiently couple light into highly compact and functional sub-micrometer silicon waveguides are imperative but remain challenging. The 220 nm silicon-on-insulator (SOI) platform, poised to enable large-scale integration, is the most widely adopted by foundries, resulting in established fabrication processes and extensive photonic component libraries. The development of a highly efficient, scalable, and broadband coupling scheme for this platform is therefore of paramount importance. Leveraging two-photon polymerization (TPP) and a deterministic free-form micro-optics design methodology based on the Fermat’s principle, this work demonstrates an ultra-efficient and broadband 3-D coupler interface between standard SMF-28 single-mode fibers and silicon waveguides on the 220 nm SOI platform. The coupler achieves a low coupling loss of 0.8 dB for the fundamental TE mode, along with 1 dB bandwidth exceeding 180 nm. The broadband operation enables diverse bandwidth-driven applications ranging from communications to spectroscopy. Furthermore, the 3-D free-form coupler also enables large tolerance to fiber misalignments and manufacturing variability, thereby relaxing packaging requirements toward cost reduction capitalizing on standard electronic packaging process flows.

Effect of Silicone Rubber on the Properties of Epoxy/Recovered Carbon Black (rCB) Conductive Materials

The primary focus of this study is to investigate the effect of silicone rubber (SR) content on the mechanical, thermal, electrical conductivity, and morphological properties of epoxy/recovered carbon black (rCB) conductive material. The conductive material is used to produce the electrostatic discharge (ESD) tray for the electronic packaging industry. This study investigated the effect of silicone rubber content (0, 5, 10, 15, and 20 vol.%) on the properties of epoxy/SR/rCB conductive materials, with the rCB content fixed at 15 vol.% for its optimum electrical conductivity. The silicone rubber acts as a toughening agent for epoxy. Through the fracture toughness result, it can be identified that silicone rubber plays a role in improving the toughness properties of the epoxy/SR/rCB conductive material. The optimum results for mechanical properties were recorded at 5 vol.% SR. The addition of SR to the epoxy matrix enhances the electrical properties of the epoxy/SR/rCB conductive material. The effect of thermal aging on epoxy/SR/rCB conductive materials was also studied to determine the properties of the conductive material materials at high temperatures for a long period of time. After thermal aging, the mechanical, thermal, electrical conductivity, and morphological properties of the epoxy/SR/rCB conductive material were slightly reduced.

Engineering lightweight Poly(lactic acid) graphene nanoribbon nanocomposites for sustainable and stretchable electronics: Achieving exceptional electrical conductivity and electromagnetic interference shielding with enhanced thermal conductivity

The challenge of creating flexible and sustainable electronics with properties such as lightweight, electrical and thermal conductivity, and electromagnetic interference (EMI) shielding is addressed in this study. Carbon nanotubes and graphene are commonly used in flexible electronic devices, but gaps exist in their conductivity and flexibility. A novel and scalable fabrication method is introduced, involving the creation of bio-based nanocomposites by integrating flexible and high aspect-ratio graphene nanoribbons (GNRs) into a poly (lactic acid) (PLA) matrix. The nanocomposites were drawn above the glass transition temperature (Tg) of PLA, resulting in the formation of extended shish structures, as observed in scanning electron microscope (SEM) images. These structures significantly enhanced thermal and electrical conductivities, as well as EMI shielding features. The combination of flexible GNR nanofillers with uniaxial stretching led to a substantial increase in Young's modulus, tensile strength, and toughness by approximately 550 %, 440 %, and 600 %, respectively, most likely due to the increased network connection despite the higher flexibility of GNRs. Moreover, in-plane thermal conductivity registered a notable enhancement of approximately 110 %. The EMI shielding reached 26 dB, with an absorption contribution to EMI shielding of around 45 %. Additional improvement was achieved through foaming of the stretched samples, resulting in multilayer structures with alternative extended shish and foam structures. Furthermore, a significant augmentation of approximately 33 dB in total EMI shielding of the foamed samples, accompanied by an 85 % increase in SEA was documented. These promising findings underscore potential applications across diverse domains, including thermal interface materials, electronic packaging, capacitors, and energy storage devices, with a specific emphasis on the realm of sustainable and stretchable electronics.