Electronic Packaging Research Articles

Low-temperature lead-free SnBiIn solder for electronic packaging

Low-temperature lead-free SnBiIn solder for electronic packaging

Synergistic enhancement of toughness and flame retardation for cyanate ester composites through hyperbranched polyborosiloxane

AbstractExcellent flame resistance is supposed to be taken into consideration for electronic packaging materials due to the spontaneous combustion of short circuits, except for good mechanical and dielectric properties. Herein, a hyperbranched polyborosiloxane (HPSiB) flame retardant was synthesized via a simple one‐pot transesterification as a multifunctional additive for cyanate ester (CE) resin. The HPSiB with many active terminals features good compatibility with the resin matrix, while catalyzing the curing reaction that conducts at a lower temperature. With as little as 2 wt% HPSiB incorporated, the HPSiB/bisphenol A cyanate ester (BADCy) resin achieves a UL‐94 V0 rating and 32.4% LOI value, and its peak heat release and total smoke production are simultaneously reduced. Its flexural strength and impact strength were significantly enhanced by 30.0% and 85.4%. Besides, the minimum values of dielectric constant and loss can reach 2.77 and 0.0024 at 10 GHz, which are, respectively, reduced by 7.9% and 88.5%. The integration of unique hyperbranched SiOB backbone of HPSiB with CE crosslinked network was responsible for the enhanced overall performance. This work paves a facile strategy to develop multifunctional flame retardant as a promising candidate for the high‐performance electronic packaging materials.Highlights A novel hyperbranched polyborosiloxane flame retardant was synthesized. HPSiB shows good compatibility and catalyzes the curing reaction of CE resin. HPSiB/CE resin with significantly enhanced flame retardancy was obtained. Simultaneously high toughness and low dielectric loss were achieved. Hyperbranched structure containing SiOB chains led to the great enhancement.

Rational design of high‐performance epoxy/expandable microsphere foam with outstanding mechanical, thermal, and dielectric properties

AbstractPrevious studies on epoxy foams were subjected to the specific property, and improvements in thermal insulation or dielectric property were usually accompanied by the sacrifice of mechanical strength or thermal stability. The current research reported a high‐performance epoxy foam by the pre‐curing process using E‐51/DDS and expandable microsphere (EMP) as polymer matrix and physical blowing agent, respectively. The effect of EMP loading on the structure & property of epoxy foam was reported. The mean diameter of E‐51/EMP foam was in the range of 19–21 μm. The compression property of E‐51/EMP foam was fit for the power‐law model and its integrity was well maintained during compressive test. Compared with bulky epoxy, a significant decrease of thermal conductivity of 62.93% was observed in 10 wt% EMP‐filled epoxy foam. E‐51/EMP foam showed superior thermal stabilities, with a T5% of over 300°C. The dielectric constant was decreased by 54.5% from 4.92 in bulky epoxy to 2.24 in E‐51/EMP foam (10 wt% EMP). Notably, there was a percolation phenomenon of EMP (6 wt%) regarding on the structure & property of E‐51/EMP foam. This study provides lightweight, robust, high‐temperature‐resistant, and low‐dielectric‐constant epoxy foams with the wide application prospects in buoyant, electronic packaging, and energy‐saving industries.

Review on Shear Strength and Reliability of Nanoparticle Sintered Joints for Power Electronics Packaging

Review on Shear Strength and Reliability of Nanoparticle Sintered Joints for Power Electronics Packaging

Research on Silicon Carbide Dispersion-Reinforced Hypereutectic Aluminum-Silicon Electronic Packaging Materials

The objective of this study is to improve the mechanical properties and machining performance of high thermalconductivity and low expansion silicon carbide dispersion-strengthened hypereutectic aluminum-silicon electronic packaging materials to meet the needs of aviation, aerospace, and electronic packaging fields. We used the powder metallurgy method and high-temperature hot pressing technology to prepare SiC/Al-Si composite materials with different SiC contents (5vol%, 10vol%, 15vol%, and 20vol%). The results showed that as the SiC content increased, the tensile strength of the composite material first increased and then decreased. The tensile strength was the highest when the SiC content was 15%; the sintering temperature significantly affected the composite material’s structural density and mechanical properties. Findings indicated 700 ℃ was the optimal sintering and the optimal SiC content of SiC/Al-Si composite materials was between 10% and 15%. Besides, the sintering temperature should be strictly controlled to improve the material’s structural density and mechanical properties.

Surface modification of spherical silica micro‐powder using silane coupling agents and their application in epoxy resin‐based composite materials

AbstractIn recent years, the packaging industry has utilized electronic packaging materials with epoxy resin (EP) and high‐performance fillers, exhibiting superior mechanical properties and thermal conductivity. Spherical silica micro‐powder (SSP) is a critical thermal conductive filler but faces challenges due to its inorganic nature. Surface modification is essential to improve SSP's compatibility and dispersion in organic matrices for effective use in EP‐based composites. In this paper, the effects of the following four modification methods on SSP/EP composites were studied: (1) the processes include co‐modification with dimethyldimethoxysilane (DMDMS) and trimethylethoxysilane (MTES), (2) modification with NaOH, (3) co‐modification with DMDMS and MTES in an alkaline environment after NaOH modification, and (4) co‐modification with methyltrimethoxysilane (MTMS) and propyltrimethoxysilane (PTMOS). Through comprehensive characterization and evaluation, it is evident that modification schemes 1, 3, and 4 significantly enhance SSP's hydrophobicity, dispersibility, and compatibility with EP. This led to the improvement of thermal conductivity and stability of the composite, and modification scheme 4 showed the highest enhancement, with a 42.6% increase in thermal conductivity. Moreover, the mechanical properties of modified composite materials, such as bending strength, impact resistance, and tensile strength, surpass those of unmodified SSP/EP composite materials. The study provides valuable insights for reducing manufacturing costs and enhancing productivity in the electronic packaging sector.

A novel approach of fatigue testing and evaluation of electronic systems based on phase tracking

This paper presents an experimental approach to perform fatigue testing of a lightly damped electronic assembly subjected to harmonic excitation. By leveraging the power of the phase locked loop control algorithm, our proposed work aims to accurately track the phase of the system. This innovative approach enables precise measurement of the drop in resonant frequency due to fatigue, enhancing overall damage prediction. The proposed approach exploits the characteristics of the materials that the phase at the resonance is constant and for a lightly damped system, the value is close to pi/2. In the event that the test article experiences fatigue, and the resonant frequency undergoes a change, the controller will promptly adapt to the new frequency while upholding a constant phase, ensuring the uninterrupted continuity of the testing process. The proposed approach is demonstrated by using the Ball Grid Array (BGA) electronic package as an example, where the test setup, data acquisition, and data monitoring for identifying the interconnect failure are presented. Failure analysis of the test article shows that the primary failure mode is the solder joint failure at the Intermetallic (IMC) layer. A finite element model is developed and correlated with experimental modal analysis to accurately estimate maximum stress and deflection in solder joints. By utilizing the obtained results, one can create a more accurate SN curve for the tested material. This will allow for a better understanding of the material's fatigue behavior and enable more precise predictions of its durability in real-world applications.

Liquid metal-modified boron nitride for polytetrafluoroethylene composites with enhanced thermal conductivity and peel strength

Polytetrafluoroethylene (PTFE)/boron nitride (BN) composites has ultra-low dielectric loss and thermal conductivity, making it a suitable choice for high-frequency communication copper-clad laminate. However, the low peel strengthens of these composites restricted the further application, due to the low polarity and smooth surface of BN. Here, we assemble liquid metal (LM) on BN filler (LM-BN) via a mechanochemistry method. The surface polarity and roughness of BN can be enhanced by the oxidized layer from LM. The thermal interfacial overlap between BN sheets can be enhanced by LM droplets. Consequently, at filler content of 50 vol%, the thermal conductivity increases from 0.3 W/m⋅K of PTFE to 1.90 W/m⋅K for PTFE/BN composites, to 2.05 W/m⋅K for PTFE/LM-BN composites, and the peel strength exhibit a nearly 100% increment from 0.19 of PTFE/BN to 0.39 N/mm of PTFE/LM-BN. Along with low dielectric loss, excellent thermal conductivity, peel strength, and reduced thermal expansion, this method ensures a wider application of PTFE/LM-BN composites in electronic packaging.

Preparation of Ag-Cu nanoparticle film using a dual-beam pulsed laser deposition for power electronic packaging

Ag-Cu nanoparticles, integrating the advantages of Ag and Cu, are promising materials for power electronic packaging. In this work, a novel dual-beam pulsed laser deposition method was proposed to prepare an Ag-Cu nanoparticle film with various component ratios and used for die attach at low temperatures. The as-deposited Ag-Cu nanoparticle film was mainly composed of Ag-Cu solid solution, Ag element, and Cu element, and most of the nanoparticles were in the alloying state. The Ag-Cu sintered joint presented a dense microstructure with 10.8% porosity, and the shear strength of Ag-Cu sintered joints could reach 60 MPa at 250 °C. The sintered joint porosity increased as more Cu were added in the Ag-Cu nanoparticle film, resulting in a decrease in the interfacial connection ratio. The fracture mode of sintered joints gradually changed from the sintered layer to the mixed sintered layer and interface fracture. The dual-beam pulsed laser deposition method could guide in designing the component ratios of bimetallic nanoparticles.

Fused deposition modelling of dense complex-shaped SiCp/Al composites with excellent properties

SiCp/Al composites are widely used in space vehicles, electronic packaging, automobiles, rail vehicles and other fields due to their excellent mechanical and thermal properties. Complex-shaped SiCp/Al parts are usually manufactured by mechanical processing, which is expensive and time-consuming due to the high hardness of SiC phase. As a highly effective 3D molding method, Fused Deposition Modelling (FDM) of the complex-structure SiCp/Al composites was reported for the first time in this paper. SiCp/Al composites was densified by pressureless infiltration after FDM, and as-acquired bulk possessed high densification of 92.67 % and the SiC volume fraction of 43.2 %. Moreover, excellent performances were also presented, including flexural strength of 211 MPa, thermal conductivity of 112(W/m·K), and the thermal expansion coefficient of 8.67 × 10-6K−1.

Sintering Mechanism of Bimodal-Sized Cu Nanoparticle Paste for Power Electronics Packaging

Sintering Mechanism of Bimodal-Sized Cu Nanoparticle Paste for Power Electronics Packaging

Recent Advances in Nanoclay‐ and Graphene‐Based Thermoplastic Nanocomposites for Packaging Applications

ABSTRACTOver the past few years, thermoplastic nanocomposites reinforced with different types of nanofillers have seen widespread use in the automotive, pharmaceutical, food packaging and electronic sectors. Among the different nanofillers used to fabricate thermoplastic composite–based packaging materials, nanoclay and graphene are very beneficial for producing high‐barrier packaging materials. The high aspect ratio and large surface area of both nanoclay and graphene facilitate uniform filler dispersion and tortuous path in the thermoplastic matrix, which ultimately improves the physico‐mechanical, thermal and barrier to oxygen, water vapour and light as well as antimicrobial properties, which are key requirements for packaging materials. Because graphene nanomaterials are electrically and thermally conductive, these thermoplastic nanocomposites may display excellent electrical‐, thermal‐ and microwave‐shielding capabilities, allowing them to be used in electronic packaging. This review aims to summarize the preparation and characterization of thermoplastic nanocomposites based on different types of nanoclay, graphene and graphene derivatives, as well as their prospective applications in food and electronic packaging. This review paper also discusses the factors that can affect the performance and attributes of these packaging materials, such as processing conditions, types of nanofillers, functionalization or modification of nanofillers for better filler dispersion and so forth. This paper presents a comprehensive and state‐of‐the‐art article on nanoclay‐ and graphene‐loaded thermoplastic nanocomposite–based packaging materials.

Interface stress analysis and bonding strengthening exploration of metal layer on the laser-activated copper-clad AlN

Aluminum nitride ceramics has excellent thermal conductivity and insulation property, making it a kind of excellent electronic packaging material. But enhancing the bonding strength between the metal layer and aluminum nitride (AlN) ceramic is a challenging problem. Especially regarding the lack of accurate data analysis on the stress between interfaces, enhancing adhesive strength still relies on blind attempts. By using the finite element method, this study reveals that the shear stress generated between the metal/ceramic interface is concentrated at the interface edge. Based on this finding, a method of inserting micro-pore arrays at the edge is proposed to enhance the interfacial bonding strength. The simulation results show that by inserting micro-pores with an appropriate density, the interface shear stress between metal and ceramic can be reduced obviously by 36 %. Finally, vertical peel-off verification experiments were designed. After inserting micro-pores to the interface, the bonding strength of the interface increased from 8.75 MPa to 11.69 MPa, and the performance was improved by 33.6 %. The experimental results were consist with the simulation results and indicated that the micro-pores had a significant effect on improving the bonding strength.

Interface regulation of micro-sized sintered Ag-10Al composite based on in-situ surface modification and enhanced microstructure stability in power electronic packaging

The increasing demand for high-power SiC semiconductors necessitate the development of a die attachment material that combines high-temperature resistance, reliability, and cost-effectiveness. In this study, a novel micro-sized composite, Ag-10Al paste, containing 10 wt% Al particles, was designed. A remarkable phenomenon, the ejection of ultrafine Ag nanoparticles from micron-sized Ag flakes, was observed for the first time. The phenomenon was utilized for the in-situ surface modification of Al. Subsequently, the microstructure and mechanical properties of the sintered Ag-10Al/direct bonded copper (DBC) joints were studied. Results indicated that the Ag-10Al composite exhibited superior microstructure stability compared to sintered Ag. The Ag/Al interface was systematically analyzed, revealing a unique Ag/nano Ag2O/Al2O3 amorphous/Al structure. This structure was formed through the Ag nanoparticle jetting effect of Ag flakes, achieving effective bonding between nano Ag2O and Al2O3 amorphous phases through mutual dissolution at the atomic level. Moreover, the sintered Ag-10Al joint demonstrated enhanced mechanical performance stability over the sintered Ag joint. After 1000 h aging at 300 ℃, the shear strength of the sintered Ag-10Al joint reached 34.1 MPa, meeting the requirements for power semiconductor packaging. In conclusion, the Ag-10Al composite paste was thoughtfully designed, excelling in both performance and cost-effectiveness.

Bioinspired Thermal Conductive Cellulose Nanofibers/Boron Nitride Coating Enabled by Co-Exfoliation and Interfacial Engineering.

Thermal conductive coating materials with combination of mechanical robustness, good adhesion and electrical insulation are in high demand in the electronics industry. However, very few progresses have been achieved in constructing a highly thermal conductive composites coating that can conformably coat on desired subjects for efficient thermal dissipation, due to their lack of materials design and structure control. Herein, we report a bioinspired thermal conductive coating material from cellulose nanofibers (CNFs), boron nitride (BN), and polydopamine (PDA) by mimicking the layered structure of nacre. Owing to the strong interfacial strength, mechanical robustness, and high thermal conductivity of CNFs, they do not only enhance the exfoliation and dispersion of BN nanoplates, but also bridge BN nanoplates to achieve superior thermal and mechanical performance. The resulting composites coating exhibits a high thermal conductivity of 13.8 W/(m·K) that surpasses most of the reported thermal conductive composites coating owing to the formation of an efficient thermal conductive pathway in the layered structure. Additionally, the coating material has good interface adhesion to conformably wrap around various substrates by scalable spray coating, combined with good mechanical robustness, sustainability, electrical insulation, low-cost, and easy processability, which makes our materials attractive for electronic packaging applications.

Mechanical Properties of Doped Solder SAC-Q for High Strain Rate Testing at Extreme Surrounding Temperatures for 6 Months of Isothermal Aging

Abstract In various industries, including automobile industry, oil and gas, aerospace, and medical technology, electronic components are subjected to significant strain during shocks, vibrations, and drop conditions. Electronic components of this type are frequently subjected to extreme temperatures ranging from –65 °C to 200 °C. These electronic equipment are frequently subjected to strain rates of 1 to 100 sec−1 in sensitive conditions. SAC-Q, SAC-R, Innolot, and other doped SAC solder alloys have recently been introduced to electronic components and packages. SAC-Q refers to the addition of Bi to the Sn-Ag-Cu composition. The mechanical characteristic results and statistics for lead-free solder alloys are particularly important for increasing electronic package stability and high-temperature storage and strain rates. Furthermore, the mechanical characteristics of solder alloys can be dramatically altered owing to thermal aging, which causes microstructure alteration. For high-temperature aging for longer durations and testing at extremely low to very high working temperatures, SAC-Q solder alloy data is not available. The SAC-Q solder material was tested and studied at working temperatures ranging from −65 °C to 200 °C, with strain rates of up to 75 sec−1, for this study. A comparison was also done with the SAC305 solder, which had been thermally aged and tested under identical conditions. Isothermal aging specimens were kept at 100 °C for up to 180 days following manufacturing and reflowing when tensile studies were conducted at various operating temperatures. This study develops and describes stress–strain curves for a wide variety of strain rates and test temperatures. In addition, the test results and data collected were matched to the Anand viscoplasticity model, and Anand constants were calculated by estimating high strain rate behavior throughout a wide range of operating temperatures and stress levels. In addition, for BGA package assembly with PCB, FE analysis was performed for drop/shock events. For varied aging circumstances of SAC-Q solder ball joints, hysteresis stress–strain curves and plastic work density curves are generated.

Fused Deposition Modeling of Isotactic Polypropylene/Graphene Nanoplatelets Composites: Achieving Enhanced Thermal Conductivity through Filler Orientation.

High-performance thermally conductive composites are increasingly vital due to the accelerated advancements in communication and electronics, driving the demand for efficient thermal management in electronic packaging, light-emitting diodes (LEDs), and energy storage applications. Controlling the orderly arrangement of fillers within a polymer matrix is acknowledged as an essential strategy for developing thermal conductive composites. In this study, isotactic polypropylene/GNP (iPP/GNP) composite filament tailored for fused deposition modeling (FDM) was achieved by combining ball milling with melt extrusion processing. The rheological properties of the composites were thoroughly studied. The shear field and pressure field distributions during the FDM extrusion process were simulated and examined using Polyflow, focusing on the influence of the 3D printing processing flow field on the orientation of GNP within the iPP matrix. Exploiting the unique capabilities of FDM and through strategic printing path design, thermally conductive composites with GNPs oriented in the through-plane direction were 3D printed. At a GNP content of 5 wt%, the as-printed sample demonstrated a thermal conductivity of 0.64 W/m · K, which was 1.5 times the in-plane thermal conductivity for 0.42 W/m · K and triple pure iPP for 0.22 W/m · K. Effective medium theory (EMT) model fitting results indicated a significantly reduced interface thermal resistance in the through-plane direction compared to the in-plane direction. This work shed brilliant light on developing PP-based thermal conductive composites with arbitrarily-customized structures.

Microscopic fracture toughness of notched porous sintered Cu micro-cantilevers for power electronics packaging

To fulfill the high-temperature application requirement of high-power electronics packaging, Cu nanoparticle sintering technology, with benefits in low-temperature processing and high-melting point, has attracted considerable attention as a promising candidate for the die-attach interconnect. Comprehensive mechanical characterization of the sintered layer at a microscale is necessary to deepen the understanding of the fracture behavior and improve the reliable design of materials. In this study, microscale cantilevers with different notch depths were fabricated in a 20 MPa sintered interconnect layer. Continuous dynamical fracture testing of the microcantilevers was conducted in situ in a scanning electron microscope to detail the failure characteristic of the porous sintered structure. The microscopic fracture toughness of different notched specimens was obtained from the J-integral in the frame of elastic-plastic fracture mechanics. Specimens with deeper notches presented higher resistance to crack extension, while geometry factors of notch-to-width ratio between 0.20 and 0.37 exhibited a relatively stable microscopic fracture toughness ranging from 3.2 ± 0.3 to 3.6 ± 0.1 MPa m1/2.

Reducing anisotropy of rhombohedral Bi-rich phase for high-performance Ag-alloyed Sn–Bi low-temperature solders

The rhombohedral structure is with anisotropic properties, leading to brittle mechanical properties. However, it is one of the major constituent phases, the (Bi) phase, in the Sn–Bi-based low-temperature solders, which is demanding in the electronic industry for reducing the soldering temperature and alleviating the warpage in high-density fine-pitch electronic packaging. Herein, we proposed a high-performance Ag-alloyed Sn–Bi (SBA) low-temperature solder by reducing the fraction and, more importantly, the anisotropy of the (Bi) phase. We found that the (Bi) phase exhibited considerable solubility for Ag and Sn, even after thermal aging, without any nanoprecipitates as confirmed with both CALPHAD-type thermodynamic modeling and high-resolution TEM. The solution effects of Ag and Sn in the (Bi) phase is elaborated based on in situ nano-indentation, EPMA compositional analyses, EBSD characterizations, and ab initio calculations. The presence of Ag and Sn in the (Bi) phases resulted in both solid solution hardening and softening effects, depending on the Schmid factor of the grain. As a result, in (Bi) polycrystals, alloying could effectively mitigate the anisotropic mechanical properties of the (Bi) phase and facilitated a more uniform dispersion of forces exerted among (Bi) grains in all orientations. Consequently, the designed SBA solder exhibited superior mechanical properties, e.g., an ultimate tensile strength (UTS) of 55 MPa, elongation of 46%, and toughness of 20.6 × 106 J/m3 at a strain rate of 0.0005 s−1. This understanding opens the door for enhanced rhombohedral phase in alloy design for various applications.

Application of Machine Learning Methods for Process Optimization in Electronic Packaging Processes

Epoxy resins are commonly used as encapsulation materials in electronic packaging processes. Fluctuations in the materials lead to both changes in processability and to varying quality. Ideally, these variations should be identified, and measures taken as quickly as possible to reduce scrap parts and thus costs. A promising optimization approach for encapsulation processes are machine learning models, which have already shown good results in quality predictions, especially for injection molding. Subsequent quality measurements are avoided with good quality prediction models. With this type of models, not only predictions can be made, but also optimal parameter combinations can be found. In this paper, models for predicting quality criteria warpage and residual enthalpy of the epoxy molding compound were set up, trained and validated. Time series of in-situ sensors were used, from which relevant features were extracted and which, together with machine parameters, provide a dataset for prediction. The most promising prediction models are random forest regression and gradient boosting regression. T hey predict warpage with an accuracy of 90% to 91% and the residual enthalpy with an accuracy of 95%. Subsequently, optimization models of the machine parameters were set up. All relevant target variables were considered in a cost function, through the minimization of which an optimal parameter set was found. The gradient boosted tree and Bayesian optimization were determined to be the most promising models, as they lead to the lowest values of the respective cost function.