Electronic Packaging Applications Research Articles

In situ de-wetting of liquid–solid interface to fabricate spherical Ag@Ni immiscible alloys

Spherical Ag@Ni immiscible alloy powders were successfully fabricated combining in situ de-wetting of metal droplets from a metalloid solid medium with phase separation of immiscible alloys. The effects of atom ratio and temperature on morphology, structure, and phase separation were investigated. The spherical morphology of alloy powders confirmed the de-wetting of the liquid–solid interface between the liquid Ni–Ag immiscible alloy and the solid alumina powder medium. The Ni-rich phase was scattered in the Ag-rich phase matrix at 1673 K while the spherical Ni-core at the center was surrounded by a ring-shaped shell of Ag at the outer layer with an egg-type structure at 1753 K. The egg-type microstructure of the Ni–Ag particle resulted from the liquid–liquid immiscible phase separation. Such spherical Ag@Ni alloy powders with an egg-type microstructure have a good combination of a high strength Ni-rich phase core and a high electric and thermal conductivity Ag-rich phase shell with many potential advanced applications in electronic packaging.

Fineline circuits realization with liquid photoresist and DMD-based photolithographic technique for space electronics applications

Background: High-density interconnect (HDI) printed circuit board (PCB) packaging technology has gained greater significance in military and aerospace sectors. Manufacturing with fineline features and the impedance-controlled circuit pattern is a major technical challenge for which several methods have been reported. Aim: Herein, a novel process of HDI PCB fabrication has been presented using liquid photosensitive resist spray coating followed by digital micromirror device (DMD)-based micro-opto-electromechanical direct imaging photolithography to realize fineline circuit pattern. Approach: A fineline HDI circuit has been developed with minimum conductor trace width of <40 μm and spacing from the copper foil (18-μm thickness) cladded to dielectric substrate that comply the requirements of high reliability space electronics packaging. Such fineline conductor features have been exemplified with optical microscopy, SEM, and subjected to micro-sectioning. Results: The resulting undercut values and etched pattern have been found to be excellent. Leveraging the standard test method, the peel strength values of the realised fineline circuit patterns were measured to be more than 1.2 kg / cm2 required for high reliability space electronics packaging applications. Conclusions: The output paraments meet the space high-reliability requirements withstanding the stringent environmental conditions of ultra-high vacuum, vibration, and the extreme temperatures for longer durations.

Biodegradable and Nanocomposite Materials as Printed Circuit Substrates: A Mini-Review

Biodegradables are a promising path for the future of electronics in a greener mindset. The review study focuses on their applications and past and current research results. The paper also investigates the application of nanomaterials as fillers to control or increase the physical (electrical, mechanical, thermal) properties of biodegradable biopolymers. These biodegradables and nanocomposites are already effectively used in prototypes and advanced application areas with demanding requirements, such as flexible and wearable electronics, implantable or biomedical applications, and traditional commercial electronics. The nano-enhanced biopolymer substrates (e.g., with improved gas and water barrier functionalities) sometimes also with integrated, nano-enabled functionalities (such as electromagnetic shielding or plasmonic activity) can be beneficial in many electronics packaging and nanopackaging applications as well.

3D TSV hybrid pixel detector modules with ATLAS FE-I4 readout electronic chip

The through silicon via (TSV) technology has been introduced in a wide range of electronic packaging applications. Hybrid pixel detectors for X-ray imaging and for high-energy physics (HEP) can benefit from this technology as well. A 3D TSV prototype using the ATLAS FE-I4 readout electronic chip is described in this paper. This type of readout chip is already prepared for the TSV backside process providing a TSV landing pad in the first metal layer of the backend-of-line (BEOL) layer stack. Based on this precondition a TSV backside via-last process is developed on ATLAS FE-I4 readout chip wafer. The readout chip wafers were thinned to 100 µm and 80 µm final thickness and straight sidewall vias with 60 µm in diameter has been etched into the silicon from wafer backside using deep reactive ion etching (DRIE). The filling of the TSVs and the formation of the wafer backside interconnection were provided by a copper electroplating process. ATLAS FE-I4 readout chips with through silicon vias has been successfully tested, tuned and operated. In addition, hybrid pixel detector modules have been flip chip bonded using ATLAS FE-I4 TSV readout chips and planar sensor chips. After mounting the bare modules onto a support PCB, its full functionality has been verified with a source scan.

Horizontal Crack Induced Vertical Crack Formation in Epoxy Mold Compound for Electronic Packaging

Epoxy mold compound (EMC) has been widely applied as the packaging material in the electronic industry. It is due to the unique property of EMC such as high temperature stability, low coefficient of thermal expansion (CTE), excellent electrical properties and manufacturability. Despite of superior properties of EMC, several failures have been reported regarding on the electronic packaging application such as crack on the body (EMC). Most of the research reported that the crack defect was originated from the moisture absorption. This research is intended to examine the phenomenon and effect of moisture absorption on the vertical and horizontal crack formation. A comparison between control and conditioned sample was studied where the conditioned sample was subjected to humidity chamber according to the Moisture Sensitivity Level 3 (MSL3) requirement. Horizontal crack occurrence has been observed at the interface EMC. While vertical crack occurrence could be linked with the horizontal crack. Further analysis suggest that horizontal crack occurrence induced vertical crack occurrence. Thus, controlling moisture absorption pathway probably minimize horizontal crack and prohibit vertical crack occurrence.

A review on high thermally conductive polymeric composites

AbstractPolymers are known as thermally insulated materials with reported effective thermal conductivity (Keff) in the range of 0.1 to 0.5 Wm−1 K−1. However, increasing demand for smaller and more powerful electronics has created the need for thermally conductive polymers for use in heat exchangers and electronic packaging applications. Given this background, much research has been done over the past two decades to increase the Keff of polymers. Based on the strategy involved, those works can be divided into two main categories: (i) increasing the Keff of the neat polymer by aligning its chains orientation; and (ii) increasing polymer Keff by fabrication of polymeric composites with thermally conductive filler networks. Among these two strategies, the former is limited to nanoscale laboratory research and is difficult to scale up for mass production. Therefore, this work is mainly focused on the latter category, thermally conductive polymeric composites, which has a higher potential for large‐scale production. This work aims to summarize, evaluate, and highlight the successful strategies of the recent efforts in enhancing the thermal conductivity of polymer composites. The major achievements, future challenges, and the outlooks of high thermally conductive polymeric composites are presented by analyzing the results of about 300 works.

Thermomechanical Characterization Of Organo-Clay Epoxy Nanocomposites for Use in Civil Infrastructure

ABSTRACT Epoxy nanocomposites based on organically treated clays been researched extensively for use in aerospace, automotive, and electronic packaging applications. The potential low cost, decreased diffusivity and moisture uptake, and increase in stiffness and toughness, as well as the ability of the nanoclay particles to serve as a flame retardants and decrease flammability make these materials of immense interest for civil infrastructure applications especially as related to addressing long-term durability. This work analyzes the cure, thermomechanical (DMTA), moisture uptake and tensile characteristics of montmorillonite-epoxy nanocomposites. It is shown that the organo-clays serve as a catalyst for the curing reaction and reduced the exothermal peak temperatures with an increase in activation energy of cure at higher degrees of conversion. The nanocomposites demonstrated enhanced stiffness, relatively minor drops in glass transition temperature, increased thermal stability, and substantially decreased water uptake and diffusion rates, emphasizing their potential for use in civil infrastructure applications wherein nonaerospace cure techniques are used.

Dielectric properties of Steel Melting shop (SMS) slag

Many researchers have been focused on the better way to increase the utilization of industrial by-products for the road construction and tile productions. However, none of the research results have reported the functional characteristics of SMS slag. This paper deals with the processing and functional characterization of SMS slag using novel powder metallurgy method. The particle sizes, mineralogical phases, and dielectric constant were determined by XRF, BET, XRD and Impendence analyzer respectively. The effect of reduction of particle size on the functional properties of SMS slag was revealed that reduction in particles of slag decreases the dielectric properties of slag at 600 °C. As results, 50.65 wt% of free CaO phase was present in the slag samples. It is suggested that SMS slag can be useful for the electronic packaging applications.

Use of Full-Field X- ray Imaging and Ptychographic X-ray Computed Tomography for the Investigation of 3D Morphology of Micro-Nano Silver Materials for Advanced Electronics Packaging Applications

Use of Full-Field X- ray Imaging and Ptychographic X-ray Computed Tomography for the Investigation of 3D Morphology of Micro-Nano Silver Materials for Advanced Electronics Packaging Applications - Volume 27 Issue S1

Electrical and thermal performances of epoxy-based micro–nano hybrid composites at different electric fields and temperatures

This paper investigates the electrical and thermal properties of pure epoxy resin (EP) and its micro–nano hybrid composites (20 wt% micro-AlN fillers with 1 wt% and 3 wt% nano-Al2O3 fillers; 50% micro-AlN with 3% nano-Al2O3 fillers) for power electronic packaging applications. Electrical properties such as space charge distribution, electrical conductivity and surface potential decay are measured. The thermal performance of the fabricated samples is estimated using thermal analysis devices. The hybrid composite consisting of 20 wt% micro-AlN and 1 wt% nano-Al2O3 fillers exhibits the least space charge accumulation, higher thermal conductivity and better thermal stability. However, the excessive addition adversely affects space charge and electrical conductivity properties. The micro–nano hybrid composites significantly exhibit higher electrical conductivity than pure EP. The microfiller addition from 20 wt% to 50 wt% significantly improves the thermal conductivity of the EP. The reduced space charge injection and accumulation in the hybrid micro–nano composites are attributed to the enhancement of the injection barrier and reduction of the charge carrier traps in these materials. A theoretical mechanism of the charge dynamics inside the samples under different test conditions is proposed to support the experimental results.

A Review of Sintering-Bonding Technology Using Ag Nanoparticles for Electronic Packaging.

Metal nanoparticles (NPs) have attracted growing attention in recent years for electronic packaging applications. Ag NPs have emerged as a promising low-temperature bonding material owing to their unique characteristics. In this study, we mainly review our research progress on the interconnection of using polyol-based Ag NPs for electronic packaging. The synthesis, sintering-bonding process, bonding mechanism, and high-temperature joint properties of Ag NP pastes are investigated. The paste containing a high concentration of Ag NPs was prepared based on the polyol method and concentration. A nanoscale layer of organic components coated on the NPs prevents the coalescence of Ag NPs. The effects of organic components on the bondability of the Ag NP paste were studied. Compared to the aqueous-based Ag NP paste, the polyol-based Ag NP with the reduction of organic component can improve the bondability, and the coffee ring effect was successfully depressed due to the increased Marangoni flow. The sintering behaviors of Ag NPs during the bonding process were investigated using the classical sphere-to-sphere approach. The mechanical property of joints using this Ag paste was better than that using Pb95Sn5 solders after storage at high temperatures. The sintering–bonding technology using polyol-based Ag NPs was helpful to the low-temperature interconnection for electronic packaging applications.

Synthesis of dispensable PDMS/Al2O3/GO thermal gap filler and performance comparison with commercial thermal gap fillers for electronics packaging applications

ABSTRACT In response to the critical needs of high power density, advanced thermal gap fillers (TGF) are required for the long-term reliability of electronics packaging. In this study, dispensable thermal gap filler (Al87GO6) with 87 wt.% Al2O3, 6 wt.% graphene oxide and 7 wt.% polymers were fabricated as two parts (Part A and Part B). The thermal conductivity of cured Al87GO6 (3.87 W/m.K) was 1.03, 1.11 and 1.24 times higher than commercially available thermal gap fillers TGF A, TGF B and TGF C, respectively. Part A and Part B components of Al87GO6 TGF exhibit a higher plateau value of zero shear viscosity. The lightweight graphene oxide has significantly reduced Al87GO6 TGF’s density by ~30–48%. The dielectric constant of Al87GO6 TGF was around ~6–17% lower than commercial TGF. Hence, the fabricated Al87GO6 TGF can be used as an alternative TGF for efficient heat dissipation.

Novel micro-nano epoxy composites for electronic packaging application: Balance of thermal conductivity and processability

Epoxy (EP) composites with comprehensive good processability, low coefficient of thermal expansion (CTE), and high thermal conductivity, but electrical insulation properties are largely demanded in the higher power electric devices. However, micro-fillers have a positive effect on maintaining the good flowability of epoxy composites, while do not bring high thermal conductivity enhancement per unit mass. While nano-fillers with high specific surfaces offer very promising opportunities for heat-conducting network construction, but the nano-fillers dispersion is difficult to control and will cause increased viscosity and processing difficulties. Herein, we expect that the addition of small amounts of silver nanowires (AgNWs) at 0.5 vol% into the EP/S-Al2O3 composites could largely enhance the thermal conductivity but not sacrifice their processability. Owing to the bridging effects of rigid nanowires between the main spherical particles, the thermal conductivity of the micro-nano EP/AgNWs/S-Al2O3 composites with 40 vol% S-Al2O3 and 0.5 vol% AgNWs exhibits a 106.5% increment comparing to that without AgNWs. The limitation of both single micro or nano-sized thermal conductive fillers can be offset by the micro-nano filler network structure. The best combination properties of the EP/AgNWs/S-Al2O3 composites can reach the high thermal conductivity (1.602 W/m·K), low viscosity (55.6 Pa s), low CTE (37.1 ppm/°C), and high glass transition temperature (Tg, 152.1 °C). These results demonstrate that adding multiscale fillers into epoxy composites may solve the tradeoff between thermal conductivity and processability performances and fit the applications in high-power density electronic devices.

Polymer Composites with Improved Dielectric Properties: A Review

Materials exhibiting high dielectric constant (k) values find applications in capacitors, gate dielectrics, dielectric elastomers, energy storage device, while materials with low dielectric constant are required in electronic packaging and other such applications. Traditionally, high k value materials are associated with high dielectric losses, frequency-dependent dielectric behavior, and high loading of a filler. Materials with low k possess a low thermal conductivity. This creates the new challenges in the development of dielectric materials in both kinds of applications. Use of high dielectric constant filler materials increases the dielectric constant. In this study,the factors affecting the dielectric constant and the dielectric strength of polymer composites are explored. The present work aims to study the effect of various parameters affecting the dielectric properties of the materials. The factors selected in this study are the type of a polymer, type of a filler material used, size, shape, loading level and surface modification of a filler material, and method of preparation of the polymer composites. The study is focused on the dielectric enhancement of polymer nanocomposites used in the field of energy storage devices. The results show that the core-shell structured approach for high dielectric constant materials incorporated in a polymer matrix improves the dielectric constant of the polymer composite.

Characteristics and grinding performance evaluation of the high-fraction GNFs/SiCp/6061Al matrix hybrid composites

The poor machinability of the high-fraction SiCp/Al matrix composites is one of the key factors that hinders its application in electronic packaging. In this study, (0−15) wt% GNFs/SiCp/6061Al matrix hybrid composites are prepared by vacuum hot pressing at 590 °C and 50 MPa with the graphene nanoflakes (GNFs) partially replacing SiCp, the microstructure and ground surface properties of the composite and their effects on the mechanical and thermal properties of the composite are studied, and the machining performance is comprehensively evaluated. The results show that the interface of the composite is well-bonded and no Al4C3 products exist. With increasing GNFs content, the GNFs in the composites tend to agglomerate, the density decreases, and the damage to the ground surface and microstructure increases. Compared to the 54.2 wt% SiCp/6061Al matrix composites, the 5 wt% GNFs/48.4 wt% SiCp/6061Al matrix composites have lower strength but better thermal properties, and show lesser damage of the microstructure and lesser attenuation of the mechanical and thermal properties after grinding. However, with the further increase in the GNFs content, the SiCp crack and drop off and GNFs pull out and peel severely, leading to the greater degradation of the properties of the surface of the GNFs/SiCp/6061Al matrix composites.

Poly(vinyl alcohol)/reduced graphene oxide multilayered coatings: The effect of filler content on gas barrier and surface resistivity properties

Polymer-filler multilayered coatings fabricated by layer-by-layer (LbL) methods exhibit enhanced gas barrier properties alongside with transparency and flexibility. However, the traditional LbL methods which consist of repeated cycles of dipping (or spinning), washing, and drying, are time-consuming and complex to industrialize. Here, it is proposed an easy-operating and time-saving rod-coating assisted LbL method for the fabrication of poly(vinyl alcohol)/reduced graphene oxide (PVA/rGO) multilayered coatings on poly(ethylene terephthalate) (PET) substrates. Scanning electron microscopies revealed that PVA/rGO multilayered coatings exhibited a brick-and-wall structure with PVA able to bind the rGO buildings blocks. The oxygen transmission rate of the films coated with five layers of PVA/rGO coatings (8.4 cm3 m-2 day-1 atm-1) is about 92% lower than that of the uncoated PET substrate, whereas the optical transparency is still 94%. The water permeability of films coated with the multi-layered PVA/rGO coatings is about 30% lower than that of pristine PET substrate. Furthermore, the resulting films exhibited a low surface resistivity, which contrasts the negative effects of static electricity accumulation, and high mechanical property, fulfilling the technological requirements for traditional application in electronic packaging.

Explicit microstructure and electrical conductivity of epoxy/carbon nanotube and green silver nanoparticle enhanced hybrid dielectric composites

Carbon nanotubes (CNTs) decorated with silver nanoparticles (AgNPs) are promising nanomaterials for improving the dielectric properties of polymer materials for energy storage and micro-capacitor applications. However, the cost of AgNPs limits their wide application. This work describes the synthesis of green silver nanoparticles (GAgNPs) from cashew leaves and their hybridization with CNTs. These new hybrid nanocomposites were developed by adding 0.1, 0.2, 0.3, 0.4 and 0.5% CNTs and 0.5% GAgNPs in an epoxy matrix. Electrical conductivity, dielectric constant, and capacitor raised as CNTs content increased from 0.1 to 0.5% with 0.5% GAgNPs. The high dielectric constant reported in this work was made possible because of the high electron mobility of GAgNPs, which helps to enhance the conductivity of the epoxy. The highest electrical conductivity and dielectric constant were obtained for hybrid nanocomposites based on 0.5% CNTs and 0.5% GAgNPs. It was established that GAgNPs modified CNTs can be used to enhanced the electrical conductivity, dielectric constant and capacitance of epoxy resins for isotropic conductive adhesives, assemblies, and electronic packaging applications.

Laser-Assisted Sintering of Silver Nanoparticle Paste for Bonding of Silicon to DBC for High-Temperature Electronics Packaging

This article presents the development of a laser-assisted sintering method of a silver nanoparticle paste for bonding of a silicon chip to a direct bonded copper (DBC) substrate for high-temperature electronics packaging applications. The effects of the bonding parameters such as laser power, bonding pressure, and time on shear strength were studied. For comparison, samples using hotplate bonding were also produced and studied. Shear strength, cross section, and fracture surface analysis were carried out in reliability studies. The results show that shear strength of 10 MPa can be achieved at the bonding pressure of 3 MPa, laser power of 70 W, and a very short irradiation time of 1 min. The shear strength reached 20 MPa when the irradiation time was increased to 5 min. The research indicates that the shear strength can be improved by increasing the bonding pressure, laser power, and hence the sintering temperature and the irradiation time. The laser-assisted method with a short irradiation time of 5 min can produce the same level of shear strength as compared with the hotplate-based approach requiring a sintering time of tens of minutes. With the ability of fast and localized heating effect, the laser-assisted sintering method can improve the manufacturing efficiency for packaging of high-temperature electronics and sensors.

Enhanced adhesion strength of silver paste on AlN ceramic substrate via sintered nano-CuO

We have optimized a CuO-doped silver paste to significantly improve the adhesion strength of silver thick film on AlN ceramic substrate, which can be widely applied in power electronic packaging applications. Via a combination of scanning electron microscope and X-ray diffraction, we have systematically studied the silver layer morphology on top of AlN ceramic substrate, and the interphases between the silver thick film and AlN substrate. Due to the CuAl2O4 intermediate formed at the silver layer/AlN interface, the adhesion strength of silver thick film can be greatly improved. Particularly, the silver paste with 3 wt% nano-CuO sintered on AlN ceramic substrate exhibits high adhesion strength of 15.3 MPa with good electrical conductivity of 0.9 mΩ/□.

Combining Alumina Particles with Three-Dimensional Alumina Foam for High Thermally Conductive Epoxy Composites

Ceramic/polymer composite with a high thermal conductivity is a candidate of insulating materials for electronic packaging. However, traditional polymer composites filled with alumina (Al2O3) powders present limited enhancement in thermal conductivity even at a high loading due to thermal resistance on the filler/filler and filler/matrix interfaces. Herein, a contiguous 3D network of alumina foam (AF) filled with different diameters of Al2O3 microparticles via vacuum-assisted filtration proves to be a promising filler structure for thermal conductivity composites. The fabricated epoxy/AF/Al2O3 composite exhibits a high thermal conductivity of 4.1 W/mK and a significant thermal conductivity enhancement (TCE) of 2097%. Further study reveals a prominent synergistic effect between the 3D interconnected AF and Al2O3 microparticles, which plays a critical role in the formation of thermal percolation networks to promote thermal conductivity dramatically. Meanwhile, compared to previous reports, the composite resulted in a lower coefficient of thermal expansion (CTE) than those of most epoxy-based composites, showing great potential for heat conduction applications in microelectronics. This result paves an effective way of developing epoxy composites with high thermal conductivity in electronic packaging applications.