Electronic Packaging Technology Research Articles

Combined effect of Ag element and temperature gradient on the formation of highly orientated Sn grains in micro solder joints

Sn-Ag solders are widely used for advanced electronic packaging. The combined effect of Ag element and temperature gradient (TG) on the formation of Sn grains in Cu/Sn-xAg/Cu micro solder joints was elucidated systematically. Numerous small-sized β-Sn grains were formed in both Cu/Sn/Cu and Cu/Sn-0.5Ag/Cu micro solder joints after reflow with or without TG. The Cu/Sn-0.5Ag/Cu joint was found to have more twinning β-Sn structures. The formation of the multiple β-Sn grains in these two joints was attributed to the presence of multiple tetrahedral metastable short-range order (SRO) structures which acted as nuclei for the nucleation and growth of β-Sn. The existence of TG slightly enhanced the preferred orientation characteristics of Sn grains. For the joints with Ag content was or higher than 2 wt.%, several Sn grains were formed without TG, while a single or highly oriented Sn grains were observed with TG. The number and orientation of Sn grains were affected by the combined effect of Ag element and TG significantly. The β-Sn grains formed without TG were based on the {101} type cyclic twinning configuration clusters that stabilized by Ag atoms and acted as nuclei. The formation of a single or highly preferred β-Sn grains was benefit from the combined effect of Ag element and TG. The results provide theoretical guidance for optimizing the composition of Sn-Ag solders and controlling the microstructure of the joints, thereby contributing to the advancement of electronic packaging technologies.

Enhancement of Cu-to-Cu bonding property by residual stress in Cu substrate

This study investigated the use of copper nanoparticles (Cu NPs) as a novel material for interconnecting joints in advanced electronic packaging technology. Cu NPs offered a promising alternative due to their excellent electrical and thermal properties. Cu NPs were characterized as single crystals by a transmission electron microscope, and electron backscatter diffraction confirmed that the grain size of the Cu substrate was about 11 μm and only became slightly larger after thermal annealing. Surface diffusion was determined to be the dominant kinetic path for Cu NP sintering on the substrate. An additional driving force for sintering was validated by measuring the stress state using X-ray diffraction. The characterization results provided evidence for proposing a mechanism to explain how residual stress influenced atomic behavior during the sintering process. High residual stress enhanced the strength of the Cu NP joints and improved the reliability of electronic devices.

Experimental and Numerical Investigation of Single-Phase Liquid Cooling for Heterogeneous Integration Multichip Module

Abstract The variety of new electronic packaging technologies has grown significantly over the last 20 years as a result of market demands for higher device performance at lower costs and in less space. Those demands have pushed for heterogeneous packaging, where computer chips with different stack heights are closely packed, creating nonuniform heat flux and temperature and additional challenges for thermal management. Without implementing an appropriate thermal management strategy for heterogeneous packages, large temperature gradients can be observed within the package, which would increase the thermal stresses on the chip and raise reliability issues. To mimic this real-life scenario of such packaging, an experimental setup was designed and built. The design of the new experimental setup consists of four identical 1.2 cm × 1.2 cm ceramic heaters, each of which is connected to a separate power supply and can reach a heat flux of 140 W/cm2. Accordingly, this mock package is capable of delivering different power levels to mimic different multicore microprocessor conditions. To give the heater the ability to move precisely in the x-, y-, and z-directions, each heater is mounted to an XYZ linear stage. Deionized water (DI) was used as the working fluid, and a pin-fin heat sink was used to run the initial steady-state tests on the experimental rig. The tests showed how different flow rates at a constant fluid temperature and input power affect the temperatures of the heaters and the thermohydraulic performance of the heat sink. In addition, a three-dimensional numerical model has been developed and validated with experimental data in terms of heat sink pressure drop and the temperatures of the heaters.

First-Principles Study of Cu Addition on Mechanical Properties of Ni3Sn4-Based Intermetallic Compounds

Ni–Cu under-bump metallisation (UBM) can reduce stress and improve wetting ability in technology for electronic packaging technology advances with three-dimensional integrated circuit (3D IC) devices. The bond between the Sn-based solder and Ni–Cu UBM is affected by the formation of intermetallic compounds (IMCs), specifically Ni3Sn4 and (Ni,Cu)3Sn4. This paper investigates the mechanical properties of IMCs, which are critical in assessing the longevity of solder joints. First-principles calculations were carried out to investigate the phase stability, mechanical properties and electronic structures of Ni3Sn4, Ni2.5Cu0.5Sn4, Ni2.0Cu1.0Sn4, and Ni1.5Cu1.5Sn4 IMCs. The calculated formation enthalpies show that the doping of Cu atoms leads to a decrease in the stability of the phases and a reduction in the mechanical properties of the Ni3Sn4 crystal structure. As the concentration of Cu atoms in the Ni3Sn4 cells increases, the bulk modulus values of (Ni,Cu)3Sn4 formed with different compositions decrease from 107.78 GPa to 87.84 GPa, the shear modulus decreases from 56.64 GPa to 45.08 GPa, and the elastic modulus decreases from 144.59 GPa to 115.48 GPa, indicating that the doping of Cu atoms into the Ni3Sn4 cells may adversely affect their mechanical properties and increase the possibility of microcracking at the interface during actual service. The anisotropy of (Ni,Cu)3Sn4 is more significant than that of Ni3Sn4, with Ni2.0Cu1.0Sn4 showing the highest anisotropy. After evaluating the electronic structures, the metallic properties of Ni3Sn4 and the Ni2.5Cu0.5Sn4, Ni2.0Cu1.0Sn4, and Ni1.5Cu1.5Sn4 phases are revealed by electronic structure analysis. The total density of states (TDOS) for (Ni,Cu)3Sn4 structures is mainly influenced by Ni-d and Cu-d states. The addition of Cu atoms can increase the brittleness of Ni3Sn4. In addition, the region where d and p hybridisation occurs gradually increases with increasing Cu content. The electronic properties suggest that the binding energy between Ni and Sn atoms weakens with the addition of Cu atoms, resulting in a decrease in the elastic modulus. This research can serve as a valuable reference and theoretical guide for future applications of these materials.

Micro-cones Cu fabricated by pulse electrodeposition for solderless Cu-Cu direct bonding

In the post-Moore’s era, Cu-Cu direct bonding has garnered significant attention as a promising alternative to solder joints for chip interconnection in advanced electronic packaging technology. Its advantages lie in reduced process restrictions and steps, as well as lower bonding temperature, which align with the demands for low cost and high compatibility. In this study, (110)-oriented micro-cones Cu was fabricated via template-free pulse electrodeposition, enabling solderless Cu-Cu direct bonding at 250 ℃ under three distinct bonding pressures without chemical mechanical polishing (CMP). The contact bonding area and shear strength gradually increased corresponding to the applied bonding pressure. Seamless bonding interface was achieved under high bonding pressure, leading to high shear strength of 116.4 MPa for Cu-Cu bonding joints. The obtuse polygon pyramid micro-cones, characterized by an enlarging cross-sectional area from apex to base, coupled with inherent mechanical properties, induce high applied stress at micro-cone’s tip and a low yield stress, facilitating the initiation and propagation of plastic deformation during the bonding process. This study has demonstrated the feasibility of utilizing the micro-cones Cu for low-temperature bonding without CMP treatment, offering valuable insights into the advanced interconnection technologies.

(Invited) Hybrid Bonding for 3D Applications: Improvements and Limitations

Wafer direct bonding has attracted considerable concerns since it takes advantage of the ability to achieve strong adherence between flat, clean, and smooth surface without the use of intermediate materials. This technology experienced a consequent rise with the More than Moore's law. With this trend, added value to devices is provided by incorporating functionalities that do not necessarily scale according to "Moore's Law”. Indeed, this aims to realize three-dimensional (3D) integration systems by stacking devices and interconnecting them using Through-Silicon-Via (TSV) or Cu-Cu interconnections. Hybrid bonding is preferred to other chip stacking technologies because Cu-Cu hybrid bonding is easily capable of scaling down and present excellent reliability results.Hybrid bonding is key technology to address several applications especially images sensor. Even more specialized applications or better performances could be obtained through hybrid bonding pitch reduction [1]. High quality bonding for 3D technology has been demonstrated using an accurate wafer bonding tool with optimized metrology [2]. The total overlay values reached is below 110 nm with residuals values below 80 nm and scaling inferior to 0.5 ppm for interconnect pitches from 6.9 µm down to 0.6 µm. The electrical properties have been checked and confirmed the robustness of the fine pitch hybrid bonding module and the stability of the bonding interface [3]. The latest process and hardware developments have made it possible to greatly reduce scaling. However, distortion remains the most complicated parameter to optimize. It is strongly linked to the design of the chip (number of metal levels, stress...). Today, a minimum critical dimension design rule should be respected to avoid short between front side and backside layers and this is preventing pixel shrink. To reduce pixel size, distortion value needs to be decreased. For that purpose, in situ monitoring of the bonding wave is necessary as well as bonding chucks multiple vacuum zones in order to achieve homogenous bonding wave propagation.Even if hybrid bonding integration and performance have been considerably improved, we can notice that thermal budget is a main limitation for this technology. Indeed, to reach strong bonding energy which is mandatory for subsequent mechanical manufacturing; a bonding anneal of 800°C is required. By using plasma treatment prior bonding, anneal temperature can be decreased to 400°C. However, some devices cannot withstand such thermal budget because of thermosensitive materials integration (GST or quantum dots for example). To overcome this limitation, many studies have been performed on developing low temperature direct bonding process. Surface activated bonding (SAB) is a promising method to achieve high bonding energy at room temperature, but chemical surface treatments (as amino-alcohol organic molecule for example [4]) are easiest to implement for mass volume production and allows highly strong bonding at 200°C that can stand high stress process steps (grinding, CMP and dicing).Although specific plasma or surface preparation could decrease the required annealing temperature, the copper oxide will limit electrical performances with annealing below 250°C for standard hydrophilic bonding. That is why, new ECD Cu deposition like oriented nano-twin Cu is very promising to facilitate oxygen diffusion. [5][1] AYOUB, B., LHOSTIS, S., MOREAU, S., et al. Impact of Process Variations on the Capacitance and Electrical Resistance down to 1.44 µm Hybrid Bonding Interconnects. In : 2020 IEEE 22nd Electronics Packaging Technology Conference (EPTC). IEEE, 2020. p. 453-458.[2] DETTONI.Florent, DELOFFRE, Emilie, GRAUER, Yoav, et al. Advanced overlay metrology for CIS bonding applications. ECTC 2023 to be published[3] AYOUB, Bassel, LHOSTIS, Sandrine, MOREAU, Stéphane, et al. Sub 1µm Pitch Achievement for Cu/SiO 2 Hybrid Bonding. In : 2022 IEEE 24th Electronics Packaging Technology Conference (EPTC). IEEE, 2022. p. 418-424.[4] FOURNEL, Frank, CALVEZ, Aziliz, LARREY, Vincent, et al. Impact of an Amino-Alcohol Organic Molecule on SiO2 and Si Bonding Energy. ECS Transactions, 2020, vol. 98, no 4, p. 3.[5] CHEN, Chih, JUANG, Jing-Ye, CHANG, Shih Yang, et al. Low-temperature Cu-to-Cu direct bonding enabled by highly (111)-oriented and nanotwinned Cu. In : 2019 6th International Workshop on Low Temperature Bonding for 3D Integration (LTB-3D). IEEE, 2019. p. 38-38.

Direct Digital Manufacturing (DDM) Workflow for Printed Circuit Structures (PCS)

Digitally based manufacturing has been around for years and has been the basis of turnkey lights out manufacturing processes and systems. Moving forward is the concept of Direct Digital Manufacturing (DDM) which brings together conceptualizing the electronic device, developing a digital twin of the product, and digitally merging workflow with the manufacturing process. This would further extend through to physical product. This paper will illustrate DDM is the basis of developing the capability of conceptualizing, designing, and digitally manufacturing electronic devices and more specifically printed circuit structures or PCS and printed circuit cylinders, PCC. Unlike tradition PCB’s or multichip module technology, the goal is fully printed electronic devices that can merge structure with electronic functionality. This paper will explore the current state of practice in manufacturing workflow and extend to the emerging factory in a Box concept of multi-material printing of next generation electronic controller and packaging technology. This will also include exploring design tools that provide the capability of co-design mechanical function with electronic function and modeling the manufacturing process and electronic device using digital twin concepts and workflow enabling smart manufacturing of printed electronic devices and precision of DDM technology.

Laser Processing of Polyimide and Molybdenum Substrates for Extreme Environment Electronics

A desire in today’s electronic packaging technologies is to create more dense electronic packaging schemes. One method to achieve more dense electronic package integration is to use three-dimensional interconnects to minimize interconnect physical dimensions. Three-dimensional interconnect technologies, such as interposers, require a method of connecting electronics to electronic packages vertically. Thru silicon vias are a widely studied and explored vertical interconnect technology used in a variety of electronic packaging applications. Though silicon has high material hardness, the brittle nature of silicon substrates is a concern for robustness and reliability. These concerns only increase when the desired interconnect application is in extreme environments, such as cryogenic temperatures. A potential alternative to silicon in thru-via applications in extreme environments is molybdenum. Molybdenum is a commonly used material in many applications, such as automotive and aerospace, and has high material strength. Molybdenum is also a low coefficient of thermal expansion material, comparable to silicon, which in combination with high material strength lends to high reliability at extreme temperatures. A challenge of working with refractory metals such as molybdenum is that conventional CNC machining techniques require the use of machining coolants that may not be compatible with fabricated electronics and/or processes can become costly due to tool wear and the need for specialized equipment. Additionally, using molybdenum as a thru-via substrate requires the need for an electrically insulated layer, such as polyimide, within drilled molybdenum thru-holes to prevent the molybdenum substrate from shorting via connections. One potential solution to the above challenges is developing laser processing techniques to cut and drill molybdenum and polyimide. Laser processing is becoming a preferred method for inexpensive prototyping with high resolution and design versatility. This work seeks to meet the challenges described by developing laser cutting and drilling techniques for both molybdenum and polyimide for the use in cryogenic applications. This work will describe two laser processing configurations utilizing two different lasers to laser machine molybdenum and polyimide. This work will first describe the process strategies of laser cutting and drilling molybdenum as a stand-alone substrate. Aspects of laser processing on molybdenum, such as pattern repetitions and scanning speeds, will be described. Process parameter variations will be compared directly and evaluated. Additionally, post-laser processing steps, such as abrasive blasting, will be described and discussed. Next, the fabrication steps to achieve an insulating layer of polyimide in laser drilled holes as well as on each surface of the molybdenum will be detailed. Once polyimide has been cured, laser processing parameters to realize thru-holes in the polyimide-filled molybdenum drills will be presented. Adhesion of polyimide on the molybdenum substrate will be verified and demonstrated through the use of confocal scanning acoustic microscopy before and after polyimide laser processing. Cryogenic performance will be verified by completing confocal scanning acoustic microscopy after submersion in liquid nitrogen (~77 K) and compared with the pre-submersion microscopy images. Processes detailed in this work will open opportunities for future development of molybdenum-based interconnect structures for use in cryogenic applications. Acknowledgement We thank the Alabama Micro/Nano Science and Technology Center (AMNSTC) for providing access to fabrication and characterization facilities used in this work.

Long shelf life, intrinsically flame retardant, transparent, high-performance one-component epoxy resin based on phosphorus-containing imidazole derivatives

Highly evolving 5G and electronic packaging technologies require one-component epoxy resins with high flame retardancy, long shelf life, and fast curing while maintaining transparency & mechanical properties. However, it's tricky and challenging to meet this requirement simultaneously. Herein, two latent phosphorus-containing imidazole curing agents (PHI-HPP and EMI-HPP) were synthesized from 2-ethyl-4-methylimidazole (EMI) and 2-phenylimidazole (PHI). PHI-HPPx/EP exhibits a superior shelf life than EMI-HPPx/EP. PHI-HPPx/EP allows stable storage at room temperature exceeding 91 days, which is better than previous one-component epoxy resins cured by phosphorus-containing imidazole. PHI-HPP20/EP and EMI-HPP20/EP allow for fast curing at 150 °C and also feature excellent fire safety. In particular, PHI-HPP20/EP features a limiting oxygen index (LOI) of 35.8% and achieves the UL-94 V-0 rating. Its peak heat release rate (PHRR) is reduced by 59.3% compared to PHI/EP. Notably, PHI-HPPx/EP and EMI-HPPx/EP maintain the inherent excellent transparency, mechanical properties and glass transition temperature (Tg) of epoxy resins. Therefore, this research presents a viable approach for preparing one-component epoxy resin with long shelf life, fast curing, flame retardant, transparency and high performance.

Additive Manufacturing of Liquid-Cooled Ceramic Heat Sinks: An Experimental and Numerical Study

With recent advances in power electronic packaging technologies, liquid-cooled ceramic heat sinks have been considered as a promising solution for further improving the performance of power electronic devices. In this study, several aluminum oxide heat sinks were fabricated and tested using the digital light processing-based additive manufacturing method, to verify their practical performance. The results showed that the complex cooling structures inside the heat sinks can be completely formed and exhibited high surface quality. The experimental thermal and hydraulic performances of the heat sinks were consistent with the numerically modeled predictions. Furthermore, by exploiting the advantages of additive manufacturing, a direct manifold microchannel (MMC) configuration was designed to reduce the vertical flow of the traditional MMC configuration and achieve an improved cooling efficiency. At a constant volumetric flow rate of 1 L/min, the direct MMC configuration achieved a 19.8% reduction in pressure drop and an 11.8% reduction in thermal resistance, as well as a more uniform temperature distribution.

30 Years Life in Asia+ with Electronics Packaging Technology

30 Years Life in Asia+ with Electronics Packaging Technology

Study on the properties of epoxy-based Sn[sbnd]58Bi solder joints

In electronic packaging technology, Sn58Bi alloy solder has the advantages of low-temperature soldering and high shear strength of solder joint. It has a wide range of application in the electronics industry for low-temperature soldering, especially for temperature-sensitive substrates. Epoxy-based Sn58Bi solder paste is a mixture of curable flux and Sn58Bi solder powder. During the soldering process, the curable flux, in addition to the functions of a conventional flux, forms a cured epoxy shell around the periphery of the solder joint, which can effectively improve the shear strength and thermal stability of the solder joint. In this study, a self-made epoxy-based Sn58Bi solder paste was prepared and the properties of the solder joints were investigated. The results show that epoxy-based Sn58Bi solder paste has better wettability than traditional Sn58Bi solder paste without epoxy resin. And the shear strength of epoxy-based Sn58Bi solder joint is about 25 % higher than that of traditional Sn58Bi solder joint. Furthermore, the electrical conductivity of epoxy-based Sn58Bi solder joint has the same order of magnitude as that of traditional Sn58Bi solder joint, which means that non-conductive epoxy resin has no effect on the electrical conductivity of the epoxy-based Sn58Bi solder joint.

Research Progress of Electroplated Nanotwinned Copper in Microelectronic Packaging.

Copper is the most common interconnecting material in the field of microelectronic packaging, which is widely used in advanced electronic packaging technologies. However, with the trend of the miniaturization of electronic devices, the dimensions of interconnectors have decreased from hundreds of microns to tens of or even several microns, which has brought serious reliability issues. As a result, nanotwinned copper (nt-Cu) has been proposed as a potential candidate material and is being certified progressively. Firstly, the physical properties of nt-Cu have been widely studied. Notably, the higher thermal stability and oxidation resistance of the (111) texture causes nt-Cu to maintain excellent physical properties under high-temperature serving conditions. Secondly, recent works on the electrolyte and electroplating processes of nt-Cu on wafer substrates are summarized, focusing on how to reduce the thickness of the transition layer, improve the twin density, and achieve complicated pattern filling. Thirdly, nt-Cu can effectively eliminate Kirkendall voids when it serves as UBM or a CuP. Additionally, the high (111) texture can control the preferred orientation of interfacial intermetallic compounds (IMCs) at the Cu-Sn interface, which should be helpful to improve the reliability of solder joints. nt-Cu has superior electromigration resistance and antithermal cycling ability compared to ordinary copper RDLs and TSVs. Above all, nt-Cu has attracted much attention in the field of microelectronic packaging in recent years. The preparation-performance-reliability interrelationship of nt-Cu is summarized and displayed in this paper, which provides a solid theoretical basis for its practical applications.

Degradation-controlling mechanisms in natural organic acid solutions of CaO–Al2O3–SiO2–B2O3 glass-ceramics by partially substituting Ca2+ with Ba2+ and Sr2+

The degradation of environmentally friendly CaO–Al2O3–SiO2–B2O3 (CASB) glass-ceramics, which consist of anorthite and glass phase, was investigated in three natural organic acid solutions. The results indicated that citric acid had the most significant effect on the degradation of CASB glass-ceramics. While the chemical stability of anorthite is relatively poor, the glass phase also contributed significantly to the effective degradation of CASB glass-ceramics. Subsequently, Ba2+ or Sr2+ was used for full or partial substitution of Ca2+ in CASB glass-ceramics, and the degradation-controlling mechanism of the substituted CASB glass-ceramics was further researched. The full substitution of Ca2+ in CASB glass-ceramics by the two cations resulted in the occurrence of borate [BO4] units in the glass phases, and the interlinkage of [BO4] with broken silicate [SiO4] network structures caused a complementary network effect. Consequently, the degradation of CASB glass-ceramics by organic acids was reduced due to the improvements in the chemical stability of the modified glass-ceramics. Additionally, degradation control can also be achieved based on a mixed-alkali effect, originating from the partial substitution of Ca2+ in CASB glass-ceramics by Ba2+ or Sr2+. The degradable glass-ceramics have the potential to be applied in low-temperature co-fired ceramic technology because of their good physical properties, which include a dielectric constant of 3–5, a dielectric loss as low as 10−3, a coefficient of thermal expansion of 3–9 × 10−6/°C, and an average bending strength of about 47 MPa. Noticeably, the development of the degradable glass-ceramics is helpful to the low-cost and pollution-free recycling of valuable metal electrodes, which is significant for the sustainable development of electronic packaging technologies.

Investigation of the Interfacial Reactions between the CoCuFeNi High Entropy Alloy and Sn Solder

The CoCuFeNi high entropy alloy (HEA) has excellent electrical, thermal, and mechanical properties. In electronic packaging technology, Sn is the major element of lead-free solders. In this study, we used the CoCuFeNi HEA as the substrate and Sn as the solder and investigated the liquid/solid interfacial reactions of the Sn/CoCuFeNi system at 300, 375, and 450 °C for 30, 60, 100, 150, 360, and 480 min. The results indicated that the (Fe, Co)Sn2 phase was formed in the Sn/CoCuFeNi couples for all various reaction temperatures and at different durations. Additionally, the (Co, Ni)Sn2 phase was precipitated at the solder side and near the (Fe, Co)Sn2 phase when the reaction time increased. The thickness of the (Fe, Co)Sn2 phase increased with the increase in reaction temperature and time, and it was proportional to the square root of the reaction time. Overall, our results showed that the growth mechanism of the (Fe, Co)Sn2 phase was diffusion-controlled in the Sn/CoCuFeNi couples.

Advanced Electronic Packaging Technology: From Hard to Soft

Packaging is a pivotal step in electronic device manufacturing, determining the translational performance of bare chips [...].

Paper Batteries: A Flexible and Multifunctional Energy Storage Technology

Abstract: Paper batteries are a new class of flexible, lightweight, and low-cost energy storage devices that have the potential to revolutionize the way we use and interact with energy. They are formed by combining carbon nanotubes with a conventional sheet of cellulose-based paper, resulting in a thin and flexible device that has a high specific energy and power density. In addition to their energy storage capabilities, paper batteries can also be used as a platform for the integration of other functional materials and devices, such as sensors, transistors, and energy harvesting elements. This makes them a versatile and multifunctional technology with a wide range of potential applications, including in portable electronic devices, smart packaging, and wearable technology. In this paper, we review the current state of the art in paper battery research and development, including the materials and fabrication methods used to create these devices, their electrochemical performance, and their potential applications. We also discuss the challenges and opportunities that lie ahead for the further development and commercialization of paper batteries.

Preparation and Heat Dissipation Performance of Vertical Graphene Nanosheets/Carbon Fibers Composite Film

High-efficient heat dissipation materials are urgently required in advanced electronic packaging technology because effectively releasing the internal heat flow density of electronic devices is a key factor during their operation. In this work, a novel vertical graphene nanosheets/carbon fibers (VGNs/CF) composite film, with a vertically oriented structure and excellent heat dissipation properties, is fabricated on the stainless steel substrate by a facile thermochemical growth method. The preparation of composite film is green, safe, and highly efficient. CF is used as a thermally conductive filler to provide thermal conductivity channels for VGNs, and both of them construct a continuous thermally conductive network. The through-plane thermal conductivity of the VGNs/CF composite film could reach 17.7 W/(m·K), and the addition of CF significantly improved the heat dissipation performance of the composite film compared with the pure VGNs film (13.9 W/(m·K)). Conclusively, the simple preparation method and outstanding thermal conductivity capacity of the VGNs/CF composite film are expected to meet the application requirements of the electronics industry.

Assessment of AF4 Parylene Cohesion/Adhesion on Si and SiO2 Substrates by Means of Pull-Off Energy

Advanced packaging solutions require insulation and passivation materials with exceptional properties which can also fulfill the reliability needs of electronics devices such as MEMS, sensors or power modules. Since bonding (cohesive/adhesive) properties of packaging coatings are very important for reliable functioning of electronics devices, the bonding of aliphatic fluorinate-4 (AF4) parylene coatings was assessed in this work. As there is a lack of data regarding its bonding towards different substrates, pull-off tests of 1.6 and 2.5 μm thick AF4 coatings on silicon (Si) and glass (SiO2) substrates were performed. These showed a clear difference in the pull-off F/s curves between the AF4 coatings on Si and SiO2 substrates. This difference is parameterized by the pull-off energy, which will be presented in this work. To further understand the origin of the distinction in the pull-off energies between the AF4-Si and AF4-SiO2 samples and subsequently the cohesive/adhesive properties, mechanical and structural characterization was conducted on the AF4 coatings, where a clear difference in the E-modulus and crystallinity was observed. The Si and SiO2 wafers were shown to facilitate the CVD growth of the AF4 film distinctively, which likely relates to the divergent thermal properties of the substrates. Understanding of the cohesive/adhesive properties of AF4 coatings on different substrate materials advances the usage of the AF4 in electronics packaging technologies.

Failure-oriented-accelerated-testing (FOAT) and its role in assuring electronics reliability: review

A highly focused and highly cost-effective failure-oriented-accelerated-testing (FOAT) suggested about a decade ago as an experimental basis of the novel probabilistic design for reliability (PDfR) concept is intended to be carried out at the design stage of a new electronic packaging technology and when high operational reliability (like the one required, e.g., for aerospace, military, or long-haul communication applications) is a must. On the other hand, burn-in-testing (BIT) that is routinely conducted at the manufacturing stage of almost every IC product is also of a FOAT type: it is aimed at eliminating the infant mortality portion (IMP) of the bathtub curve (BTC) by getting rid of the low reliability “freaks” prior to shipping the “healthy” products, i.e., those that survived BIT, to the customer(s). When FOAT is conducted, a physically meaningful constitutive equation, such as the multi-parametric Boltzmann-Arrhenius-Zhurkov (BAZ) model, should be employed to predict, from the FOAT data, the probability of failure and the corresponding useful lifetime of the product in the field, and, from the BIT data, as has been recently demonstrated, - the adequate level and duration of the applied stressors, as well as the (low, of course) activation energies of the “freaks”. Both types of FOAT are addressed in this review using analytical (“mathematical”) predictive modeling. The general concepts are illustrated by numerical examples. It is concluded that predictive modeling should always be conducted prior to and during the actual testing and that analytical modeling should always complement computer simulations. Future work should be focused on the experimental verification of the obtained findings and recommendations.