CSPs for Portable Electronics

The Wafer Level Chip Scale Package (WLCSP) is gaining popularity for its performance and for its ability to meet miniaturization requirements of portable consumer electronics, such as cell phones. Due to differential bending between the silicon die and the PCB and the large stiffness difference, board level drop/bend tests are widely accepted methods to evaluate damage in the parts when a handheld device is dropped by the consumer. Through an aggressive product development program which includes experiment and simulation Amkor has developed the next level of WLCSP (CSP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nlTM</sup> ), a product which exhibits superior board level reliability when subjected to drop impact, a strong requirement for portable electronics. The common industrial qualification criterion is for the product to withstand at least 40 drops before first failure (FF) under the JEDEC drop test condition of 1500 G/0.5 ms. With optimal CSP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nl</sup> and PCB designs, recent test results show that a typical Amkor CSP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nl</sup> with a die size of 5.4 mm × 5.4 mm has a minimum failure-free life of over 1000 drops. For an enhanced CSP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nl</sup> design, first-failure life of 4860 drops. was recorded in actual drop testing. These excellent results imply that much larger die are possible for future CSP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nl</sup> products, opening the door for wider applications of WLCSP devices, e.g. in next-generation portable electronics with greater function integration.

The industry demand for high-capacity cells with a small footprint is a result of demands for improved products and new applications. However, this presents challenges in terms of safety. While standards, such as UL 1642, have been developed for battery safety assessment, including impact testing, this paper shows that cell manufacturers are facing difficulties with UL 1642 safety tests. This is leading to alterations in the test procedures, where `golden samples' are tested, while production cells cannot pass the safety tests. This is a flaw in the process that is being accepted by UL. This paper reviews the UL 1642 standard and similar standards used in portable electronics, provides experimental support for the concerns, and presents recommendations.

Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mAh/g), low density (0.59 g/cm3) and the lowest negative electrochemical potential (-3.04 V vs. the standard hydrogen electrode, SHE). Li battery based on Li metal anode is expected to have an order of magnitude higher energy density than today's Li-ion battery. This will enhance energy and power capability of battery devices used in portable electronics, hybrid electric cars, aerospace, telecommunication, military, etc.). The Li metal battery will fulfill the high energy demand that cannot be met through the current Li-ion batteries (e.g. all electric transportation or many other applications which require light weight, high energy density, high power density batteries with small battery footprint and safest). But, to date, uncontrolled dendritic Li growth and limited Coulombic efficiency (CE) during Li deposition/stripping of a bulk Li anode, are the main reason behind low cycle life, which has limited their practical applications. Furthermore, the rate of dendrite growth gets amplified when the cell is cycled at high charge-discharge current density, high charge voltage, and high areal discharge. Increasing anode surface area would reduce the effective charge/discharge current. Additionally, thin films and high surface area Li anodes exhibit high ionic and electronic conductivity contributing to the high efficiency of the current collection required for high capacity battery. Although low CE can be partially compensated by an excess amount of Li (at the expense of lower useable Li energy), fire and other hazards associated with the dendrite growth have limited the development of rechargeable Li metal batteries. Most approaches to dendrite prevention focus on improving the stability and uniformity of the solid-electrolyte interface (SEI) on the bulk Li surface by adjusting electrolyte components and optimizing SEI formation additives. It is very difficult to achieve sufficient passivation on Li electrode due to the thermodynamic instability of Li with electrolytes [1,2]. As an alternative, various mechanical barriers have been proposed to block dendrite penetration [3]. These approaches rely on a strong mechanical barrier provided by an SEI film or a separator to suppress Li dendrite penetration but do not change the fundamental, self-amplifying behavior of the dendrite growth. Also, it is hard to find a mechanical barrier material with required shear modulus (required > 109 Pa) with desired conductivity. In other words, these methods did not prevent Li dendrites from growing during long-term cycling at high charge-discharge current density, high charge voltage, and high areal discharge, or hardly improved the CE and safety in Li deposition/stripping which is not suitable for practical rechargeable Li batteries [1]. We have developed a novel ionic-electronic-mechanical membrane (an artificial SEI), which allows long-term Li cycleability and improved safety by reducing dendrite formation. The new artificial SEI is comprised of three different materials to fulfill the desired SEI criteria such as: (a) facilitate uniform Li ion dispersion and deposition on entire Li surface, (b) desired SEI conductivity (c) mechanical separation of Li and electrolyte and flexibility to contain anode volume change during Li stripping and deposition. The combined effect of the invented SEI result into more than 300% increase in number of cycles and 3-4 times increase in usable Li energy density (i.e. high Coulombic efficiency (CE)) of a wet battery composed of protected Li metal anode, liquid electrolyte (e.g. lithium hexafluoro arsenate, LiAsF6) and Li-ion cathode (e.g. lithium cobalt oxide, LCO) for the advancement of a battery beyond the state-of-the-art Li-ion battery. The added advantage of the invented SEI is improved safety due to suppression of dendrite growth by mechanically strong/flexible SEI and controlled, uniform deposition/stripping of Li from Li anode surface. The protected Li anode may be incorporated into wet cell batteries or solid state batteries having transition metal oxide cathodes (more specifically the state-of-the-art Li-ion cathodes) or Sulfur cathode (Li-S battery) or Oxygen cathode (Li-O2 battery). Moreover, similar methodologies can be applied to other rechargeable metal anodes (Na, Al, Mg, etc.) used in batteries.

A freestanding, binder-free flexible polypyrrole: polystyrene sulfonate/cellulose nanopaper (PPy:PSS/CNP) electrode is successfully fabricated by a low-cost, simple, and fast vacuum filtration method for the first time. The hierarchical structure of CNP with high surface area and good mechanical strength not only provides a high electroactive region and shortens the diffusion distance of electrolyte ions, but also mitigates the volumetric expansion/shrinkage of the PPy during the charging/discharging process. The optimized PPy:PSS/CNP exhibits a high areal specific capacitance of 3.8 F cm−2 (corresponding to 475 F cm−3 and 240 F g−1) at 10 mV s−1 and good cycling stability (80.9% capacitance retention after 5000 cycles). The cyclic voltammetry curves of PPy:PSS/CNP at different bending angles indicate prominent flexibility and electrochemical stability of the electrode. Moreover, a symmetric supercapacitor device is assembled and delivers a high areal energy density of 122 µ cm−2 (15 W h cm−3) at a power density of 4.4 mW cm−2 (550 mW cm−3), which is superior to other cellulose-based materials. The combination of high supercapacitive performance, flexibility, easy fabrication, and cheapness of the PPy: PSS/CNP electrodes offers great potential for developing the next generation of green and economical portable and wearable consumer electronics.

Modern high-performance processors are embedded in portable electronics, such as smartphones, self-driving automobiles, and augmented reality wearable. These computing platforms provide real-time direction navigation, high definition video entertainment, real-time sensing and control. One of the major performance limiting factors in these platforms is the poorly designed thermal solution to prevent overheating at the processor transistor junction and at the platform surface. The former limits the maximum operating temperature of transistors to guarantee reliability and lifetime whereas the latter limits the maximum platform surface temperature to ensure user ergonomic comfort. To design effective cooling solutions for high-performance, multi-layer, multi-processor platforms, an accurate and detailed platform level temperature model is needed. In this work, we present a detailed finite volume model to predict the temperature behavior of a tightly packaged, high-performance portable platform, from the system level down to the processor architecture level. We first characterize the thermal response of real-world, representative mobile workloads and perform parametric studies to predict the processor junction and platform surface temperature based on the properties of the platform. We observe that thermal hot spots are sensitive to workload computation characteristics. In particular, for mobile workloads, such as web browsing, computations often occur in short time burst, leading to instantaneous power spikes. This results in temperature spikes as thermal hot spots. To mitigate the thermal issue, modern systems implement dynamic voltage and frequency scaling during high performance and high power scenario to prevent cores from overheating. We validate the proposed temperature model used to predict the maximum temperature at the processor chip and at the platform surface, with measurements from the embedded temperature sensors and an infrared camera. The temperature prediction accuracy for hot spots on the processor chip and on the platform surface is demonstrated to be higher than 90%. With the tool, we show that the physical construction (such as air gaps and material properties) and the floor plan of the multi-layer platform have a profound effect on the system temperature behavior. As the air gap between the different layers of the computing platform increases, the processor temperature rises significantly. Also there exists an optimal thickness setting of the air gap for platform surface thermal spreading. We hope the detailed characterization results, the developed temperature prediction tool, and the insights presented in the paper can motivate advanced thermal management solution for high-performance embedded platforms in the years to come.

Enhanced specific capacity and cycling stability of flexible nanocellulose-based pseudocapacitive electrodes by controlled nanostructuring of polyaniline

Commercial LED drivers, especially for street-light applications, mandate high performance, low cost and reliable operation. In this paper, an enhanced performance single-stage LED driver is proposed. The proposed topology adopts a fly-back based single-phase line-rectifier. The flyback converter's duty cycle is designed offline to achieve a unity power factor without an input filter. A double line frequency π-network CLC filter is utilized, featuring a reduced-value long-life ceramic non-polarized capacitor. The presented topology offers: (i) unity power factor operation, (ii) reduced LED current ripples, (iii) small footprint, (iv) non-polarized capacitor implementation, and (v) high reliability. LED driver prototype is implemented and attested. Simulation in addition to experimental results validates the proposed topology effectiveness.

Textile-based triboelectric nanogenerators with high-performance via optimized functional elastomer composited tribomaterials as wearable power source

Advanced flexible electrode materials and structural designs for sodium ion batteries

With the rapid and ever increasing growth in portable electronics, such as smartphones and tablet computers, and the growing need for safer and longer range electric and hybrid powered vehicles, there has never been a more prevalent demand for light weight, high performance batteries with high power and energy densities. Commercial Li-ion batteries are just about keeping up with advancements in electronics. However, the limited performance of today’s commercial batteries is common knowledge, with the majority of hand held electronic devices requiring charging every day. Identifying and preparing battery materials which are capable of high performance, fast charging, and stable, safe capacity retention during operation would significantly advance portable device power technology. Germanium based anode materials have attracted a lot of attention due to the high theoretical capacity of Ge (1384 mAh/g) with various nanostructures such as nanowires, nanotubes and nanoparticles being investigated as anode materials. (1-3) However the cost of preparing pure Ge nanostructures can be quite high due to the use of expensive anhydrous precursors such as diphenylgermane and the need to perform synthesis under an inert atmosphere. These factors would also impede scaling up the synthesis of these materials for industrial applications. To circumvent these issues we are investigating the electrochemical performance of GeO2 with an inverse opal (IO) morphology, which can be prepared in air using cheaper precursors. In this work we detail the preparation of GeO2 IOs with application as anode materials for Li-ion batteries. The IO samples are initially structurally characterised via electron microscopy, electron diffraction and X-ray diffraction. We demonstrate the electrochemical evaluation of our GeO2 IO samples with cyclic voltammetry, rate capability testing and long cycle life (>1000 cycles) galvanostatic testing. Previous reports on the electrochemical performance of GeO2 as an anode material have indicated that the capacity values obtained from the oxide are lower than those obtained from pure Ge. However, we demonstrate that by preparing a highly ordered, porous, three dimensionally interconnected network of GeO2 in the form of an IO, we can obtain capacity values which are comparable to the highest values previously reported for pure Ge. Acknowledgements This work was also supported by Science Foundation Ireland (SFI) through an SFI Technology Innovation and Development Award under contract no. 13/TIDA/E2761. This publication has also emanated from research supported in part by a research grant from SFI under Grant Number 14/IA/2581.

In the last few years fuel cells have attracted much interest from both academic and industrial researchers to replace current lithium-ion and similar rechargeable battery systems. A wide variety of research areas benefit from fuel cell use: electro-chemical, stationary, transportation and portable electronics can be cited as an example. Potential applications range from few watts to megawatts systems. Even concerning quite different scientific areas, fuel cell modelling is a common requirement. The complexity of such a topic relies not only on the modelling approach but also in the model structure and implementation. In this paper a steady state and dynamic fuel cell circuital model including temperature effects is presented. As an example, the MATLAB/Simulink model of a 10W Proton Exchange Membrane Fuel Cell is shown. The proposed modelling approach can be efficiently applied to any kind of fuel cell and implemented on several simulation environments, keeping high performances. The trade-off between complexity and accuracy is investigated and the comparison between experimental and simulation results shows the high efficiency and accuracy of the proposed model.

Nowadays, efficient, safe, low cost and environmentally friendly storage systems are required in response to the modern society needs. Li-ion batteries (LIBs), considered one of the promising systems to fulfill these requirements, represent the most widespread secondary battery for consumer and portable electronics and possibly for power hybrid and electric vehicles.[1] Stationary energy storage, in contrast to high energy density applications, is principally driven by cost rather than high performances in terms of energy density. Therefore, batteries with alternative chemistry, complementary to and not competing with the lithium-ion battery technology are necessary.[2,3] Recently, sodium-ion batteries have attracted large attention since, in principle, suitable to match the economic and environmental issues due to the high abundance and low cost of the employed materials.[4,5]Herein, we report a study on P-type layered sodium transition metal-based oxides, of the composition NaxMO2 (M=Ni, Fe, Mn), used as cathode materials for sodium-ion batteries employing a 1M NaPF6 in propylene carbonate (PC) as electrolyte solution.[6] Indeed, P-type layered oxides appear to be very promising in terms of high delivered capacity. [7,8] We synthesize the materials via co-precipitation method followed by an annealing step in air and a water rinsing process. Following, we fully investigate the effect of Ni to Fe ratio, annealing temperature and sodium content on the electrochemical performances of the electrodes. The impact of these parameters on the structural and electrochemical properties of the materials is revealed by X-ray diffraction, scanning electron microscopy and cyclic voltammetry, respectively. The suitability of this class of P-type materials for sodium battery application is finally demonstrated by cycling tests revealing an excellent electrochemical performance, with a delivered capacity of about 200 mA h g-1and charge-discharge efficiency approaching 100 %. [1] J.-M. Tarascon, M. Armand, Nature,414, 359 (2001); [2] J.-M. Tarascon, Nat. Chem., 2, 510 (2010) ; [3] B. W. Jaskula , Lithium, in Mineral Commodity Summaries 2012 , U. S. Geological Survey , Reston, VA 2012 , p. 94; [4] V. Palomares, P. Serras, I. Villaluenga, K.B. Hueso, J. Carretero-Gonzalez, T. Rojo, Energy Environ. Sci., 5, 5884 (2012); [5] S.-W. Kim, D.-H. Seo, X. Ma, G. Ceder, K. Kang, Adv. Energy Mater., 2, 710 (2012); [6] I. Hasa, D. Buchholz, S. Passerini, J. Hassoun, ACS Appl. Mater. Inte., (2015) in press; [7] I. Hasa, D. Buchholz, S. Passerini, B. Scrosati, J. Hassoun, Adv. Energy Mater. 2014, doi:10.1002/aenm.201400083; [8] N. Yabuuchi, M. Kajiyama, J. Iwatate, H. Nishikawa, S. Hitomi, R. Okuyama, R. Usui,Y. Yamada, S. Komaba, Nature Mater., 11, 512 (2012); Figure 1

Non-military/noncomputer electronics industry segments such as PC's, workstations, portable electronics, the automotive and medical industries, automated test equipment, and high-end consumer goods, are evolving rapidly. They demand higher complexity and higher performance circuits and components. At the same time, many of these industry segments are being driven to shrink size, weight, and power dissipation. Standard low cost packaging approaches such as thru-hole PCB and chip and wire hybrids, can no longer efficiently interconnect these more complex circuits. These industry segments are being forced to turn to new higher performance packaging approaches such as SMT, MCM, and COB. This paper describes an innovative embedded chip MCM technology that eliminates high cost structures, as well as materials and processes in current thin film MCM technologies. A plastic encapsulated multichip technology has been developed in which an epoxy encapsulant is molded around bare die to form the MCM substrate. This new MCM process readily scales-up to high volume production and is inherently high yielding, while maintaining all of the performance advantages of the GE developed overlay HDI process. This paper describes the thermal, mechanical, and chemical stability issues that drove this development, the process used to fabricate the modules, and the cost and yield advantages associated with this structure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In this work, nanogenerator (NG) devices based on gallium-doped zinc oxide (ZnO) nanorods (NRs) (Ga-doped ZnO NRs) were triumphantly developed and explored by a simple fabrication process. All one-dimensional (1-D) nanostructures were hydrothermally grown on an indium-tin-oxide (ITO) substrate at a low temperature of 90 °C for 6 h. After field-emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), and high-resolution transmission electron microscope (HR-TEM) measurement, a hexagonal wurtzite structure with good single crystallinity was exhibited, and a preferential growth with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${c}$ </tex-math></inline-formula> -axis direction was revealed. The optical properties of all samples were annealed at high temperature and explored through photoluminescence (PL) spectroscopy, displaying two different emission peaks, including ultraviolet (UV) and green emissions. The compositions of the NRs were also examined by an X-ray photoelectron spectroscopy (XPS) and an energy-dispersive X-ray (EDX) spectroscopy. As a result, the performance of ZnO NGs with Ga elements exhibits an outstanding improvement in electrical measurements compared with ZnO NGs. Furthermore, the output voltage and current of Ga-doped ZnO NG under UV irradiation were approximately 0.053 V and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.86\times10$ </tex-math></inline-formula> −6 A, respectively. It is attributed to produce numerous electrons by UV light and Ga dopant. The designed NG in this article may collect electrical energy in the people’s surroundings and has potential Internet of Thing applications (e.g., portable electronics, wireless devices, and implantable biomedical sensors).

Portable electronic products subjected to transient shock may exhibit multiple failure modes in vicinity of the interconnects. Failure is often diagnosed by loss of functionality using techniques including the built-in self test, which provides limited insight into reliability and remaining useful life. In this paper prognostic framework for electronic systems has been developed with neural network based self organizing maps. The presented approach resides in the pre-failure space with a focus on electronic systems with multiple failure modes. Unsupervised learning of the neural net has been used to train the neural net for identification of individual failure modes. Feature vectors have been developed based on damage pre-cursors from time-spectral measurements. The clustered damage pre-cursors have been correlated with failure modes of the underlying damage. Several chip-scale packages have been studied, with leadfree second-level interconnects including SAC305, SAC405 alloys. Transient strain has been measured during the drop-event using digital image correlation and high-speed cameras operating at 100,000 fps. Continuity has been monitored simultaneously for failure identification. In addition, explicit finite element models have been developed and various kinds of failure modes have been simulated such as solder ball cracking, trace fracture, package falloff and solder ball failure. Fault modes predicted by simulation based pre-cursors have been correlated with those from experimental data. Activation of different neurons in the lattice for various failure modes and combinations of failure modes has been demonstrated. Previously the authors have developed techniques based on statistical pattern recognition for leading indication of impending failure and detection of damage initiation and progression [Lall 2006 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sup> , 2007 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sup> , 2008]. Early classification of multiple failure modes in the pre-failure space is new.