This case analysis evaluates the thermal profile of 10 FETs rated at 48V, 250A under 100 secs soak time with all the thermally enhanced mechanical attachments installed. The goal was for the MOSFETs to operate at 8W peak power output, maintaining a temperature of no greater than 60°C – applying all the thermal handling enhancements. RSENSE installed targets to have the minimum allowable temperature after MOSFET’s thermal analysis. The setup is a household thermal mechanism to handle average power level systems that involve mounting of heatsink on the bottom side, attaching the RSENSE, and employing filled vias. Thermal simulations were conducted using 2D Solver for several power ramp cases and CFD (Computational Fluid Dynamics) to analyze the Airflow Application. 2D Solver investigated the electrical and thermal performance over a sweep of conditions. Boundary conditions were met at approximately 50°C measured as the highest measured temp on the range of installed MOSFETs. Thermal performance was furtherly improved by 5°C less after employing the airflow mechanism. Airflow design was modeled and simulated using CFD Solver and yielded the best thermal setup results.

Liquid metal alloys (LMAs), GaIn, and Galinstan, have been paid considerable attention as thermal interface materials (TIM) for usage of thermal management in microprocessor packages, including CPU, GPU and HPC, in PCs and super computers. However, automating mass production of LMA for TIMs presents challenges due to the change of rheologic behavior whichis associated with the oxidation of Gallium (Ga) during deposit process. In the present paper, we will report our recent research on developing novel TIMs of LMAs containing organic additives (LMO) to enhance deposit process performance of LMAsfor thermal management in electronics devices, especially for IC modules. In this research, we prepared LMO by addition of organic additives to LMAs and investigated the influence of organic compounds on viscosity, storage (G’) and loss (G”) modulus, adhesion and oxidation of the LMAs, and deposit process performance. Viscosity of LMOs and LMAs over time was measured at various shear rates of 10 (1/s) and 100 (1/s) using an industry standard rheometer, to study influence of the organic additives on the viscosity of LMAs. Storage (G’) modulus versus strain swing at the strain range of 0.1 – 100 % strain was measured to investigate effect of the organic additives on storage (G’) and loss (G”) modulus of LMAs. Dots of LMA and LMO materials were deposited by industry standard dispensers on Cu PCB board and Cu OSP FR4 coupons and the consistency and stability of the materials were evaluated. In addition, adhesion and wetting properties of the dispensed dots of LMOs and LMAs on Cu PCB, OSP Cu FR4 coupons, glass and bare Si, respectively, were extensively investigated.. Key words: Liquid metal, EGalinstan, viscosity, modulus, thermal conductivity and resistance, thermal interface material (TIM).

Modern electronics are prone to experience electromagnetic interference (EMI) which hinders proper functioning of the devices due to the increasing number of wireless devices and the miniaturization. In applications such as advanced driving assistancesystem (ADAS) and autonomous vehicles, electronic sensors tend to use higher frequency (<80GHz) radio waves to increase the resolution and comply with the regulation. Also, as modern electronic devices become more power intensive and generate more heat, proper heat dissipation from the devices is critical to prevent failure. Therefore, it is desirable to develop EMI shielding material that absorbs high frequency radio waves and thermal interface material (TIM) that facilitates efficient heat transfer within the components. In comparison to implementing two separate EMI shielding material and thermal interface material, it is beneficial to develop a single material that has both the capabilities to reduce cost and processing time. We have implemented various dielectric and magnetic fillers to study the thermal conductivity and EMI shielding across wide wavelength range (<80 GHz). Fillers that are both thermally conductive and absorb high frequency radio waves provide a significant advantage in designing the formulation for the application. The design principle to optimize the EMI shielding (reflection/absorption) for high frequency and thermal conductivity requires good understanding of the dielectric and magnetic property of the fillers. Along with EMI shielding and thermal conductivity, proper design of the polymer-based matrix is critical to achieve proper rheological, mechanical property and temperature reliability of the material. We will present performance, manufacturing, reliability of thermally conductive EMI shielding materials.

Thermal interface materials (TIMs) are ubiquitous in electronics cooling in a wide variety of applications in industrial, automotive and consumer electronics [1]. These materials are typically comprised of a soft polymeric matrix with thermally conductive fillers. By far the majority of TIMs are based on silicone polymers due to the special characteristics of thermal stability and ability to fine tune the modulus across a wide range [2]. Silicone migration– both vapor phase (outgassing) and liquid phase (bleed) – are known concerns of polymeric TIMs. With proper analysis of the application these concerns can be addressed by designing materials specifically for such applications. Migration is dependent on both TIM microstructure and application details like power density, thermal stack up and physical layouts. We will describe the underlying cause of polymer migration, possible risks, and mitigation measures.

In a previous paper [8], solid liquid hybrids (SLHs) were presented as a combination of metals that are solid at room temperature with ones that are liquid at room temperature. Those materials were categorized into liquid metal composites (liquid metal with solid metal preforms) and hybrid liquid pastes. That paper showed that adding solid metals to liquid metal can improve the properties of TIMs to yield “leakage-free” TIM, in which none of material will be pumped out. Such materials are less prone to oxidation and be able to survive a larger number of thermal cycles. At the same time, liquid metal will provide low interface resistance, which will result in lower thermal resistance. This paper focuses on the first type of SLH TIMs, known as liquid metal composites (LMC), in which different types of solid metals in LMCs—preforms, compressible TIMs, and reinforced matrixed solder composites (preforms with a copper matrix)—can be used in different TIM applications. The solid/liquid ratio of LMCs will not just define thermal resistance of the matrix, but it will also affect the reliability of the TIM. More liquid metal in LMCs will provide better thermal performance at time 0, but LMCs with a lower amount of liquid metal will perform better in thermal cycling. Another benefit of this material will be its performance during power cycling. Thermal resistance will be highly stable or can even decrease over time. This paper will show what types of LMCs will be recommended for different types of TIMs: TIM1, TIM2, and TIM1.5 (or TIM0). Finally, the most suitable type of automated process for high-volume production will be discussed for each of these LMCs.

In the present research, we have studied the influence of Ag additives on wettability, adhesion, oxidation, viscosity and modulus of liquid metal on two alloys – Liquid Metal 1 (“LM1”) (62.5Ga, 21.5In, 13Sn) and Liquid Metal 2 (“LM2”) (78.6Ga, 21.4In)– to develop new thermal interface materials for IC modules such as CPU and GPU in PC and game stations. In this study, liquid metals were first mixed with Ag powders of up to 1.5wt%, followed by treatment with 30wt% NaOH aqueous solution to remove the oxide in the liquid metal, to prepare liquid metal/Ag composites. Wettability and adhesion have been studied on bare Cu, and Ni/Au surface finish Cu. Contact angle of liquid metal with and without Ag powders was measured to evaluate wettability of liquid metal on bare Cu and Ni/Au Cu. Adhesion of the liquid metals with and without Ag additive on bare Cu and Ni/Au Cu were evaluated by temperature cycling test with a profile of -40oC to 125oC, dwell time of 20min at low and high temperature. Oxidation of the liquid metals on bare Cu and Ni/Au Cu substrate was monitored over time at ambient atmosphere and during temperature cycling test, followed by characterizing cross-section morphology with SEM. To investigate effect of Ag powders on viscosity, the viscosity was measured using a parallel plate viscometer. Thermal properties and performance of the prepared composite in this research will be evaluated by measurement of thermal resistance and conductivity, respectively.

Keyword: Liquid metal, 51E, 300E, wettability, oxidation, viscosity and modulus.

Light weight, conformal and portable standalone power solutions are becoming increasingly important for powering wearable electronics including fabric embedded sensors, to monitor the physiological and physical status of military personnel and civilians. Textile-based power-harvesting sources offer the advantage of conformability, light weight, drapability and breathability. We present the fabrication of Organic Photovoltaic (OPV) wires/fibers followed by the integration of the OPV into an electronic textile. A meniscus coating process is employed to fabricate a fiber-based OPV. Polished stainless-steelwire is used as a primary electrode that is coated with a titanium dioxide electron transport layer, followed by a coating of bulk-heterojunction Poly(3-hexylthiophene): phenyl-C61/71-butyric acid methyl ester (P3HT:PC61/71BM) active layer. A mixture comprising of a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) dispersion blended in a cross-linkable reactive diluent serves as the hole transport layer. A silver-plated copper wire serves as the secondary counter-electrode and is wrapped around the primary wire. The fiber device is then encapsulated in a UV-curable encapsulant that provides long-term stability by reducing the ingress of oxygen and water vapor. Performance and stability of these e-textiles are evaluated by characterizing the current- voltage (I-V) performance of the OPV fibers woven into a fabric. The appropriate selection of materials and the optimization of the coating parameters will enable the enhancement of power conversion efficiency (PCE) and stability of these power harvesting textiles for standalone, power.

Wearable devices for biomedical applications have become more popular due to the increasing demand on health monitoring for both consumer and medical fields. In this work, we describe a novel wireless wearable ElectroMyograph (EMG) acquisition and analysis system which employs reduced graphene oxide (rGO) coated Nylon/Polyester fabric sensors. The usability of graphene sensors was examined by comparing biceps EMG signals obtained from the graphene sensors to that from the standard Ag/AgCl sensors. Calf muscle EMG signals on both legs are measured to confirm the usability, the multi-sensor acquisition ability of the system. The measurement results indicate that graphene-based smart fabrics can be used as a viable alternative to non-reusable Ag/AgCl electrodes for high-quality EMG monitoring. The proposed EMG data acquisition and analysis device is small, lightweight providing a smart clothes platform for convenient health tracking.

Index Terms: ElectroMyography, reduced graphene oxide, e-Textiles, health monitoring, wearable

SINTEC is the project name for a Liquid metal alloy technology with the goal of creating flexible and stretchable electronics.  These stretchable electronics are applicable to wearable sensors that collect motion data of humans.   The stretching allows direct application of wearable electronics to very dynamic parts of the body.  Liquid metal alloy can be needle deposited.  

Textile-based touch sensing offers a novel solution towards creating flexible and robust tactile interfaces that fit within an existing manufacturing ecosystem.  Current fabric-based touch sensors can measure distributed and nuanced touch while maintaining textile qualities such as stretching and folding.  Recent work as described the development of a single-wire capacitive touch sensing system that consists of a textile interface and external sensing hardware that transmit recorded data to a trained neural network.  The sensing method localizes touch along a continuous conductor using a current differential measured at either endpoint.  The requisite touch sensing circuit is fully compatible with digital weft knitting, and its layout can be configured in a a variety of pathways to create complete planar textile interfaces. Each interface requires only two connections to external sensing hardware, which allows both the hardware to be reused between interfaces and the data transmitted to the network to have a similar dimension.  

Previous work focused on identifying touch location at defined points on a fabric interface through training a recognition system using labeled data.  We extend this work towards gesture recognition by using a generated intermediate model to decouple the estimated linear touch location and capacitance from the measured data.  The intermediate model forms a manifold of the normalized linear touch location and capacitance within the space of measured data points.  A measured data point, acting as a particle, is tracked through the manifold and decoupled to a unique touch location and capacitance. The decoupled linear touch location is mapped to a planar model of the textile interface, which is generated from a user-defined image of the interface.  the use of digital modeling tools creates a closed-loop interface design process which allows designers to construct a visual representation of the fabric circuit and predict its sensing performance. 

Keywords: Functional Fabrics, e-Textiles, Capacitive Sensing, Signal Processing