Flexible Circuit Technology Research Articles

Stretchable and Transparent Interconnects With Hybrid Ag-Nanomesh/Indium Tin Oxide Structure

We demonstrate a hybrid structure for both transparent and stretchable interconnects, that provides high conductance, stretchability, and transparency simultaneously. In this structure, a serpentine-shaped discrete Ag nanomesh formed by the nanotransfer printing technique works as the primary conducting layer, while an indium tin oxide thin film covering it allows planar contact with other devices for proper functions as interconnects. We have confirmed that the hybrid serpentine interconnects provide high conductance and stretching reliability comparable to that of opaque ductile metals, and the transmittance and sheet resistance can be controlled independently by modifying the structural parameters of the mesh layer. Based on conventional photolithography and etching processes compatible with the current flexible circuit technology, the new hybrid interconnect can be utilized in various devices requiring highly integrated transparent and stretchable circuits.

Flex‐circuit resonant chip with Y5V multilayer capacitor for wireless temperature tracking

This paper reports the first wireless thermometric device enabled using a surface-mount capacitor microchip as the sensing element, offering a low-cost, disposable, and flexible sensor potentially suitable for a wide range of application areas. The device is developed in the form of a resonant-circuit chip, in which a Y5V-type multilayer capacitor microchip that exhibits significant temperature dependence serves as a thermoresponsive element that varies the resonant frequency of the circuit upon a temperature change. The wireless sensor chips prototyped in conjunction with the flex-circuit technology are tested to show their intended function with the frequency responses of up to 129 kHz/°C for ambient temperature variations. Wireless temperature tracking of a fluid-flowing channel is experimentally demonstrated using the prototype.

Electromagnetic Vibrational Energy Harvester With Microfabricated Springs and Flexible Coils

In this article, an electromagnetic vibrational energy harvester (EVEH) device has been designed and fabricated based on the hybrid microelectromechanical system and flexible circuit technology. The designed EVEH is composed of a disc magnet suspended by four microfabricated silicon springs above a stack of high-density flexible planar coils. At a sinusoidal acceleration with a peak-to-peak amplitude of 1 g, an output peak-to-peak voltage of 208.3 mV, and an output power of 10.5 μW are measured at the resonant frequency of 143 Hz. At an elevated acceleration of 7 g, a maximum output peak-to-peak voltage of 333.1 mV is realized with an increased magnet-coil distance of 0.65 mm.

Ultra-focal Magnetic Stimulation Using a µTMS coil: a Computational Study.

A new miniaturized figure-of-eight coil (μCoil) for TMS applications has been developed taking advantage of the Flex circuit technology. First experiments on volunteers demonstrated the ability of the μCoil to elicit sensorial action potentials of the peripheral nervous system. The necessity of reducing the size of standard TMS stimulator arises from the poor spatial resolution of the latter. This study aims to model the μCoil and study the electromagnetic fields induced inside the arm during peripheral nerve stimulation. Results confirmed that the μCoil is capable of inducing a focalized electric field inside the tissues with amplitudes up to 70V/m consistent with the observed peripheral nerve stimulation in healthy volunteers.

Stretchable active matrix of oxide thin-film transistors with monolithic liquid metal interconnects

We demonstrate a new process scheme for fabricating stretchable active matrices of oxide thin-film transistors (TFTs), where TFTs and cross points of two metal layers on stiff islands are monolithically integrated with gallium-based liquid metal interconnects within an elastomeric matrix. As the liquid metal interconnects are formed by a photolithography-based technique compatible with conventional flexible circuit technology, this approach can provide high integration density and mechanical durability as required in stretchable displays or electronic skins. We have fabricated a 4 × 4 active matrix of oxide TFTs within a 20 × 20 mm2 area, which provides stable operation up to 40% of stretching.

أسس تصميم الدوائر المرنة کأحد التقنيات المستخدمة في إنتاج الملابس الذکية.

ملخص البحث إرتبط مفهوم الموضة سابقا بالشکل الجمالي، ولکن حاليا دخلت عليها مستجدات متنوعة بفضل التقدم العلمي والتکنولوجيا، مما أدى إلى ظهور الذکية .فلم تعد وظيفة الملابس والمنسوجات تنحصر في الوظائف الجسدية فقط مثل الحماية ولکنها إمتدت لتشمل الجانب التکنولوجي أيضا عن طريق دمج التکنولوجيا في المنسوجات من أجل الحصول علي وظائف جديدة. فلقد أدي التقدم الهائل في تکنولوجيا المنسوجات والملابس الذکية ومجال الإلکترونيات إلي نشأة جيل جديد من الملابس الوظيفية الذکية، وبناءا عليه يهدف البحث إلي التعرف علي تکنولوجيا الدوائر الإلکترونية المرنة المستخدمة في تصميم الملابس الذکية وکذلک عرض للخامات والأدوات المستخدمة في تنفيذها علي الملابس. ويتناول البحث أسس ومباديء تصميم الدوائر المرنة علي الأقمشة من خلال التطبيق العملي لعدد ست عينات منفذة بإستخدام کل من الليدات - البطاريات – الخيوط الموصلة – الحساس الضوئي - مفاتيح للتحکم بفتح وغلق الدائرة الإلکترونية، مع تطبيق طرق التوصيل المختلفة للليدات مع البطارية کالتوصيل علي التوالي والتوصيل علي التوازي، وتوظيف بعض إکسسوارات الملابس کمفتاح لفتح وغلق الدائرة الإلکترونية. Summery The concept of fashion was previously associated with aesthetics, but now it has undergone various innovations through scientific progress and technology, leading to the emergence of smart clothing. Garments and textiles are no longer limited to physical functions such as protection and coverage, but they also extend to integrating technology into textiles for new function. The advancement of textile technology, smart clothing and electronics has led to a new generation of smart functional clothing. The research aims to identify the flexible circuit technology used in smart clothing design. Display of materials and electronic tools used in implementation samples. The research produce principles of soft circuit design on fabrics through the practical application of six samples were applied using: LEDs, batteries, conductive threads, light sensor and switches to control the opening and closing of the electronic circuit. Apply different ways of connecting LEDs with battery, such as parallel and Series circuit, and use some of clothing accessories as a switch to open and close the electronic circuit.

Optical Transceiver Module for 1.2 Tb/s Based on Flexible Circuit Technology

We present a versatile electro-optical packaging platform for optical transceiver modules suitable for very high aggregate I/O capacity, as required, for example, in (disaggregated) datacenters and servers. Real-estate limitations on the board or on the processor package laminate are overcome by using a flexible printed circuit board substrate that is folded around a solid body, resulting in a 3-D package assembly. A 48 $\text {Gb/s} \times 10$ Gb/s transceiver prototype is demonstrated as well as the design path toward a transceiver with 1.2-Tb/s aggregate I/O bandwidth. Accounting for large-scale manufacturing and deployment, we explicitly address the requirements of the optical, mechanical, thermal, and electrical interfaces as well as of all associated manufacturing processes.

Arbitrarily Shaped 2.5D Circuits using Stretchable Interconnects Embedded in Thermoplastic Polymers

A method to fabricate thermoplastically deformable electronic circuits is presented, with the intent of achieving low‐cost 2.5D free‐form rigid smart objects. This by utilizing existing flexible circuit technology based stretchable circuits, in combination with thermoplastic materials. After fabricating the circuit in a flat state, a thermoforming step shapes the device by heating it beyond its glass transition temperature, and pushing it against a mold. Preliminary tests show the feasibility to fabricate simple circuits using off‐the‐shelf circuit components; showing a minimal decrease in conductivity of the polyimide supported copper‐based interconnects.

HDI flexible front-end hybrid prototype for the PS module of the CMS tracker upgrade

The CMS tracker upgrade for the HL-LHC relies on different module types, depending on the position of the respective module. They are built with high-density interconnection flexible circuits that are wire bonded to silicon strip and pixel-strip sensors. The Front-End hybrids will contain several flip-chip bonded readout ASICs that are still under development. Mock-up prototypes are used to qualify the advanced flexible circuit technology and the parameters of the hybrids. This paper presents the Pixel-Strip (PS) mock-up hybrid in terms of testing, interconnection, fold-over, thermal properties and layout feasibility. Plans for circuit testing at operating temperature (-30̂) are also presented.

Planar patterned stretchable electrode arrays based on flexible printed circuits

For stretchable electronics to achieve broad industrial application, they must be reliable to manufacture and must perform robustly while undergoing large deformations. We present a new strategy for creating planar stretchable electronics and demonstrate one such device, a stretchable microelectrode array based on flex circuit technology. Stretchability is achieved through novel, rationally designed perforations that provide islands of low strain and continuous low-strain pathways for conductive traces. This approach enables the device to maintain constant electrical properties and planarity while undergoing applied strains up to 15%. Materials selection is not limited to polyimide composite devices and can potentially be implemented with either soft or hard substrates and can incorporate standard metals or new nano-engineered conductors. By using standard flex circuit technology, our planar microelectrode device achieved constant resistances for strains up to 20% with less than a 4% resistance offset over 120 000 cycles at 10% strain.

Note: Cryogenic microstripline-on-Kapton microwave interconnects

Simple broadband microwave interconnects are needed for increasing the size of focal plane heterodyne radiometer arrays. We have measured loss and crosstalk for arrays of microstrip transmission lines in flex circuit technology at 297 and 77 K, finding good performance to at least 20 GHz. The dielectric constant of Kapton substrates changes very little from 297 to 77 K, and the electrical loss drops. The small cross-sectional area of metal in a printed circuit structure yields overall thermal conductivities similar to stainless steel coaxial cable. Operationally, the main performance tradeoffs are between crosstalk and thermal conductivity. We tested a patterned ground plane to reduce heat flux.

Characterization of defects in flexible circuits with ultrasonic atomic force microscopy

Flexible circuit technology is a key factor in the continued shrinkage of microelectronic components and devices. One of the important applications of the flexible circuits is in hard disk drive industry, where they are used as an interconnection between the preamplifier and head slider assembly of a hard disk drive. At present, defect characterization of flexible circuits is often performed after manufacture usually with optical microscopy. While this may be sufficient for certain low-tech applications, for advanced ultra high-density hard disk components may not be enough. With a continuing reduction of the dimension of the current carrying conductor wires, the size of defects that may affect long-term reliability of the system is reaching the resolution limit of traditional techniques used to characterize the defects. This paper presents combined application of atomic force microscope (AFM) and ultrasonic atomic force microscope (UAFM) to characterize defects in flexible circuits. Three identical flexible circuits from different manufactures are examined using AFM and UAFM. The AFM and UAFM images of a particular region, in the flexible circuit in all the three samples are compared. Images from pure polymer region of the flexible circuit are compared with the images of the regions containing copper and polymer. In general, the UAFM images show subsurface features while AFM images show surface topography. This capability of UAFM can be used to image the grain structure of the copper film without removing the polymer cover layer film. It also detects the sub-micron defects present at the polymer/metal interface. Analysis of the grain structure of copper, distribution of defects at the polymer/metal interface is presented. Based on these observations, the applicability of AFM/UAFM to image the microstructure of copper in flexible circuits and possible effect of defects in flexible circuits on the long-term reliability of the hard disc drive are discussed.

High-Speed Flex-Circuit Chip-to-Chip Interconnects

High-speed chip-to-chip interconnect utilizing flex-circuit technology is investigated for extending the lifetime of copper-based system-level channels. Proper construction of the flex ribbon is shown to improve the raw bandwidth over standard FR-4 boards by about three times. Active testing results from a 130-nm CMOS test vehicle show the potential of up to two times higher data rates. The next-generation test vehicle with 90-nm CMOS circuits gives improved voltage and timing margins at 20 Gb/s. In an interconnect limited case a channel with 36 in (91.4 cm) of flex runs at 18.2 Gb/s data rate at a bit-error ratio (BER) of better than 10-12. The channel includes two 90-nm CMOS test chips, two organic flip-chip package substrates, and two flex connectors; crosstalk is not included in this experiment. High-speed connector solutions, including results from a ldquosplit socketrdquo assembly test vehicle, are discussed in detail. The characterization of two top-side flex connector prototypes demonstrates their basic durability and good high-frequency performance. Samples survive 100 mating cycles at an average contact resistance of less than 30 mOmega, adequate for high-speed signaling. Measured differential insertion loss is less than 1.5 dB up to 10 GHz and less than 3.5 dB up to 20 GHz. Near-end and far-end crosstalk measurements indicate that the connectors exceed crosstalk specifications.

Electromagnetomechanical coupling characteristics of plastoferrites

The impetus of this work was to investigate the electromagnetic and tensile properties of several commercially available plastoferrites (PFs) at ambient conditions. The approach involved selection of a set of PFs and measuring their complex effective permittivity ε=ε′−jε″ and permeability μ=μ′−jμ″ under uniaxial stress at microwave frequencies (0.1–4.5GHz) and room temperature. We analyze the ε and μ spectra for tensilely strained PFs up to 3%. Comparing our experimental ε data against several dielectric relaxational behaviors, we find that the main physics cannot be understood with a single relaxation mechanism. We then go on to consider the magnetic permeability spectra in the microwave range of frequencies and show that an appropriate magnetization mechanism is given by the gyromagnetic spin resonance mechanism. We use a combination of Bruggeman mean field analysis and Landau-Lifshitz-Gilbert modeling to reproduce the experimental bimodal line-shape characteristics of the effective complex magnetic permeability. These findings are discussed in light of the polydispersity in size of the ferrite gains contained in the PFs. The vibrating sample magnetometry investigations of the static magnetization are found to be consistent with this modeling. In addition, the analysis shows also how magnetized PFs respond to electromagnetic waves, and we evaluate the hysteretic behaviors of ε and μ. More importantly we show that the ε and μ measurements under stress can be explained in terms of a Gaussian molecular network model in the limit of low stress. The present results have important applications in magnetoactive smart composite materials, e.g., flexible circuit technology in the electronics industry (sensors, actuators, and micromechanical systems), functionalized artificial skin, and muscles for robotic applications.

Low-cost microelectrode array with integrated heater for extracellular recording of cardiomyocyte cultures using commercial flexible printed circuit technology

This article reports the use of commercial, flexible printed circuit technology for the fabrication of low-cost microelectrode arrays (MEAs) for recording extracellular electrical signals from cardiomyocyte cultures. A 36-electrode array has been designed and manufactured using standard, two-layer, polyimide-based flexible circuit technology, with electrode diameters of 75 and 100 μm. Copper structures defined on the backside of the array have been used for low-power thermal regulation of the culture. Electrical characterization of the gold-plated electrodes showed impedances below 250 kΩ at 1 kHz. Functional testing was conducted using HL-1 cardiac myocytes. The arrays proved biocompatible, and supported the formation of functional syncytia, as demonstrated by electrical recordings of depolarization waves across the array. A comparison with conventional, glass-based MEAs is presented, which reveals differences in signal strength (smaller for larger electrode) and variability (less for larger electrodes), but no effect of the substrate types on culture parameters such as beat rate or conduction velocity. The performance of the on-chip heating was evaluated, with typical temperature settling times (to ±0.1 °C) below 10 s, for a power consumption around 1 W (at 37 °C). Accuracy and stability are discussed. HL-1 cell responses to various temperature profiles enabled by the on-chip heating are presented, showing a remarkable correlation between temperature and beat rate.

Application of Cu-polyimide flex circuit and Al-on-glass pitch adapter for the ATLAS SCT barrel hybrid

We applied the surface build-up Cu-polyimide flex-circuit technology with laser vias to the ATLAS SCT barrel hybrid to be made in one piece from the connector to the electronics sections including cables. The hybrids, reinforced with carbon–carbon substrates, provide mechanical strength, thermal conductivity, low-radiation length, and stability in application-specific integrated circuit (ASIC) operation. By following the design rules, we experienced little trouble in breaking the traces. The pitch adapter between the sensor and the ASICs was made of aluminum traces on glass substrate. We identified that the generation of whiskers around the wire-bonding feet was correlated with the hardness of metallized aluminum. The appropriate hardness has been achieved by keeping the temperature of the glasses as low as room temperature during the metallization. The argon plasma cleaning procedure cleaned the contamination on the gold pads of the hybrids for successful wire bonding, although it was unsuccessful in the aluminum of the pitch adapters.

Interactive Guide to Flexible Circuit Technology produced by Teknoflex

Interactive Guide to Flexible Circuit Technology produced by Teknoflex

Inspection and Test of Flexible Circuits

This article comprises Chapter 6 from the recently published book ‘An Engineer’s Guide to Flexible Circuit Technology by J. Fjelstad

Novel Uses of Flexible Circuit Technology in High Performance Electronic Applications

Flexible circuits are ideally suited to solving the design demands of next generation electronics. The flexible circuit offers a number of advantages that are unavailable to those using more traditional, rigid type interconnection structures. A number of new applications for flexible circuits have been developed that may well provide a glimpse of what is yet to come in electronic packaging technology. These new applications embrace the whole spectrum of the electronics interconnection world from chip packaging to high density multilayer structures. Reviewed here are some of the more novel uses of the flex circuit for high performance electronic interconnection.

Production Engineering for Small-Size and Functional Motion of Total Arm Prosthesis

A total arm electrical prosthesis by microcomputer control is designed for patients who have both shoulders amputated by a work accident and these suffering from the disease of malignant tumour. The prothesis uses 6 coreless micro-motors as an actuator and can act flexion - extension and external - internal rotation of the shoulder, abduction - adduction of the upper arm, flexion - extension of elbow, forearm pro-supination, and openshut of fingers. Each movable part is modulated, and the prosthesis in each amputation part can be manufactured. We use a special linkage shoulder mechanism of rigid body and can obtain natural shoulder movement compatible with the human motion. The hand part can easily change an electrical cosmetic and hook-type hand in a quick change system according to the task. The control system of prosthesis is composed of three singlechip microcomputers and is stored together with a Ni-Cd battery within the dummy arm (left arm). Consequently, we set the following goals: (1) Compact and highly rigid shoulder mechanism. (2) Smaller multiple microcomputer and driven system set by flexible circuit technology. (3) The main controller keeps program in PROM, RAM area of microprocessor, and IC cord as fundamental motions and fixed motions. (4) CAD and/or artificial intelligence techniques are used to shorten the development period and the flexible accommodation. The judgement function of command by a microcomputer, the cooperative movements of each joint, and a teaching system of easy motion data by the handicapped are indispensable in order to ease the burden of operation. Therefore, the order input device which can transmit the intention of the handicapped to a control device of prosthesis and is not a burden to operation is necessary. The weight of prosthesis and control devices should realize portability. In addition the CAD/CAM of the socket for wear which is unaffected by the weight with prosthesis itself is necessary.