Polyimide Printed Circuit Board Research Articles

Soft Neural Interfacing based on Implantable Graphene Fiber Microelectrode Arrays.

Microelectrode Arrays (MEAs) neural interfaces are considered implantable devices that interact with the nervous system to monitor and/or modulate brain activity. Graphene-based materials are utilized to address some of the current challenges in neural interface design due to their desirable features, such as high conductance, large surface-to-volume ratio, suitable electrochemical properties, biocompatibility, flexibility, and ease of production. In the current study, we fabricated and characterized a type of flexible, ultrasmall, and implantable neurostimulator based on graphene fibers. In this procedure, wet-spinning was employed to create graphene fibers with diameters of 10 to 50 µm. A 10-channel polyimide Printed Circuit Board (PCB) was then custom-designed and manufactured. The fibers were attached to each channel by conductive glue and also insulated by soaking them in a polyurethane solution. The tips were subsequently exposed using a blowtorch. Microstructural information on the fibers was obtained using Scanning Electron Microscopy (SEM), and the measurements of Electrochemical Impedance Spectroscopy (EIS) were conducted for each electrode. Flexible MEAs were created using graphene fibers with diameters ranging from 10 to 50 microns with a spacing of 150 microns. This method leads to producing electrode arrays with any size of fibers and a variety of channel numbers. The flexible neural prostheses can replace conventional electrodes in both neuroscience and biomedical research.

Analyses on the large size PBGA packaging reliability under random vibrations for space applications

Large size commercially available plastic ball grid array chip packaging was tested and analyzed under random vibration to access its application feasibility on satellite electronics. Two types of the PBGA of 16 mm × 16 mm and 10 mm × 10 mm were chosen, and the chips were surface mounted without underfill on a daisy chained polyimide printed circuit boards. Then the boards were installed to an aluminum frame, a common type used to fix the boards to satellite structure, and undergone the random vibration tests. Two extreme levels of the random vibrations, the power spectrum of which were 22.48 grms and 31.78 grms, were applied sequentially to investigate the sustainability. It was found that the test results did not show any solder failure under the test conditions, indicating the robust structural integrity and providing the evidences justifying the PBGA packaging feasibility to the aerospace applications. Numerical analyses were also performed to analyze the PCB vibration behaviors and stress development mechanisms. The analyses results showed that, unlike usual expectation, the first natural mode may not be the dominant contribution to the solder stress developments, and higher natural modes could induce the maximum stress depending on the chip size and its location.

Immune-to-Detuning Wireless In-Body Platform for Versatile Biotelemetry Applications.

In-body biotelemetry devices enable wireless monitoring of a wide range of physiological parameters. These devices rely on antennas to interface with external receivers, yet existing systems suffer from impedance detuning caused by the substantial differences in electromagnetic properties among various tissues. In this paper, we propose an immune-to-detuning in-body biotelemetry platform featuring a novel tissue-independent antenna design. Our approach uses a novel slot-patch conformal antenna integrated into a flexible polyimide printed circuit board containing the device circuitry and encapsulated within a 17.7mm[Formula: see text]8.9mm biocompatible shell. The antenna is synthesized and optimized using a hybrid analytical-numerical approach and, then, characterized numerically and experimentally in terms of impedance stability. The proposed platform shows stable impedance, whereas operating in any mammalian tissue as well as in air. The system is optimized for the 434-MHz industrial, scientific, and medical band and can easily be returned for any MedRadio band in the 401-457-MHz spectrum. Ultrarobust impedance characteristics were achieved. Without any modifications, the proposed biotelemetry platform can be used, for instance, as an ingestible for humans or as an implantable for a wide range of animals: from rodents to cattle.

Ultrasensitive nanostructure sensor arrays on flexible substrates for multiplexed and simultaneous electrochemical detection of a panel of cardiac biomarkers

Multiplexed detection of protein biomarkers offers new opportunities for early diagnosis and efficient treatment of complex diseases. Cardiovascular diseases (CVDs) has the highest mortality risk in USA and Europe with 15–20 million cases being reported annually. Cardiac Troponins (T and I) are well established protein biomarkers associated with heart muscle damage and point-of-care monitoring of both these two biomarkers has significant benefits on patient care. A flexible disposable electrochemical biosensor device comprising of vertically oriented zinc oxide (ZnO) nanostructures was developed for rapid and simultaneous screening of cardiac Troponin-I (cTnI) and cardiac-Troponin-T (cTnT) in a point-of-care sensor format. The biosensors were designed by selective hydrothermal growth of ZnO nanostructures onto the working electrodes of polyimide printed circuit board platforms, resulting in the generation of high density nanostructure ZnO arrays based electrodes. The size, density and surface terminations of the nanostructures were leveraged towards achieving surface confinement of the target cTnT and cTnI molecules on to the electrode surface. Multiplexing and simultaneous detection was achieved through sensor platform design comprising of arrays of Troponin functionalized ZnO nanostructure electrodes. The sensitivity and specificity of the biosensor was characterized using two types of electrochemical techniques; electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis on the same sensor platform to demonstrate multi-configurable modes. Limit of detection of 1pg/mL in human serum was achieved for both cTnI and cTnT. Cross reactivity analysis showed the selectivity of detecting cTnT and cTnI in human serum with wide dynamic range.

Performance of a Polymer-Based Sensor Package at Extreme Temperature

There is an increasing need for inexpensive packaging structures for demanding industrial electronics applications. This paper studies the usability of a polymer-based sensor package at very high temperatures. Resistance-based temperature sensors were attached with polymer-based electrically conductive adhesives (ECAs) onto flexible polyimide (PI) printed circuit boards (PCB). The materials used in the structure were not specifically designed for high temperature use. However, they were all commercial materials, easily available and typically reliable under normal use conditions of consumer electronics. The samples were aged at 240°C and electrically monitored during the test. Electrically, the sensor samples were observed to fail after 100 h of aging. However, material characterisation revealed that the materials started to degrade much earlier. The adhesive layer in the PI PCB and the ECA materials started to degrade after just 30 h of aging at 240°C, and mechanically the materials were observed to become brittle, making them prone to cracking and delamination. The results showed that such a polymer package is usable at 240°C for relatively short exposure times, but under longer exposure times the mechanical reliability of the package deteriorates and this needs to be taken into account.

Monolithic Integration of a Flexible Micro Thermal Flow Sensor

In this paper, a novel monolithically integrated flexible thermal flow sensor combining four resistors in a Wheatstone bridge including hot-film resistor, temperature-compensating resistor and two other balancing resistors on one chip is proposed in order to improve the system integration level and sensor performances, such as signal to noise ratio (SNR), power consumption and temperature compensation. Fabricating the sensor directly on a flexible polyimide printed circuit board (PCB) by incorporating printed circuit technique with micromachining sputter technique is adopted. A complete performance test on the flow sensor demonstrates its superiorities on power consumption, SNR and temperature drift, the error of which is eliminated from 43% to 8% over a range of ambient temperature (35–75°C).

Seamless integration of CMOS and microfluidics using flip chip bonding

We demonstrate the microassembly of PDMS (polydimethylsiloxane) microfluidics with integrated circuits made in complementary metal-oxide-semiconductor (CMOS) processes. CMOS-sized chips are flip chip bonded to a flexible polyimide printed circuit board (PCB) with commercially available solder paste patterned using a SU-8 epoxy. The average resistance of each flip chip bond is negligible and all connections are electrically isolated. PDMS is attached to the flexible polyimide PCB using a combination of oxygen plasma treatment and chemical bonding with 3-aminopropyltriethoxysilane. The total device has a burst pressure of 175 kPA which is limited by the strength of the flip chip attachment. This technique allows the sensor area of the die to act as the bottom of the microfluidic channel. The SU-8 provides a barrier between the pad ring (electrical interface) and the fluids; post-processing is not required on the CMOS die. This assembly method shows great promise for developing analytic systems which combine the strengths of microelectronics and microfluidics into one device.

Durability of Polyimide Printed Circuit Board under High Temperature and High Humidity

Durability of Polyimide Printed Circuit Board under High Temperature and High Humidity

Characteristics of environmental factor for electrochemical migration on printed circuit board

This study investigates whether electrochemical migration (ECM) is affected by factors such as the printed circuit board (PCB) material, distance between the conductors, bias voltage, contamination and underfill process under water drop (WD), temperature and humidity bias (THB), and polarization tests. The resistance of ECM with polyimide PCB was greater than that with FR-4 (flame resistant-4) PCB. The ECM rate was increased by decreasing the distance between the conductors of opposite polarity and increasing the bias voltage. The cured underfill on PCB protected the ECM growth, while contamination with chlorine ions accelerated the ECM growth.

High Temperature DC-DC Converter Performance Comparison Using SiC JFETs, BJTs and Si MOSFETs

The performance and characterization of SiC JFETs and BJTs, used as inverter switching devices, in a 2 kW, high temperature, 33 kHz, 270-28 V DC-DC converter has been accomplished. SiC and Si power devices were characterized in a phase shifted H-bridge converter topology utilizing novel high temperature powdered ferrite transformer material, high temperature ceramic filter capacitors, SiC rectifiers, and 10 oz. 220oC polyimide printed circuit boards. The SiC devices were observed to provide excellent static and dynamic characteristics at temperatures up to 300oC. SiC JFETs were seen to exhibit on-resistance trends consistent with temperature-mobility kinetics and temperature invariant dynamic loss characteristics. SiC BJTs exhibited positive temperature coefficients (TCE) of VCE and negative β TCEs, with only a 2-fold increase in on-resistance at 300oC. Both SiC power devices possessed fast inductive switching characteristics with τon and τoff ~100-150 ns when driving the transformer load. The SiC converter characteristics were compared to Si-MOSFET H-bridge operation, over its functional temperature range (30-230oC), and highlights the superiority of SiC device technology for extreme environment power applications.