Fabrication and functionalization of PCB gold electrodes suitable for DNA-based electrochemical sensing

The request of high specificity and selectivity sensors suitable for mass production is a constant demand in medical research. For applications in point-of-care diagnostics and therapy, there is a high demand for low cost and rapid sensing platforms. This paper describes the fabrication and functionalization of gold electrodes arrays for the detection of deoxyribonucleic acid (DNA) in printed circuit board (PCB) technology. The process can be implemented to produce efficiently a large number of biosensors. We report an electrolytic plating procedure to fabricate low-density gold microarrays on PCB suitable for electrochemical DNA detection in research fields such as cancer diagnostics or pharmacogenetics, where biosensors are usually targeted to detect a small number of genes. PCB technology allows producing high precision, fast and low cost microelectrodes. The surface of the microarray is functionalized with self-assembled monolayers of mercaptoundodecanoic acid or thiolated DNA. The PCB microarray is tested by cyclic voltammetry in presence of 5 mM of the redox probe K3Fe(CN6) in 0.1 M KCl. The voltammograms prove the correct immobilization of both the alkanethiol systems. The sensor is tested for detecting relevant markers for breast cancer. Results for 5 nM of the target TACSTD1 against the complementary TACSTD1 and non-complementary GRP, MYC, SCGB2A1, SCGB2A2, TOP2A probes show a remarkable detection limit of 0.05 nM and a high specificity

An approach to produce a stack of photo definable polyimide based flat UTCPs

Getting output of multiple chips within the volume of a single chip is the driving force behind development of this novel 3D integration technology which has a broad range of industrial and medical electronic applications. This can be achieved by laminating multiple layers of spin-on polyimide based ultrathin chip packages (UTCPs) with fine pitch through hole interconnects

In-body path loss models for implants in heterogeneous human tissues using implantable slot dipole conformal flexible antennas

A wireless body area network (WBAN) consists of a wireless network with devices placed close to, attached on, or implanted into the human body. Wireless communication within a human body experiences loss in the form of attenuation and absorption. A path loss model is necessary to account for these losses. In this article, path loss is studied in the heterogeneous anatomical model of a 6-year male child from the Virtual Family using an implantable slot dipole conformal flexible antenna and an in-body path loss model is proposed at 2.45 GHz with application to implants in a human body. The model is based on 3D electromagnetic simulations and is compared to models in a homogeneous muscle tissue medium

Stretchable mould interconnect optimization : peeling automation and carrierless techniques

The primary bottleneck of the stretchable mold interconnect (SMI) technology is its reliance on carrier boards. These are necessary to handle the meandered circuit during production and to ensure dimensional stability of the flexible circuit board before encapsulation. However, for all the problems it solves, it also introduces a new major problem by requiring a peeling step – which is difficult to automate. This manuscript aims to present some of the work that went into eliminating this problem, discussing both unsuccessful and functioning methods to tackle this conundrum and some of the experimental work that went into verifying these techniques. First, alterations to the design to simplify peeling are considered, followed by adhesivebased peeling processes and mechanical pin-based systems. Next, masking and structuring of the carrier board adhesive are considered. Finally, two carrierless methods which circumvent the problems are discussed, a two-step process – which cuts temporary support structures after partial encapsulation – and a technique whereby the frame is designed to fail in a controlled manner during the first use of the circuit, creating a carrierless process feasible for high-volume production

One-time deformable thermoplastic devices based on flexible circuit board technology

This contribution describes an efficient process flow for production of one-time deformable electronic devices based on standard circuit board technology and demonstrates multiple devices fabricated using this technique. The described technology has the potential to streamline and simplify the production of complex user interfaces which typically require extensive mechanical design and many components. The employed technique allows for the production of complex 3D shapes without the need to modify existing circuit board manufacturing equipment or processes significantly. To achieve this the device is manufactured in a flat state, encapsulated in a thermoplastic polymer laminate and deformed afterwards. This allows the usage of standard electronic components in surface mount packages, which are assembled using lead-free high-temperature solder. The circuit is deformed using a high-volume cost-effective thermoforming approach, where the encapsulating polymer is heated above its glass transition temperature and forced against a mold where it is allowed to cool down again. To enable significant out-of-plane deformations stretchable meandering interconnects are used, which were traditionally developed for dynamically stretchable devices. Fabrication of the circuit starts using a standard flexible copper clad laminate which is processed using the default techniques, the resulting circuit is then attached to a carrier board coated with a reusable high-temperature pressure sensitive adhesive. The interconnect and circuit outline is then defined using laser routing or punching, cutting the flexible circuit without damaging the carrier. The residuals not part of the circuit are removed, in a process akin to protective film removal, and solder paste is stencil printed on the circuit. Afterwards components are placed using a pick-and-place machine and the boards are reflow soldered. After functional testing and repair (if necessary) the circuits are placed in a vacuum press with a thermoplastic laminate, consisting of a thermoplastic elastomer and a rigid thermoplastic sheet. During this lamination the components are protected by a highly conforming press pad. Because the adhesion between the elastomer and the circuit far exceeds that between the circuit and the carrier the circuit is released readily as the thermoplastic laminate is peeled away. The resulting laminate is built up further using thermoplastic films and sheets, and finally deformed using a vacuum forming machine. The resulting device, which is trimmed to remove the clamping edges, can then be mounted in the final assembly. The advantages of this approach are demonstrated using a series of test vehicles, demonstrating the integration of complex circuits, connectors, and power circuitry. Finally, a series of design considerations that became apparent after initial reliability testing are discussed, together with the resulting design rules

High-yield embedding of 30µm thin chips in a flexible PCB using a photopatternable polyimide based ultra-thin chip package (UTCP)

Thinning down ICs is a well-known approach to reduce the volume of chip packages. In this work ICs are thinned down to 30um, followed by a package procedure in polyimide with copper fan out, which allows their embedding in adhesives used for laminating flexible printed circuit boards (PCBs). In this way the chip does not consume PCB area, hence other circuit components can be assembled on top or at the bottom of the chip, enabling extreme circuit miniaturization. Furthermore, our ultra-thin chip package (UTCP) is highly flexible, enabling flexible electronic circuits without large rigid chip packages. Spin-on photo-definable polyimide precursors are used to build an interposer which can be embedded later in the flexible PCB. The chip is fixed in between three polyimide layers using BCB as adhesive. The central polyimide layer forms a cavity for the chip, the top layer of polyimide is exposed and developed to fabricate vias contacting the chip. An 8um thick copper layer is deposited and patterned using lithography and etching to form the fan-out, essential to match the fine IC pitch to the larger PCB pitch. The final chip package is about 75um thick, and is easily embedded using only small adaptations of the standard flexible PCB fabrication process. Last year, both the UTCP concept and the embedding in a flexible PCB were optimized in order to obtain a very high yield. Three types of chips were UTCP-packaged and embedded in a flexible PCB: two types of microcontrollers (MSP430F1611 and a proprietary digital signal processor) and an RF-chip. The yield of the tested UTCPs ranges in between 65% (proprietary IC) and 85% (MSP430F1611). The performance of the RF-chips can only be tested after embedding in a flexible substrate. Although the testing is still ongoing, 95% of the embedded UTCPs are fully functional after embedding