Hanna Yousef

79 GHz Slot Antennas Based on Substrate Integrated Waveguides (SIW) in a Flexible Printed Circuit Board

The design, fabrication and characterization of 79 GHz slot antennas based on substrate integrated waveguides (SIW) are presented in this paper. All the prototypes are fabricated in a polyimide flex foil using printed circuit board (PCB) fabrication processes. A novel concept is used to minimize the leakage losses of the SIWs at millimeter wave frequencies. Different losses in the SIWs are analyzed. SIW-based single slot antenna, longitudinal and four-by-four slot array antennas are numerically and experimentally studied. Measurements of the antennas show approximately 4.7%, 5.4% and 10.7% impedance bandwidth (S11=-10 dB) with 2.8 dBi, 6.0 dBi and 11.0 dBi maximum antenna gain around 79 GHz, respectively. The measured results are in good agreement with the numerical simulations.

Vertical Thermopiles Embedded in a Polyimide-Based Flexible Printed Circuit Board

A fabrication process for vertical thermopiles embedded in a 75-mum-thick polyimide foil has been developed for flexible printed circuit boards (flex PCBs). The vertical connections consist of electrodeposited antimony-and nickel-plated through-hole vias. The plated through-hole vias consist of multiple wires, with a total metal content that is 1% of the total via volume. The via fabrication technique is similar to standard flex PCB wet etch and metallization processes. The main difference is that the foils are pretreated with ion irradiation to induce highly selective vertical etch rates. The thermopiles were characterized by measuring their voltage response to an applied temperature difference across the foil thickness.

Reliable small via interconnects made of multiple sub-micron wires in flexible PCB

A fabrication process for small through-hole vias consisting of multiple sub-micron electrodeposited wires has been developed for flexible printed circuit boards (PCB). The resistance of the vias is controlled by adjusting the number of wires per via, as well as the dimensions of the wires. The process steps include modification of the foils by irradiation with energetic ions, wet etching and metallization of the through-hole vias, double-sided surface metallization of the dielectric layer and interconnection lithography. Series of up to 360 interconnected vias of electrodeposited nickel are demonstrated in a flexible PCB foil (75 µm Kapton HN polyimide). The vias have a lateral size of 26 µm. The metal content of the demonstrated vias is 0.12% and 10% of their total volume, corresponding to a metal cross-section of 3.2 µm2 and 270 µm2, respectively. The electrical resistance per interconnected via is 2.6 Ω and 0.07 Ω, respectively. The vias can carry a current density of at least 4 × 106 A cm−2.

A PCB-like process for vertically configured thermopiles

Thermopiles are important components in infrared thermal detectors, thermoelectric generators and thermoelectric coolers. We present a thermopile structure with up to 224 vertically arranged thermocouple legs in a polyimide flex material. The thermopile is optimized for infrared thermal radiation detection and is fabricated using printed circuit board-like (PCB-like) processing. Each thermoelectric leg consists of a bundle of a few hundred sub-micrometre-sized strands of either antimony or nickel. These metal wire bundles were achieved by employing ion track technology on the polyimide foil, resulting in a porous dielectric material. Electrochemical methods were used to grow the thermoelectric materials in the pores. The plating mask was produced in a laminated dry photoresist. A small metal cross section, 20 µm2 (1 vol%), ensured a low heat exchange between the two surfaces of the flex. The typical resistance per thermocouple was 34 Ω. A responsivity to irradiance of 4.3 V mm2 W−1 was measured when heating with a white light source (irradiance 1 mW mm−2).

Plated Through-Hole Vias in a Porous Polyimide Foil for Flexible Printed Circuit Boards

A fabrication process for high aspect ratio plated through-hole vias is presented for flexible printed circuit boards. A 75 ?m thick porous Kapton foil that allows direct definition of high aspect ratio through-hole vias by dry photoresist film lithography and electrodeposition is presented. Pretreatment with swift heavy ion irradiation and wet etching define the pore density and porosity of the foil, similar to ion-track-etched filter membranes. Thin film metallization of a seed layer and lithography of a laminated dry photoresist film define the via sizes and positions. Subsequent through-hole electrodeposition produces vias consisting of multiple wires, where each open pore defines one wire. The via geometries are characterized by scanning electron microscopy. The electrical properties of the vias are characterized by resistance measurements. Vias with an aspect ratio over 2 and a side length of 33 ?m show high yield with low resistance and low variation in resistance.

Substrate Integrated Waveguides (SIWs) in a Flexible Printed Circuit Board for Millimeter-Wave Applications

Substrate integrated waveguides (SIWs) are presented and demonstrated in a flexible printed circuit board (flex PCB) for application in the 77-81 GHz range. The vertical walls of the SIWs presented in this paper consist of multiple electrodeposited metallic wires. The diameters of these wires and the spacing between them are on the order of hundreds of nanometers. Hence, the walls can be seen as continuous metallic walls, and the leakage losses through them become negligible. In turn, the SIWs presented in this paper can operate at higher frequencies compared with previously presented structures that are realized with PCB fabrication processes. The attenuation of the SIWs is comparable to that of microstrip lines on the same sample. The SIWs are successfully demonstrated in a SIW-based slot antenna. The antenna gain along the z-axis (normal-to-plane) was found to be around 2.8 dBi at 78 GHz which is in agreement with the simulated values. [2008-0047]

Ion Track Enabled High Aspect Ratio Flexible PCB Via Technology

By combining ion track technology with ordinary low-resolution printed circuitboard lithography it is possible at low cost to create high aspect ratios via connectors, as solid plugs or consisting of bundles of sub-micron connector wires at a small total cross-section. Ion track enabled microwave circuits in flexible printed circuit boards are suggested to be used in applications like inductors, ferromagnetic resonance microwave filters, circulators and magnetoresistive sensors. In this paper we demonstrate this technology with integrated printed circuitboard devices in two different flexible polyimide-based foils (Espandex and Kapton HN), using the ultra-high-density vias and the sub-micron wires.

Flexible PCB Vertical Thermopile IR Sensor

We present the design, fabrication and characterization of vertical thermopile infra-red (IR) sensors. The sensors are produced in batches in a standard flexible printed circuit board (flex PCB) material. The vertical design opens up for large area detection and longer thermopile chains. The sensors consist of series of 88 vertically interconnected thermocouples in a 75 mum thick polyimide foil (Kapton HNtrade). The sensors showed a voltage response to an IR pulse of 1.2 V/(W/mm2).