Anna Młożniak

Enhanced electrical conductivity of silver nanoparticles for high frequency electronic applications.

An enhancement in the electrical performance of low temperature screen-printed silver nanoparticles (nAg) has been measured at frequencies up to 220 GHz. We show that for frequencies above 80 GHz the electrical losses in coplanar waveguide structures fabricated using nAg at 350 °C are lower than those found in conventional thick film Ag conductors consisting of micrometer-sized grains and fabricated at 850 °C. The improved electrical performance is attributed to the better packing of the silver nanoparticles resulting in lower surface roughness by a factor of 3. We discuss how the use of silver nanoparticles offers new routes to high frequency applications on temperature sensitive conformal substrates and in sub-THz metamaterials.

Silver nanoparticles effect on the wettability of Sn‐Ag‐Cu solder pastes and solder joints microstructure on copper

Purpose – The purpose of this paper is to investigate the influence of silver nanoparticle additions on the wetting properties of Sn‐Ag‐Cu (SAC) solder paste. In this investigation, the basic solder paste contained 85 wt.% of commercial Sn 96.5 Ag 3 Cu 0.5 powder (with the particle sizes in the range of 20‐38 μm) and 15 wt.% of self‐prepared middle activated rosin flux. To this paste was added 0.5, 1, 2 and 4 wt.% of self‐prepared silver nano‐powders of different grain sizes (from 9 to 138 nm). After the pastes had stabilized, their wetting properties were tested. The main goal of these investigations was to improve the wetting properties of SAC solder paste and to find correlations between the results of the wetting of solder paste with nanoparticles on the copper substrate with the microstructure of the solder joints.Design/methodology/approach – The following methods were applied for the wetting solder paste investigation: spreading on the copper substrate, contact angle measurement on the copper and w...

Electroluminescent structures printed on paper and textile elastic substrates

Purpose – New types of substrates were used for fabrication of printed electroluminescent structures. Polymer foils mainly used as substrates for such optoelectronic elements were replaced with paper and textiles. Printing on non-transparent substrate requires elaboration of printed transparent electrode, while usually polyester foils with sputtered ITO transparent electrodes are used. The paper aims to discuss these issues. Design/methodology/approach – Electroluminescent structures were fabricated with elaborated polymer compositions filled with nanomaterials, such as carbon nanotubes and graphene platelets, dielectric and luminophore nanopowders. Structures were printed as “reverse stack”, where transparent electrode is printed on top of the last luminophore layer. For that carbon nanotubes and graphene platelets filled composition was used, deposited with spray-coating technique. Findings – Main issue with new substrates is proper wetting with the use of screen-printing pastes, and much higher roughne...

Investigation on a new silver photoimageable conductor

A new thick film photoimageable silver paste of improved properties has been elaborated. The paste is less sensitive to the visible light. Certain disadvantages of most commercially available materials, such as necessity of operating with the paste in the room illuminating with yellow, green or red light has been eliminated. Further improvement of conductive silver pastes to enable reducing lines width down to 10 μm has been done.

Mechanical durability of RFID chip joints assembled on flexible substrates

Purpose – The purpose of this paper is to investigate the durability of radio‐frequency identification (RFID) chips assembled on flexible substrates (paper and foil), with materials evaluated with regard to mechanical stresses and dependence on the applied substrate, antenna materials, chip pad printing and chip encapsulation.Design/methodology/approach – RFID chips were assembled to antennas screen printed on flexible substrates. Shear and bending tests were conducted in order to evaluate the mechanical durability of the chip joints depending on the materials used for mounting the RFID chip structures. X‐ray inspection and cross sectioning were performed to verify the quality of the assembly process. The microstructure and the resistance of the materials used for chip pads were investigated with the aim of determining the conductivity mechanism in the printed layers.Findings – Addition of carbon nanotubes to the conductive adhesive (CA) provided a higher shear force for the assembled RFID chips, compared...

Screen printed UHF antennas on flexible substrates

Printed electronics belongs to the most important developing electronics technologies. It provides new possibilities to produce low cost and large area devices. In its range several applications can be distinguished like printed batteries, OLED, biosensors, photovoltaic cells or RFID tags. In the presented investigation, antennas working in UHF frequency range were elaborated. It can be applied in the future for flexible RFID tags. To produce these antennas polymer paste with silver flakes was used. It was deposited on two flexible substrates (foil and photo paper) with screen printing techniques. After printing process surface profile, electrical and microwave parameters of performed antennas were measured using digital multimeter and network analyzer, relatively. Furthermore, a thickness of printed layers was measured.

Electrical and mechanical properties of RFID chip joints assembled on flexible substrates

Purpose – The purpose of this paper is to examine electrical and mechanical properties of radio frequency identification (RFID) chip joints assembled on a flexible substrate and made from isotropic conductive adhesives (ICAs) reinforced with graphene nanoplatelets (GPNs) or graphite nanofibers (GFNs). Design/methodology/approach – The ICAs reinforced with GPNs or GFNs were prepared and screen printed on a test pattern to investigate resistance and thickness of these adhesive layers. Differential Scanning Calorimetry (DSC) was performed to assess a curing behaviour of the prepared ICAs. Then, RFID chips were mounted with the prepared ICAs to the pattern of silver tracks prepared on foil. Shear test was carried out to evaluate mechanical durability of the created chip joints, and resistance measurements were carried out to evaluate electrical properties of the tested ICAs. Findings – The 0.5 per cent (by weight) addition of GFNs or GPNs to the ICA improved shear force values of the assembled RFID chip joint...

Noise properties of Pb/Cd-free thick film resistors

Low-frequency noise spectroscopy has been used to examine noise properties of Pb/Cd-free RuO2- and CaRuO3-based thick films screen printed on alumina substrates. Experiments were performed in the temperature range 77–300 K and the frequency range 0.5–5000 Hz with multiterminal devices. The measured noise has been recognized as resistance noise that consists of background 1/f noise and components generated by several thermally activated noise sources (TANSs) of different activation energies. The total noise has been composed of the contributions generated in the resistive layer and in the resistive/conductive layers interface. These noise sources are non-uniformly distributed in the resistor volume. Noise intensity of new-resistive layers has been described by the noise parameter Cbulk. Pb/Cd-free layers turned out to be noisier than their Pb-containing counterparts; however, the removal of Pb and Cd from resistive composition is hardly responsible for the increase in the noise. In the case of RuO2 layers noise increases most likely due to larger grain size of RuO2 powder used to prepare resistive pastes. Information on the quality of the resistive-to-conductive layers interface occurred to be stored in the values of noise parameter Cint. Pb/Cd-free RuO2-based resistive pastes form well-behaved interfaces with various Ag-based conductive pastes. In contrast, CaRuO3-based paste forms bad contacts with AgPd terminations because the density of TANSs increases in the interface area.

Multiwalled carbon nanotubes deposition in thick film silver conductor

New method of fabrication conductive paste for screen printing in thick film technology was investigated. Fabrication of electronic paste with addition of multiwalled carbon nanotubes and nanoscale silver powder leads to many technological problems in the stir process of nanosized particles. A specialist ultrasonic method was applied to obtain homogeneous mixture. To obtain paste with proper reological properties and usable in thick film technology a selection process of suitable organic resin was conducted. Obtained mixtures with optimal parameters will be used for further experiments.

SAC solder paste with carbon nanotubes. Part II: carbon nanotubes’ effect on solder joints’ mechanical properties and microstructure

Purpose – The purpose of this work is to investigate the influence of carbon nanotube additions to solder paste on the solder joints mechanical strength and their microstructure. In our investigation, the basic solder paste contains 85 wt.% of the commercial Sn96.5Ag3Cu0.5 powder (with the particle sizes in the range of 20‐38 μm) and 15 wt.% of the self‐prepared middle activated rosin flux. To this paste we added the 0.01, 0.05 and 0.1 wt.% of the self‐modified CNT by functionalized them by mineral acid and than esterificated by methanol (FCNTMet) or polyethylene glycol 400 (FCNTPG). After the pastes had stabilized, the reflow soldering process of “zero ohm” chip resistors on PCBs with Ni/Au and SAC (HASL) finishes was carried out and then shear strength of the solder joints was measured. The correlations between the mechanical strength of solder joins without and with the carbon nanotubes and their microstructure were analysed.Design/methodology/approach – For shear strength measurement of solder joints,...