Alena Pietrikova

Surface analysis of polymeric substrates used for inkjet printing technology

Purpose – This paper aims to find an optimal surface treatment of commonly used polymeric substrates for achieve the high adhesion of printed structures. For this reason, the investigation of substrates surfaces from different perspectives is presented in this paper. Design/methodology/approach – The contact angle measurements as well as the roughness measurements were realised for the analysis of surface properties of investigated substrates. The impact of applied chemical agents for surface treatment onto the wettability is analysed for polyimide, polyethylene terephthalate and polyethylene naphthalene substrates. Findings – The results prove the correlation among wettability, surface energy and work of adhesion with respect to the theoretical background. The surface treatment of polymeric substrates by chemical agents, such as acetone, toluene, ethanol, isopropyl and fluor silane polymer, has a significant impact onto the wettability of substrates which affects the final deposition process of nanoinks....

Real-time profiling of reflow process in VPS chamber

Purpose This paper aims to present a new method of real-time monitoring of thermal profiles applied in vapour phase soldering (VPS) reflow processes. The thermal profile setting is a significant variable that affects the quality of joints. The method allows rapid achievement of a required thermal profile based on software control that brings new efficiency to the reflow process and enhanced joint quality, especially for power electronics. Design/methodology/approach A real-time monitoring system based on computerized heat control was realized in a newly developed laboratory VPS chamber using a proportional integral derivation controller within the soldering process. The principle lies in the strictly accurate monitoring of the real defined reflow profile as a reference. Findings Very accurate maintenance of the required reflow profile temperature was achieved with high accuracy (± 2°C). The new method of monitoring and control of the reflow real-time profiling was verified at various maximal reflow temperatures (230°C, 240°C and 260°C). The method is feasible for reflowing three-dimensional (3D) power modules that use various types of solders. The real-time monitoring system based on computerised heat control helped to achieve various heights of vapour zone. Originality/value The paper describes construction of a newly developed laboratory-scale VPS chamber, including novel real-time profiling of the reflow process based on intelligent continuously measured temperatures at various horizontal positions. Real-time profiling in the laboratory VPS chamber allowed reflow soldering on 3D power modules (of greater dimensions) by applying various flux-less solder materials.

Optimisation of Lead Free Solders Reflow Profile

The solder reflow profile is one of the key variables in the manufacturing process that significantly impacts product yield. In this paper we discuss the details of developing solder profiles for IR and vapor phase soldering (VPS). This paper reviews the background of smaller process windows, along with specific comparisons to common practice with tin/lead and SAC alloys. The impacts on oven set-up and operation were investigated for significant differences between these profiles. Optimal reflow profile was determined based on the number of experiments realized for tin/lead and SAC solder pastes: mechanical properties, analyze of structures and electrical properties of solder joints.

Electrically conductive adhesive filled with mixture of silver nano and microparticles

Electrically conductive adhesive with isotropical electrical conductivity modified with addition of silver nanoparticles has been investigated. The electrical resistance, nonlinearity of a current vs. voltage characteristic and the tensile strength of adhesive joints formed of this adhesive have been measured. The specimens have also been aged at the temperature of 125degC and at the combined climate 80degC/80 % relative humidity for 700 hours. It has been found that silver nanoparticles added into the electrically conductive adhesive cause decrease of its conductivity, increase of its nonlinearity and increase of the tensile strength.

Potentiality of LTCC for sensor applications

The potential of low temperature cofired ceramic (LTCC) multilayer technology allows realization of different structures for sensor applications. Examples of sensors realised at the Department of Hybrid Microelectronics in the Faculty of Electrical Engineering and Informatics at the Technical University in Kosice have shown the potential and development possibilities of LTCC for a wide field of thick film sensor applications. Other sensor applications were realized on a special shaped body based on LTCC multilayers.

Microstructure analysis and measurement of nonlinearity of vapour phase reflowed solder joints

The goal of the study is to compare quality of lead-free vapour phase reflowed solder joints soldered on different printed circuit board (PCB) surface finishes. The solder joints quality comparison is based on evaluation of microstructure development of the solder, solder/PCB pad interface and on the measurement of the solder joints nonlinearity of the current-voltage (C-V) characteristics. The microstructure is evaluated before and after accelerated ageing.

Design of microstrip band pass filter based on LTCC for UWB sensor system

This paper deals with design, simulation, manufacturing and experimental testing of microstrip bend pass (BP) filter for I - Q (In-phase Quadrature) demodulator that is a part of Ultra Wide-Band (UWB) sensor system. Paper refers to the needs that should be focused on the design and manufacturing of microstrip filters based on LTCC (Low Temperature Co-fired Ceramic) with emphasis on issues of quality of transmitted signals in the high frequency (HF) area in the terms of actual production. There are presented simulated and measured results of insertion loss (S21) and return loss (S11) of microstrip BP filter for I - Q demodulator made from material system Green Tape 951 XP. This paper demonstrates the design and full-wave electromagnetic simulation of microstrip BP filter using the HyperLynx 3D EM Designer (from Mentor Graphics). It assesses the suitability of LTCC material system Green Tape 951 XP as well as conductor paste DuPont 6145 for the production of microstrip BP filters for HF area. The presented filters should be used as a BP filter mean for I - Q demodulator presented in [1] which is a part of laboratory UWB sensor system.

Investigation of rheology behavior of solder paste

This paper presents results of investigation of rheology behavior of three solder pastes with various densities (approaching viscosities). Comparison of three viscosity structural models and one thixotropy model were used for description of rheological flow curve of these solder pastes samples. Solder pastes are metal alloys suspended in flux medium and spotlight of this paper is on modeling of viscosity structural models of solder paste. Solder paste rheology is the most important parameter which affects the paste printing process, the reflow soldering performance, and wherefore the resulting solders joint quality and reliability. The rheology behavior can be correlated to the performance of the materials during the stencil printing (dispensing) process. Solder pastes exhibit non-Newtonian rheological characteristics such as shear thinning i.e. the reduction of viscosity with increased shear in dependency on temperature and time. Thixotropy and viscosity structural models help to understand the rate of structural change of solder paste. The viscosity values from structural models are compared with empiric measured values.

Boundary value of rheological properties of solder paste

This work has been focused on viscosity and rheological measurement of some solder pastes as non-Newtonian. The results of the analysis show that increasing amount of metal powder content in solder paste show on influences of rheology changes of the solder paste. It is known that viscosity increases with increasing metal content. Aim of this work was determination of boundary value of viscosity and rheological properties without losses of thixotropy and pseudo plastic character. This typical feature of non-Newton liquid is important for better understanding of philosophy for high quality of solder paste deposition. Significant differences between the results were observed, which demonstrate the importance of measuring thixotropy and non-recovery rate R of non- Newtonian properties for realistic representation of the flow behaviours of solder paste.

Structure and thermal behavior of lead-free solders prepared by rapid solidification of their melt

Purpose The paper aims to investigate the structure and thermal stability of newly developed lead-free Sn-based alloys which can be used as novel materials in the soldering of electronic components. Design/methodology/approach Rapid solidification was used to prepare the alloys. Findings The results showed that the microstructure of these solders exhibited uniform distribution and small-sized intermetallic compounds. Also, smaller crystalline size can be expected compared to commercially available counterparts. The analyses revealed a uniform and homogenous distribution of the small intermetallic particles of Cu6Sn5 and Ag4Sn in the microstructure of solders. The practical implications mean an improvement in mechanical properties and thermal stability of such solder joints, which is a precondition of low mechanical, thermo-mechanical stresses in their structure. Originality/value The originality lies in the production of these alloys by the melt spinning technique which was not previously used in the electronics industry.