Alena Pietrikova | Technical University of Kosice (original) (raw)
Papers by Alena Pietrikova
Soldering & Surface Mount Technology, Feb 6, 2017
Purpose This paper aims to present a new method of real-time monitoring of thermal profiles appli... more 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.
Electrically conductive adhesive with isotropical electrical conductivity modified with addition ... more 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 125°C and at the combined climate 80°C/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.
Microelectronics International, Jun 8, 2022
Purpose The purpose of this paper is to show a possibility to measure a change of a contact angle... more Purpose The purpose of this paper is to show a possibility to measure a change of a contact angle during the melting in real-time and to reveal significant factors of a wettability. Influence of the flux with combination of plasma on copper surface was investigated in experiment as well. Design/methodology/approach Laboratory equipment consists of heating and optical part that was developed and tested for real-time contact angle’s measurements. Solder balls based on Sn96.5/Ag3/Cu0.5 and Sn63Pb37 spread out on a copper substrate during a melting process. The wettability of pure copper surface was compared with copper surface treated with flux or combination plasma–flux. The contact angle and spreading rate of a melted solder balls observed by the charged-coupled device camera were analyzed in real-time and measured using the JavaScript. Findings Laboratory equipment allows for analysis of contact angle and spreading rate in real-time during the melting process. The contact angle decreases more noticeable after applying the plasma-flux treatment in contrast to no flux or flux treatment only. Using the plasma treatment before application of the flux improves the wettability and the effectivity of the flux activity on the copper surface during the melting process. Originality/value The interpretation of the results of such a comprehensive measurement leads to a better understanding of the mutual relation between flux and combination plasma–flux of the wetting during the melting process. The simple, cheap, fast and accurate laboratory equipment, which consists of the heating and the optical part, allows for the wettability evaluation of the melting process in real-time.
This paper shows how a surface finish does affect wettability. Four standard lead-free alloys sel... more This paper shows how a surface finish does affect wettability. Four standard lead-free alloys selected for surface finishes on PCB (LF HASL, ImSn, ENIG, and Cu) with a newly developed surface finish based on SnAg7 alloy were compared. Wetting characteristics of surface finishes were analysed using the spreading rate method and a method based on wetting reflow pattern, both in laboratory condition. Experiments were supplemented by analysis of the effect of plasma on the flux activity, and eventually on wettability. A self-developed equipment was applied to evaluate the spreading rate. The spreading rate method allows for real-time measurement of contact angle of liquid SAC 305 solder balls on various PCB surface finishes. The method based on wetting reflow pattern by SAC 305 solder paste applied on various PCB surfaces confirms these wetting characteristics. The wettability of the new and relatively cheap SnAg7 surface finish is almost comparable with surface finish based on ENIG. This new surface finish is a prospective material that offers interesting properties for application in electronics.
Circuit World, Feb 4, 2019
PurposeThe purpose of this paper was to investigate an influence of a low temperature pressureles... more PurposeThe purpose of this paper was to investigate an influence of a low temperature pressureless sintering process of silver paste on the quality of sintered joints.Design/methodology/approachThe authors analyzed various curing conditions of the paste during its sintering process: 175°C/90 min, 200°C/60 min, 250°C/30 min, 250°C/60 min, 350°C/30 min and 350°C/60 min. They analyzed an influence of the surface plating applied on a ceramic substrate/layer (Cu, Ag, AgPt and Au thick film) on the joints quality. The authors analyzed microstructure and electrical resistance of the joints. They evaluated these properties from the point of view of thermal aging process and changing resistance, after a constant current loading of the sintered joints.FindingsThe nanoscale pressureless silver paste can be applied for replacing a pressure-assisted micro-sized silver paste. It was found that the quality of the metal plating applied on the ceramic substrate/layer has a significant impact on the quality of the sintered joints. Copper and AgPt plating have better impact on quality of sintered joints in compare with Ag plating.Originality/valueThis investigation of the quality of the pressureless sintered joints at the silver-silver interface reveals an evident cracking immediately after the silver paste curing. Rapid sintering process typical for silver-based films on the substrate is because of the inter-diffusion between the micro and nanoparticles of silver at interfacial interface.
This paper is oriented to fundamental understanding of mechanical characterization techniques tha... more This paper is oriented to fundamental understanding of mechanical characterization techniques that assist in probing the nature of failure in glass/epoxy multilayer and sandwich structure of electronic boards after multi reflow processes. We have tested and compared multilayer PCB and a new type of electronic boards based on sandwich structures after multiply thermal exposure based on macroscopic observation and three bent point tests. New type of electronic boards based on the sandwich structure is characterized by high stiffness and good thermal stability. Such new type of structure would be applied for Face-down technology within embedding electronic components in the core of the sandwich structure.
Iet Microwaves Antennas & Propagation, Mar 5, 2018
The study deals with the application of low-temperature co-fired ceramic (LTCC) technology for de... more The study deals with the application of low-temperature co-fired ceramic (LTCC) technology for design of a higherorder mode dielectric resonator antenna element operating at centre frequency 25.7 GHz. The LTCC material that the authors use provides very low dielectric losses and enables us to design an antenna element with very high radiation efficiency. The authors follow by examining the mutual coupling between two resonators and the authors propose a small (1 × 4) onedimensional antenna array composed of such elements. In order to minimise the dimensions of the ground plane and to place the connector at a convenient location, the authors design a parallel feed network in substrate integrated waveguide technology, thus reducing the radiation losses of the feeding structure. The experiments verify the four-element antenna array concept with maximum measured gain of 16.3 dBi.
This paper presents novel application of using micro channels integrated in LTCC (Low Temperature... more This paper presents novel application of using micro channels integrated in LTCC (Low Temperature Co-fired Ceramics) structure as new solution for cooling in power electronics. The aim of this paper is detailed investigation of the thermal resistance, flow analysis and distribution of coolant inside LTCC substrates with internal micro channels. Three different LTCC multilayer structures with integrated micro channel and thermal vias were designed, simulated, fabricated and measured. It was applied various micro channel widths and various quantities of thermal vias under the power chip for improving cooling affect. The impact of the volume flow of liquid coolant, structures of multilayer substrate and thermal vias on thermal resistance of substrate was simulated by using the simulation software Mentor Graphic FloEFD™. The fluidic channel was integrated in the third layer from the top of 6 layers substrate. Thermal vias were embedded inside substrate and channel excluding the top dielectric layer. This cooling concept improves homogeneity and effectivity of heat transfer between the power chips and the coolant. The coolant is pumped through channel for cooling down the 2 tested chips. Principle of thermal resistance measuring was on investigation of the impact of the first chips' thermal load on the second chip. The heat transfer is characterized by the decrease of maximum working temperature, thermal resistance of substrate, temperature distribution, fluid pressure and flow velocity. The main advantage of presented cooling concept is effective and homogenous cooling of critical components.
ABSTRACT The paper deals with the principle of X-ray investigation of 96,5Sn3Ag0,5Cu solder alloy... more ABSTRACT The paper deals with the principle of X-ray investigation of 96,5Sn3Ag0,5Cu solder alloy. The goal of the paper is to simply introduce method of the solder microstructure research via synchrotron X-ray radiation at the B2 bending magnet beamline of DORIS III positron storage ring at HASYLAB/DESY, Hamburg, Germany. The method is suitable especially for in-situ analysis of materials - evaluation of the phase changes.
Connecting to motor aggregate reliability and operational life it is very important to reliably o... more Connecting to motor aggregate reliability and operational life it is very important to reliably observe the oil change interval. Determination of critical parameters of motor oil is important for correct statement of its condition in engine. By implementation of sensor system which directly acquires several parameters simultaneously, it is possible to achieve the better sight onto degradation process of motor oil. Some most relevant, mainly electric parameters were investigated at samples of standard semi-synthetic motor oil and discussed with inscribed the subsequent interest.
Soldering & Surface Mount Technology, Feb 6, 2017
Purpose The paper aims to investigate the structure and thermal stability of newly developed lead... more 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.
ABSTRACT This work has been focused on viscosity and rheological measurement of some solder paste... more ABSTRACT 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.
The goal of the study is to compare quality of lead-free vapour phase reflowed solder joints sold... more 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.
ABSTRACT Comparison of the stability and reliability of thick film resistors prepared by differen... more ABSTRACT Comparison of the stability and reliability of thick film resistors prepared by different techniques is discussed in this work. This aim was accomplished by comparison of the thick film resistors prepared by etching and conventional thick film technology. The etching technique as a combination of three techniques (photolithography, LTCC processing and PCB patterning technology) was introduced for construction of "planar" resistors as a new idea. We show that it is possible to develop devices that are useful in standard thick film technology and that it is possible to fabricate 3D (planar) resistors with higher stability and reliability. As operating material we selected low temperature co-fired ceramic (LTCC), because it allows the fabrication of three-dimensional structures, and it is compatible with the screen-printing process.
The aim of the work is to investigate the possibilities of capacitive sensing of driver position,... more The aim of the work is to investigate the possibilities of capacitive sensing of driver position, and by virtue of the results, to design and to realize a few models which will demonstrate the principle, practically. The paper describes two types of capacitive driver. Each of them differently defines its present position. They were made by polymer thick film technology
This paper is focused on quality of solder joints. Solder joint were realized on the surface of t... more This paper is focused on quality of solder joints. Solder joint were realized on the surface of the substrate as well as embedded into the substrate. Two types of substrate materials (low Tg and high Tg) were used for this research. The objective of this research was determining the realistic lifetime of embedded solder joints. This lifetime was determined by comparison of embedded solder joints with standard solder joints on the surface of the substrate. Lifetime of the samples was evaluated by thermal cycling test between 125°C and -45°C. 1000 thermal cycles were performed. Electrical properties of the samples were measured by 4-point probe method. Microstructure of the cross-sections of the tested samples were analyzed as well.
ABSTRACT The solder reflow profile is one of the key variables in the manufacturing process that ... more ABSTRACT 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.
This paper present designs of inset feeding rectangular microstrip antennas on different substrat... more This paper present designs of inset feeding rectangular microstrip antennas on different substrates with different dielectric constants (FR4 laminate, Green Tape™ 951 LTCC from DuPont and RT/duroid 6010LM from Rogers Corporation). All of antennas were designed for 2.45 GHz frequency band that is one of the most common frequency band for modern wireless communication (WiFi or Bluetooth). Antennas were simulated and results were realized from antenna miniaturization point of view. For antenna miniaturization were used substrates with higher dielectric constant ($\varepsilon_{r}$) at approximately similar substrate thickness. CST Microwave Studio was used for design and optimization of antennas. As a result of our simulations, we find that with an increase of varepsilonr\varepsilon_{r}varepsilonr the antenna area will be reduced but at the detriment of the reduction of the bandwidth at −10 dB. It is possible to eliminate this problem with the increase of the thickness of the substrate. In this way it is possible to achieve required miniaturization while maintaining the possibility of using this antenna in the WiFi area.
Materials Science Forum, 2019
This work is focused on a development and research of a new lead-free Sn-Mg solder, alloy compati... more This work is focused on a development and research of a new lead-free Sn-Mg solder, alloy compatible with the human body. Tin and magnesium are biocompatible elements which do not cause an inflammation or allergic reactions with living tissues. We have prepared the Sn97Mg3 solder (wt. %) by a rapid solidification of its melt on a copper wheel (melt-spinning technique). This solder may find applications in electronic devices for intracorporeal utilisation. The microstructure of the prepared solder exhibits a heterogeneous distribution of the SnMg2 intermetallic particles within the β-Sn matrix. Structure of the solder was studied by an in-situ high energy X-ray diffraction experiment (energy of an X-ray photon: 60 keV) where 2D XRD patterns were collected from the sample in the temperature range from 298 K to 566 K. The experiment was performed at a high brilliance 3rd generation synchrotron source of radiation (PETRA III storage ring, DESY, Hamburg, Germany) at the P02 undulator beamline. From the measured X-ray diffraction data by applying the Rietveld refinement technique we have obtained thermal volume expansion data, mean positions of atoms as well as isotropic atomic displacement parameters of the constituent SnMg2 and the β-Sn crystalline phases. Thermal behaviour was studied by differential scanning calorimetry at heating rates of 5, 15, 30 and 60 K.min-1 and compared with the measured X-ray data. Our main goal lies in a preparation of a lead-free solder with fine grain structure made exclusively of biocompatible elements. We demonstrated that the rapid melt solidification technique leads to in an improvement and better thermal stability of this alloy.
Soldering & Surface Mount Technology, Feb 6, 2017
Purpose This paper aims to present a new method of real-time monitoring of thermal profiles appli... more 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.
Electrically conductive adhesive with isotropical electrical conductivity modified with addition ... more 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 125°C and at the combined climate 80°C/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.
Microelectronics International, Jun 8, 2022
Purpose The purpose of this paper is to show a possibility to measure a change of a contact angle... more Purpose The purpose of this paper is to show a possibility to measure a change of a contact angle during the melting in real-time and to reveal significant factors of a wettability. Influence of the flux with combination of plasma on copper surface was investigated in experiment as well. Design/methodology/approach Laboratory equipment consists of heating and optical part that was developed and tested for real-time contact angle’s measurements. Solder balls based on Sn96.5/Ag3/Cu0.5 and Sn63Pb37 spread out on a copper substrate during a melting process. The wettability of pure copper surface was compared with copper surface treated with flux or combination plasma–flux. The contact angle and spreading rate of a melted solder balls observed by the charged-coupled device camera were analyzed in real-time and measured using the JavaScript. Findings Laboratory equipment allows for analysis of contact angle and spreading rate in real-time during the melting process. The contact angle decreases more noticeable after applying the plasma-flux treatment in contrast to no flux or flux treatment only. Using the plasma treatment before application of the flux improves the wettability and the effectivity of the flux activity on the copper surface during the melting process. Originality/value The interpretation of the results of such a comprehensive measurement leads to a better understanding of the mutual relation between flux and combination plasma–flux of the wetting during the melting process. The simple, cheap, fast and accurate laboratory equipment, which consists of the heating and the optical part, allows for the wettability evaluation of the melting process in real-time.
This paper shows how a surface finish does affect wettability. Four standard lead-free alloys sel... more This paper shows how a surface finish does affect wettability. Four standard lead-free alloys selected for surface finishes on PCB (LF HASL, ImSn, ENIG, and Cu) with a newly developed surface finish based on SnAg7 alloy were compared. Wetting characteristics of surface finishes were analysed using the spreading rate method and a method based on wetting reflow pattern, both in laboratory condition. Experiments were supplemented by analysis of the effect of plasma on the flux activity, and eventually on wettability. A self-developed equipment was applied to evaluate the spreading rate. The spreading rate method allows for real-time measurement of contact angle of liquid SAC 305 solder balls on various PCB surface finishes. The method based on wetting reflow pattern by SAC 305 solder paste applied on various PCB surfaces confirms these wetting characteristics. The wettability of the new and relatively cheap SnAg7 surface finish is almost comparable with surface finish based on ENIG. This new surface finish is a prospective material that offers interesting properties for application in electronics.
Circuit World, Feb 4, 2019
PurposeThe purpose of this paper was to investigate an influence of a low temperature pressureles... more PurposeThe purpose of this paper was to investigate an influence of a low temperature pressureless sintering process of silver paste on the quality of sintered joints.Design/methodology/approachThe authors analyzed various curing conditions of the paste during its sintering process: 175°C/90 min, 200°C/60 min, 250°C/30 min, 250°C/60 min, 350°C/30 min and 350°C/60 min. They analyzed an influence of the surface plating applied on a ceramic substrate/layer (Cu, Ag, AgPt and Au thick film) on the joints quality. The authors analyzed microstructure and electrical resistance of the joints. They evaluated these properties from the point of view of thermal aging process and changing resistance, after a constant current loading of the sintered joints.FindingsThe nanoscale pressureless silver paste can be applied for replacing a pressure-assisted micro-sized silver paste. It was found that the quality of the metal plating applied on the ceramic substrate/layer has a significant impact on the quality of the sintered joints. Copper and AgPt plating have better impact on quality of sintered joints in compare with Ag plating.Originality/valueThis investigation of the quality of the pressureless sintered joints at the silver-silver interface reveals an evident cracking immediately after the silver paste curing. Rapid sintering process typical for silver-based films on the substrate is because of the inter-diffusion between the micro and nanoparticles of silver at interfacial interface.
This paper is oriented to fundamental understanding of mechanical characterization techniques tha... more This paper is oriented to fundamental understanding of mechanical characterization techniques that assist in probing the nature of failure in glass/epoxy multilayer and sandwich structure of electronic boards after multi reflow processes. We have tested and compared multilayer PCB and a new type of electronic boards based on sandwich structures after multiply thermal exposure based on macroscopic observation and three bent point tests. New type of electronic boards based on the sandwich structure is characterized by high stiffness and good thermal stability. Such new type of structure would be applied for Face-down technology within embedding electronic components in the core of the sandwich structure.
Iet Microwaves Antennas & Propagation, Mar 5, 2018
The study deals with the application of low-temperature co-fired ceramic (LTCC) technology for de... more The study deals with the application of low-temperature co-fired ceramic (LTCC) technology for design of a higherorder mode dielectric resonator antenna element operating at centre frequency 25.7 GHz. The LTCC material that the authors use provides very low dielectric losses and enables us to design an antenna element with very high radiation efficiency. The authors follow by examining the mutual coupling between two resonators and the authors propose a small (1 × 4) onedimensional antenna array composed of such elements. In order to minimise the dimensions of the ground plane and to place the connector at a convenient location, the authors design a parallel feed network in substrate integrated waveguide technology, thus reducing the radiation losses of the feeding structure. The experiments verify the four-element antenna array concept with maximum measured gain of 16.3 dBi.
This paper presents novel application of using micro channels integrated in LTCC (Low Temperature... more This paper presents novel application of using micro channels integrated in LTCC (Low Temperature Co-fired Ceramics) structure as new solution for cooling in power electronics. The aim of this paper is detailed investigation of the thermal resistance, flow analysis and distribution of coolant inside LTCC substrates with internal micro channels. Three different LTCC multilayer structures with integrated micro channel and thermal vias were designed, simulated, fabricated and measured. It was applied various micro channel widths and various quantities of thermal vias under the power chip for improving cooling affect. The impact of the volume flow of liquid coolant, structures of multilayer substrate and thermal vias on thermal resistance of substrate was simulated by using the simulation software Mentor Graphic FloEFD™. The fluidic channel was integrated in the third layer from the top of 6 layers substrate. Thermal vias were embedded inside substrate and channel excluding the top dielectric layer. This cooling concept improves homogeneity and effectivity of heat transfer between the power chips and the coolant. The coolant is pumped through channel for cooling down the 2 tested chips. Principle of thermal resistance measuring was on investigation of the impact of the first chips' thermal load on the second chip. The heat transfer is characterized by the decrease of maximum working temperature, thermal resistance of substrate, temperature distribution, fluid pressure and flow velocity. The main advantage of presented cooling concept is effective and homogenous cooling of critical components.
ABSTRACT The paper deals with the principle of X-ray investigation of 96,5Sn3Ag0,5Cu solder alloy... more ABSTRACT The paper deals with the principle of X-ray investigation of 96,5Sn3Ag0,5Cu solder alloy. The goal of the paper is to simply introduce method of the solder microstructure research via synchrotron X-ray radiation at the B2 bending magnet beamline of DORIS III positron storage ring at HASYLAB/DESY, Hamburg, Germany. The method is suitable especially for in-situ analysis of materials - evaluation of the phase changes.
Connecting to motor aggregate reliability and operational life it is very important to reliably o... more Connecting to motor aggregate reliability and operational life it is very important to reliably observe the oil change interval. Determination of critical parameters of motor oil is important for correct statement of its condition in engine. By implementation of sensor system which directly acquires several parameters simultaneously, it is possible to achieve the better sight onto degradation process of motor oil. Some most relevant, mainly electric parameters were investigated at samples of standard semi-synthetic motor oil and discussed with inscribed the subsequent interest.
Soldering & Surface Mount Technology, Feb 6, 2017
Purpose The paper aims to investigate the structure and thermal stability of newly developed lead... more 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.
ABSTRACT This work has been focused on viscosity and rheological measurement of some solder paste... more ABSTRACT 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.
The goal of the study is to compare quality of lead-free vapour phase reflowed solder joints sold... more 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.
ABSTRACT Comparison of the stability and reliability of thick film resistors prepared by differen... more ABSTRACT Comparison of the stability and reliability of thick film resistors prepared by different techniques is discussed in this work. This aim was accomplished by comparison of the thick film resistors prepared by etching and conventional thick film technology. The etching technique as a combination of three techniques (photolithography, LTCC processing and PCB patterning technology) was introduced for construction of "planar" resistors as a new idea. We show that it is possible to develop devices that are useful in standard thick film technology and that it is possible to fabricate 3D (planar) resistors with higher stability and reliability. As operating material we selected low temperature co-fired ceramic (LTCC), because it allows the fabrication of three-dimensional structures, and it is compatible with the screen-printing process.
The aim of the work is to investigate the possibilities of capacitive sensing of driver position,... more The aim of the work is to investigate the possibilities of capacitive sensing of driver position, and by virtue of the results, to design and to realize a few models which will demonstrate the principle, practically. The paper describes two types of capacitive driver. Each of them differently defines its present position. They were made by polymer thick film technology
This paper is focused on quality of solder joints. Solder joint were realized on the surface of t... more This paper is focused on quality of solder joints. Solder joint were realized on the surface of the substrate as well as embedded into the substrate. Two types of substrate materials (low Tg and high Tg) were used for this research. The objective of this research was determining the realistic lifetime of embedded solder joints. This lifetime was determined by comparison of embedded solder joints with standard solder joints on the surface of the substrate. Lifetime of the samples was evaluated by thermal cycling test between 125°C and -45°C. 1000 thermal cycles were performed. Electrical properties of the samples were measured by 4-point probe method. Microstructure of the cross-sections of the tested samples were analyzed as well.
ABSTRACT The solder reflow profile is one of the key variables in the manufacturing process that ... more ABSTRACT 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.
This paper present designs of inset feeding rectangular microstrip antennas on different substrat... more This paper present designs of inset feeding rectangular microstrip antennas on different substrates with different dielectric constants (FR4 laminate, Green Tape™ 951 LTCC from DuPont and RT/duroid 6010LM from Rogers Corporation). All of antennas were designed for 2.45 GHz frequency band that is one of the most common frequency band for modern wireless communication (WiFi or Bluetooth). Antennas were simulated and results were realized from antenna miniaturization point of view. For antenna miniaturization were used substrates with higher dielectric constant ($\varepsilon_{r}$) at approximately similar substrate thickness. CST Microwave Studio was used for design and optimization of antennas. As a result of our simulations, we find that with an increase of varepsilonr\varepsilon_{r}varepsilonr the antenna area will be reduced but at the detriment of the reduction of the bandwidth at −10 dB. It is possible to eliminate this problem with the increase of the thickness of the substrate. In this way it is possible to achieve required miniaturization while maintaining the possibility of using this antenna in the WiFi area.
Materials Science Forum, 2019
This work is focused on a development and research of a new lead-free Sn-Mg solder, alloy compati... more This work is focused on a development and research of a new lead-free Sn-Mg solder, alloy compatible with the human body. Tin and magnesium are biocompatible elements which do not cause an inflammation or allergic reactions with living tissues. We have prepared the Sn97Mg3 solder (wt. %) by a rapid solidification of its melt on a copper wheel (melt-spinning technique). This solder may find applications in electronic devices for intracorporeal utilisation. The microstructure of the prepared solder exhibits a heterogeneous distribution of the SnMg2 intermetallic particles within the β-Sn matrix. Structure of the solder was studied by an in-situ high energy X-ray diffraction experiment (energy of an X-ray photon: 60 keV) where 2D XRD patterns were collected from the sample in the temperature range from 298 K to 566 K. The experiment was performed at a high brilliance 3rd generation synchrotron source of radiation (PETRA III storage ring, DESY, Hamburg, Germany) at the P02 undulator beamline. From the measured X-ray diffraction data by applying the Rietveld refinement technique we have obtained thermal volume expansion data, mean positions of atoms as well as isotropic atomic displacement parameters of the constituent SnMg2 and the β-Sn crystalline phases. Thermal behaviour was studied by differential scanning calorimetry at heating rates of 5, 15, 30 and 60 K.min-1 and compared with the measured X-ray data. Our main goal lies in a preparation of a lead-free solder with fine grain structure made exclusively of biocompatible elements. We demonstrated that the rapid melt solidification technique leads to in an improvement and better thermal stability of this alloy.