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The purpose of this paper is to assess the reliability of thermoelectric generators after ageing at elevated temperature and to determine the influence of the technology used (i.e. type of thermoelectric material, type of substrate and soldering technology) for thermogenerator (TGE) assembly.

In this paper, the Seebeck coefficient and the current voltage were measured for lead telluride doped with either manganese (PMT), germanium (PGT) or sulfur (PST) TGEs. The Seebeck coefficient measurements were taken at temperatures between 230 and 630 K.

The Seebeck coefficient determined for PMT, PGT and PST TGEs increases approximately linearly with increasing temperature and is greater by about 40 per cent for PST and about 30 per cent for PMT than in commercially available PbTe TGEs. The best outcome in terms of stability after long-term ageing was that of PMT material.

The choice of proper technology (i.e. thermoelectric materials, type of substrate and soldering technology) for the TGE assembly is essential for their functioning overtime and reliability.

The paper aims to present a comparative study of various thermocouple (TC) attaching methods for the proper measurement of soldering temperature profiling during vapour phase soldering (VPS). The heat transfer process during VPS is different from common methods, while the required heat for reflow is provided by the condensation. The condensate is a flowing layer on the board, where the dynamic behaviour also affects the local conditions on the surfaces. Temperature measurements based on TCs are also affected this way; it is important to investigate the process for deeper understanding.

Bare printed circuit boards (PCBs) were prepared for standard K-Type TCs attachment with industry standard materials: kapton polyimide tape, aluminium tape, SMD adhesive and high-temperature solder (HTS). Heating experiments were performed in a batch-type VPS oven with Galden LS240 fluid and fixed oven parameters.

According to the specific attachment requirements, HTS and Alu-tape are the suggested methods for better profiling reliability and repeatability. Alu-tape is the preferred all-around method, for fast, exchangeable, cheap, reliable and repeatable profiling in a VPS oven. It was presented that the heating factor (Q?) gives more reliable comparison overview; the time period-based comparisons may be affected by the thermal inertia, while heating factor also includes temperature conditions at the given time points.

The paper presents the reliability of the presented methods for VPS and present suggestions for the use of different TC ends and attaching materials during condensation heating of the PCBs. Also a new approach on profiling data evaluation based on the heating factor is presented and suggested for wider use.

After technical textiles and functional textiles, smart textiles came into force a few years back. The term “smart textiles” covers a broad range. The application possibilities are only limited by our imagination and creativity. Hence it is not simple for the readers of the many articles that have been published to distinguish where reality ends and where fiction begins. In this paper, it is further explored what smart textiles precisely mean. In a second part, an analysis is made of the possibilities, the state of affairs and the need for further research, including research in the Department of Textiles at the Ghent University (Belgium).

This paper aims to present certain issues in direct bonded copper (DBC) technology towards the manufacture of Al2O3 or AlN ceramic substrates with one or both sides clad with a copper (Cu) layer.

As part of the experimental work, attempts were made to produce patterns printed onto DBC substrates based on four substantially different technologies: precise cutting with a diamond saw, photolithography, the use of a milling cutter (LPKF ProtoMat 93s) and laser ablation with differential chemical etching of the Cu layer.

The use of photolithography and etching technology in the case of boards clad with a 0.2-mm-thick Cu layer, can produce conductive paths with a width of 0.4 mm while maintaining a distance of 0.4 mm between the paths, and in the case of boards clad with a 0.3-mm-thick copper layer, conductive paths with a width of 0.5 mm while maintaining a distance of 0.5 mm between paths. The application of laser ablation at the final step of removing the unnecessary copper layer, can radically increase the resolution of printed pattern even to 0.1/0.1 mm. The quality of the printed pattern is also much better.

Etching process optimization and the development of the fundamentals of technology and design of power electronic systems based on DBC substrates should be done in the future. A limiting factor for further research and its implementation may be the relatively high price of DBC substrates in comparison with typical PCB printed circuits.

Several examples of practical implementations using DBC technology are presented, such as full- and half-bridge connections, full-wave rectifier with an output voltage of 48 V and an output current of 50 A, and part of a battery discharger controller and light-emitting diode illuminator soldered to a copper heat sink.

The paper presents a comparison of different technologies used for the realization of precise patterns on DBC substrates. The combination of etching and laser ablation technologies radically improves the quality of DBC-printed patterns.

This paper aims to present a review of the recent developments in vapour phase soldering (VPS) technology. This study focuses on the following topics: recent developments of the technology, i.e. soft and vacuum VPS; measurement and characterization methods of vapour space, i.e. temperature and pressure; numerical simulation of the VPS soldering process, i.e. condensate layer and solder joint formation; and quality and reliability studies of the solder joints prepared by VPS, i.e. void content and microstructure of the solder joints.

This study was written according to the results of a wide literature review about the substantial previous works in the past decade and according to the authors’ own results.

Up to now, a part of the electronics industry believes that the reflow soldering with VPS method is a significant alternative of convection and infrared technologies. The summarized results of the field in this study support this idea.

This literature review provides engineers and researchers with understanding of the limitations and application possibilities of the VPS technology and the current challenges in soldering technology.

This paper summarizes the most important advantages and disadvantages of VPS technology compared to the other reflow soldering methods, as well as points out the necessary further developments and possible research directions.

Vapor phase soldering (VPS), also known as condense soldering, is capable of improving the mechanical reliability of solder joints in electronic packaging structures. The paper aims to discuss this issue.

In the present study, VPS is utilized to assemble two typical packaging types (i.e. ceramic column grid array (CCGA) and BGA) for electronic devices with lead-containing and lead-free solders. By applying the peak soldering temperatures of 215°C and 235°C with and without vacuum condition, the void formation and intermetallic compound (IMC) thickness are compared for different packaging structures with lead-containing and lead-free solder alloys.

It is found that at the soldering temperature of 215°C, CCGA under a vacuum condition has fewer voids but BGA without vacuum environment has fewer voids despite of the existence of lead in solder alloy. In light of contradictory phenomenon about void formation at 215°C, a similar CCGA device is soldered via VPS at the temperature of 235°C. Compared with the size of voids formed at 215°C, no obvious void is found for CCGA with vacuum at the soldering temperature of 235°C. No matter what soldering temperature and vacuum condition are applied, the IMC thickness of CCGA and BGA can satisfy the requirement of 1.0–3.0 µm. Therefore, it can be concluded that the soldering temperature of 235°C in vacuum is the optimal VPS condition for void elimination. In addition, shear tests at the rate of 10 mm/min are performed to examine the load resistance and potential failure mode. In terms of failure mode observed in shear tests, interfacial shear failure occurs between PCB and bulk solder and also within bulk solder for CCGA soldered at temperatures of 215°C and 235°C. This means that an acceptable thicker IMC thickness between CCGA solder and device provides greater interfacial strength between CCGA and device.

Due to its high I/O capacity and satisfactory reliability in electrical and thermal performance, CCGA electronic devices have been widely adopted in the military and aerospace fields. In the present study, the authors utilized VPS to assemble a typical type of CCGA with the control package of conventional BGA to investigate the relation between essential condition (i.e. soldering temperature and vacuum) to void formation.

A measurement method has been developed to reveal the viscosity change of solder pastes during stencil printing. This paper aimed to investigate thixotropic behaviour, the viscosity change of a lead-free solder paste (Type 4).

The viscosity change of the solder paste during stencil printing cycles was characterised in such a way that the time-gap between the printing cycles was modelled with a rest period between every rheological measurement. This period was set as 15, 30 and 60 s during the research. The Cross model was fitted to the measurement results, and the η₀ parameter was used to characterise the viscosity change. The number of printing cycles necessary for reaching a stationary state in viscosity was determined for various rest periods.

It was found that the decrease in zero-shear viscosity is significant (25 per cent) in the first cycles, and it starts to become stationary at the sixth-seventh cycles. This means a printing process can provide the appropriate deposits only after the 7th cycle with the investigated Type 4 solder paste.

Time-dependent rheological behaviour of solder pastes was studied in the literature, but only the viscosity change over continuous time at constant shear rates was examined. The time-gap between stencil printing cycles was not considered, and thixotropic behaviour of solder pastes was also neglected. Therefore, the authors developed a measurement set which is able to model the effect of time-gap between printing cycles on the viscosity change of solder pastes.

The purpose of this paper is to present a novel approach on investigating critical current densities in the solder joints of chip-size surface mounted device (SMD) components. The investigation involves a numerical approach and a physical validation with selected track-to-pad connections and high current loads (CXs).

During the investigations, shape of solder fillets was calculated in Surface Evolver, and then the current densities were calculated accordingly in the given geometry. For the verification, CX tests were performed on joints at elevated temperatures. The joints were qualified with X-ray microscopy, cross-section analysis and shear tests.

This study ascertained that the inhomogeneity in current density depends on the track-to-pad structure of the joint. Also this study found that the heavy CX decreases the mechanical strength, but the degradation does not reach the level of electromigration (EM)-induced voiding.

The heavy CX significantly affects joint reliability and the results point out to EM-induced failure-limitations on printed circuit board (PCB)-based assemblies due to the thermomechanical weakness of the FR4 material.

The experiments investigate current density from a novel aspect on more frequently used small-scale components with different track-to-pad configurations – pointing out possible failure sources.

The paper aims to present an investigation of heating during vapour phase soldering (VPS) on inclined printed circuit board (PCB) substrates. The PCB is a horizontal rectangular plate from the aspect of filmwise condensation with a given inclination setting.

The paper focuses on the measurement of temperature distribution on the PCBs with a novel setup immersed in the saturated vapour space. The measuring instrumentation is optimized to avoid and minimize vapour perturbing effects.

The inhomogeneity of the heating is presented according to the lateral dimensions of the PCB. The inclination improves temperature uniformity, improves heat transfer efficiency; however, a minor misalignment may affect the flow and result in uneven heating.

The results can be implemented for practical improvements in industrial ovens with the use of intended inclination. The improvements may consequently point to more efficient production and better joint quality.

The novel method can be used for deeper investigation of inclination during and can be complemented with numerical calculations. The results highlight the importance of precise PCB holding instrumentation in VPS ovens.