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This paper presents the results of the investigations of LED modules soldered with the use of different soldering pastes.

The tested power LED modules are soldered using different solder pastes and soldering processes. Thermal parameters of the performed modules are tested using indirect electrical methods. The results of measurements obtained for different modules are compared and discussed.

It was shown that the soldering process visibly influences the results of measurements of optical and thermal parameters of LED modules. For example, values of thermal resistance of these modules and the efficiency of conversion of electrical energy into light differ between each other even by 15%.

The obtained results of investigations can be usable for designers of the assembly process of power LED modules.

This paper shows the investigations results in the area of effective assembly of power LEDs to the metal core printed circuit board (MCPCB) using different soldering pastes (REL22, REL61, LMPA-Q6, OM-5100, OM-338-PT, M8, OM-340, CVP-390). It was shown that the best thermal and optical properties of these modules are obtained for the OM5100 paste by Alpha Assembly.

This paper aims to present the results of the influence of a manner of soldering light emitting diodes (LEDs) to the metal core printed circuit board on thermal parameters of the module LED containing these diodes.

Using the authors’ elaborated measuring method and the dedicated measurement set-up, transient thermal impedances of LED modules, mounted using different soldering processes and mounted to the heat-sink with different values of the moment of force, are measured. The obtained results of measurements are discussed.

It was shown experimentally that the manner of soldering could strongly influence efficiency of dissipation of heat generated in the module. The best thermal properties were obtained for soldering using vapour phase technology with vacuum and paste LFS-216LT. It was also proved that the moment of force used while mounting the considered modules on the heat-sink can result in a change of the value of thermal resistance of this module exceeding even 12 per cent.

The investigations were performed for five LED modules operating at one, arbitrarily selected value of power dissipated in these modules mounted on the heat-sink of arbitrarily selected dimensions.

The obtained results of measurements could be usable for designers of mounting processes of power LED modules.

This paper presents the results of investigations of thermal properties of LED modules, in which different techniques of soldering are used. It was shown experimentally that the manner of soldering could strongly influence efficiency of dissipation of heat generated in the module. It was also proved that the moment of force used while mounting the considered modules on the heat-sink is important.

The aim of this paper is to find the electrical representation of a solid oxide fuel cell (SOFC) that enables the application of typical exploitation characteristics of fuel cells for estimation of fuel cell parameters (for example, exchange current) and easy analysis of phenomena occurred during the fuel cell operation.

Three-layer structure of an SOFC, where a thin semi-conducting layer of electrolyte separates the anode from the cathode, shows a strong similarity to typical semiconductor devices built on the basis of P-N junctions, like diodes or transistors. Current–voltage (I-V) characteristics of a fuel cell can be described by the same mathematical functions as I-V plots of semiconductor devices. On the basis of this similarity and analysis of impedance spectra of a real fuel cell, two electrical representations of the SOFC have been created.

The simplified electrical representation of SOFC consists of a voltage source connected in series with a diode, which symbolizes a voltage drop on a cell cathode, and two resistors. This model is based on the similarity of Butler-Volmer to Shockley equation. The advanced representation comprises a voltage source connected in series with a bipolar transistor in close to saturation mode and two resistors. The base-emitter junction of the transistor represents voltage drop on the cell cathode, and the base-collector junction represents voltage drop on the cell anode. This model is based on the similarity of Butler-Volmer equation to Ebers-Moll equation.

The proposed approach based on the Shockley and Ebers-Moll formulas enables the more accurate estimation of the ion exchange current and other fuel cell parameters than the approach based on the Butler-Volmer and Tafel formulas. The usability of semiconductor models for analysis of SOFC operation was proved. The models were successively applied in a new design of a planar ceramic fuel cell, which features by reduced thermal capacity, short start-up time and limited number of metal components and which has become the basis for the SOFC stack design.

This paper aims to investigate voiding phenomena in solder joints under thermal pads of light-emitting diodes (LEDs) assembled in mass production environment by reflow soldering by using seven low-voiding lead-free solder pastes.

The solder pastes investigated are of SAC305 type, Innolot type or they are especially formulated by the manufacturers on the base of (SnAgCu) alloys with addition of some alloying elements such as Bi, In, Sb and Ti to provide low-void contents. The SnPb solder paste – OM5100 – was used as a benchmark. The solder paste coverage of LED solder pads was chosen as a measure of void contents in solder joints because of common usage of this parameter in industry practice.

It was found that the highest coverage and, related to it, the least void contents are in solder joints formed with the pastes LMPA-Q and REL61, which are characterized by the coverage of mean value 93.13% [standard deviation (SD) = 2.72%] and 92.93% (SD = 2.77%), respectively. The void diameters reach the mean value equal to 0.061 mm (SD = 0.044 mm) for LMPA-Q and 0.074 mm (SD = 0.052 mm) for REL61. The results are presented in the form of histograms, plot boxes and X-ray images. Some selected solder joints were observed with 3D computer tomography.

The statistical analyses are carried out on the basis of 2D X-ray images with using Origin software. They enable to compare features of various solder pastes recommended by manufacturers as low voiding. The results might be useful for solder paste manufacturers or electronic manufacturing services.

The purpose of the paper is to experimentally evaluate the impact of voids on thermal conductivity of a macro solder joint formed between a copper cylinder and a copper plate by using reflow soldering.

A model of a surface mount device (SMD) was developed in the shape of a cylinder. A copper plate works as a printed circuit board (PCB). The resistor was connected to a power supply and the plate was cooled by a heat sink and a powerful fan. A macro solder joint was formed between a copper cylinder and a copper plate using reflow soldering and a lead-free solder paste SAC305. The solder paste was printed on a plate through stencils of various apertures. It was expected that various apertures of stencils will moderate the various void contents in solder joints. K-type thermocouples mounted inside cylinders and at the bottom of a plate underneath the cylinders measured the temperature gradient on both sides of the solder joint. After finishing the temperature measurements, the cylinders were thinned by milling to thickness of about 2 mm and then X-ray images were taken to evaluate the void contents. Finally the tablets were cross-sectioned to enable scanning electron microscopy (SEM) observations.

There was no clear dependence between thermal conductivity of solder joints and void contents. The authors state that other factors such as intermetallic layers, microcracks, crystal grain morfologyof the interface between the solder and the substrate influence on thermal conductivity. To support this observation, further investigations using metallographic methods are required.

Results allow us to assume that the use of SAC305 alloy for soldering of components with high thermal loads is risky. The common method for thermal balance calculation is based on the sum of serial thermal resistances of mechanical compounds. For these calculations, solder joints are represented with bulk SAC305 thermal conductivity parameters. Thermal conductivity of solder joints for high density of thermal energy is much lower than expected. Solder joints’ structure is not fully comparable with bulk SAC305 alloy. In experiments, the average value of the solder joint conductivity was found to be 8.1 W/m·K, which is about 14 per cent of the nominal value of SAC305 thermal conductivity.

The aim of this paper is to evaluate using statistical methods how two soldering techniques – the convection reflow and vapour phase reflow with vacuum – influence reduction of voids in lead-free solder joints under Light Emitted Diodes (LEDs) and Ball Grid Arrays (BGAs).

Distribution of voids in solder joints under thermal and electrical pads of LEDs and in solder balls of BGAs assembled with convection reflow and vapour phase reflow with vacuum has been investigated in terms of coverage or void contents, void diameters and number of voids. For each soldering technology, 80 LEDs and 32 solder balls in BGAs were examined. Soldering processes were carried out in the industrial or semi-industrial environment. The OM340 solder paste of Innolot type was used for LED soldering. Voidings in solder joints were inspected with a 2D X-ray transmission system. OriginLab was used for statistical analysis.

Investigations supported by statistical analysis showed that the vapour phase reflow with vacuum decreases significantly void contents and number and diameters of voids in solder joints under LED and BGA packages when compared to convection reflow.

Voiding distribution data were collected on the basis of 2D X-ray images for test samples manufactured during the mass production processes. Statistical analysis enabled to appraise soldering technologies used in these processes in respect of void formation.

The purpose of this paper is to evaluate selected methods of reduction voidings in lead-free solder joints underneath thermal pads of light-emitting diodes (LEDs), using X-ray inspection and Six Sigma methodology.

On the basis of cause and effect diagram for solder voiding, the potential causes of voids and influence of process variables on void formation were found. Three process variables were chosen: the type of reflow soldering, vacuum incorporation and the type of solder paste. Samples of LEDs were mounted with convection and vapour phase reflow soldering. Vacuum was incorporated into vapour phase soldering. Two types of solder pastes OM338PT and LFS-216LT were used. Algorithm incorporated into X-ray inspection system enabled to calculate the statistical distribution of LED thermal pad coverage and to find the process capability index (C_pk) of applied soldering techniques.

The evaluation of selected soldering processes of LEDs in respect of their thermal pad coverage and statistical C_pk indices is presented. Vapour-phase soldering with vacuum is capable (C_pk > 1) for OM338PT and LFS-216LT paste. Convection reflow without vacuum with LFS-216LT paste is also capable (C_pk = 1.1). Other technological soldering processes require improvements. Vacuum improves radically the capability of a reflow soldering for an LED assembly. When vacuum is not accessible, some improvement of capability to a lower extent is possible by an application of void-free solder pastes.

Six Sigma statistical methodology combined with X-ray diagnosis was used to check whether applied methods of void reduction underneath LED thermal pads are capable processes.

The paper aims to present the innovative design of a planar multilayered high temperature solid oxide fuel cell (SOFC), which is easy to manufacture, and features high resistance to rapid temperature changes. Temperature resistance was accomplished thanks to easy to heat, thin flat ceramic structure of the cell and elimination of metallic interconnections.

The ceramic fuel cell consists of the anode core made of six to eight layers of nickel/yttria-stabilized zirconia tapes (Ni/YSZ) isostatically pressed into a laminate. Two networks of fuel distribution microchannels are engraved on both sides of the anode laminate. The microchannels are subsequently covered with a thin layer of the functional anode tape made of Ni/YSZ and a solid electrolyte tape made of YSZ.

The single planar double-sided ceramic SOFC of dimensions 19 × 60 × 1.2 mm3 provides 3.2 Watts of electric power. The prototype of the battery which consists of four SOFCs provides an output power of > 12 W. Tests show that the stack is resistant to the rapid temperature change. If inserted into a chamber preheated to 800°C, the stack provides the full power within 5 minutes. Multiple cycling does not destroy the stack.

This anode-supported fuel cell structure is provided with thin anode functional layers suspended on a large number of fine beams. The whole anode structure is made with the same ceramic material, so the mechanical stress is minimized during the cell operation.

The purpose of this paper is to present the embossing as a replication technique for structuring fuel channels in the anode-supported solid oxide fuel cells (SOFCs).

The anode laminate, which was exposed to embossing, consisted of eight layers of isostatic pressed Ni-yttria-stabilized zirconia tapes (Ni-YSZ). Preheating the mould and soaking the laminate in the plasticizer was applied before structuring of the channels to soften the laminate. Compressing tests were carried out to investigate the embossing ability of the Ni-YSZ laminate and to find the optimal processing parameters. Embossing was carried out with a testing machine, and the samples were exposed to embossing forces in the range up 20 kN with a certain speed of compression and a dwell time.

The embossing parameters (force of compression, speed of compression and dwell time) suitable for proper fuel channels formation were established. Shapes, profiles and dimensions of the embossed channels were analysed and compared to the micromachined channels. The model of the SOFC with embossed fuel channels was completed, and its current-voltage characteristic was measured.

Experiments proved that embossing can be the alternative method for patterning fuel microchannels in SOFCs. Embossing simplifies the process of fuel channel formation and reduces the time of SOFC fabrication. It is necessary to improve the geometry and quality of the mould formation to make the fuel channels deeper and of better surface finish.

The paper presents the application of two advanced thick‐film techniques: etching of fired thick‐films and photoimaging of photosensitive thick‐films for fabrication bandpass microwave filters operating in the frequency range from 6 to 14 GHz. Modified screen printing through ultra‐thin calendered screens is used for comparative goals. Advanced techniques are combined with novel thick‐film conductors including photosensitive pastes and etchable pastes.