Laser transmission welding as an assembling process for high temperature electronic packaging.

Higher efficiency, power density, reliability and longer lifetime of power electronic devices would stem from progresses in material science. In this work, we propose to use a high performance thermoplastic polymer PAEK as packaging box to extend the operating temperature above 200°C. More, the laser transmission welding process has been applied to PAEK to join the two-part module. In order to validate this assembling process, the temperature distribution inside the specimens was measured during laser transmission welding. The assembly consists of a quasi-amorphous sample as the upper part and a semi-crystalline sample as the lower part. The temperature fields were measured by infrared thermography with the camera sensor perpendicular to the welded interface. With an energy beam of 28 J.mm-2 and irradiation time of 15 s, we have noticed that the maximum temperature inside the sample is kept far from the PAEK degradation one. Moreover, the temperature at the interface reaches the melting temperature thus assuring enough mobility for polymeric chains to get adhesion at the interface. The location and size of the heat-affected zone has been determined. Finally, some frames were machined and successfully welded

Exploring the high-temperature electrical performance of Ca3-xLaxCo4O9 thermoelectric ceramics for moderate and low substitution levels

Aliovalent substitutions in Ca3Co4O9 often result in complex effects on the electrical prop-erties and the solubility, and impact of the substituting cation also depends largely on the prepara-tion and processing method. It is also well-known that the monoclinic symmetry of this material’s composite crystal structure allows for a significant hole transfer from the rock salt-type Ca2CoO3 buffer layers to the hexagonal CoO2 ones, increasing the concentration of holes and breaking the electron–hole symmetry from the latter layers. This work explored the relevant effects of relatively low La-for-Ca substitutions, for samples prepared and processed through a conventional ceramic route, chosen for its simplicity. The obtained results show that the actual substitution level does not exceed 0.03 (x < 0.03) in Ca3-xLaxCo4O9 samples with x = 0.01, 0.03, 0.05 and 0.07 and that further introduction of lanthanum results in simultaneous Ca3Co4O9 phase decomposition and secondary Ca3Co2O6 and (La,Ca)CoO3 phase formation. The microstructural effects promoted by this phase evolution have a moderate influence on the electronic transport. The electrical measurements and determined average oxidation state of cobalt at room temperature suggest that the present La sub-stitutions might only have a minor effect on the concentration of charge carriers and/or their mobil-ity. The electrical resistivity values of the Ca3-xLaxCo4O9 samples with x = 0.01, 0.03 and 0.05 were found to be ~1.3 times (or 24%) lower (considering mean values) than those measured for the pris-tine Ca3Co4O9 samples, while the changes in Seebeck coefficient values were only moderate. The highest power factor value calculated for Ca2.99La0.01Co4O9 (~0.28 mW/K2m at 800 °C) is among the best found in the literature for similar materials. The obtained results suggest that low rare-earth substitutions in the rock salt-type layers can be a promising pathway in designing and improving these p-type thermoelectric oxides, provided by the strong interplay between the mobility of charge carriers and their concentration, capable of breaking the electron–hole symmetry from the conduc-tive layers.publishe

In-situ infrared thermography measurements to master transmission laser welding process parameters of PEKK

The temperature field along the thickness of the specimens has been measured during transmission laser welding. Polyetherketoneketone (PEKK) is a very high performance thermoplastic with tunable properties. We have shown that this grade of PEKK can be turned to quasi-amorphous or semi-crystalline material, due to its slow kinetics of crystallization. Its glass transition temperature is 150 °C. The effect of its crystalline rate directly impacts its optical properties: the transmittance of quasi-amorphous PEKK is about 60% in the NIR region (wavelength range from 0.4 to 1.2 μm) whereas it is less than 3% for the semi-crystalline material. The welding tests have been carried out with an 808 nm laser diode apparatus. The heat field is recorded during the welding experiment by infrared thermography with the camera sensor perpendicular to the lasersheet and to the sample’s length to focus on the welded interface. The study is divided in two steps: firstly, a single specimen is irradiated with an energy density of 22 J.mm − 2 : the whole sample thickness is heated up, the maximum temperature reaches 222 ± 7 °C. This temperature corresponds to about T g + 70 °C, but the polymer does not reach its melting temperature. After that, welding tests were performed: a transparent (quasi-amorphous) sample as the upper part and an opaque (semi-crystalline) one as the lower part were assembled in static conditions. The maximum temperature reached at the welded interface is about 295 °C when the upper specimen is irradiated for 16 s with an energy density of 28 J.mm − 2 . The temperature at the welded interface stays above T g during 55 s and reached the melting temperature during 5 s before rapid cooling. These parameters are suitable to assemble both polymeric parts in a strong weld. This work shows that infrared thermography is an appropriate technique to improve the reliability of laser welding process of high performance thermoplastics

The ERA Registry Annual Report 2019 : summary and age comparisons

Background Data on renal replacement therapy (RRT) for end-stage renal disease were collected by the European Renal Association (ERA) Registry via national and regional renal registries in Europe and countries bordering the Mediterranean Sea. This article provides a summary of the 2019 ERA Registry Annual Report, including data from 34 countries and additional age comparisons. Methods Individual patient data for 2019 were provided by 35 registries and aggregated data by 17 registries. Using these data, the incidence and prevalence of RRT, the kidney transplantation activity and the survival probabilities were calculated. Results In 2019, a general population of 680.8 million people was covered by the ERA Registry. Overall, the incidence of RRT was 132 per million population (p.m.p.). Of these patients, 62% were men, 54% were >= 65 years of age and 21% had diabetes mellitus as primary renal disease (PRD), and 84% had haemodialysis (HD), 11% had peritoneal dialysis (PD) and 5% had pre-emptive kidney transplantation as an initial treatment modality. The overall prevalence of RRT on 31 December 2019 was 893 p.m.p., with 58% of patients on HD, 5% on PD and 37% living with a kidney transplant. The overall kidney transplant rate was 35 p.m.p. and 29% of the kidney grafts were from a living donor. The unadjusted 5-year survival probability was 42.3% for patients commencing dialysis, 86.6% for recipients of deceased donor grafts and 94.4% for recipients of living donor grafts in the period 2010-14. When comparing age categories, there were substantial differences in the distribution of PRD, treatment modality and kidney donor type, and in the survival probabilities.Peer reviewe

General approach of the photothermoelectric technique for thermal characterization of solid thermoelectric materials

International audienceThis work focuses on the photothermoelectric (PTE) technique allowing the thermal characterization of solid-state thermoelectric (TE) materials. Previously, this technique was restricted to TE materials having low electrical conductivities. Here, the PTE technique is extended and generalized to all solid-state TE materials with low or high electrical conductivities. This is achieved by taking into account the Gaussian shape of the thermal excitation source. The formalism of this new methodology is developed and the procedure for extracting thermal parameters is proposed. For illustration, two different TE materials are studied with relatively high electrical conductivity (Bi2Te2.4Se0.6) and relatively low electrical conductivity (Bi2Ca2Co1.7Ox). The thermal properties of these two materials (thermal diffusivity, effusivity and conductivity) are found and compared to those obtained by the photothermal radiometry which is a well established technique. The good concordance between the results obtained by these two techniques demonstrates the relevance of the generalized PTE technique. One of the main advantages of this technique is its non use of an external sensor

Very large superconducting currents induced by growth tailoring

The efforts of carrying forward superconducting materials to commercialization can be overcome by materials with high performance potentiated by a suitable processing technique. In this work, extreme critical currents up to 241 A @ 77 K were attained by tuning the crystal growth in a directional solidification process. Bulk rods of textured Bi-2212/2.9 wt % Ag were obtained by changing the conventional laser floating zone technique through the application of a d.c. electrical current during the crystallization process. Using an optimized composition, the electrically assisted laser floating zone (EALFZ) allowed obtaining 5800 A/cm2 in rods exhibiting only 2.3 mm in diameter, the highest value reported so far for bulk samples. This behavior is a consequence of the texture enhancement and radial phase distribution, exceeding a 2-fold increase in Jc compared with samples grown without electrical current. Morphological and structural observations are discussed and correlated with the results from the electrical characterization. Applications on extremely efficient electrical current leads working at temperatures below 77 K using the above-described materials grown by EALFZ are anticipated.The authors wish to thank the MINECO-FEDER (Project MAT2013-46505-C3-1-R) and Gobierno de Aragón and Fondo Social Europeo (Research Groups T12 and T87) for financial support. M. A. Madre acknowledges the MINECO-FEDER (Project MAT2011-22719) for funding. The authors acknowledge the financial support from the Portuguese Science and Technology Foundation (FCT) through the program UID/CTM/50025/2013.Peer reviewe