Developing new joining materials for low-temperature electronics assembly

International audienceThe present work focuses on a new kind of lead-free joining method for surface-mount technology based on precursor chemistry. The interest of metal oxalates as new soldering materials for die attachment (1st level packaging) was previously demonstrated with silver oxalate. The thermal decomposition of metal oxalates under controlled atmosphere can be used to produce small metal particles below their melting point. These particles are found to be in a highly active particulate form. First experimental studies are focusing on several metal oxalates (tin oxalate and bismuth oxalate) to assess their suitability for low-temperature metal particle production. The main work is dealing with controlled chemical precipitation synthesis and characterization of the compounds as well as study of the properties of decomposition solid products (powder X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy and thermal analyses under different atmospheres)

Matériaux innovants sans plomb pour l'assemblage de composants électroniques à basse température

Dans le cadre du développement de nouveaux matériaux d’assemblage sans plomb, les premiers résultats de synthèse et de caractérisations physicochimiques d’oxalate de bismuth sont présentés. Par une méthode de décomposition thermique de précurseurs métal-organiques, la possibilité de produire des particules métalliques en dessous de la température de fusion du bismuth massif (271°C) est discutée ici. L’étude du comportement en température de l’oxalate de bismuth montre l’influence de l’atmosphère (air ou azote) sur la nature des produits de décomposition (oxyde ou métal). Sous une atmosphère inerte contrôlée, les échantillons d’oxalate préparés se décomposent en bismuth métallique entre 210 et 250°C

Bi2(C2O4)3·7H2O and Bi(C2O4)OH Oxalates Thermal Decomposition Revisited. Formation of Nanoparticles with a Lower Melting Point than Bulk Bismuth

Two bismuth oxalates, namely, Bi2(C2O4)3·7H2O and Bi(C2O4)OH, were studied in terms of synthesis, structural characterization, particle morphology, and thermal behavior under several atmospheres. The oxalate powders were produced by chemical precipitation from bismuth nitrate and oxalic acid solutions under controlled pH, then characterized by X-ray diffraction (XRD), temperature-dependent XRD, IR spectroscopy, scanning electron microscopy, and thermogravimetric differential thermal analyses. New results on the thermal decomposition of bismuth oxalates under inert or reducing atmospheres are provided. On heating in nitrogen, both studied compounds decompose into small bismuth particles. Thermal properties of the metallic products were investigated. The Bi(C2O4)OH decomposition leads to a Bi−Bi2O3 metal−oxide composite product in which bismuth is confined in a nanometric size, due to surface oxidation. The melting point of such bismuth particles is strongly related to their crystallite size. The nanometric bismuth melting has thus been evidenced ∼40 °C lower than for bulk bismuth. These results should contribute to the development of the oxalate precursor route for low-temperature soldering applications

Low temperature joining materials for electronics : on the interest of metal oxalates and formates

Dans le domaine de la microélectronique, les préoccupations environnementales et sanitaires et l'évolution de la législation ont contraint l'industrie à limiter son utilisation du plomb. Les matériaux (à base d'étain, d'argent, de cuivre, de bismuth...) destinés au brasage de composants électroniques font l'objet de nombreux développements pour être conformes aux exigences réglementaires et techniques. Le potentiel des carboxylates de métaux en électronique a déjà été démontré dans le cadre du développement de procédés de décomposition métal-organique. La décomposition thermique sous atmosphère contrôlée de tels précurseurs mène à la création de nanoparticules métalliques avec une réactivité accrue par rapport à celle de particules de taille micronique. L'utilisation de nanomatériaux est une des voies explorées pour mettre au point des procédés d'assemblage à basse température pour l'électronique. Elle s'appuie sur le fait que les températures de fusion et de frittage de nanomatériaux diminuent avec la taille des particules. C'est dans ce contexte que s'inscrivent les travaux de cette thèse, qui présente l'étude de la décomposition contrôlée de précurseurs métal-organiques destinés à être intégrés à un procédé d'assemblage sans plomb à basse température. Le comportement en température de différents précurseurs métal-organiques d'étain et de bismuth et l'influence de l'atmosphère de décomposition ont été étudiés. La relation entre la taille des particules métalliques et leur point de fusion a été soulignée, ainsi que l'influence majeure de l'oxydation sur l'évolution de la taille des particules et leur capacité à former des assemblages.Due to environmental and health concerns, new regulations led to a restriction in the use of lead in electronic equipment. Joining materials (based on tin, silver, copper, bismuth ...) for surface-mount technology are subject to many development work in order to comply with regulatory and technical requirements. The potential of metal carboxylates in electronics has already been demonstrated in the development of metal-organic decomposition processes. The thermal decomposition under controlled atmosphere of such precursors leads to the creation of metal nanoparticles with an increased reactivity compared to that of micron sized particles. The use of nanomaterials is a seriously considered way for developing low temperature joining processes for electronics. It is based on the well-known decrease of melting and sintering temperatures of nanomaterials with particle size. In this context, this work of thesis presents the study of the controlled decomposition of metal-organic precursors intended to be integrated into a low-temperature lead-free joining process. The thermal behavior of several metal-organic precursors of tin and bismuth, as well as the influence of the decomposition atmosphere, were studied. The relationship between the metal particles size and their melting point has been emphasized, as well as the major influence of oxidation on the evolution of particles size and their ability to make reliable joints

Matériaux d'assemblage basse température pour applications électroniques : de l'intérêt des oxalates et formiates de métaux

Due to environmental and health concerns, new regulations led to a restriction in the use of lead in electronic equipment. Joining materials (based on tin, silver, copper, bismuth ...) for surface-mount technology are subject to many development work in order to comply with regulatory and technical requirements. The potential of metal carboxylates in electronics has already been demonstrated in the development of metal-organic decomposition processes. The thermal decomposition under controlled atmosphere of such precursors leads to the creation of metal nanoparticles with an increased reactivity compared to that of micron sized particles. The use of nanomaterials is a seriously considered way for developing low temperature joining processes for electronics. It is based on the well-known decrease of melting and sintering temperatures of nanomaterials with particle size. In this context, this work of thesis presents the study of the controlled decomposition of metal-organic precursors intended to be integrated into a low-temperature lead-free joining process. The thermal behavior of several metal-organic precursors of tin and bismuth, as well as the influence of the decomposition atmosphere, were studied. The relationship between the metal particles size and their melting point has been emphasized, as well as the major influence of oxidation on the evolution of particles size and their ability to make reliable joints.Dans le domaine de la microélectronique, les préoccupations environnementales et sanitaires et l'évolution de la législation ont contraint l'industrie à limiter son utilisation du plomb. Les matériaux (à base d'étain, d'argent, de cuivre, de bismuth...) destinés au brasage de composants électroniques font l'objet de nombreux développements pour être conformes aux exigences réglementaires et techniques. Le potentiel des carboxylates de métaux en électronique a déjà été démontré dans le cadre du développement de procédés de décomposition métal-organique. La décomposition thermique sous atmosphère contrôlée de tels précurseurs mène à la création de nanoparticules métalliques avec une réactivité accrue par rapport à celle de particules de taille micronique. L'utilisation de nanomatériaux est une des voies explorées pour mettre au point des procédés d'assemblage à basse température pour l'électronique. Elle s'appuie sur le fait que les températures de fusion et de frittage de nanomatériaux diminuent avec la taille des particules. C'est dans ce contexte que s'inscrivent les travaux de cette thèse, qui présente l'étude de la décomposition contrôlée de précurseurs métal-organiques destinés à être intégrés à un procédé d'assemblage sans plomb à basse température. Le comportement en température de différents précurseurs métal-organiques d'étain et de bismuth et l'influence de l'atmosphère de décomposition ont été étudiés. La relation entre la taille des particules métalliques et leur point de fusion a été soulignée, ainsi que l'influence majeure de l'oxydation sur l'évolution de la taille des particules et leur capacité à former des assemblages

Using X-ray imaging for the study of crack development in solder reliability testing

The possibility of monitoring the progressive damage and cracking in solder joints is investigated through a non-destructive method. As X-ray 3D Computed Tomography is known to require small sample dimensions in order to ensure a good resolution, Computed Laminography was used to get a high-resolution top view of various types of solder joints located on a large printed circuit board. In a first step, the assemblies were cross-sectioned after X-ray imaging in order to verify the findings and confirm the crack morphology. Then, by avoiding a destructive sample preparation step, it was possible to identify in a single sample the effects of solder fatigue during a standard reliability test. Firstly, multiple crack initiation sites could be highlighted in a single X-ray analysis. Moreover, the study gave an interesting insight of the time evolution of voids in solder joints. X-ray laminography produces 3D-like images that contain more information than a conventional cross section. By improving the recognition of horizontal cracks in this unusual point of view of solder joints, the refinement of this imaging and monitoring method can result in a real progress in failure analysis time and efficiency

Salidroside supplementation associated with resistance exercise enhances physical performance in old mice

National audienc

Early Deconditioning of Human Skeletal Muscles and the Effects of a Thigh Cuff Countermeasure

International audienceMuscle deconditioning is a major consequence of a wide range of conditions from spaceflight to a sedentary lifestyle, and occurs as a result of muscle inactivity, leading to a rapid decrease in muscle strength, mass, and oxidative capacity. The early changes that appear in the first days of inactivity must be studied to determine effective methods for the prevention of muscle deconditioning. To evaluate the mechanisms of muscle early changes and the vascular effect of a thigh cuff, a five-day dry immersion (DI) experiment was conducted by the French Space Agency at the MEDES Space Clinic (Rangueil, Toulouse). Eighteen healthy males were recruited and divided into a control group and a thigh cuff group, who wore a thigh cuff at 30 mmHg. All participants underwent five days of DI. Prior to and at the end of the DI, the lower limb maximal strength was measured and muscle biopsies were collected from the vastus lateralis muscle. Five days of DI resulted in muscle deconditioning in both groups. The maximal voluntary isometric contraction of knee extension decreased significantly. The muscle fiber cross-sectional area decreased significantly by 21.8%, and the protein balance seems to be impaired, as shown by the reduced activation of the mTOR pathway. Measurements of skinned muscle fibers supported these results and potential changes in oxidative capacity were highlighted by a decrease in PGC1-α levels. The use of the thigh cuff did not prevent muscle deconditioning or impact muscle function. These results suggest that the major effects of muscle deconditioning occur during the first few days of inactivity, and countermeasures against muscle deconditioning should target this time period. These results are also relevant for the understanding of muscle weakness induced by muscle diseases, aging, and patients in intensive care

Bi₂(C₂O₄)₃·7H₂O and Bi(C₂O₄)OH Oxalates Thermal Decomposition Revisited. Formation of Nanoparticles with a Lower Melting Point than Bulk Bismuth

Two bismuth oxalates, namely, Bi₂(C₂O₄)₃·7H₂O and Bi­(C₂O₄)­OH, were studied in terms of synthesis, structural characterization, particle morphology, and thermal behavior under several atmospheres. The oxalate powders were produced by chemical precipitation from bismuth nitrate and oxalic acid solutions under controlled pH, then characterized by X-ray diffraction (XRD), temperature-dependent XRD, IR spectroscopy, scanning electron microscopy, and thermogravimetric differential thermal analyses. New results on the thermal decomposition of bismuth oxalates under inert or reducing atmospheres are provided. On heating in nitrogen, both studied compounds decompose into small bismuth particles. Thermal properties of the metallic products were investigated. The Bi­(C₂O₄)­OH decomposition leads to a Bi–Bi₂O₃ metal–oxide composite product in which bismuth is confined in a nanometric size, due to surface oxidation. The melting point of such bismuth particles is strongly related to their crystallite size. The nanometric bismuth melting has thus been evidenced ∼40 °C lower than for bulk bismuth. These results should contribute to the development of the oxalate precursor route for low-temperature soldering applications

Acute and chronic effects of Rhaponticum carthamoides and Rhodiola rosea extracts supplementation coupled to resistance exercise on muscle protein synthesis and mechanical power in rats

International audienceBackground: Owing to its strength-building and adaptogenic properties, Rhaponticum carthamoides (Rha) has been commonly used by elite Soviet and Russian athletes. Rhodiola rosea (Rho) is known to reduce physical and mental fatigue and improve endurance performance. However, the association of these two nutritional supplements with resistance exercise performance has never been tested. Resistance exercise is still the best way to stimulate protein synthesis and induce chronic muscle adaptations. The aim of this study was to investigate the acute and chronic effects of resistance exercise coupled with Rha and Rho supplementation on protein synthesis, muscle phenotype, and physical performance. Methods: For the acute study, fifty-six rats were assigned to either a trained control group or one of the groups treated with specific doses of Rha and/or Rho. Each rats performed a single bout of climbing resistance exercise. The supplements were administered immediately after exercise by oral gavage. Protein synthesis was measured via puromycin incorporation. For the chronic study, forty rats were assigned to either the control group or one of the groups treated with doses adjusted from the acute study results. The rats were trained five times per week for 4 weeks with the same bout of climbing resistance exercise with additionals loads. Rha + Rho supplement was administered immediately after each training by oral gavage. Results: The findings of the acute study indicated that Rha and Rha + Rho supplementation after resistance exercise stimulated protein synthesis more than resistance exercise alone (p < 0.05). After 4 weeks of training, the mean power performance was increased in the Rha + Rho and Rha-alone groups (p < 0.05) without any significant supplementation effect on muscle weight or fiber cross-sectional area. A tendency towards an increase in type I/ type II fiber ratio was observed in Rha/Rho-treated groups compared to that in the trained control group. Conclusion: Rhodiola and Rhaponticum supplementation after resistance exercise could synergistically improve protein synthesis, muscle phenotype and physical performance