Silver oxalate-based solders: New materials for high thermal conductivity microjoining

Micrometric oxalate powders can be decomposed starting from temperatures as low as 90°C, leading to the formation of temporary nanometric grains of metallic silver with a high propensity for sintering. The decomposition being highly exothermic, this additional energy favours the sintering, i.e. the soldering, process. Solders processed at 300°C and very low pressure (<0.5 MPa) displayed a thermal conductivity close to 100 W m-1 K-1, making silver oxalate very promising for safe, moderate temperature and very low pressure bonding

Pâtes à braser à base d'oxalate d'argent pour applications électroniques fortement dissipatives : de l'intérêt des particules nanométriques issues de la décomposition de l'oxalate d'argent

Dans le domaine de la micro-électronique hyperfréquence nouvelle génération, les technologies de fabrication des transistors pour amplification de puissance ont fait une percée remarquable, avec des performances permettant d'accroitre le gain de puissance d'un ordre de grandeur par rapport aux solutions actuelles. Cette augmentation s'accompagne d'un dégagement de puissance thermique et les matériaux utilisés actuellement pour le report des puces ne permettent pas de tirer pleinement profits de ces composants à cause de leurs propriétés thermiques limitées. C'est dans ce contexte que s'inscrivent les travaux de cette thèse, qui présente le développement d'un nouveau matériau de report de puce à forte conductivité thermique, mis en œuvre en dessous de 300°C et sous faible pression. Cette méthode tire notamment son originalité de l'utilisation d'un précurseur chimique, l'oxalate d'argent, et de la création transitoire de nanoparticules d'argent au sein même de la brasure, évitant ainsi leur manipulation. Mots-clés: oxalate d'argent, argent, nanoparticules, électronique de puissance, conductivité thermique, spatial Title: Silver oxalate-based solder paste for high power electronic applications: on the interest of nanometric particles formed during silver oxalate decompositionIn the field of new generation power electronic devices, transistor manufacturing technologies made a spectacular breakthrough, with properties that enable to increase the output power by ten, in comparison to currently used solutions. This rise is accompanied by a heat release and currently used die-attach materials, with limited thermal properties, don't enable taking full advantage of these new components. Within this context, this thesis presents the development of a new high thermal conductivity interconnection material, processed under 300°C and a low pressure. This method finds its originality in the several aspects, such as the use of a chemical precursor, silver oxalate, and the transitional creation of silver nanoparticles inside the solder itself, enabling to avoiding their direct handling

Paramagnetic behaviour of silver nanoparticles generated by decomposition of silver oxalate

International audienceSilver oxalate Ag2C2O4, was already proposed for soldering applications, due to the formation when it is decomposed by a heat treatment, of highly sinterable silver nanoparticles. When slowly decomposed at low temperature (125 °C), the oxalate leads however to silver nanoparticles isolated from each other. As soon as these nanoparticles are formed, the magnetic susceptibility at room temperature increases from -3.14 10-7 emu.Oe-1.g-1 (silver oxalate) up to -1.92 10-7 emu.Oe-1.g-1 (metallic silver). At the end of the oxalate decomposition, the conventional diamagnetic behaviour of bulk silver, is observed from room temperature to 80 K. A diamagnetic-paramagnetic transition is however revealed below 80 K leading at 2 K, to silver nanoparticles with a positive magnetic susceptibility. This original behaviour, compared to the one of bulk silver, can be ascribed to the nanometric size of the metallic particles