Inert Drying System for Copper Paste Application in PV

AbstractIn this study we show that the electrical characteristics of low temperature polymer pastes are improved by carrying out the curing process in an inert nitrogen atmosphere. In order to reduce the solar cell production costs, numerous scientific works are devoted to the question, whether the commonly used silver paste can be replaced by a copper based paste. However, a major problem with the latter is, that copper tends to oxidate during the thermal treatment. Hence, this work focuses on the development of an inert inline drying system to avoid the oxidation of copper based polymer pastes. For reference, silver based polymer pastes are investigated simultaneously. Therefore the influence of different nitrogen curing atmospheres on the electrical resistance and the weight loss of the pastes is evaluated. The electrical resistance of both silver and copper based pastes is improved by reducing the residual oxygen concentration. To investigate the reason for this, the samples are analyzed by micrographics. Furthermore it is shown, that the weight loss of the pastes shows no dependence on the curing atmosphere

Ventil aus einem keramischen Werkstoff und ein Verfahren zu seiner Herstellung

The invention relates to a valve made of a ceramic material, which is joined together from a first base body (100) and a second base body (200) by means of a joining material (300), and in which a cavity (204) is formed between the first and the second base body, wherein the first and the second base body are each formed from multiple layers of a ceramic material. In the first base body, a feed (102) for a fluid into the cavity is formed in a wall facing the second base body, and a sealing element (101) is applied circumferentially around the feed on the surface of the wall in the interior of the cavity. Fixed in the cavity, between the first base body and the second base body, is a diaphragm (206), which is formed from a ceramic material and is elastically deformable. In addition, a passage (207) for the fluid is formed in the valve in the form of a bypass line, and a drain (205) for the fluid from the cavity out of the valve is formed in the second base body

PrintPOWER - Paste systems for multifunctional copper power modules

Power electronic systems are the backbone of the energy transition and environmentally friendly individual electromobility. Modules in which power semiconductors and other components are integrated form the heart of such systems. Copper thick films combine the advantages of DCB substrates, which are dominant in the module sector, and the silver thick-film technology used for highly reliable signal processing circuits. The focus of the work was the development of copper-compatible paste systems (conductive and dielectric pastes) and their combination to create multilayer module structures on ceramic substrates. The printed modules on the multifunctional substrates should be able to contain, in addition to the power semiconductors, various other active and passive components. This integrated functionality at the module level, let these modules count to the class of the “Intelligent Power Modules” (IPM). In future, the main aim is to develop power modules, which are more compact, functional and cost effective by using the thick-film technology. For this purpose, thick-film pastes were developed at Fraunhofer IKTS, which allow the application of high-current structures with copper layer thicknesses of up to 300 μm as well as filigree multilayer circuits for the production of control and driver circuits. This was to be achieved using novel, multifunctional substrates, which allow a particularly high integration density with simultaneously excellent heat dissipation and high current carrying capacity. The used multifunctional substrates consist of an Al2O3 ceramic plate onto various thick-film pastes were applied by a high-definition printing process (screen, stencil printing, dispensing). This makes it possible, in addition to conductors with a high cross-section, to apply electrically from these insulated areas of fine line conductors and three-dimensional structures. By using copper thick film pastes and adapted insulation pastes for inert firing or curing, several functions can be embedded in the module structure. Furthermore, new contacting options were evaluated via 3D-printed silver polymer suspensions, which could replace established technologies, such as bonding or Siemens Planar Interconnect Technology (SiPLIT), more cost-effectively and with high reliability. As part of these investigations, the following single paste-systems have been developed: Copper thick film pastes for thick print and fine line applications: By varying the composition of copper pastes, in particular with rheological additives, it was possible to specifically set different layer geometries, which enable both thick printing and fine line printing. / Glass insulations for nitrogen atmospheres: Two glasses were evaluated which sinter densely and transparently at temperatures of up to 955 ° C and have only small carbon residues within the layer. This makes it possible to use the developed glass pastes as dielectric layers, but also as covering layers. Furthermore, the development of glass insulation for sintering temperatures ≥ 850 ° C allows a multilayer structure with HT-Cu systems, so that robust circuits can be integrated in several levels. / Silver polymer pastes: For the low temperature range, a silver metallization has been developed, which has very good conducting properties and can be deposited by means of dispensing printing processes. This will allow future use of new 3D contacting options that can replace established technologies such as bonding or the SiPLIT method more cost-effectively and with higher reliability. / Al2O3 polymer insulation: In addition, an Al2O3 polymer insulation was developed, which has good insulation properties and can complete the assembly of a power multilayer module. // To verify the compatibility of the individual developed paste systems, a printed multi-layer module was set up and the layers tested for functionality. It could be shown that the developed paste systems can be combined with each other and can be sintered or hardened under nitrogen atmosphere without suffering a loss of function. Accordingly, it is possible in the future to build application-oriented power modules with the previously developed paste systems

Consideration of inhomogeneous shrinkages for LTCC-applications in panel-level processes

The aim of our study is a knowledge-based consideration of the inhomogeneous lateral shrinkage (shrinkage field) of commercial Low temperature co-fired ceramic (LTCC-) materials under free sintering conditions to improve the geometrical design fidelity and productions yield of system packages and microsystems fabricated in LTCC. Thus the phenomenological investigations of LTCC materials under various lamination and sintering conditions are presented. Deduced from this, feasible approaches for the compensation of the inhomogeneous shrinkages are introduced. Further thermal as well as thermomechanical analysis distinguish the origin of the shrinkage fields and enable the knowledge-based control of the shrinkage behavior in the design and fabrication process as well as in the material development

Fabrication possibilities and characterisation of chalcogenide glass-based sensors for bromide determination

The fabrication and characterization of potentiometric chalcogenide glass (CG) electrodes with selectivity for bromide in aqueous media are reported. The focus is on the production of chalcogenide glasses of the material system AgBr Ag2S As2S3 and their investigation by means of a series of physico-chemical methods, as well as on their fabrication with the aid of precision mechanical manufacturing and assembly techniques to form usable sensors and their testing. In addition to the production of conventional rod electrodes, it will be examined whether it is also possible to realize planar electrodes using thick-film technology

Sinter kinetics and interface reactions of silver thick films on aluminium nitride

The advantages of Aluminium nitride (AlN) ceramics are a high bulk thermal conductivity, insulating resistance, dielectric strength, flexural strength and a coefficient of thermal expansion, which is well matched to semiconductor materials, like silicon carbide. AlN ceramics show high potential as substrate materials for thick film- / hybrid applications in the field of power electronics and multichip modules. These applications require metallisations with high ampacity. Herein, the direct copper bond technology (DBC) is state of the art. Nevertheless, DBC shows several disadvantages in the circuit building process, for instance the etching process for patterning the foil, what limits the structure resolution on the one hand. On the other hand, this subtractive process is expensive along with a high chemicals consumption. The use of copper thick film pastes (thick print copper-TPC) instead of DBC results in higher structure resolutions, is an easier industrial applicable, energy-saving and environmentally friendlier process [Gun16]. Due to the fact that copper thick films have to be fired in nitrogen atmosphere and the actual bottlenecks in copper production, what might rise the copper price [Wie17], thick print silver (TPS) seems to be a promising alternative to TPC. Moreover, the conductivity of silver is slightly higher than those of copper and silver can be fired in air. The aim of this study is to get insight the silver films sinter kinetics and the interface formation on AlN. Therefore, systematic variations in the paste recipe where done and the resulting film shrinkage, blister behaviour, solderability and adhesion strength where correlated with the sintering kinetics and the microstructure of the films. A significant role in this process play the inorganic components bismuth oxide and the glass. This is because of the ability of bismuth oxide solution in the glass matrix, what shifts the softening down to lower temperatures. The influence of the glass and bismuth oxide volume fractions on the glass-viscosity, sintering behaviour of silver pastes as well as the interfacial reactions with AlN were investigated by means of thermomechanical analysis, FESEM-cross sections of fired films and XRD. Phase transformation mechanisms and root causes for blister formation are investigated. It was found out that sinter kinetics in combination with the simultaneous glas softening and phase redistribution are crucial for the interface reaction, film adhesion and blistering. Ways to attain evaporation possibilities via controlled sintering retardation of the thick films are examined

Adaption of functional ceramic materials for the laser sintering process in integrated sensor applications

The ceramic thick-film technology enables the build-up of miniaturised and robust integrated multilayer-circuits and sensors by means of sequential screen-printing and firing of different functional materials. However, the manufacturing of integrated electronics does not succeed if the components are temperature sensitive or too large for the process in a sintering furnace. At present, large components like wind power rotors, axles or roller bearings are monitored by vulnerable hybrid sensor systems. In order to implement the advantages of integrated devices, like the direct surface contact and the high thermomechanical stability, functional ceramic-based materials are adapted or newly developed to accommodate the needs of laser sintering techniques of printed sensor layers on structural components. Exemplarily, it is shown on steel components that the defect-free densification of functional layers crucially depends on the particular material composition in combination with adapted laser treatment (parameters). A first generation of functional layers is presented, comprising different electrical materials. The films are tested in demonstrator setups and show functional properties comparable to those of the furnace sintering technology. Future aspects of material optimization and the adaption to specific application requirements will be discussed

Mikrofluidisches System zur Kultivierung von oder der Analyse an lebenden Zellen oder Biomolekülen sowie ein Verfahren zu seiner Herstellung

Bei dem mikrofluidischen System zur Kultivierung von oder der Analyse an lebenden Zellen oder Biomolekülen sind mehrere übereinander angeordnete Laminate aus einem polymeren Werkstoff fluiddicht und stoffschlüssig miteinander verbunden. In mindestens einem der Laminate ist mindestens eine Öffnung oder mindestens ein Ausschnitt ausgebildet, mit der/dem ein Kanal oder eine Reservoir für die Aufnahme lebender Zellen oder Biomoleküle ausgebildet ist. In mindestens einem der Laminate ist mindestens eine weitere Öffnung ausgebildet, in die ein aus einem keramischen oder einem halbleitenden Werkstoff gebildeter Aktor/Sensor oder ein aus einem keramischen oder halbleitenden Werkstoff gebildeter Träger für einen Aktor/Sensor eingesetzt ist. Auf der Oberfläche des Laminats in das der Aktor/Sensor oder der Träger eingesetzt ist oder auf der Oberfläche eines unmittelbar an dieses Laminat angrenzenden Laminats ist mindestens eine elektrische Leiterbahn gedruckt, mit der eine elektrische Kontaktierung des Aktors und/oder Sensors erreichbar ist. Der mindestens eine Aktor/Sensor steht in berührendem Kontakt mit einer Flüssigkeit für die Kultivierung von Zellen, einer Flüssigkeit in der Biomoleküle enthalten sind oder den in einem Kanal oder Reservoir enthaltenen Zellen oder Biomolekülen

LTCC-Based Sensors for Mechanical Quantities

Besides their excellent dielectric and thermo-mechanical characteristics Low Temperature Cofiring Ceramics (LTCC) are also well suited for the fabrication of 3D micromechanical components such as sensors for mechanical quantities. This paper describes the development of such sensors covering some material and technological aspects. Furthermore, the design process for mechanical sensors is discussed as well as application examples of sensors for the detection of pressure, force, acceleration and flow

Chalcogenide Glass Based Heavy Metal Sensors

A number of chalcogenide glasses for the fabrication of potentiometric electrodes selective for heavy metal ions were melted and characterised. The focus was directed on the detection of Cu2+ and Pb2+ ions. Until now, for measurements, only rod electrodes were available. In addition to the preparation of conventional rod electrodes, the purpose of the research was the realisation of corresponding planar electrodes in thick film technology. Therefore, the bulk material of the chalcogenide glasses was milled to glass powder and the sintering behaviour of the glasses was investigated. Non-crystallising, densely sintered glasses were processed into thick film pastes for the deposition of heavy metal ion selective chalcogenide glass membranes on a ceramic substrate. Miniaturised electrodes were achieved for the case of copper ion determination, whereupon several glass compositions were tested. The sintering behaviour of the investigated lead ion selective glasses did not allow the fabrication of an ion selective electrode by the thick film process. The requirement to add AgI to the initial mix is associated with light sensitivity of corresponding sensors