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

Mapping of N−C bond formation from a series of crystalline peri‐substituted naphthalenes by charge density and solid‐state NMR methodologies

A combination of charge density studies and solid state nuclear magnetic resonance (NMR) 1JNC coupling measurements supported by periodic density functional theory (DFT) calculations is used to characterise the transition from an n–π* interaction to bond formation between a nucleophilic nitrogen atom and an electrophilic sp2 carbon atom in a series of crystalline peri‐substituted naphthalenes. As the N⋅⋅⋅C distance reduces there is a sharp decrease in the Laplacian derived from increasing charge density between the two groups at ca. N⋅⋅⋅C = 1.8 Å, with the periodic DFT calculations predicting, and heteronuclear spin‐echo NMR measurements confirming, the 1JNC couplings of ≈3–6 Hz for long C−N bonds (1.60–1.65 Å), and 1JNC couplings of 2.1 Å

Wettability of rapid thermal firing silver-pastes

Photovoltaic technology is evolving rapidly with new concepts and ideas to systematically improve module efficiency. Cell metallizations based on thick film pastes have to be fired less than one minute. It has already been shown that the solder interconnection of these rapid thermal firing pastes is critical in terms of wettability [1]. Main problems are solder leaching of commercially available pastes and paste adhesion to the silicon substrate. The correlation between paste composition and solder wettability has not been investigated yet. The aim of this work is to evaluate the wettability of rapid thermal firing pastes in dependence on paste composition and firing temperature. Pastes with spherical silver particles and lead free glass composition have been developed and fired with an industrial standard rapid thermal firing profile between (760...840) °C. Thick film surfaces and cross sections have been inspected. Solder wettability was evaluated with solder dip and solder reflow tests. Correlations between resulting thick films and their wetting or leaching characteristics have been investigated to improve the solder interconnection for rapid thermal firing solar cell metallizations

Development and analysis of high temperature stable interconnections on thick films using micro resistance welding for sensors and MEMS

Many sensor applications, particularly that of harsh environmental conditions, require high temperature stable interconnection techniques and materials. Monometallic Au-Au or Al-Al bonds have already been evaluated to be acceptable for temperatures over 300 °C. Nevertheless, novel concepts for surface applied thermocouples (TC) or surface acoustic wave sensors (SAW) need reliable bonding techniques for over 500 °C. Micro resistance welding of platinum alloys is a promising joining method for the production of high thermally stable bonds in such kind of packages. This study is focused on the mechanical stability of platinum-based interconnection joints. Therefore, characterization samples with commercially available thick film pastes were produced and welded using a parallel gap resistance welder. Pull and shear stability of the joints were evaluated and compared before and after long time isothermal treatment at high temperatures

Complementary EIS/FTIR study of the degradation of adhesives in electronic packaging

Adhesives are widely used in electronic packaging and of vital importance of the reliability of electronic systems. A deep understanding of the degradation mechanism of adhesives under corrosion load plays a key role in life time prediction. Unfortunately, most of the common reliability test are destructive. The present approach combine the non-destructive methods Electrochemical Impedance Spectroscopy (EIS) and the Fourier Transformed Infrared Spectroscopy (FTIR) as a powerful tool in complementary manner to describe the degradation mechanism and kinetics of two epoxy based adhesives, which are commonly used in electronic packaging. It is demonstrated that the application quality is the dominating impact on the optimization of the life time

High-Temperature packaging for sensors

Sensors are used industrially for a wide variety of measuring and testing tasks. Measuring in harsh environments is not only a challenge for the sensor element but for the package, too. At ambient temperatures up to 600 °C, the classic assembling technology of electronic packaging is reaching its limits. This concerns technological processes, thermal parameters and assembly materials. Therefore, existing connection technologies need to be evaluated when facing high operation temperatures. Based on the research results of this work, the existing connection technologies are either to be adapted for the high-temperature environment or even new ones based on new material combinations are to be developed. This paper focuses on the packaging of sensors operating at temperatures up to 600 °C. First results concerning the selection and the characterization of ceramic packages, as well as the mounting of the sensors, are presented

Evaluation of long time stability of solder joints on Ag thick film conductors on Al2O3

The long time stability of solder joints on Ag-based thick film pastes has been studied. Therefore shear strength, electrical resistance, temperature coefficient of resistance (TCR), optical inspections of solder surface and cross section analyses have been performed. Samples of 1206 and 0805 SMD-components mounted with SnAgCu, SnPbAg, SnBi and SnCu on Ag/Pd or Ag/Pt conductors were prepared. To detect the influence of intermetallic phase growth, high temperature storage according JESD22-A103C at 150 °C (125 °C for SnBi-solder) up to 500 h has been applied. Shear fatigue life of the interconnection joints was studied with temperature cycling according JESD22-A104D between +125 °C/-40 °C for up to 1000 cycles. Differences in shear fatigue and electrical characteristics will be evaluated and discussed

Thermoelektrisches Element sowie ein Verfahren zu dessen Herstellung

Die Erfindung betrifft ein thermoelektrisches Element insbesondere Thermoelement sowie ein Verfahren zu dessen Herstellung. Das thermoelektrische Element ist mit zwei mit jeweils unterschiedlichem Metall gebildeten Thermoschenkeln, die sich in einem Bereich, bevorzugt einer Temperaturmessstelle berührend überlappen und ansonsten elektrisch voneinander isoliert sind, gebildet. Jeder der Thermoschenkel ist an seinem dem Bereich abgewandten Ende über Kontaktdrähte und/oder elektrische Leiterbahnen mit einem Voltmeter oder einer elektrischen Stromquelle verbunden. Die Thermoschenkel sind mit miteinander versinterten Metallen, jeweils mit einem Metallanteil von mindestens 50 Masse-% unmittelbar auf einer Oberfläche eines Bauteils oder einer auf einer Oberfläche eines Bauteils ausgebildeten elektrisch isolierenden Schicht ausgebildet

Entwicklung von miniaturisierten Dickschicht-Thermoelement-Arrays für automobile und industrielle Anwendungen

Temperature control of components and systems is often realized by using rod thermocouples. The suitability of these elements is limited in terms of their size and installation requirements. Therefore, temperature supervision of high thermally stressed components is often realized in only one measuring point. Application of thermocouple arrays offers the possibility for temperature supervision on complete component surfaces, even in previously inaccessible areas. Temperature monitoring and management could be significantly increased in that way. The present paper is focussing on miniaturized thick film thermocouples and their application on complex surfaces. Recent results of material characterizations, development of printing technologies and long-time characterizations were shown and discussed

Entwicklung neuartiger thermoelektrischer Module für automotive und industrielle Anwendungen

Das Vorhaben befasst sich mit der Entwicklung neuartiger thermoelektrischer Module aus herkömmlichen, kommerziell verfügbaren Blechen bzw. pastösen metallischen Werkstoffen. Diese Elemente eröffnen neue Freiheitsgrade in der Gestaltung der Temperaturmessstelle und eigenen sich für vielfältigste Temperaturmessaufgaben bis in den Hochtemperaturbereich. Die Blechthermoelemente sind im Stande hohe Axialkräfte aufzunehmen und können so als funktionsintegrierte Dichtung mit einer Temperaturmessstelle fungieren. Die Pastenthermoelemente zeichnen durch eine geringe thermische Eigenmasse aus, was eine Temperaturmessung ohne Strömungsbeeinflussung möglich macht. Die in diesem Vorhaben durchgeführten Untersuchungen der Blechthermoelemente umfassen Heißgasprüfstands- und Motorenversuche sowie begleitende 3D-CFD Simulationen. Für die Pastenthermoelemete wurden geeignete Materialpaarungen ermittelt und deren Einsatzneigung unter Labor- und Realbedingungen evaluiert