Thermal Stress Assessment for Transient Liquid-Phase Bonded Si Chips in High-Power Modules Using Experimental and Numerical Methods

The potential of transient liquid-phase (TLP) bonding for chip packaging applications has been evaluated, focusing on three interlayer arrangements (Ag-Sn-Ag, Ni-Sn-Ni, and Ag-Sn-Ni). Shear tests on TLP-bonded components provided the interlayer-dependent mechanical strength as well as failure mode and position. Critical local stresses, i.e., failure criteria, within the intermetallic compound (IMC) layer were derived by replicating the shear test conditions with finite-element methods. The missing coefficient of thermal expansion for Ag₃Sn IMC was obtained by producing small IMC bulk samples and subjecting them to dilatometric measurements. The experimental results were implemented into a finite-element model of a representative power module architecture to provide first predictions on thermally induced residual stresses that could be classified into fail/safe, as successfully validated by TLP chip bonding experiments. A numerical parameter study then assessed thermal stresses, including failure prediction and design optimization for TLP-bonded Si chips, considering the influence of process temperature, service conditions, TLP interlayer system, and metallization layers within the TLP joint. The presented procedure serves as a guideline to choose an appropriate TLP interlayer system for predefined boundary conditions, or vice versa.     

History matters: The inherited disciplinary structure of the post-communist science in countries of central and eastern Europe and its restructuring

The inherited disciplinary structure of the science of post-communist countries of CEE carries a strong common features of its past. The communist heritage is present in: a) a relatively homogeneous research profile among post-communist countries; b) the similar structure of disciplinary comparative advantages of post-communist countries; c) the unbalanced and concentrated disciplinary structure of comparative advantages. The analysis is based on ISI databases and uses statistics on papers and citations for the 1992–1997 period for all central and eastern European countries as well as for other world regions. In the conclusions we discuss the relevance of the results for the restructuring of science in the countries of Central and Eastern Europe. Part of the research which forms the basis for this paper has been funded by the DGXII TSER project ‘Restructuring and reintegration of S&T systems in economies in transition’.     

Electromagnetic Fields and Induced Voltages on Underground Pipeline in the Vicinity of AC Traction System

Various regulations, aimed at the protection of human beings and electrical equipment against possible adverse effects resulting from exposure to electromagnetic fields, have been issued in many countries. Most of them are based on safety guidelines published by international expert groups. In this paper, electric and magnetic fields are calculated in the vicinity of 25 kV traction line supplying railway traction systems. Calculation results are compared to exposure limits specified by safety guidelines and regulations. Possible countermeasures for reduction of electromagnetic fields are proposed. Also, this paper presents a method for calculation of the induced voltages to an underground gas pipeline from a neighbouring 25 kV electric traction overhead line in case of short circuit. Calculations are performed with EMTP-ATP software. Possible countermeasures for reduction of induced voltages are proposed.     

Three monoclonal IgG components, an IgG4(lambda), an IgG2(kappa) and an IgG1/IgG3 (kappa) Gm(f,b) hybrid, in a single myeloma patient

An unusual triclonal IgG combination in the serum of a 56-year old male with clinical stage IIIB multiple myeloma is reported. The patient initially had an IgG4(lambda) monoclonal protein in his serum and later developed an IgG2(kappa) and an IgG (kappa) which possessed the characteristics of both IgG1 and IgG3 subclasses with an unusual combination of allotypic markers. Three M-proteins did not share idiotypic determinants. A rare class-switch recombination followed by mutation has been considered as a possible mechanism leading to this combination.     

Measuring S&T activities in the Former Socialist Economies of Central and Eastern Europe: Conceptual and methodological issues in linking past with present

The economic and social transformation of countries of central and eastern Europe has deeply affected their S&T systems. However, conceptual and methodological problems in monitoring transformation of their S&T systems are not trivial. In this paper we analyse conceptual and methodological issues involved in measuring S&T activities in the socialist and post-socialist period across the most important S&T indicators (R&D, US and national patents; innovation surveys; bibliometrics). Our conclusions are that: i) the process of methodological harmonisation of S&T indicators has progressed considerably and we have provided some evidence in that respect; ii) the use of similar or identical indicators (business R&D, innovation counts, patents, citations) when making inter-country or inter-temporal comparisons should be approached with caution because of the significant differences between the socialist and post-socialist periods as well as between post-socialist R&D systems and R&D in other market economies. This latter applies especially to the interpretation of business R&D data in the post-socialist period. A first version of this paper was presented at the Conference on the implementation of OECD methodologies for R&D/S&T statistics in central and eastern European countries' which was held in Budapest from 6.–8. November 1996. Research which formed the basis for this paper was funded in case of one of the authors by the EC TSER programme. Correspondence should be addressed to: SlavoRadosevic, SPRU, University of Sussex, BN1 9RF, Brighton. We are grateful to SylvanKatz for stimulative discussions and to two anonymous referees for comments in revisions of this paper. The views expressed in this paper are those of the authors and do not necessarily reflect those of the organisations for which they work.