Christine Kallmayer

Embroidered Interconnections and Encapsulation for Electronics in Textiles for Wearable Electronics Applications

This document explains different approaches to integrating electronics in textiles. It discusses reliability standards and tests for electronics in textiles. Encapsulation technologies are evaluated concerning their applicability in textile integrated electronics. Furthermore a specific assembly with embroidered wiring and embroidered interconnections has been developed and improved. Two different encapsulation technologies have been developed for this assembly. Standardized tests have been carried out to assess the reliability of the assembly and its encapsulations. Finally the achievements are critically discussed.

Investigations of Au-Sn alloys on different end-metallizations for high temperature applications [solders]

Au-Sn solder is becoming increasingly important in the field of microelectronic packaging. For high temperature and fluxless applications in particular, for example in optoelectronics, Au-Sn solder bumps are used. The Au-Sn solders come in contact with different end-metallization systems such as nickel, platinum or palladium used as underbump-metallization. Information about the Au-Ni-Sn, Au-Pd-Sn and Au-Pt-Sn ternary systems in terms of metallurgical fundamentals are very important for understanding and controlling the technological processes. This knowledge is the base for investigations of reliability, phase formations, growth and stability, diffusion mechanisms and diffusion pathways. This paper summarizes the work done on different Au-Ni-Sn, Au-Pd-Sn and Au-Pt-Sn alloys with maximum 20 at.% Ni, Pd and Pt contents, and investigations on diffusion and interface reactions of Au-Sn solders on Ni, Pd and Pt. Isothermal sections of the solid state are introduced. The presence of unknown Au-Ni-Sn and Au-Pd-Sn phases in the tie-triangle is discussed. Results of diffusion investigations and interface reactions are shown.

Fully untegrated EKG shirt based on embroidered electrical interconnections with conductive yarn and miniaturized flexible electronics

A T-shirt has been developed that measures an EKG signal. This work is different to other research in the field as it focuses more on advanced interconnection and integration technologies for electronics in textiles rather than on the EKG shirt as functionality. It is the first application using an interconnection technology based on embroidery of conductive yarn that has been developed recently and published in T. Linz et al. (2005)

Stretchable Circuit Board Technology and Application

An innovative technology for the mass production ofstretchable printed circuit boards (SCBs) will bepresented in this paper. This technology makes itpossible for the first time to really integrate fine pitch,high performance electronic circuits easily into textilesand so may be the building block for a totally newgeneration of wearable electronic systems. Anoverview of the technology will be given andsubsequently a real system using SCB technology ispresented.

Long time reliability study of soldered flip chips on flexible substrates

Abstract Due to the requirements of new light, mobile, small and multifunctional electronic products the density of electronic packages continues to increase. Especially in medical electronics like pace makers the minimisation of the whole product size is an important factor. So flip chip technology becomes more and more attractive to reduce the height of an electronic package. At the same time the use of flexible and foldable substrates offers the possibility to create complex electronic devices with a very high density. In terms of human health the reliability of electronic products in medical applications has top priority. In this work flip chip interconnections to a flexible substrate are studied with regard to long time reliability. Test chips and substrates have been designed to give the possibility for electrical measurements. Solder was applied using conventional stencil printing method. The flip chip contacts on flexible substrates were created in a reflow process and underfilled subsequently. The assemblies have been tested according to JEDEC level 3. The focus in this paper is the long time reliability up to 10,000 h in thermal ageing at 125 °C and temperature/humidity testing at 85 °C/85% relative humidity as well as thermal cycling (0 °C/+100 °C) up to 5000 cycles. Daisy chain and four point Kelvin resistances have been measured to characterise the interconnections and monitor degradation effects. The failures have been analysed in terms of metallurgical investigations of formation and growing of intermetallic phases between underbump metallisation, solder bumps and conductor lines. CSAM was used to detect delaminations at the interfaces underfiller/chip and underfiller/substrate respectively.

Fluxless flip-chip attachment techniques using the Au/Sn metallurgy

With the use of the Au/Sn system as solder metallurgy different fluxless flip-chip processes are possible. In the studies for this paper Au/Sn bumped chips are used for soldering in an infrared oven under activated atmosphere with the self-alignment mechanism. A new approach is the successful application of the Au/Sn metallurgy for vapor phase soldering which provides the self-alignment effect as well. Flip-chip bonding on rigid and flexible substrates using a pulse heated thermode is also demonstrated. The scope of this paper is to show the development of different fluxless flip-chip processes with Au/Sn metallurgy on thin film and thick film substrates. The wetting of the pads, the fillet formation and the growth of /spl zeta/-phase are the major subjects of the studies as they determine the bonding result. Shear tests were performed in order to quantify the quality of the interconnection. The results obtained by the different methods are compared and conclusions about the investigated processes drawn.

Stretchable electronic systems: Realization and applications

Commonplace electronic appliances for consumer or industrial use are still mostly rigid or at maximum flexible entities. The flexibility of foldable units like laptops or cell phones is usually realized through flexible circuit board (FCB) interconnectors. Although flexibility allows for considerably enhanced degrees of freedom in design, it is not compatible with more complex three dimensional curvatures and dynamics thereof. In the past years a number or approaches to realize stretchable electronic circuits in order to reach beyond unidirectional bending or folding of electronics have been reported. In the frame of the European Project STELLA a particular fabrication technology for stretchable electronic systems has been developed at Technische Universitaet Berlin. This technology, termed ?stretchable circuit board? (SCB) technology, is derived from conventional printed circuit board manufacturing. Stretchability of the boards is enabled by (i) using polyurethane instead of FR4 or polyimide as a carrier material of the copper structures and (ii) a meandering design of the Cu interconnects between commercial (rigid) electronic components. Such boards can be (once) extended by up to 300% before fracture of the Cu interconnections. For repeated elongation/relaxation cycles elongations with a few percent are allowable in order reach high cycle numbers. Electronic components are assembled after local application of a solder mask and surface finish for solderability. The electronic interconnection is established using a low temperature solder alloy (SnBi, Tm=142?C). For protection and enhanced system robustness all components are subsequently encapsulated within a polyurethane capping. Systems thus realized can be readily attached to different kinds of surfaces. Most interesting for various application cases is the easy attachment to textile substrates by a simple lamination process. The field use case studies of stretchable systems in the frame of the STELLA are mostly sensor applications in the field of medical electronics like a breathing frequency monitor for babies, a shoe insole pressure sensor for diabetes patients, or a band aid inlay to measure pressure and humidity of an acute wound when pressure therapy is applied. The latter application will be described in more detail since different aspects of bio-medical applications can be explained with this example. Another emerging field of applications is textile electronics, where it has been proven, that stretchable electronics can serve a versatile building blocks for complex electronic systems integrated in textiles.

Current loadability of ICA for flip chip applications

Miniaturization is a key issue to achieve advanced performance of electronic devices and to decrease the overall cost of an electronic package. In this respect the flip chip technology provides excellent capabilities to meet the demands of recent and future products. Although solder joining is still the most common technology a great deal of research work has been conducted on conductive adhesives. They are successfully used as die attach, display and hybrid assembly. Progress with its application to flip chip devices has still to be made. Recently, the current carrying capability of isotropic conductive adhesive (ICA) has been a matter of great interest. Predominantly, corresponding characteristics of anisotropic conductive adhesives (ACAs) have been studied by several groups. Though interest, mainly on part of the automotive industry is shown, little is known about ICAs high current behaviour. This paper is part of a broad study focused on the current capabilities of isotropic conductive adhesives. Tests have been carried out on flip chip assemblies. The contact resistivities depending on different DC loads and increased environmental temperatures have been monitored. In-situ measurements have been carried out with an automated measuring system. TGA measurements were made to find out about degradation temperatures of the used materials. The results contribute to the following discussion about the failure mechanisms due to high current loads.The first part of the study focuses on fundamental investigations performed on printed ICA test structures (epoxy vs. thermoplastic resin). Measurings of the conductivity during cure have been made. The results have been related with DSC/TMA data. As well electrical performance of the cured adhesives under elevated temperature/humidity and high current loads have been determined. In the second part of the study first results obtained from high current tests on Flip Chip packages are presented. Limitations and mechanisms of failure are discussed.

Large area sensor integration in textiles

In recent years, the integration of electronics in technical textiles has gained increasing attention especially in Europe. Many industry driven projects have already been started in this area on national as well as on European level. An example is the European project PASTA. In order to make the step towards industrial manufacturing of wearable electronics as well as smart large area technical textiles it is necessary to develop modular concepts as well as integration processes suitable for high volume production. Within PASTA new electronic packaging technologies and the development of new textile structures are investigated. By introducing new concepts for electronic packaging and module interconnects, a seamless, more comfortable and more robust integration of electronics in textiles will be possible. The main technological developments concentrate on different levels of integration: a new concept for bare die integration into a yarn, a new interconnect technology based on mechanical crimping, and the development of a stretchable interposer serving as a stress relief interface between the rigid component and the elastic fabric. The technologies will also be analyzed and evaluated regarding functionality and reliability. The proposed solutions for integration of electronics in textiles will cover a whole range of components, from ultra-small LEDs to complex multichip modules for sensor data processing. Moreover, a system design task will address the power distribution and system partitioning aspects to provide a complete solution for integration of a distributed sensor/actuator system in fabric. Different approaches are possible for large area sensors in textiles. The scope of this paper is to show which technologies enable the use of conductive yarns in a fabric for pressure and damage detection and in-situ monitoring of accumulated stress in composites to predict the residual lifetime and to indicate damage of industrial components.

A new approach to chip size package using meniscus soldering and FPC-bonding

A Chip Size Package was developed using a tape carrier for interconnection and redistribution of the pads of high pincount ICs. The complete package is 650 /spl mu/m thick including a 550 /spl mu/m thick chip and a 100 /spl mu/m thick flexible carrier. A three layer tape with gold or gold/nickel surface finish on the copper layer was used as flexible interposer. The production line which was established includes a low cost bumping on wafer level. The chips were provided with electroless Ni bumps on which a layer of eutectic Au-Sn solder was deposited by meniscus soldering. The bonding of these bumps to the flexible substrate was performed by FPC technology, a laser bonding method. Mechanical stability between the tape and the chip was achieved by application of a low stress adhesive prior to bonding. In a last step solder balls were placed on the tape and reflowed using a novel solder ball placement machine with an incorporated laser reflow unit. The package obtained is fully surface mount compatible, allowing easy processability.