Klaus-Jurgen Wolter

Nano Packaging - A challenge for Non-destructive Testing

The challenge of nano packaging requires new non-destructive evaluation (NDE) techniques to detect and characterize very small defects like transportation phenomenon, Kirkendall voids or micro cracks. Imaging technologies with resolutions in the sub-micron range are the desire. Possible evaluation methods are for example x-ray microscopy, x-ray tomography, ultrasonic microscopy and thermal microscopy. However, techniques with the necessary resolution can not be found on the market. The Center for Non-Destructieve Nano Evaluation of Electronic Packaging (nanoeva®) is taken up to develop this equipment in cooperation with the electronics industry and to transfer the knowledge to colleagues in industries and research institutions. The new center is a common organization of Fraunhofer IZFP-D and the Electronics Packaging Lab with its Centre of Microtechnical Manufacturing (Z¿P) of the Technische Universitat Dresden. This paper will focus on the new possibilities of nano x-ray CT and shows first results.

Optimization of SMT solder joint quality by variation of material and reflow parameters

It is the objective of all PCB manufacturers to assure that each and every PCB supplied to the customer meets the specified quality requirements. Quality can be subdivided into two essential factors: the actual function of the PCB, and its reliability. Whereas function can, as a rule, be tested, only indirect substantiation is possible for reliability. The descriptions included in the IPC 610 D [1] standard are especially helpful in this respect, which indicate, amongst other things, which peculiarities the respective characteristics must demonstrate relative to product classes 1 through 3 in order to assure high reliability. At the same time, the number of repairs should be minimized to the greatest extent possible.

3D-microfluidic reactor in LTCC

The study and verification of fluids and chemical reactions in the macroscopic range is widespread in the pharmacy, in the chemical engineering and in the medical and biotechnological industry. By transferring the reactor structures in microfluidic solutions the process parameters can be improved, analyses optimized as well as new ranges of applications opened. The preliminary works of our department show that the thick layer technology and especially the multilayer technology by means of Low Temperature Cofiring Ceramic (LTCC) offer a promising possibility for the miniaturizations of fluidic devices. The aim of this work was the conversion of parameter specifications from the chemical engineering in a first pattern construction of a LTCC microreactor. Thereby sensors for the measurement of the fluidic characteristics had to be integrated into this compound and their utilizability had to be proved.

Fracture behaviour of adhesive bonds by different shear speed

Electrically conductive adhesives are an interesting alternative for environmentally friendly electronic packaging. Polymers are insufficient examinated regarding their mechanical behaviour in comparison with solder materials. The chemical constitution of polymers is more complicated than metals and ceramics. Based on structural constitution the visco-elastic and the visco-plastic deformation behaviour of polymers show an intense dependence on temperature and speed of strain. The glass transition temperature Tg is a significant parameter for polymers [1], [2]. For destructive testing with a mechanical load it is important on which working temperature the stress occurs: below, above or near glass transition temperature Tg [1]. All kinds of polymers (thermoplastic, elastomer, duromer) are based on linear molecular chains. Dipole, hydrogen or van-der-Waals-bonds can appear depending on the molecular structure. Additional the linear molecular chains are bonded more or less with covalent bonds getting a molecular network. Epoxide resins are amorphous duromer and have a high cross linking density (10-2...10-1)[1]. A high cross linking density has an important effect on the properties of the adhesive, for example high strength and chemical stability. In comparison with metals and ceramics the elastic modules of polymers are much lower and the kind of bonds between molecular chains determines the mechanical stiffness.

Membrane behaviour of Parylene C as housing material

Investigation methods on polymer encapsulation were implemented to determine the quality of a polymer coating on electronic devices against migration and diffusion. Therefore the major goal was to evaluate a membrane of Parylene C clamped in a frame. Two different fluids in chambers on each side of the membrane, bi-distillated water and water with solute salt, generate concentration gradient. The potential drop drives ions through the membrane. With the analysis of the conductivity in the chamber with bi-distilled water the transmission rate of the molecules can be determined in dependence of mass and thickness to area and time. These tests have shown a coefficient for the transmission rate of NaCl. The inspection with the scanning electron microscope as well as measuring the surface roughness conducted to first information about thin Parylene C layers.

Surface degradation of Sn-contained electronic packaging materials in simulated body fluids

For electronic medical devices which are intended to function inside the human body is very important to keep unchangeable their structural and functional properties under an influence of aggressive physiological factors. For stability testing of some electronic materials in laboratory conditions a simulation of human body fluid environment has been used. Sn-contained electronic packaging materials as a) FR4 + 1.2 44 m chemical Sn; b) FR4 + hot air leveling (HAL) Sn and c) FR4 + Sn 3.5 Ag 0.7 Cu were brought in dynamical interaction with artificial blood plasma, cerebrospinal fluid and 0.9% NaCl solution. Alterations in the surface topography and its chemical composition were studied. Materials mass losses in the surface ratio were determined depending on the soaking time. As a protection procedure against the influence of aggressive fluidic environment 1 mum and 2.5 mum layers of parylene C were deposited on chemical Sn and HAL Sn surfaces. Hydrolytic stability of protected materials has been determined.

Nano Evaluation in Electronics Packaging

The challenge of nano packaging requires new non-destructive evaluation (NDE) techniques to detect and characterize very small defects like transportation phenomenon, Kirkendall voids or micro cracks. Imaging technologies with resolutions in the submicron range are the desire. Possible evaluation methods are for example x-ray microscopy, x-ray tomography, ultrasonic microscopy and thermal microscopy. However, techniques with this resolution can not be found on the market. The ldquocenter for non-destructive nano evaluation of electronic packagingrdquo (nanoevareg) is taken up to develop this equipment in cooperation with the electronics industry and to transfer the knowledge to colleagues in industries and research institutions. The new center is a common organization of Fraunhofer IZFP-D and the electronics packaging lab with its centre of microtechnical manufacturing (ZmuP) of the Technische Universitat Dresden.

Nano-scaled functional layers for current and heat transport in electronics packaging

The amount of information capable of being stored on a computer chip doubles every two years as stated first by Gordon Moore in 1965. Electronics packaging technology has to adopt the resulting requirements of this tremendous development of the microelectronic industry. In view of future applications it is necessary to establish new interconnect materials for high-density electronics packaging because common materials are facing physical barriers and fail to meet the requirements of nano-scale miniaturisation. These requirements will be steady miniaturisation of the electronic devices, higher current density per device, pitches down to 20 mum and higher thermal dissipation loss. Current joining elements cannot meet these requirements. For common joining element materials there are also limitations with regard to their thermomechanical behaviour. Downscaling of traditional solder bump materials to lower pitch cannot satisfy the reliability requirement [1]. For example, lead and lead-free solders typically fail when scaled down to less than 100 micron pitch due to poor fatigue resistance. On the other hand compliant interconnections do not meet the high frequency electrical requirements. Consequently, there is a need for new joining materials in electronics packaging. Carbon nanotubes (CNTs) are promising candidates for functional layers for packaging in the nanometre scale because of their superior mechanical, thermal and electrical properties. The reproducibility and the performance of such structures for thermal and electrical transport on common packaging substrates are not sufficiently known and were investigated by our groups. Latest results concerning the preparation of CNT films and their structural and functional properties are described in the present paper. Using a ldquobottom uprdquo approach the CNTs are grown with a defined wall structure on a catalyst layer by chemical vapour deposition (CVD). The catalyst layer is a nano-structured deposit on a Si wafer formed by a self assembly mechanism. The nano-scaled structuring is the most important requirement for manufacturing CNTs with defined properties. Unlike state-of-the-art methods a layer of a conducting material is deposited on the Si surface as finish. This conducting layer could be the basis for the following die bonding process transferring the CNT layer on common packaging substrates. The application potential is exemplarily shown.

Novel optical transmitter and receiver for parallel optical interconnects on PCB-level

In this contribution a concept of ceramic transmitter and receiver module for assembly on electro-optical printed circuit board with parallel optical interconnects is presented. The realized pitch of parallel optical interconnection amounts to 250 mum. The solution for realization of the indirect optical coupling basing on micro-optical coupling element will be shown. Described optical analysis in regard to the optical coupling between link components (VCSEL, micro-optical coupling elements and p-i-n-photodiode array) will define the conditions for alignment process of optoelectronic devices and micro-optics. The design and realization of an optical multi-chip module basing on ceramic interposer will be presented in detail. An approach for the flux free solder-bumped flip chip assembly process of optoelectronic components will be shown. Finally the first demonstrator of the optical transmitter and receiver module will be demonstrated.

Interfacing fluidic sensors based on LTCC

Fluidic sensors can be easily integrated in Low Temperature Cofiring Ceramic (LTCC) systems. This article describes electronic circuits for interfacing typical fluidic sensors, e.g. piezoresistive pressure transducers, anemometric flow meters and capacitive transducers. Due to their character the sensor signal have to be amplified, offset and temperature compensated and filtered. Furthermore the original physical value of these electrical signals has to be recalculated. On this basis some models for the transducers were designed.