Electronics Materials, Packaging and Reliability Techniques (EMPART)

Professor Seppo Leppävuori, Microelectronics Laboratory,
Department of Electrical Engineering, University of Oulu
Professor Risto Rautioaho, Materials Engineering Laboratory,
Department of Mechanical Engineering, University of Oulu
seleee.oulu.fi, rrautiome.oulu.fi
http://www.infotech.oulu.fi/empart

Background and Mission

The EMPART (Electronic Materials, Packaging and Reliability Techniques) research group consists of specialists in microelectronics, materials engineering and measurement techniques; 9 professors and doctors, 11 graduate students and 15 others. The research supervisors are Professor Seppo Leppävuori and Professor Jouko Vähäkangas from the Microelectronics Laboratory, Professor Risto Rautioaho from the Materials Engineering Laboratory and Professor Markku Moilanen from the Optoelectronics and Measurement Technology Laboratory.

The research activities of the group are aimed at developing a skilled workforce, new materials and future manufacturing technologies required especially in developing novel information technology products. The group will play a high international level role in the research for next generation electronics materials, high-density electronics packaging and reliability techniques.

The research of the group is concentrated on:

• Electronics materials and components (with special reference to (i) telecommunication applications and (ii) piezoelectric micro actuators and motors).
• Packaging and reliability (with focus areas of (i) thick-film and low temperature multilayer ceramic technologies (LTCC), laser processing and focused ion beam technology, (ii) the reliability of joining technologies and fault and materials analysis, (iii) environmental and functional testing).

Active co-operation with several universities, research institutes and companies outside Finland is characteristic of the research of the group.

Representative examples of the research are:

A) Research into the manufacture of piezo actuators and motors, in which the group is engaged to use LTCC and thick-film technology, which has been a speciality of the group since 1972. The group
participated for example in an EU Brite/Euram project "Thick Film Ferroelectric Actuators for New Design Industrial Applications" (TIFFANI), in which special thick-film processes for realising piezoelectric motors were developed, and in an EU SMT project "ACTUATE", which was concerned with the development of measuring and testing standards for piezoelectric actuators (the project ended year 1999). The size of the devices in the TIFFANI project was to the scale of some square millimetres. Piezoelectric micro actuators and motors have unlimited applications; for example, in micro robotics and in telecommunications. An EU IST project "Micro air vehicles for multi-purpose remote monitoring and sensing" (MARVEL), directed mainly at this research area, started in the year 2000.

B) Realising multilayer ceramics using a low temperature co-fired ceramics (LTCC) process. A breakthrough for multichip LTCC modules is in progress in telecommunication, medical electronics and in automobile electronics. The group has been a pioneer in building a manufacturing facility and in design activity for LTCC circuit technology. The know-how and facilities have now reached the level where the technology is being studied more deeply and prototype modules are being manufactured for industry. There are several industrial projects going on in this field, for example a Tekes project entitled `'Integrated ceramic micromodules - LTCC II''. A new EU IST project called "Microwave Electronics with Tuneable Dielectric Layers" (Melody) started in the year 2001.

C) Laser processing applications in electronics manufacturing have been studied in the Microelectronics Laboratory for nearly twenty years. Laser ablation deposition (LAD) and repair of IC circuits using both laser and focused ion beam (FIB) technology are the most important examples of the present activity.

D) Non-destructive testing of BGA (ball grid arrays), CSP and flip-chip bonding joints and dense multilayer conductor structures using novel micro-focus X-ray microscopy (µXRM), scanning acoustic microscopy (SAM) and Moiré techniques. This research is performed in co-operation with VTT Electronics and industry to develop existing production testing methods.

The research of the EMPART group has been funded mainly by the Technology Development Center of Finland (TEKES), the EU, the Academy of Finland, the University of Oulu and national industry. During the period, international research co-operation has been active. A project "Development of a high-resolution printing process for cost-effective production of ultra-fine line electronic circuitry" (Hi-ReCiPri) of the EU Brite/Euram III Program continues and an EU IST Program project Marvel and a new Thematic Network for R&D activities of polar electroceramics, strategically important for European industry will be continued. The EMPART group has also started in a new EU IST project Melody in the field of future multilayer high frequency devices for telecommunication purposes.

Scientific Progress

During the research year of 2001, long term research in the focus areas of the group has continued. From the scientific progress of the research, the following activities are of importance:

1. Research on pulsed laser deposited layered thin film ferroelectric structures has continued, now in a project called "Miniaturization effects in ferroelectric nanocapacitors and nanoactuators" funded by the Academy of Finland. The purpose of the project is to investigate and develop the preparation methods, properties, basic phenomena and applications of the ferroelectric thin films. Research is concentrated on the deposition, structure, chemical ordering, epitaxy, and dielectric and ferroelectric properties of lead-containing perovskite relaxor films and their heterostructures with conducting oxides. These materials have excellent electromechanical, electro-optic and dielectric properties, and their thin film heterostructures are promising candidates for microelectromechanical applications. However, the properties achieved in thin films have not been as good as those in the bulk material. This requires the development of preparation methods and better understanding of the peculiarities of the relaxor ferroelectric state in thin films. Special attention has been paid to the epitaxy in the heterostructures and the atomic ordering effects in
the relaxor ferroelectric material, and their effect on the dielectric properties. In international co-operation, the electrical properties of heterostructures are being investigated in cooperation with the Institute of Solid State Physics at University of Latvia, Riga (Dr. A. Sternberg). The electronic structure and bonding has been studied by synchiotron radiation x-ray absorbtion spectroscopy at the MAX-laboratory of the University of Lund, Sweden. In the study of basic phenomena associated with relaxor thin film heterostructures, good progress has been achieved in the project: a new method has been developed to separate the effect of the film-electrode interface and to reconstruct the true dielectric properties of the relaxor ferroelectric thin film, and a study of the dynamics of the relaxor state in thin films has been published for the first time.

2. Research on laser-induced deposition of metals on polymers and other substrates has been performed as a continuation of the Hungarian-Finnish S&T Cooperation Program (1997-1999). The main goal was to develop methods - involving Ar⁺, XeCl, KrF lasers - in order to carry out tailored micro structuring of different materials (metals, oxides etc.) on polymers, semiconductors, as well as on ceramic substrates for potential applications in opto and microelectronics. The first investigations dealt with the development and modelling of Laser-induced Chemical Vapour-phase Deposition (LCVD) of Cu and Ni for maskless IC prototype repairs. Parallel to the LCVD studies, research has also been taken up on Laser-induced Chemical Liquid-phase Deposition of Cu and Pd on polymers such as PI (Kapton) and PET (Mylar). As a result, a novel Pd-seeding precursor has been invented and proposed to use in multi-step chemical metallization techniques (laser-induced deposition of Pd film followed by electroless plating of Ni or Cu). The developed metallization method has been utilized in lithography, maskless fabrication of horizontal and vertical interconnects in flexible printed circuit board materials, preparation of reflective coatings on optical fibres and activation of Si substrates for carbon nanotube growth. Owing to the fascinating physical and chemical properties of porous silicon (PS) - which recently has been an extensively investigated novel material - we have performed studies towards its fabrication and metallization as well. Besides the non-localised metallization of PS by Pd and Ag immersion plating (in order to create catalyst material for redox chemical reactions), we have introduced a new maskless process for the area-selective deposition of Ni (with high lateral resolution) on the surface of PS using various lasers. Recently, we have been performing studies on direct applications based upon metallized PS substrates.

3. Research on piezoelectric actuators for fine and micro mechanical applications has continued in the framework of the national TUKEVA program of the Academy of Finland and the PRESTO program of the National technology agency. The main part of the work is concerned with pre-stressed bending actuators realized by bulk and tape cast ceramic technology. Increased actuation is suitable for various solutions currently focusing on pump, valve and motor applications. Simultaneously with development of new actuators, modeling active structures with ATILA software has continued. Comparison between modeled and measured results has revealed a good comparison between them. The effect of laser machining for ceramic structures has been studied and new structures realized for deflector applications. 3D tape cast LTCC/HTCC structures have been constructed and techniques for realizing them is under examination while working on optimization of the sintering process. Within the POLECER network (Polar Electroceramics European network organization) LTCC compatible PLZT paste was realized through co-operation with Dr. Andrzej Lozinski (TU, Gdansk, Poland). Co-operation will continue within material and application development.

Simulated displacement of a multilayer piezo actuator structure in the z-axis direction.

Simulated maximum displacement in the z-axis direction is 2253 nm and the measured value 2300 nm.

4. The Academy of Finland financed a project called "Investigation of Fabrication Processes and Properties of Microstructures of Ferroelectric and Ferromagnetic Materials" which was completed in July 2001. The main task of the project was the research and development of large displacement screen-printed piezoelectric actuators for domestic applications, primarily for electronic water tap valves. In these valves, the actuators should operate at temperatures of 5-95 ŗC and generate forces about 1 N and displacements about 1 mm. For achieving the necessary output displacement bending actuators were used, realized by printing PZT thick films on metal substrates. To gain the necessary force, it is necessary to sum the forces of plurality of bending elements. The effect of different connection members between the cantilever elements, enabling the shift of element tips at bending, on the compound beam tip's deflection magnitude was studied analytically and numerically. The best performance demonstrated rollers, while in the case of elastomer and sliding members, the magnitude of the tip's deflection and the blocked force were significantly lower. Also the temperature change-induced deflection of the printed piezo beams on metal was investigated. It was found that the thermal deflection of the beam in interval of 5-95 ŗC is of the same order of magnitude as the electrically induced deflection, and should be compensated by the actuator's driver. The problems of fluid dynamics and hydrodynamic instability of the system `moving liquid _ elastic beam at an orifice' were studied introductorily by FEM simulation as well.

5. The European IST project Micro Air Vehicles for Multi-purpose Remote Monitoring and Sensing was continued in the year 2001. The Microelectronics Laboratory was involved in the development of a radio link between a vehicle and a base station and in the selection and integration of proper sensors (GPS, image, acoustic, chemical, inertial) into the system. The need to keep the mass of the vehicle low requires the use of non-conventional architectural, circuitry and packaging solutions. In the year 2001, a model radio link system including GPS and television sensors was created and field-tested. The problems of introducing of a miniature zoom lens for the TV camera have been evaluated, and a principal solution for zoom lens of less than 1 gram has been presented. Other partners in the project are Centro Riserche Fiat (Italy), Politechnico of Turin (Italy) and CNRS (France).

6. Novel dielectric compositions especially for telecommunication purposes have been developed. The basic characteristics for these materials are set by requirements of the final products. Special attention has been paid to the high frequency electrical properties without neglecting the thermomechanical and productional properties required for reliable telecommunication devices. The research included the characterisation of commercial Low Temperature Co-fired Ceramics (LTCC), their microstructural, thermomechanical, productional and electrical properties as well as development of a novel LTCC composition especially beneficial to high frequency applications. The group has been able to integrate a large area of knowledge and measurements into a complete instruction guiding the research and selection of these materials for further utilisation. The group has also started research on low temperature firing ferroelectric materials, which are to be used for phase shifters, antennas and tuneable filters operating at up to 50 GHz. This research is related to an EU project called Melody ("Microwave Electronics with Tuneable Dielectric Layers") co-ordinated by Ericsson, SE. The investigation has produced several scientific articles in international journals and one doctoral thesis, with another one being prepared. Simulations, design and measurements of RF and microwave properties of substrates, transmission lines, resonators, capacitors, coils, dividers, filters and amplifiers in the GHz frequency region have been realized to gain a deeper understanding of LTCC technology. The work is continuing on the basis of the research described above in a project entitled `'Integrated ceramic micromodules - LTCC II'', which has designed, manufactured and measured the first LNA module and is developing other modules using better new materials. It belongs to a program called NCEM (Northern Center of Electronics Manufacturing), which is a 25 million euro program for the years 2000-2004 concentrating on life-cycle testability, future connection and packaging technologies, factory engineering and integration of materials research, design and electronics manufacturing. 

The target of the group is to become a leading centre of excellence in this field and now the useful frequency range extends up to 50 GHz. The research group has close co-operation with the Microperipheric Group of the Technical University of Ilmenau, Germany (Professor H. Thust) and with the Department of Microelectronics of St. Petersburg Electrotechnical University, Russia (Professor I. Vendik's group). The reliability of LTCC / printed circuit board assemblies has constituted an essential part of the INKEMO project (Integrated Ceramic Micromodules). LTCC modules provided with non-collapsible lead-rich spheres were attached to printed circuit boards of two types (FR-4 and Hitachi) with a difference in the coefficient of thermal expansion (CTE). Test boards have been thermally cycled until fatigue failures were encountered in the joint regions of the samples. Fatigue crack initiation and propagation were monitored by scanning acoustic microscopy and resistance measurements. The reasons for failures have been investigated using optical microscopy and SEM/EDS.

Dissolution of thick film joint metallisation and reactions of tin with metallisation were observed and the effects of these phenomena on reliability were clarified. Nucleation and propagation of fatigue cracks in the ceramic modules provided with long vias were observed, and these effects together with intermetallic layers near via roots were found to make a negative contribution to reliability. The decrease in CTE (Hitachi board) improved the fatigue performance of the assemblies. The results will be used in future projects aimed at developing LTCC modules for industrial applications.

7. Expertise in development of focused ion beam (FIB) technology for solving problems of on-chip rede
sign and electrical access on finished IC products has been acquired. Repair and modification, including cutting and rewiring of sub-micrometer linewidth IC circuits can be carried out using FIB. The FIB facility (MICRION 2500 System) also strengthens the expertise of the group in the field of sub-micrometer and nanometer technologies, enabling the construction of the sensor and actuator structures required for micro and nanomechanics. Examples of nanotechnology applications are photonic band gap and quantum wire structures. The research was financed by the TEKES, the Academy of Finland and industry.

8. In the field of fine-line techniques, the interest of the group has been especially focused on the gravure printing techniques. The group is one of the pioneers of the gravure-offset printing technique and is participating in an EU Brite/Euram project ("Development of a high-resolution printing process for cost-effective production of ultra-fine line electronic circuitry" (Hi-ReCiPri), 1998-2002, co-ordinated by Philips-CFT, NL). The target is to realise lines and spaces down to 25 µm in width on up to 50 x 60 cm² substrates with options for using non-planar substrates. Another gravure technique method, Direct Gravure Printing (DGP), has been developed and studied in a TEKES and industry financed project to print down to 25 µm wide lines on ceramic substrates. The application areas of the gravure printing techniques are multichip modules and conformal structures in, for example, filters and antennas both on ceramic and organic substrates.

Exploitation of Results

Materials and technologies developed by the group are already widely applied in the electronics industry, especially in the mobile phone industry. As important example of the future exploitation, LTCC micro modules must be mentioned. In the inspection processes for novel electronics production, expertise and services in X-ray and acoustic microscopies will be provided.

Researchers of the EMPART group have developed a repairing facility of ASIC's based on an FIB and a laser-chemical method. This facility significantly improves the prospects for commercial IC design companies to find and repair faults in their prototype designs. The group initiated the FIB and laser-assisted IC repair and failure analysis service for national and international industry establishing a spin-off company Laser Probe LP Oy. The Microelectronics Laboratory is a member of NEXUS (a Network of Excellence in Multifunctional Microsystems) and EUSPEN (European Society for Precision Engineering and Nanotechnology) and POLECER (Polar Electroceramics European network organization).

Future Goals

The long term research of the EMPART research group is planned to continue with the focus areas of electronics materials, packaging and reliability techniques. A growing research area of the group is LTCC micro modules, flip chip and ball grid joining technology and their reliability in an LTCC environment, in which thermomechanical modelling, structural analysis and testing are used for reliability evaluations. A new professorship in the field of electronics production technology with specialisation in electronics packaging technology and micromodules has been created in the Microelectronics Laboratory strengthening the EMPART research group in these focus ares. The group started research in the year 2001 on a new EU project called "Melody", concentrating on microwave electronics with tuneable dielectric layers for telecommunication purposes.

The EMPART group will form a high excellence research and education organization in the field LTCC RF and micro module technologies.

Personnel

External Funding