Electronics Materials, Packaging and Reliability Techniques

Professor Seppo Leppävuori, Microelectronics Laboratory, Department of Electrical Engineering, University of Oulu
Assoc. Professor Risto Rautioaho, Materials Engineering Laboratory,Department of Mechanical Engineering, University of Oulu

seleee.oulu.fi, rrautiome.oulu.fi

 Background and Mission

The research group of Electronics Materials, Packaging and Reliability Techniques (EMPART) consists of specialists and students in microelectronics and materials engineering and measuring techniques. The research of the group is concentrated on:

1. electronics materials and components (with focus areas of (i) dielectric materials and components (ii) piezoelectric micro actuators and motors and (iii) high temperature superconductor (HTS) materials with special reference to telecommunication applications)

2. packaging and reliability (with focus areas of (i) thick-film and multilayer (LTCC) ceramic technologies (ii) sputtering, laser ablation and sol-gel thin film technologies, (iii) laser processing, (iv) the reliability of joints and novel soldering technology, (v) fault and materials analysis, (vi) environmental testing and (vii) functional testing).

The EMPART group is engaged in research into the manufacture of piezo actuators and motors using thick-film technology. It is currently participating in a Brite/Euram project "Thick Film Ferroelectric Actuators for New Design Industrial Applications" (TIFFANI), in which special thick-film processes for realising micro actuators and motors will be developed, and in an SMT-project ACTUATE, which is concerned with the development of measuring and testing standards for actuators. The size of the devices is in the scale of some square mm. When the size of the devices decreases to the nano technology scale, sol-gel thin-film methods will open up new possibilities. Piezoelectric micro actuators and motors have almost unlimited applications, for example in micro robotics and in telecommunications. In realising multilayer ceramics, the low temperature LTCC process is now entering the market. A breakthrough for multichip LTCC technology is expected both in telecommunication and medical electronics and in auto electronics. The EMPART group and VTT Electronics are partners in a national project related to LTCC technology and are together building a manufacturing facility for LTCC circuits.

In the field of fine-line techniques, the interest of the group has especially been focused on the gravure-offset printing technique. The purpose is to realise, through this technique, lines and spaces less than 50 µm in width. The group is one of the pioneers of this technique in Europe and has been invited to participate in a Brite/Euram project. Application areas of the technique are multi-chip modules and conformal structures in, for example, filters and antennas.

Laser processing applications in electronics manufacturing have been studied in the laboratory for nearly twenty years Laser ablation deposition and repair of IC circuits are representative examples of the laser processing research objectives of the research group. Laser ablation deposition is a new thin-film technique for growing almost all inorganic materials and multilayer structures, even layer by layer. The research objectives are amorphous diamond-like carbon films, epitaxial ferroelectric thin-films and layer structures comprising these films and conducting oxide-materials, high Tc superconductors and nano-crystalline silicon films and superlattices.

With regard to the novel deposition methods of packaging technology, sol-gel technology is especially interesting as a possible production method for those seeking novel packaging solutions. The EMPART group will study non-destructive testing of BGA (ball grid arrays), flip-chip bonding joints and multilayer conductor structures. In co-operation with industry, existing production testing methods will be developed.

Scientific Progress

During the research year of 1997, the following research has been performed:

1. Design of a broad band filter, based on an HTS dual-stripline, with a middle frequency of 1.75 GHz and a bandwidth of 75 MHz, has been finalised. In the realisation of the filter, high quality double-sided YBCO deposited substrates were used. HTS films have been manufactured using RF sputtering. Properties of the filters are superior compared with corresponding copper-based structures.

2. The gravure-offset fine-line printing technique has been used to manufacture microstrip lines and their attenuation properties determined up to 50 GHz.

3. Sol-gel type chemical solution deposition (CSD) and controlled thermal processing have been used to manufacture heteroepitaxial PZT/LSCO structures. Polycrystalline BST films for tuneable filter applications have also been realised.

4. Epitaxial layered thin film structures containing ferroelectric (PZT, PLZT) and conducting ceramic (LSCO) electrodes have been deposited in an in-situ process by laser ablation deposition. The structures were grown on MgO, LaAlO₃, Si and silicon-on-sapphire substrates. The characterisation of the laser ablation deposition of diamond-like carbon films has been performed by studying the carbon species and their energies in order to find correlations between the deposition parameters and the structure and properties of the films. The ablation process has been studied through measurement of time-of-flight spectra of carbon ions to determine the energy distribution of the ions.

Exploitation of Results

Material and component technologies developed by the group are now widely applied in the electronics industry, especially in the mobile phone industry. As important examples of the next exploitation, LTCC micro modules and other high density interconnection substrates must be mentioned.

Researchers of the EMPART research group have developed a repairing facility based on a so-called laser-chemical method. This facility significantly improves the prospects for commercial companies specialising in IC circuit design to find and repair faults in their prototype designs without delay. Thus the most important exploitation of the research of the group was starting the laser-assisted IC repair and failure analysis service for national and international industry at OuluTech Oy under the LaserProbe project. The IC repair technique used is based on laser writing of copper lines and laser cutting of the conducting lines of ICs.

Future Goals

In repairing sub-micrometer level IC circuits, the cutting and new rewiring can be carried out only by the focused ion beam (FIB) method. This kind of facility will strengthen the expertise of the group in the field of sub-micrometer and nanometer technologies. The FIB facility, in addition to uniting the beneficial features of the LaserProbe and FIB techniques, also will enable the construction of the sensor and actuator structures required for micro and nano mechanics.

 Personnel

External Funding

Selected Publications in 1997

Moilanen H, Remes J & Leppävuori S (1997) Low resistivity LCVD direct write Cu conductor lines for IC customisation. Physica Scripta T69: 237-241.

Wang F & Leppävuori S (1997) Properties of epitaxial ferroelectric PbZr0.56Ti0.44O3 hetero-structures with La0.5Sr0.5CoO3 metallic oxide electrodes. Journal of Applied Physics 82 (3): 1293-1298.

Wang F, Uusimäki A & Leppävuori S (1997) Preparation of electrical properties of Ba0.6Sr0.4TiO3 thin films deposited by the sol-gel method. Physica Scripta T69: 332-335.

Kemppinen E, Mikkonen P & Leppävuori S (1997) Performance of Cu and Ag based microstrips up to millimeter wave frequencies. Proc. of 11th European Microelectronics Conference, May 14 - 16, 1997, Venice, Italy: 100-108.

Lozinski A, Wang F, Uusimäki A & Leppävuori S (1997) PLZT thick films for pyroelectric sensors. Mes. Sci. Technol.8: 33-37.