Wolfgang Eberhardt

UV-sintering of inkjet-printed conductive silver tracks

In this paper we report an alternative sintering method for conductive silver tracks by UV radiation. The silver patterns have been obtained by inkjet printing from a commercially available silver nanoparticle ink. Different polymer materials such as polyimide, polycarbonate and liquid crystal polymer have been used as substrate materials. UV-curing resulted in highly conductive patterns with resistivities as low as four times that of bulk silver. The choice of substrate material has shown to greatly influence the achievable conductivity values. Furthermore it was demonstrated that UV-sintering resulted in lower substrate temperature as compared to thermal sintering to get similar resistance values.

Inkjet printed differential mode touch and humidity sensors on injection molded polymer packages

Todays printed electronics are mainly focused on producing sensors on thin, flexible, smooth foils, which limits their use on 2D applications. Within this study we report on the design of inkjet printed capacitive touch and humidity sensors on thermoplastic substrates, to fabricate printed functional structures on injection molded 3D components. Both sensors are based on printed differential interdigital capacitors (IDC) made of silver ink and a printed sensitive layer. Reproducible results and low hysteresis were achieved, proving the concept to be able to improve sensitivity and to reduce drift effects due to temperature as well as moisture absorption by the substrate.

Aluminium wedge-wedge wire bonding on thermoplastic substrates made by LPKF-LDS ® technology

Due to its high capability for miniaturisation as well as for reducing the number of components and process steps, MID (Moulded Interconnect Devices) technology is a very interesting alternative for packaging of miniature devices. Meanwhile several MID based products have been introduced to industry mainly in the field of medical technology, automotive engineering, automation and communication technology. Laser based MID technologies enable the fabrication of fine pitch circuitry in three dimensions on complex thermoplastic devices. The assembly of bare dies extends the application range of MID as a system carrier for micro systems and micro mechatronic systems. Wire bonding is an important assembly technology for bare dies. However for wire bonding the roughness of the electroless plated conductor path on the MID substrate has to be minimised. In this paper we report on basic investigations of aluminium wedge-wedge wire bonding on laser patterned and metallized MID using LPKF-LDS® technology. Comprehensive studies have been carried out to optimize the set of laser parameters with regard to roughness and adhesion of electroless plated Cu/Ni/Au layers on MID substrates. Furthermore the influence of CO2 snow jet cleaning or stamping after laser patterning have been investigated as leveling steps in order to decrease roughness. A significant reduction of the average surface roughness was achieved for different laser-activatable thermoplastics. The feasibility of aluminium wedgewedge wire bonding on leveled and electroless plated laser-activatable substrates has been tested successfully.

Properties of Polymer Bumps for Flip Chip Mounting on Moulded Interconnect Devices xs(MID)

MID technology offers a very interesting alternative for many applications in MEMS and MOEMS suitable for multifunctional 3D packages due to its high capability in miniaturization as well as in reducing the number of components and process steps. To make use of the full potential of MID technology not only SMD assembly has to be considered but also mounting of bare dies. For flip chip mounting MID technology offers a unique assembly solution consisting of polymer bumps (MID bumps) fabricated simultaneously while moulding the substrate. In this paper investigations of the mechanical and geometrical properties and the deformation behaviour of metallized polymer bumps for flip chip assembly are described

Mit Inkjet und Aerosol Jet® gedruckte Sensoren auf 2D- und 3D-Substraten

Zusammenfassung Digitale kontaktlose Drucktechnologien wie Inkjet oder Aerosol Jet® werden aufgrund ihrer Vorteile wie einfacher Layoutanpassung, kurzer maskenloser Prozessketten, einer großen Auswahl an nutzbaren Substraten und Tinten – häufig auf der Basis von Nanomaterialien – und einer gewissen 3D-Fähigkeit immer interessanter für die Herstellung elektronischer Bauteile. In diesem Beitrag werden gedruckte Sensoren beispielsweise zur Detektion von Temperatur, Stress, Intrusion, Feuchtigkeit oder Magnetfeldern vorgestellt, die mittels Inkjet oder Aerosol Jet®-Technologie hergestellt wurden.

Analysis of thermal vias in molded interconnect devices

The ongoing miniaturization of micro-opto-electro-mechanical-systems requires compact multifunctional packaging solutions like offered by the three-dimensional MID (molded interconnect device) technology which combines integrated electronic circuitry and mechanical support structures directly into one compact housing. Due to the inherently large thermal resistance of thermoplastic MID substrate materials, temperature-sensitive applications require carefully arranged thermal vias in order to reduce the thermal resistance of the packaging effectively. This paper presents the analysis and optimization of various laser-drilled thermal via design parameters of MIDs including hole diameter, pitch, plating thickness of the Cu/Ni/Au metallization layers as well as the void level of the filling material inside the vias.

Heat dissipation for MID applications in lighting technology

Molded Interconnect Device (MID) Technology features excellent design freedom and great potential for functional integration for applications in indoor lighting. Spatial arrangement of LEDs and intelligent control elements enable highly efficient, situation aware lighting concepts with attractive design. Even more than in PCB based LED lighting technologies, there are significant degrees of freedom for improved thermal management when designing and manufacturing an MID. In this work, measures suitable for thermal management of MID for lighting applications manufactured with LPKF-LDS technology are identified and compared. Focus is on design for thermal management and application of recently developed high thermal conductivity polymers. To compare the effects of the different measures, simulations are performed with a range of combinations of individual measures for thermal management. The simulation results of the individual combinations are evaluated using design of experiments statistical methods. Low cost measures relying on design for thermal management are compared to measures implying higher manufacturing costs and to substrates manufactured from high thermal conductivity polymer compounds.