André Zimmermann

Using unique surface patterns of injection moulded plastic components as an image based Physical Unclonable Function for secure component identification

A Physical Unclonable Function uses random and inherent properties of a physical entity and can be used to uniquely identify components e.g., for anti-counterfeiting purposes. In this work we demonstrate that the surface patterns of injection moulded plastic components themselves are inherently unique and hence can be used as a PUF for reliable and secure identification. We further demonstrate that these unique surface patterns are easily accessible since they can be photographed with a simple camera set-up. This is exemplarily demonstrated for two different plastic materials on an overall of 200 injection moulded components. A set of brief experiments further examines the PUF’s robustness towards real life conditions. This approach might be useful for secure identification and authentication of components or a label-free tracking.

Void Formation and Their Effect on Reliability of Lead-Free Solder Joints on MID and PCB Substrates

Since the introduction of lead-free solder alloys, the impact of voids in solder joints has rapidly gained in importance. Particularly in power electronics, voids in solder joints can reduce their reliability due to less heat dissipation and a significant reduction of the cross-sectional area. While void formation in the printed circuit board (PCB) technology has been the focus of many research projects, the increasing application of molded interconnect devices (MIDs) demands a vivid understanding of void formation and its impact on reliability. This report will show that those processes specific to MID technology do not significantly influence the void formation in SAC305 solder deposits. The processed different roughness levels on Vectra, Vestamid, and FR4 substrate materials show no significant impact on void formation. The surface finish metallization was detected as the most important factor. Especially, the chemical-Sn (iSn) surface finish is inclined to having more voids compared to a nickel–phosphor–gold (NiP-Au) finish. Furthermore, three solder processes were investigated: convection, condensation, and vacuum-condensation soldering. The vacuum-condensation processes significantly reduced the voids in the Sn–3.0Ag–0.5Cu (simplified as SAC305) solder joints of CR0805, MLF20, and switches on all the investigated substrates. An accelerated thermal cycling test of these components according to JESD22-A104D demonstrates no significant effect of the void content of <19% on the solder joints’ reliability. Finally, the result of accelerated thermal cycling shows the possibility to achieve an equivalent lifetime of the solder joints on Vectra in comparison to the FR4 substrate.

Packaging of Small-Scale Thermoelectric Generators for Autonomous Sensor Nodes

This paper focuses on packaging of small-scale thermoelectric generators (TEGs) for energy harvesting applications in sensor nodes for industry 4.0 and for the Internet of Things. The TEGs are suitable to enable self-powered sensor systems with unlimited energy lifetime, but they have to withstand high mechanical loads during the assembly and packaging process and further stress due to the mismatch of the coefficient of thermal expansion of the different materials. Devices with different underfills (UFs) and stress decoupling thermal adhesives were evaluated with a shear force test apparatus and a four-line bending test together. In addition to these mechanical tests, the thermal influence of the UF on the system performance was investigated with measurements, finite element method, and computational fluid dynamics simulations. The shear force per area could be enhanced up to the factor of two by using capillary UF. All TEGs with and without UFs passed the reliability investigations without any electrical defects. All TEGs with UF passed the given quality criteria with the four-line bending test. With some of the stress decoupling thermal adhesives, the TEGs could withstand the loads without UF. The simulation model was evaluated with a measurement setup, and the differences between the simulation model and the measurements concerning the temperature difference of the TEGs were in an acceptable range (<21%). Furthermore, the influence of the UF on the temperature difference of the TEGs in the given measurement scenario was smaller than 15%, which makes the application of a UF a realistic approach.

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.

Application of human motion energy harvesters on industrial linear technology

Energy autonomous sensors for I4.0 applications powered by kinetic energy harvesters (KEHs) are widely discussed – especially in terms of vibration harvesting. Typically, industrial linear stages offer weak vibrations, so other inertia-based harvesting methods are investigated. This study investigates the usability of human motion energy harvesters in industrial linear motion technology for the first time. Two KEHs – harvesting swing or shocks, respectively – are tested while controlling the parameters velocity, acceleration, and jerk-limitation according to the real applications’ parameter ranges. The swing-KEH and the shock-KEH harvested up to 106 and 124 mW, respectively. Furthermore, a parameter study is performed assuming constant driving lengths with optimised stroke rates to obtain a generalised power and energy profile for each harvester. The analytically obtained overall average power is 22 mW for the swing-KEH and 14 mW for the shock-KEH. The analytical investigation revealed that a reciprocal dependency of performance and velocity exists for both KEHs, respectively. Both experimental and analytical parts show that the wireless sensor node for I4.0 on industrial linear stages can be powered by harvesters made for human motions.

A Product Development Approach in the Field of Micro Assembly with Emphasis on Conceptual Design

Faster product lifecycles make long-term investments in machines for micro assembly riskier. Therefore, reconfigurable manufacturing systems gain more and more attention. But most companies are uncertain if a reconfigurable manufacturing system can fulfill their needs and justify the initial investment. New and improved techniques for product development have the potential to foster the utilization and decrease the investment risk for such systems. In this paper, four different methods for product development are reviewed. A set of criteria regarding micro assembly on reconfigurable manufacturing systems RMS is established. Based on those criteria and the assessment, a novel approach for a product development method is provided, which tries to combine the strengths of the beforehand presented approaches. It focuses on the conceptual design phase to overcome the customers’ uncertainty in the development process. For this, an abstract representation of a micro-assembly product idea as well as a decision tree for joining processes are established and validated by real product ideas using expert interviews. The validation shows that the conceptual design phase can be used as a useful tool in the product development process in the field of micro assembly.

Injection Compression Molded Microlens Arrays for Hyperspectral Imaging

In this work, a polymer microlens array (MLA) for a hyperspectral imaging (HSI) system is produced by means of ultraprecision milling (UP-milling) and injection compression molding. Due to the large number of over 12,000 microlenses on less than 2 cm², the fabrication process is challenging and requires full process control. The study evaluates the process chain and optimizes the single process steps to achieve high quality polymer MLAs. Furthermore, design elements like mounting features are included to facilitate the integration into the final HSI system. The mold insert was produced using ultraprecision milling with a diamond cutting tool. The machining time was optimized to avoid temperature drifts and enable high accuracy. Therefore, single immersions of the diamond tool at a defined angle was used to fabricate each microlens. The MLAs were replicated using injection compression molding. For this process, an injection compression molding tool with moveable frame plate was designed and fabricated. The structured mold insert was used to generate the compression movement, resulting in a homogeneous pressure distribution. The characterization of the MLAs showed high form accuracy of the microlenses and the mounting features. The functionality of the molded optical part could be demonstrated in an HIS system by focusing light spectrums onto a CCD image sensor.

Effect of voids on thermo-mechanical reliability of chip resistor solder joints: Experiment, modelling and simulation

Abstract With the introduction of lead-free solder alloys, the effect of voids on solder joint reliability has rapidly gained importance. In this study, a first analysis of X-rayed CR0805 solder joints shows a significant reduction in void content, from 20% down to 2.5%, after vacuum soldering. The statistical analysis of the void distribution demonstrates that the vacuum option reduces number of voids and median diameter of voids in comparison to the convection soldering process. A subsequent accelerated thermal cycling test of these analysed test vehicles, according to JESD22-A104D, indicates the tendency of a higher characteristic life time for higher void content. In contrast to these findings, the 1% to failure criterion reveals a higher reliability for lower voiding. During the finite element method (FEM) modelling part of this study, two modelling approaches of void implementation into solder joint geometry are investigated: modelling with a constant volume of the standoff for different void contents, and a modelling approach with a random combination of void content and volume of standoff. The modelling approach with the random combination reveals that voids can reduce the lifetime in the “worst case” parameter combination. In particular, the 1% time to failure rate indicates a quantitative correlation with the experimental results. Furthermore, the FEM results suggest a higher impact on reliability for a single void in comparison to a distribution of multiple voids with similar void content. Finally, the FEM study shows a high sensitivity of predicted life time with respect to the standoff height. Based on this finding, the CR0805 solder joint geometry is examined using optical inspection and cross-section polishes with the outcome that the better wetting behaviour during vacuum soldering causes a reduction of the solder alloy volume and consequently further decreases the standoff height.

Flexible Packaging by Film-Assisted Molding for Microintegration of Inertia Sensors

Packaging represents an important part in the microintegration of sensors based on microelectromechanical system (MEMS). Besides miniaturization and integration density, functionality and reliability in combination with flexibility in packaging design at moderate costs and consequently high-mix, low-volume production are the main requirements for future solutions in packaging. This study investigates possibilities employing printed circuit board (PCB-)based assemblies to provide high flexibility for circuit designs together with film-assisted transfer molding (FAM) to package sensors. The feasibility of FAM in combination with PCB and MEMS as a packaging technology for highly sensitive inertia sensors is being demonstrated. The results prove the technology to be a viable method for damage-free packaging of stress- and pressure-sensitive MEMS.

Reliability in MID

The MID technology is used in more and more industrial applications. There are strong interactions between the materials used and the manufacturing process, which can have a direct influence of the quality and reliability of the final product. Hence, a comprehensive product and process qualification is necessary, because the available guidelines and directives are not sufficient to fulfill the specific requirements around MID.