Wissenschaftliche Publikationen "Fertigungstechnologien"

Elektronische Baugruppen werden in der Industrietechnik oder der Kraftfahrzeugtechnik häufig unter rauen Umgebungsbedingungen betrieben und müssen daher vor Umwelteinflüssen geschützt werden. Zu diesen Umwelteinflüssen zählen neben extremen Umgebungstemperaturen auch aggressive Medien.

Die Herstellung von dreidimensionalen Schaltungsträgern aus spritzgegossenen Thermoplasten, welche mittels Laserdirektstrukturierung und anschließender außenstromloser selektiver Metallisierung funktionalisiert werden, ist mittlerweile Stand der Technik. Bei erhöhter thermischer und/oder mechanischer Belastung z.B. durch Steigerung der elektrischen Leistungsdichte, stoßen Thermoplaste jedoch an ihre Grenzen. Hier bieten keramische Substratmaterialien klare Vorteile. Die Herstellung von solchen keramischen Schaltungsträgern mittels laserinduzierter Direktmetallisierung wurde erfolgreich realisiert. Hierfür wurden zwei Unterschiedliche Varianten an Al2O3-Keramiken untersucht. In der ersten Variante erfolgte das Sintern der Al2O3-Keramiken in H2-Atmosphäre, in Variante 2 wurden die Al2O3-Keramiken mit Cr2O3 dotiert und an Luft gesintert. Anschließend erfolgte für beide Varianten eine Laserstrukturierung mit darauffolgender außenstromloser Metallisierung. Somit ließen sich 3D-Schaltungsträger mit hoher thermischer Belastbarkeit, einer geringen Wärmeausdehnung und einer guten elektrischen Isolation herstellen. Die abgeschiedenen Metallschichten zeigten vergleichbare und zum Teil bessere Eigenschaften als solche auf klassischen thermoplastisch

Quality and reliability are two fundamental requirements for molded interconnect devices to be able to compete with other circuit carriers in various application fields, such as automotive, sensor technology, medical technology and communication technology. In this context, especially the laser direct structuring and metallization process, which govern the adhesion between the substrate and the metal layer, along with the mechanical integrity of the conductor tracks, are considered as critical in terms of the complete circuit carriers’ performance. This study focuses on the laser direct structuring of thermoplastic LCP Vectra E840i LDS substrates and the subsequent electroless metallization of the well-established layer system Cu/Ni/Au to identify the major influencing factors for the conductor tracks’ mechanical stability, using a customized flexural fatigue test setup. For the present molded interconnect device, increasing the roughness of the laser direct structured surface as well as decreasing the nickel layer thickness, while increasing its phosphorous content led to an improvement of up to three orders of magnitude in the number of bending cycles before fracture. These results thus provide valuable design rules for molded interconnect devices with enhanced reliability

Bladder tumor recurrence is a serious problem in urooncology, as it increases the risk of fatal progession and makes further surgeries necessary. The possibility of intraoperative tissue differentiation can help for diagnostic purposes as well as for ensuring that the entirety of the tumor is removed. The latter not only differ visually from healthy tissue, but also in their mechanical and electrical properties due to an altered physiology. A possible base for intraoperative tissue differentiation are impedance measurements, which are, however, difficult to obtain passing through the limited space of the urethra. This work presents two impedance sensors, which are obtained by laser direct structuring and rely on a four terminal measurement. The miniaturized sensors are suitable for minimally invasive usage. Circular electrodes are placed in a square for a first sensor, whereas a novel combination of one circular electrode and three concentric rings is designed for the second sensor. For each sensor, the specific geometry factor is determined and the impact of sensitivity towards small conductivity changes inside the tissue investigated. Furthermore, multiple ex vivo measurements on fresh pig bladders are carried out with each sensor. It is shown that both sensors reliably determine tissue impedance data that fit empirical tissue models. Conductivity values close to listed data of human urinary bladder are obtained. Ultimately, the novel ring sensor configuration turns out to more favorable in terms of sensitivity distribution and yields more reproducible results than the square electrode arrangement.

Hermeticity of an electronic package defines its effectiveness to seal and protect the encapsulated electronics from the ingress of contaminants, gases and moisture, as well as helping avoid toxic materials from inside the capsule contacting tissue. Using accelerated testing by methods of leak detection analysis, the theoretical limit of the lifetime due to water ingress of an encapsulated device can be estimated. However, classical methods are not sufficient for micro-encapsulations and exhibit limitations due to the resolution of the detection mechanisms required for such small cavities. With the availability of cumulative helium leak detection (CHLD) the detection limits can be extended by several magnitudes of resolution. However, limitations due to the physics of leakage apply. This paper discusses the limitations concerning the ability for combined gross, and fine leak testing in combination with outgassing effects using CHLD for miniaturized implantable medical devices. Practical aspects are evaluated regarding the applicability of CHLD for such micro encapsulations at the example of an AuSn sealed alumina package.

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Thermoset materials offer a multitude of advantageous properties in terms of shrinkage and warpage as well as mechanical, thermal and chemical stability compared to thermoplastic materials. Thanks to these properties, thermosets are commonly used to encapsulate electronic components on a 2nd-level packaging prior to assembly by reflow soldering on printed circuits boards or other substrates. Based on the characteristics of thermosets to develop a distinct skin effect due to segregation during the molding process, the surface properties of injection molded thermoset components resemble optical characteristics. Within this study, molding parameters for thermoset components are analyzed in order to optimize the surface quality of injection molded thermoset components. Perspectively, in combination with a reflective coating by e.g., physical vapor deposition, such elements with micro-integrated reflective optical features can be used as optoelectronic components, which can be processed at medium-ranged temperatures up to 230 °C. The obtained results indicate the general feasibility since Ra values of 60 nm and below can be achieved. The main influencing parameters on surface quality were identified as the composition of filler materials and tool temperature.

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Reconfigurable manufacturing systems (RMS) can be used to produce micro-assembled products that are too complex for assembly on flat substrates like printed circuit boards. The greatest advantage of RMS is their capability to reuse machine parts for different products, which enhances the economical efficiency of quickly changing or highly individualized products. However, often, process engineers struggle to achieve the full potential of RMS due to product designs not being suited for their given system. Guaranteeing a better fit cannot be done by static guidelines because the higher degree of freedom would make them too complex. Therefore, a new method for generating dynamic guidelines is proposed. The method consists of a model, with which designers can create a simplified assembly sequence of their product idea, and another model, with which process engineers can describe the RMS and the procedures and operations that it can offer. By combining both, a list of possible machine configurations for an RMS can be generated as an automated response for a modeled assembly sequence. With the planning tool for micro-assembly, an implementation of this method as a modern web application is shown, which uses a real existent RMS for micro-assembly.

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This project took place in cooperation with Organska Elektronika d.o.o. and the International Iberian Nanotechnology Laboratory (INL). The company Organska Elektronika d.o.o. is developing a new system for the detection of myco-toxin in food i.e. milk. The main goals of this project were the development of a plastic catridge and the development of a portable incubator. The catridge was designed for its functionality with a simple microfluidic circuit. The middle part of the catridge can be produced by injection molding for high-volume production. Several sealing methods for the fluidic circuit were introduced. In addition a portable incubator was developed for the simultaneous use of four catridges.

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Thermoset materials offer a multitude of advantageous properties in terms of shrinkage and warpage as well as mechanical, thermal and chemical stability compared to thermoplastic materials. Thanks to these properties, thermosets are commonly used to encapsulate electronic components on a 2nd-level packaging prior to assembly by reflow soldering on printed circuits boards or other substrates. Based on the characteristics of thermosets to develop a distinct skin effect due to segregation during the molding process, the surface properties of injection molded thermoset components resemble optical characteristics. Within this study, molding parameters for thermoset components are analyzed in order to optimize the surface quality of injection molded thermoset components. Perspectively, in combination with a reflective coating by e.g., physical vapor deposition, such elements with micro-integrated reflective optical features can be used as optoelectronic components, which can be processed at medium-ranged temperatures up to 230 °C. The obtained results indicate the general feasibility since Ra values of 60 nm and below can be achieved. The main influencing parameters on surface quality were identified as the composition of filler materials and tool temperature.

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