Sören Majcherek

Microwave emission from lead zirconate titanate induced by impulsive mechanical load

This paper focuses on microwave emission from Lead zirconate titanate Pb [ZrxTi1−x] O3 (PZT) induced by mechanical stressing. The mechanical stress was initiated by impact of a sharp tungsten indenter on the upper surface of PZT ceramic. The sequences of microwave and current impulses, which flew from indenter to electric ground, were detected simultaneously. The voltage between the upper and lower surface of ceramic was measured to obtain the behavior of mechanical force acting on ceramic during the impact. It was found that the amplitude, form, and frequency of measured microwave impulses were different by compression and restitution phase of impact. Two different mechanisms of electron emission, responsible for microwave impulse generation, were proposed based on the dissimilar impulse behavior. The field emission from tungsten indenter is dominant during compression, whereas ferroemission dominates during restitution phase. Indeed, it was observed that the direction of the current flow, i.e., sign of ...

Development of a mechanical stress-analysing-tool to characterize packaging processes

This paper reports on the development of a measurement system to detect mechanical stress caused by packaging processes. A piezoresistiv silicon test chip is used to convert the inducted mechanical stress into a resistance change, measured by a developed resistance analyser. The sensor interface is capable to measure a high number of resistors with a high measurement rate. Thus, also rapid proceeding packaging processes can be characterized. Furthermore, the developed software calculates the stress distribution along the whole die, which includes a compensation of the systematic errors e.g. the temperature dependence of the piezoresistive coefficients.

Micro- and nanostructure of a titanium surface electric-spark-doped with tantalum and modified by high-frequency currents

We have studied the characteristics of the porous microstructure of tantalum coatings obtained by means of electric spark spraying on the surface of commercial grade titanium. It is established that, at an electric spark current within 0.8–2.2 A, a mechanically strong tantalum coating microstructure is formed with an average protrusion size of 5.1–5.4 µm and pore sizes from 3.5 to 9.2 µm. On the nanoscale, a structurally heterogeneous state of coatings has been achieved by subsequent thermal modification at 800–830°C with the aid of high-frequency currents. A metal oxide nanostructure with grain sizes from 40 to 120 nm is formed by short-time (~30 s) thermal modification. The coating hardness reaches 9.5–10.5 GPa at an elastic modulus of 400–550 GPa.

Structure of metal-oxide Ti-Ta-(Ti,Ta)xOy coatings during spark alloying and induction-thermal oxidation

The study focuses on combined spark alloying of titanium and titanium alloy surface and porous matrix structure oxidation. The metal-oxide coatings morphology is the result of melt drop transfer, heat treatment, and oxidation. The study establishes the influence of technological regimes of alloying and oxidation on morphological heterogeneity of metal- oxide system Ti-Ta-(Ti,Ta)xOy.

A MEMS-based measurement approach for contact normal force measurement in crimp terminals

With the increasing number of plug connections in products, which are proportionally less and less space consuming, the potential for device failure caused by defect connectors increases. Therefore, it will be increasingly important to ensure the proper functioning of the electrical connections. Within the framework of a research transfer project, sensors are being developed to test the contact normal force in sub-millimeter plug connectors. The basis of the sensors is the use of silicon based micro electro mechanical systems (MEMS), which act as mechanical-electrical converters. The presented test method is a further development of a technology published in 2015, with the background of the lifetime increase and an enhanced industrial usability. The number of measurement points was reduced to the resolution of contact point pairs. The measuring range of the contact normal force is 0.5 to 8 N for the realized sensors. An XYZTEC Condor Sigma and an adapted sensor unit have been used to record the mating force and the contact normal force of terminals with a 1.2 × 0.6 mm2 opening dimension.

Characterization of Ultrasonic Wire Bonding for LDS MID Prototyping

Functional prototyping during development of new molded interconnect device (MID) products offers benefits such as evaluation of design specifications, validation of manufacturing technologies, and functional testing of the entire product. Introduction of ProtoPaint laser direct structuring (LDS) by LPKF Laser and Electronics AG has opened new possibilities to develop MID prototypes using LDS of additive manufactured plastic parts. In this experimental work, selective laser sintered (SLS) substrates of three different plastic materials-polyether ether ketone, PA12, and Duraform HST-are used to manufacture MID prototypes. These SLS substrates are functionalized by coating with ProtoPaint LDS lacquer, to produce laser-activable surface, followed by subsequent laser activation and electroless chemical plating processes to metallize conductive patterns. The compatibility of this LDS metallization on the MID prototypes toward aluminum wire bonding as a common contacting technology is evaluated. Pretreatment procedures-namely, ultrasonic cleaning in isopropanol solution, ultrasonic cleaning in ethanol solution, plasma treatment using H2 and N2, and coating with 1k plastic primer, 1k plastic filler, and 2k primer filler-are adopted for the blank SLS plastic substrates to further study and improve the coating of ProtoPaint functional layer, which attributes to better metallization of substrates.

Investigation of adhesion strength of metallization on thermoplastic and ceramic substrates

One essential reliability criteria for Laser Direct Structured Molded Interconnect Devices is the adhesion between substrate and metallization. Low adhesion values are indicative of premature failure of the metallization and are often due to inadequate laser activation of the substrate. A measure of the adhesion is the force at which the metallization fails. Pull-off adhesion testing according to DIN EN ISO 4624 is used to assess the adhesive force between MID-substrate and metal layer. Besides thermoplastic LDS materials (LCP Vectra 840i LDS, TECACOMP® LCP LDS black 4107V, PEEK LDS black 3980, PPA LDS black 4108V), aluminum-nitride ceramic (Alunit®) plates were also laser-activated and metallized according to LPKF-LDS process. Furthermore 3D-printed plastic parts (PA2200 and PEEK), manufactured by Selective Laser Sintering (SLS) have been used. These SLS substrates are functionalized by coating with LPKF ProtoPaint LDS paint, which makes the plastic parts compatible to the LDS process. After IR-laser activation with LPKF MicroLine3D 165i system, the metallization is formed on the activated surface by electroless plating of copper, nickel and immersion gold consecutively. The adhesion strength of metallization was investigated by performing pull-off test of dollies with a shaft diameter of 2 mm. The pull tool for the 4 mm wide dolly head can easily be adapted to different bond testers. The copper dollies are lead-free soldered to the metallization. Due to the lower melting point of PA 2200, adhesive bonding was adopted to bond the dollies to the substrate metallization to reduce the bonding process temperature. This paper will investigate the influence of laser parameters such as laser power and scanning velocity on adhesion between metallization and LDS substrate.

A microfluidic interposer based on three dimensional molded substrate technology

Three dimensional molded interconnect devices (MID) with fluidic features offer new possibilities for the packaging of microfluidic components. This paper reports about an MID based fluidic interposer to bridge the micro-macro gap of fluid delivery in microfluidic systems. The interposer is fabricated by standard MID fabrication technology and includes a metallization for electrical signals and channel structures for fluidic functions. A microfluidic test chip is assembled to the interposer by a flip-chip process. The proposed interposer is suitable for pressure and capillary driven flows. Results from pressurization testing with liquids and gases are given.

Microwave Emission of Carbon Fibres during Electrical Breakdown

A new method of reliability monitoring of electrical devices based on carbon fibres is presented. Due to the thermo-mechanical stress on electronic circuits a loss of fibre network integrity can take place and potential difference may appear between the edges of broken carbon fibres. This potential difference causes an intensive field-emission from surfaces of these broken carbon fibres and an acceleration of emitted electrons. Due to the acceleration of electrons a microwave emission is generated. A CFRP was used to simulate the behaviour of a carbon based electronic device. The sequence of microwave impulses was detected in a frequency bandwidth from 8 to 12 GHz. The rise time of detected microwave impulses is about of few nanoseconds. This time is in agreement with crack formation time in carbon fibre. The correlation between the change of electrical resistance of composites and microwave impulses by fibres fracture is observed. Thus, the breakdown of current that flows through carbon fibres induces detectable microwave emission. That means that defects in electrical circuits can be wireless detected online.

An in situ measurement system for the mechanical impact of the PCB processing chain on stress sensitive devices

In the past, silicon based measurement system were used to characterize packaging induced stresses of electronic devices [1]. In this paper a new approach for qualifying mechanical PCB manufacturing processes is presented. Silicon based package equivalents (S3MD; Stress Sensitive Surface Mounted Devices) are used instead of real devices at locations of expected dangerous mechanical impact. The silicon based package equivalents have strain sensitive structures implemented. These structures are formed by thin film processes and are designed as strain sensitive metal resistors. Therefore, the mechanical impact of the following steps in the PCB process chain can be monitored. The sensor devices are qualified in the AEC Q200 “board flex” test to get the limiting strain values. In the result, we show a new method to get in situ measured data of the mechanical impact of PCB manufacturing processes.