Ralf Rieske

Novel method for crystal defect analysis of laser drilled TSVs

Beyond doubt through silicon vias (TSVs) will pave the way for 3D interconnects and therefore initiate what is widely considered as the next revolution for electronic packaging and hetero system integration. During the last years the manufacturing of through silicon vias has been intensely studied in Advanced Packaging and starts industrial commercialization at the moment.

Demonstration of board-level optical link with ceramic optoelectronic multi-chip module

This paper demonstrates a complete short-distance parallel optical interconnection on PCB-level basing on ceramic transmitter/receiver modules for high-speed signal conversion, integrated polymeric waveguides and the optical coupling elements. The novel technology for the structuring of PCB-compatible high density parallel optical interconnects will be described in detail. The solution for the optical coupling into the integrated waveguides is based on a micro-optical indirect coupling element with wave guiding structures. The demonstrated optoelectronic modules are 4-channel BGA ceramic multi-chip modules with 4 × 10 Gbps transmission capacity.

Conformal Antennas on Liquid Crystalline Polymer Based Rigid-Flex Substrates Integrated With the Front-End Module

Recent developments in liquid crystalline polymer (LCP)-based processing technology have shown that highly-integrated, fully-packaged radio-frequency (RF) front-end modules with high-performance can be designed by using the system-on-package (SOP) approach. However, the direct integration of a large antenna element to a small module package still remains an issue. This paper presents a novel conformal antenna structure, which results in a compact integration of the antenna and the module package for 5 GHz WLAN/WiMAX applications. The extension of 5 GHz single-band operation to 2.4/5 GHz dual-band operation is also discussed in this paper. The antenna is an inverse L-shaped monopole printed on a 25-mum-thick flexible LCP layer, which protrudes from a rigid multilayer organic substrate. The shielding effects of a grounded metal case, which can house the associated module circuitry, are also considered during the design process. The metal case serves as a vertical ground plane for the antenna in addition to protecting the module circuitry from the near-fields of the antenna. The flexible LCP substrate can be bent and folded over the module case, resulting in a compact design and the tight integration of the antenna with the front-end module. The details of the design and the fabrication of the proposed structure as well as the simulation and the measurement data are presented in this paper.

Application of copper-Carbon Nanotubes composite in packaging interconnects

This paper concentrates on the work done on utilizing Carbon Nanotubes (CNTs) for Electronic Packaging. CNTs have been utilized in various aspects of Electronic Packaging, for instance in solder joints, as filler materials for copper-CNT composites and CNTs themselves to replace copper for future interconnect technology. This paper also discusses the fabrication of copper-CNT composite.

Design and optimization of planar multimode waveguides for high speed board-level optical interconnects

This paper describes the experimental investigation on the influence of geometrical waveguide parameters and material combination (refractive index contrast) onto relevant waveguide characteristics: optical attenuation, mode conversion, assembly tolerances and calculated bandwidth. For achieving waveguide structures with different geometries a test mask with a variation of the line width was developed. The application of a material system with tunable refractive index enables the change of numerical aperture (NA) of the waveguide. The fabricated waveguides will be characterized in their far field in order to define the NA at the waveguides output. The realization of these measurements for different waveguide lengths and core cross sections enables the characterization of the numerical aperture change caused by mode conversion and mode dependent attenuation. These phenomena have influence on intermodal dispersion, which limits the bandwidth capacity of the waveguide. The additional near-field analysis on the end face of the waveguide for the aforementioned design parameters variations will illustrate the mode filling and conversion along the waveguide. Additionally, the paper will analyze the influence of waveguide design parameters on the optical propagation loss by using attenuation measurements. On the other hand, the requirement for a robust optical coupling into the board-level optical interconnects call for relaxed assembly tolerances, which are also dependent on geometrical waveguide parameters. Finally the achieved experimental results will be analyzed in order to derive design rules for low-loss, robust optical link basing on multimode waveguides and ultimately enable multi Gbps m performance.

Assembly tolerance requirements for photonics packaging of multi-cell laser power converters

Power over fiber or photonic power is an attractive alternative for powering remote sensors in electromagnetically sensitive environments. Compared to energy harvesting, it can deliver uninterrupted energy in larger amounts (up to few hundreds of milliwatts) to enable more elaborate sensing, computation or even actuation along with continuous communication requirements. From the photonic packaging perspective, the passive fiber chip coupling becomes a challenge, since non-uniform illumination causes changes in the series resistance of individual cells and varying current-voltage characteristics. The paper at hand characterizes multi-cell laser power converters in depth and describes the integral coupling efficiency from 3D spatial mapping of its maximum power point. Besides the scans for the series connected cells, individual contributions of the segments are studied by single cell characterization to discover intra-individual deviations of cell resistance and conversion efficiency, which might affect the optimal power distribution. Moreover, the spatial responsivity distribution of individual cells, depending on different finger electrode and bus bar configurations. The measurements ultimately yield an assembly tolerance analysis for passive photonic packaging of multi-cell laser power converters. The results are well suited to optimize the packaging process as well as predict the expected device performance.

Laser drilled through silicon vias: Crystal defect analysis by synchrotron x-ray topography

Three dimensional (3D) chip or wafer stacking and through silicon via (TSV) technologies are regarded as key technologies for next generation high-speed memories and microprocessors. In comparison to conventional chip technologies, three dimensional electrical networks allow much shorter wire lengths. This allows higher frequencies, less power consumption and smaller devices. A main technology to realise through silicon vias is laser drilling. Using laser drilling instead of deep reactive ion etching or the Bosch process makes masks unnecessary and thus allows great flexibility and lower costs. Today, vias with diameters of 10-80 mum are possible and can be laser drilled at speeds of about 2000 vias/s. However, laser drilling technology causes damages to the surrounding single-crystalline silicon. The paper surveys existing methods for defect structure analysis and evaluates them concerning their suitability for analysis of silicon TSV wafers. White beam X-ray topography at the synchrotron radiation source ANKA, Research Centre Karlsruhe, was selected as the best non-destructive method. For this paper three different laser types with normal (ns), short (ps) and ultra-short (fs) pulse width with varying parameter sets were used to drill TSVs into silicon wafers. For the first time, large area and section transmission topography were used to measure the strain affected zone around the TSVs. On the basis of these measurements femtosecond lasers were identified as superior to laser with longer pulse widths. The methodology presented in this paper is well suited for continuing studies with UV lasers and miniaturised vias, while at the same time electrical measurements become essential to finally answer how this affects the circuit performance of transistors, capacitors etc. adjacent to the through silicon vias.

Assembly tolerant design of multi-cell laser power converters for wafer-level photonic packaging

Power over fiber is an attractive alternative for powering remote sensors in electromagnetically sensitive environments. Compared to energy harvesting, it can deliver uninterrupted energy to sufficiently supply elaborate sensing, computation or even actuation along with a continuous communication requirement in distributed sensor networks, as for example in structural health monitoring. For the photonic packaging the passive fiber-chip-coupling is one of the biggest challenges. Due to non-uniform illumination of the individual sub-cells and their technological mismatch in electrical characteristics the assembly tolerances are comparatively tight and therefore the manufacturing costs are respectively high. Hence, an assembly tolerant design of the laser-power-conversion (LPC) chip has to be developed to relax the photonic packaging demands. The paper will aggregate comprehensive real characterization results of existing multi-cell laser power converters and real-life fiber light sources into a dedicated design tool. In order to decrease the tolerance requirements and to adjust the LPC to a specific output power at an optimized efficiency, various LPC designs with different cell numbers and arrangements are numerically optimized and reviewed in comparison. The model initially calculates the overlap integral with an ideal uniform illumination. Then, the model can be enhanced by using real power distributions of typically used multimode fibers. The results presented in this paper are well suited to fabricate both efficient LPCs and validate their passive alignment for wafer-level packaging.

Laser Power Converters for optical power supply

Laser Power Converters are dedicated semiconductor devices that convert optical energy into electrical energy. Opposed to solar cells they are optimised for high energy density and conversion efficiency mostly under laser illumination. These cells are applied as power supply in electromagnetically sensitive areas or for galvanic decoupling of transmitter and receiver. Depending on the application in remote sensor or actuator networks, different power needs have to be satisfied. In this paper a couple of single cells were connected in series to increase the voltage, the power and the efficiency. The measurement set-up developed for the characterisation of the cells is presented.

Application of computer tomography in electronic technology

The cone-beam computer tomography (CT) is a new non-destructive testing method, which can be used in electronics industry. In the same manner like in the well-established X-ray microscopy the information of the inside structure of the tested sample results from the attenuation of the X-ray radiation while transition through the object. In contrast to the known principle of fan-shaped CT in medical application, the cone-beam CT uses a volumetric beam to scan the test object and therefore obtains a series of 2D images. The reconstruction of these scans leads to a 3-dimensional model of the tested object. The typical application of this method is the visualization of the inner and outer structures of electronic components, packaging and interconnection technologies, e.g. flip chip (FC) and (micro) ball grid arrays (BGA, /spl mu/BGA). The radiation of an X-ray tube is usually polychromatic, which means that the X-ray photons have different energies. Low energetic radiation is better absorbed in the material than the higher energetic one. For best imaging results the cone-beam CT requires monochromatic radiation and therefore beam-hardening is performed. The resulting hardened radiation is still not be monochromatic and causes artifacts in the imaging of the object, which have to be corrected. The paper describes the basics of computer tomography and beam hardening and furthermore discuss methods to reduce the influence of beam hardening on the imaging quality of the measured objects.