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We demonstrate the embedding of heat pipes as a solution for heat management in high density applications where heat spreading and heat guiding can be extremely important. Measurements results describe the advantages of the presented technology in comparison with thick copper inlays in the PCB. Further, this paper will also discuss the transient aspects of the heat transport in PCBs with embedded heat pipes.

Rapidly ongoing miniaturization in combination with increasing electronic functionality — particularly in high end applications — leads to the need of progresses in the PCB cooling technology. Improved thermal performance of PCBs should allow, at lowest possible cost, to remove the power loss from components without exceeding the specified maximum temperature. Heat decentralization, i.e., heat spreading and heat guiding in the PCB is one opportunity to achieve high cooling effectiveness from passive systems. In order to provide an effective heat transport from the heat source into the lateral direction of the PCB, embedded miniaturized heat pipes are a promising solution for the heat spreading problem. Heat pipes have an extremely high effective thermal conductivity compared to solids because they are based on a different heat transfer mechanism. Heat pipes are basically a closed vessel (usually a copper pipe) whereas fluid and gas (often water and air) are trapped inside at low pressures. Inner structures called wick are made in such way to provide means for fluid water flow inside the vessel. When heat is applied on the evaporator section of the heat pipe, the fluid inside is vaporized and flows to the other end of the heat pipe (condenser) due to the difference in pressure. At the condenser section the heat flow is absorbed, so that the vapor condenses into a so called wick structure. Capillary forces acting inside the porous wick structure drives the liquid back to the evaporator. However, since this process is governed by vaporization and condensation of the medium inside the heat pipe along a certain distance, the heat transport capacity is limited related to the geometrical dimensions. Within the scope of this work, the heat transfer performance of miniaturized heat pipes (diameters 1.5 mm and 2.0 mm) is quantified by thermal 3D simulations. The heat spreading capability of miniaturized heat pipes embedded in four different test PCBs are investigated. The effective thermal conductivity and the thermal resistances between the location of the temperature maximum and a defined point of the heat pipe at ambient temperature are determined in dependence on different design parameters, respectively. One important parameter is the thermal interconnection between the copper structure of the PCB and the heat pipe: interconnects by copper filled slots or vias — both standard manufacturing steps in the AT&S embedding process — proved to be superior solutions. The simulation results are compared with experimental ones from a previous study and are in satisfying agreement.

In this study, we demonstrate the embedding of non-classical heat conducting components (heat pipes) as a possible solution for heat management in tightly packed applications whereas heat spreading and heat guiding can be of extreme importance. Measurements results and simulations will describe the advantages of the presented technology. Further, this paper discusses possible bottlenecks and proposes solutions accordingly.

Within the scope of this work, we study the impact of embedded mini heat pipes on the overall thermal performance of PCBs. In a first step, the heat transfer of miniaturized heat pipes is quantified by measurements. The effective thermal conductivity and the maximum admissible heat flow are determined in dependence of the environment temperature and gravitational field orientations. In a second step, the heat spreading properties of miniaturized heat pipes embedded in PCBs are investigated experimentally. Finally, the combination of precise thermal characterization together with reliable FEM simulations establish a basis for the design and the expected performance of solutions for heat spreading based on PCB-Embedded mini heat pipes.

Estimating the junction temperature and its dynamic behavior in dependence of various operating conditions is an important issue, since these properties influence the optical characteristics as well as the aging processes of a light-emitting diode (LED). Particularly for high-power LEDs and pulsed operation, the dynamic behavior and the resulting thermal cycles are of interest. The forward voltage method relies on the existence of a time-independent unique triple of forward-voltage, forward-current, and junction temperature. These three figures should as well uniquely define the optical output power and spectrum, as well as the loss power of the LED, which is responsible for an increase of the junction temperature. From transient FEM-simulations one may expect an increase of the temperature of the active semiconductor layer of some 1/10 K within the first 10 μs. Most of the well-established techniques for junction temperature measurement via forward voltage method evaluate the measurement data several dozens of microseconds after switching on or switching off and estimate the junction temperature by extrapolation towards the time of switching. In contrast, the authors developed a measurement procedure with the focus on the first microseconds after switching. Besides a fast data acquisition system, a precise control of the switching process is required, i.e. a precisely defined current pulse amplitude with fast rise-time and negligible transient by-effects. We start with a short description of the measurement setup and the newly developed control algorithm for the generation of short current pulses. The thermal characterization of the LED chip during the measurement procedures is accomplished by an IR thermography system and transient finite element simulations. The same experimental setup is used to investigate the optical properties of the LED in an Ulbricht-sphere. Our experiments are performed on InGaN LED chips mounted on an Al based insulated metal substrate (IMS), giving a comprehensive picture of the transient behavior of the forward voltage of this type of high power LED.

When specifying change for an existing system, the history and functionality of the system to be replaced has to be considered. This avoids neglecting important system functionality and repeating errors. The properties and the rationale behind the existing system can be elicited by analysing concrete system-usage scenarios [Pohl, K., Weidenhaupt, K., Domges, R., Haumer, P., Jarke, M., Klamma, R., 1999. Process-integrated (modelling) environments (PRIME): foundation and implementation framework. ACM Transactions on Software Engineering and Methodology (TOSEM), vol. 8, no. 4, pp. 343–410]. The results of the analysis of the existing system are then typically represented using conceptual models. To establish conceptual models of high quality reviewing the models is common practice. The problem faced with when reviewing conceptual models, is that the reviewer cannot assess and therefore understand the basis (concrete system usage) on which the conceptual models were built. In this paper, we present an approach to overcome this problem. We establish Extended Traceability, by recording concrete system-usage scenarios using rich media (e.g. video, speech, graphic) and interrelating the recorded observations with the conceptual models. We discuss the main improvements for review processes and illustrate the advantages with excerpts from a case study performed in a mechanical engineering company.

A requirements specification defines the requirements for the future system at a conceptual level (i.e., class or type level). In contrast, a scenario represents a concrete example of current or future system usage. In early RE phases, scenarios are used to support the definition of high level requirements (goals) to be achieved by the new system. In many cases, those goals can to a large degree be elicited by observing, documenting and analyzing scenarios about current system usage. To support the elicitation and validation of the goals achieved by the existing system and to illustrate problems of the old system, we propose to capture current system usage using rich media (e.g., video, speech, pictures, etc.) and to interrelate those observations with the goal definitions. Thus, we aim at making the abstraction process which leads to the definition of the conceptual models more transparent and traceable. We relate the parts of the observations which have caused the definition of a goal or against which a goal was validated with the corresponding goal. These interrelations provide the basis for: 1) explaining and illustrating a goal model to, e.g., untrained stakeholders and/or new team members; 2) detecting, analyzing, and resolving a different interpretation of the observations; 3) comparing different observations using computed goal annotations; and 4) refining or detailing a goal model during later process phases. Using the PRIME implementation framework, we have implemented the PRIME-CREWS environment, which supports the interrelation of conceptual models and captured system usage observations. We report on our experiences with PRIME-CREWS gained in an experimental case study.

When defining a new system, the history and functionality of the system to be replaced should be considered. This avoids repeating errors and neglecting important system functionality. The properties and the rationale behind the existing system are typically elicited by analysing concrete system usage-scenarios. The results of the analysis of the existing system are typically represented using conceptual models. To establish conceptual models of high quality, reviewing the models is common practice. The problem faced with when reviewing conceptual models, is that the reviewer cannot assess and therefore understand the basis (concrete system usage) on which the conceptual models where build. In this paper, we present an approach to overcome this problem. We argue to establish extended traceability, by recording concrete system usage scenarios using rich media (e.g. video, speech, graphic) and interrelating the recorded observations with the conceptual models. We discuss the main improvements for review processes resulting from the extended traceability and illustrate the advantages with excerpts from a case study performed in a mechanical engineering company.

Summary form only given. Scenario-based approaches are attracting more and more interest in requirements engineering research and practice. The research literature offers an increasing number of scenario-related methods, models and notations which highlight the consideration of concrete system descriptions from a usage-oriented perspective, prior to abstract conceptual modelling of function, data and behavior. Scenario use is also becoming a pervasive phenomenon in industrial practice, but comprehensive and expressive studies on the practical relevance of the techniques proposed by research are still rare. The European ESPRIT project CREWS (Cooperative Requirements Engineering With Scenarios) aims at a deeper understanding of the diversity of scenarios, in order to help improve methodological and tool support for scenario-based requirements engineering. The authors consider the two-pronged strategy being followed to gain this understanding.

Scenario based approaches are becoming ubiquitous in systems analysis and design but remain vague in definition and scope. A survey of current practices indicates we must offer better means for structuring, managing, and developing their use in diverse contexts. The European Esprit project Crews (Cooperative Requirements Engineering with Scenarios) are seeking a deeper understanding of scenario diversity, necessary to improve methodological and tool support for scenario based requirements engineering. They follow a two pronged strategy to gain this understanding. First, following the "3 dimensions" requirements engineering framework developed in the precursor Nature project (K. Pohl, 1994), they developed a scenario classification framework based on a comprehensive survey of scenario literature in requirements engineering, human computer interaction, and other fields. They used the framework to classify 11 prominent scenario based approaches. Secondly, to complement this research framework, they investigated scenario applications in industrial projects through site visits with scenario user projects. The article focuses on these site visits. It was found that while many companies express interest in Jacobson's use case approach, actual scenario usage often falls outside what is described in textbooks and standard methodologies. Users therefore face significant scenario management problems not yet addressed adequately in theory or practice, and are demanding solutions to these problems.

The requirements engineering, information systems and software engineering communities recently advocated scenario-based approaches which emphasise the user/system interaction perspective in developing computer systems. Use of examples, scenes, narrative descriptions of contexts, mock-ups and prototypes-all these ideas can be called scenario-based approaches, although exact definitions are not easy beyond stating that these approaches emphasise some description of the real world. Experience seems to tell us that people react to ‘real things’ and that this helps in clarifying requirements. Indeed, the widespread acceptance of prototyping in system development points to the effectiveness of scenario-based approaches. However, we have little understanding about how scenarios should be constructed, little hard evidence about their effectiveness and even less idea about why they work. The paper is an attempt to explore some of the issues underlying scenario-based approaches in requirements engineering and to propose a framework for their classification. The framework is a four-dimensional framework which advocates that a scenario-based approach can be well defined by itsform, content, purpose andlife cycle. Every dimension is itself multifaceted and a metric is associated with each facet. Motivations for developing the framework are threefold: (a) to help in understanding and clarifying existing scenario-based approaches; (b) to situate the industrial practice of scenarios; and (c) to assist researchers develop more innovative scenario-based approaches.