Encyclopedia of Thermal Packaging

The following sections are included:

• Foreword to the Encyclopedia of Thermal Packaging

• Preface

• List of Symbols

• Contents

Thermal and fluid measurements are needed as much today as they ever have been needed in the history of electronic component design. Increasing component powers and shrinking sizes of commercial electronics both require that thermal solutions will have a smaller design margin. A rigorous experimental program is needed to ensure that design assumptions are appropriate for the intended applications. This volume is intended to provide an overview of measurement systems that can be used to establish such an experimental program. This chapter provides a roadmap for the rest of the book.

All measurement systems have common attributes. All require the use of hardware to interact with the physical systems for which property information is needed. Introducing the hardware has no choice but to interfere with the physics of the system being measured, as all measurement sensors are effectively energy conversion devices that shunt energy away from the system being measured. The hardware is also capable of interfering with the measurement process as the materials used for the measurement system have the ability to generate signals that can give the illusion of being valid. This chapter provides a general overview of measurement system components and a theoretical structure that describes the transformation of a measurement signal through a data acquisition system.

The interface between any data collection system and the environment can be classified as a sensor. The sensor specifically is any component that provides a measurable response to a change in the environment. The selection of an appropriate sensor for a given task can be daunting given the vast design options that exist. By establishing a generalized model that can be used to characterize any sensor, the process of sensor selection can be reduced to a methodical practice. The goal of this chapter is to introduce such a sensor model.

Low level electric measurement signals, many times on the order of μV, are carried from sensors to measurement instruments in wires that many times are routed through areas of electric and magnetic fields. The low level signals need to be amplified before they can be measured using conventional meters. Amplifying circuits are an effective tool to accomplish such a task. Unfortunately the signal carrying wires behave like sensors that generate spurious signals that also get amplified. The measurement engineer needs to provide adequate filtering to remove such noise. But potentially more importantly, the wise measurement engineer takes care to minimize the amount of noise that the carrier wires are subjected to through shielding and routing techniques, particularly when routing measurement signals in electronic packages with active components.

Many measurement engineers take the fundamental signal measurement process for granted. But once the mechanics of what happens inside a digital multi-meter are understood, care can be taken during the equipment procurement stages to ensure that the specifications provided by manufacturers are sufficient for the required measurements. This chapter will provide an overview of conventional analog-to-digital signal conversion techniques that are the basis for most commercial equipment.

All experimental measurements are subject to uncertainties. The uncertainties can be categorized as arising from apparently random fluctuations or constant offsets. When reporting experimental results it is important to effectively communicate the amount of uncertainty so the reader can understand the context with which the results can be interpreted. During the experiment planning stages, it is also possible to utilize uncertainty analysis to select measurement equipment and analysis techniques to ensure that the measurements will satisfy any predetermined uncertainty criteria. This chapter will describe methods for estimating uncertainties and propagating those uncertainties when using measurement results to calculate other values.

The uncertainty analysis described in the previous chapter provides the tools to help quantify the level of confidence one has in experimental results. This chapter will focus on how an estimate of measurement uncertainty can help guide the design of experiments intended to answer specific questions about a component design or the selection of components for a system. The approach utilizes statistics to make an assessment of not only the equipment variability, but also variability in operator and environmental influences.

All automated measurements require the use of an integrated system of hardware to connect sensors and the measurement equipment. While the number of offerings available to the experimenter is vast, there are general characteristics that describe the entire system. This chapter provides a brief overview for each component in an automated data collection system, from sensor to controller. The reader should note, however, that new hardware is being developed constantly, and manufacturer literature should be consulted on a regular basis to learn about new product offerings.

Temperature measurement is at the heart of virtually all thermal management analysis activity. This chapter will introduce fundamental definitions of temperature and review common methods of taking practical temperature measurements. Conventional and pioneering techniques are reviewed with respect to their application in evaluating electronic systems and their components. It should be noted, however, that previous chapters in this volume have also introduced temperature measurement techniques in passing.

Pressure is a fundamental thermodynamic property that is used to characterize the physical state of a substance. Spatial pressure differences can be related to the motion of a fluid through momentum conservation equations. Pressure measurements can therefore be used to characterize fluid behavior for electronic cooling system. Various pressure measurement techniques exist that are related to the fundamental definitions of pressure that can be used as calibration standards. Further, there are other sensor designs that can be easily integrated with automated data acquisition systems. This chapter will review those devices and provide a sampling of electronic cooling studies that have utilized pressure measurements as part of their analysis.

Fluid flow measurements are a critical component of any electronic cooling measurement program. The ambient air is typically described as the ultimate heat sink, and is the most commonly used heat transfer fluid for consumer electronics. Higher powered systems are pushing the need for liquid-based cooling systems at the point of the heat generating electric components. Miniaturization of components and the desire to reduce energy consumption are also driving the need to understand fluid flow rates more accurately. This chapter will provide a high level overview of the physical principles that are used in most common flow measurement sensors. A more in-depth description of some popular sensors is then provided. The chapter concludes with an overview of flow measurement examples in electronic system.

Effective communication of experimental data is a critical component of any experimental program. Without effectively communicating the experimental plan or the results, even Nobel Prize quality work will remain unnoticed. The purpose of this chapter is to provide some guidance in preparing written and oral reports. Guidance is also provided in preparing graphics.

The following sections are included:

• Author Index

• Subject Index

• About the Author

• About the Editor-in-Chief