Table Of ContentPHYSICAL DESIGN FOR
MULTICHIP MODULES
THE KLUWER INTERNATIONAL SERIES
IN ENGINEERING AND COMPUTER SCIENCE
PHYSICAL DESIGN FOR
MULTICHIP MODULES
by
M. Sriram
Beckman Institute for Advanced Science & Technology
University of Illinois, Urbana-Champaign
S. M. Kang
Coordinated Science Laboratory
University of Illinois, Urbana-Champaign
SPRINGER SCIENCE+BUSINESS MEDIA, LLC
ISBN 978-1-4613-6153-4 ISBN 978-1-4615-2682-7 (eBook)
DOI 10.1007/978-1-4615-2682-7
Library of Congress Cataloging-in-Publication Data
A C.1. P. Catalogue record for this book is available
from the Library of Congress.
Copyright @ 1994 by Springer Science+Business Media New York
Originally published by Kluwer Academic Publishers in 1994
Softcover reprint of the hardcover 1s t edition 1994
AlI rights reserved. No part of this publication may be reproduced, stored in
a retrieval system or transmitted in any form or by any means, mechanical,
photo-copying, recording, or otherwise, without the prior written permis sion of
the publisher, Springer Science+Business Media, LLC.
Printed an acid-free pap er.
To my parents, Jayaram and Shyamala, and my wife Deepa
- M. Sriram
To my wife Mia and my children, Jennifer and Jeffrey
- S. M. Kang
CONTENTS
PREFACE
IX
1 INTRODUCTION 1
1.1 The Packaging Bottleneck 1
1.2 MCM Technologies 4
1.3 Advantages of Multichip Packaging 11
1.4 Challenges to MCM System Designers 16
1.5 Overview of the Book 22
2 ANALYSIS AND MODELING OF MCM
INTERCONNECTS 25
2.1 Introduction 25
2.2 Asymptotic Waveform Evaluation 26
2.3 Complex Frequency Hopping 31
2.4 Convolution-Based Simulation 34
2.5 Reciprocal Expansion 37
2.6 Extension to Coupled Trees 41
2.7 Direct Modeling of Distributed Elements 45
2.8 Experimental Results 51
2.9 Delay Modeling of MCM Interconnects 60
2.10 Summary 68
3 SYSTEM PARTITIONING AND CHIP
PLACEMENT
69
3.1 Introduction 69
3.2 MCM System Partitioning 71
3.3 Chip Placement 77
PHYSICAL DESIGN FOR MULTICHIP MODULES
Vlll
3.4 Summary 96
4 MULTILAYER MCM ROUTING 99
4.1 The Multilayer Routing Problem in MCMs 99
4.2 Approaches to MCM Routing 101
4.3 The SLICE Router 102
4.4 Four Via Routing 111
4.5 Rubber-Band Routing 117
4.6 Summary 120
5 PERFORMANCE-ORIENTED TREE
CONSTRUCTION 121
5.1 Performance-Driven Tree Generation 122
5.2 Tree construction based on Elmore delay 123
5.3 Global routing using A-trees 125
5.4 Tree Generation Using the RLC Delay Model 128
5.5 Minimum Congestion Routing 136
5.6 Clock Tree Routing 138
5.7 Summary 145
6 LAYER ASSIGNMENT APPROACHES 147
6.1 Introduction 147
6.2 Layer Assignment for Ceramic MCMs 148
6.3 Layer Assignment for High-Density MCMs 165
6.4 Summary 173
7 CONCLUSIONS 175
7.1 Summary 175
7.2 Open Problems for Future Work 177
REFERENCES 181
INDEX 193
PREFACE
The density and performance of VLSI chips have now increased to a point
where further improvements in system speed and size are limited by packaging.
This has become increasingly evident in recent years, and considerable effort is
now being expended to develop new packaging technologies.
Multichip modules (MCMs) have received a lot of attention lately, as a possible
solution to the packaging bottleneck. They have been demonstrated to be able
to meet the requirements of high density, high performance and low cost, while
providing a number of additional benefits as well. Most chip and system man
ufacturers are either actively involved in MCM technology, or are considering
its usage.
While MCMs provide a number of significant advantages over conventional
packaging, they also introduce some difficult design, manufacturing and testing
problems. The development of new materials with superior electrical, mechan
ical and thermal properties is one of the biggest challenges. Effective multichip
system design also requires the consideration of packaging effects, such as heat
dissipation and transmission line effects, during all stages of the system design
process.
Physical design is a very significant part of the system and package design
process. Broadly speaking, physical design is the process of laying out the
components of a system and establishing electrical connections between them,
subject to various physical, electrical and thermal constraints.
VLSI physical design algorithms have been a very important field of research
in the past 20-30 years. These algorithms have contributed significantly to the
rapid improvements in VLSI chips. Unfortunately, the tools and algorithms
that have been developed for VLSI physical design cannot be directly used for
designing MCMs. The physical constraints in MCM substrates differ consid
erably from VLSI, and the electrical and thermal requirements are also more
stringent in MCMs.
x PHYSICAL DESIGN FOR MULTICHIP MODULES
VLSI physical design problems, at least until recently, have been viewed as
combinatorial or geometrical problems, and have been solved using techniques
such as linear programming and graph algorithms, with little or no regard
for the complex electrical behavior of the objects being manipulated. These
approaches make approximations which are reasonable for VLSI design, but
are unacceptable for MCM design. For example, in VLSI design, the delay of
an interconnection net is commonly assumed to be proportional to the total
capacitance (and hence total length) of the net. Based on this assumption, a
number of delay minimization algorithms have been developed. However, none
of these can be directly applied to MCMs, where the resistance, inductance,
capacitance and topology of an interconnection all affect its delay significantly.
System designers are realizing that, in order to maximize the benefit of using
MCMs, they need CAD tools developed specifically for MCMs. A number of
CAD vendors and researchers at universities are now involved in developing
MCM-specific approaches and design tools. This book is intended to provide
these professionals with information on the physical and electrical constraints
unique to MCM design, as well as to provide them with a comprehensive survey
of existing state-of-the-art MCM physical design algorithms.
This book can also be used as a textbook for an advanced graduate level course
in physical design, or as a reference volume for graduate students conducting
research in the areas of MCM physical design and interconnect analysis. A large
amount of useful information on MCM technology and manufacturing processes
has been collected from various sources, and presented with an emphasis on the
impact on physical design. The readers of this book can thus avoid having to
read a number of articles with different emphases in order to gain an insight
into the physical nature of MCMs. A comprehensive bibliography is provided
for those requiring more detailed information on specific topics. The material
is also interspersed with a number of open problems and suggestions for future
research, which will be helpful to researchers and graduate students looking for
timely and interesting research topics.
Overview
The first chapter of this book is intended as an introduction to multichip mod
ules. It describes the MCM technology alternatives available today, and dis
cusses the relative merits of each approach. The advantages of MCMs and
Preface xi
their impacts on system performance are described, and the challenges faced
by MCM system designers are discussed.
The electrical performance of an MCM is defined by the behavior of its in
terconnects. Due to the particular dimensions and operating frequencies of
MCMs, the interconnects need to be treated as lossy coupled transmission
lines. Chapter 2 surveys a number of approaches developed recently for rapid
approximation of the time domain response of such interconnects. These ap
proaches yield good approximations of interconnect response with orders of
magnitude speedup over conventional simulation programs, and are thus very
useful during physical design.
Delay models for MCM interconnects are also presented in Chapter 2. RC delay
models suitable for lower-speed applications, as well as a new second-order RLC
delay model for high-speed interconnects, are presented.
Chapter 3 discusses the system partitioning and chip placement problems.
Performance-driven partitioning algorithms are described. The differences be
tween VLSI and MCM placement are clearly outlined, and new algorithms for
placement are presented, which take into account the effect of interconnect re
sistance on delay. Recent work on layout problems for opto-electronic MCMs
is also described.
Chapter 4 deals with the multilayer routing problem in MCM substrates. There
are many possible approaches to this problem, and these are discussed in de
tail. Some of the popular recent algorithms for MCM multilayer routing are
described.
Chapter 5 discusses a different approach to the multilayer routing problem, in
which the three-dimensional routing problem is decomposed into two stages:
two-dimensional tree construction and layer assignment. Recent work on per
formance-driven tree construction algorithms is surveyed, and algorithms for
minimizing transmission-line effects and second-order delays are described. Spe
cialized routing algorithms for clock trees are also discussed. The layer assign
ment problem in different MCM environments is investigated in Chapter 6, and
different formulations and algorithms for the problem are described in detail.
The last chapter summarizes the material in the book, and collects together the
various open problems and suggestions for future work found in the previous
chapters.
