BGA Breakouts and Routing: Effective Design Methods for Very Large BGAs

Preface – Second Edition ....................................................................... v
Chapter One - Introduction ................................................................... 1
Expedition PCB ............................................................................... 2
Figures ............................................................................................ 2
Definitions ...................................................................................... 2
Via Types ........................................................................................ 6
Stackup Types................................................................................. 6
The Problem ................................................................................. 12
Solutions ....................................................................................... 15
Chapter Two - BGA Packages .............................................................. 17
High Pin Counts ............................................................................ 17
Impact on Routing, Performance and Cost .................................. 20
Off-Matrix Ball Pads ..................................................................... 22
0.8mm Pin-Pitch ........................................................................... 23
The Near Future ........................................................................... 24
Chapter Three - HDI Layer Stackups .................................................... 25
Fabrication Vendors ..................................................................... 25
Dependencies ............................................................................... 26
Overview of Stackup Types .......................................................... 27
HDI Stackup Details ...................................................................... 31
Via Models .................................................................................... 36
Plane Layer Assignments.............................................................. 39
Layer Count .................................................................................. 42
Design Rules ................................................................................. 43
Fanout Patterns ............................................................................ 43
Signal Integrity ............................................................................. 44
Recommended HDI Stackups ....................................................... 44
Secondary HDI Stackups............................................................... 48
Any-Layer-Via Stackups ................................................................ 52
Summary ...................................................................................... 53
Chapter Four - Fanout Patterns ........................................................... 55
Theoretical Breakout Methods .................................................... 56
Signal Integrity Concerns.............................................................. 60
Minimizing the Variables .............................................................. 61
Fanout Pattern Goals and Approach ............................................ 64
Through-Vias ................................................................................ 65
Drilled Blind and Buried-vias ........................................................ 78
HDI Micro-Vias.............................................................................. 89
Summary ...................................................................................... 94
Chapter Five - Layer Biased Breakouts ................................................ 95
Board Description ......................................................................... 95
General Assessment of Original Board......................................... 95
Recommendations and Solutions ................................................ 96
Using Layer Biased Breakouts ...................................................... 97
Fanouts for Micro-Via Layers ..................................................... 101
Route Results.............................................................................. 119
Summary .................................................................................... 120
Chapter Six - 0.8mm Pin-Pitch BGA Tests .......................................... 121
Test Scenario .............................................................................. 121
Test 1: Through-Vias ................................................................... 124
Test 2: Micro-Vias and Through-Vias ......................................... 134
Test 3: Any-Layer-Vias ................................................................ 149
Summary .................................................................................... 163
Chapter Seven - Software for Generating BGA Fanouts ..................... 165
Method ....................................................................................... 166
Regions ....................................................................................... 167
Adding Blind and Through-Vias .................................................. 168
Adding Buried Vias ..................................................................... 170
Additional Example .................................................................... 173
Conclusion ........................................................................................ 175
About the Author .............................................................................. 177