OrCAD PCB Editor is a relatively new printed circuit board (PCB) design application that has replaced OrCAD Layout. The purpose of this book is to provide new users of the software with a basic introduction to OrCAD PCB Editor and the design of PCBs.
OrCAD PCB Editor is based on Allegro PCB Editor, so this book will be useful to new Allegro PCB Editor users as well. Allegro PCB Editor is a powerful, fullfeatured design tool. While OrCAD PCB Editor has inherited many of those features, it does not possess all of the tools and features. Consequently most of the basic tools and features are described here, but only a few of the more advanced tools are covered, as outlined later.
Chapter 1 introduces the reader to the basics of PCB design. The chapter begins by introducing the concepts of computer-aided engineering, computer-aided design, and computer-aided manufacturing. The chapter then explains how these tools are used to design and manufacture multilayer PCBs. Many 3-D pictures are used to show the construction of PCBs. Topics such as PCB cores and layer stack-up, apertures, D codes, photolithography, layer registration, plated through holes, and Gerber files are explained.
Chapter 2 leads new users of the software through a very simple design example. The purpose of the example is to paint a “big picture” of the design flow process. The example begins with a blank schematic page and ends with the Gerber files. The circuit is ridiculously simple, so that it is not a distraction to understanding the process itself. Along the way some of PCB Editor’s routing tools are briefly introduced along with some of the other tools, which sets the stage for Chapter 3.
Chapter 3 provides an overview of the OrCAD project files and structure and explains PCB Editor’s tool set in detail. The chapter revisits and explains some of the actions performed and tools used during the example in Chapter 2. Gerber files are also explained in detail.
Chapter 4 introduces some of the industry standards organizations related to the design and fabrication of PCBs (e.g., IPC and JEDEC). PCB performance classes and producibility levels are also described, along with the basic ideas behind standard fabrication allowances. These concepts are described here to help the reader realize some of the fabrication issues up front to help minimize board failures and identify some of the guides and standards resources that are available for PCB design.
Chapter 5 addresses the mechanical aspect of PCB design—design for manufacturability. The chapter explains where parts should be placed on the board, how far apart, and in what orientation from a manufacturing perspective. OrCAD PCB Editor’s design rule checker is then considered relative to the manufacturing concepts and IPC’s courtyard concepts. To aid in understanding the design issues, manufacturing processes such as reflow and wave soldering, pickand-place assembly, and thermal management are discussed. The information is then used as a guide in designing plated through holes, surface-mount lands, and PCB Editor footprints in general. Tables summarize the information and serve as a design guide during footprint design and PCB layout.
Chapter 6 addresses the electrical aspect of PCB design. Several good references are available on signal integrity, electromagnetic interference, and electromagnetic compatibility. Chapter 6 provides an overview of those topics and applies them directly to PCB design. Topics such as loop inductance, ground bounce, ground planes, characteristic impedance, reflections, and ringing are discussed. The idea of “the unseen schematic” (the PCB layout) and its role in circuit operation on the PCB is introduced. Look-up tables and equations are provided to determine required trace widths for current handling and impedance as well as required trace spacing for high-voltage designs and high-frequency designs. Various layer stack-up topographies for analog, digital, and mixed-signal applications are also described. The design examples in chapter 9 demonstrate how to apply the layer stack-ups described in this chapter. A demonstration on how to use PSpice to simulate transmission lines to aid in circuit design and PCB layout is also provided.
Chapter 7 explains how to construct Capture parts using the Capture Library Manager and Part Editor and the PSpice Model Editor. Heterogeneous and homogeneous parts are developed in examples using four methods. Different methods are used depending on whether a part will be used for simple schematic entry, design projects intended for PCB layout, PSpice simulations, or all of these. The chapter also demonstrates how to attach PSpice models to Capture’s schematic parts using PSpice models downloaded from the Internet and basic PSpice models developed from functional Capture projects. The Capture parts can then be used for both PSpice simulations and PCB layout as demonstrated in chapter 9.
Detailed coverage of padstacks and footprints is covered in Chapter 8. The chapter begins with an overview of PCB Editor’s symbols library, describes the various types of symbols, and explains the anatomy of a footprint. Then a detailed description of the padstack (as it relates to PCB manufacturing described in Chapters 1 and 5) is given, as it is the foundation of both footprint design and PCB routing. Design examples are provided to demonstrate how to design discrete through-hole and surface-mount devices and how to use the footprint design wizard. The IPC Land Pattern Viewer is also introduced in this chapter.
Chapter 9 provides four PCB design examples that use the material covered in the previous chapters. The first example is a simple analog design using a single op amp. The design shows how to set up multiple plane layers for positive and negative power supplies and ground. The design also demonstrates several key concepts in Capture, such as how to connect global nets, how to assign footprints, how to perform design rule checks, how to use the Capture part libraries, how to generate a bill of materials (BOM), and how to use the BOM as an aid in the design process in Capture and PCB Editor. The design also shows how to perform important tasks in PCB Editor, such as how to set up a board outline, place parts, and modify padstacks. Intertool communication (such as annotation and back annotation) between Capture and PCB Editor is also demonstrated. The second design is a mixed digital/analog circuit. In addition to the tasks demonstrated in the first example, the design also demonstrates how to set up and use split planes to isolate analog and digital power supplies and grounds. Other tasks include using copper areas on routing layers to make partial ground planes, setting up split power and ground planes, and defining anticopper areas on plane and routing layers. The third example uses the same mixed digital/analog circuit from the second example but demonstrates how to use multiple-page schematics and off-page connectors to add PSpice simulations to a Capture project used for PCB layout, all within a single project design. It also demonstrates how to construct multiple, separated power and ground planes and a shield plane to completely isolate analog from digital circuitry. The use of guard rings and guard traces is also demonstrated. The fourth example is a high-speed digital design, which demonstrates how to design transmission lines, stitch multilayer ground planes, perform pin/gate swapping, place moated ground
areas for clock circuitry, and design a heat spreader.
The last part of Chapter 9 includes a short discussion
about the differences between using negative and
positive planes in PCB design.
Chapter 10 describes taking the PCB design from
the CAD stage through fabrication. A simple design
example shows how to produce the artwork (Gerber)
files for a PCB design. PCB Editor is then used to
review the artwork files before they are sent to
a manufacturer. PCB Editor is also used to generate
a drawing (dfx) file that can be opened and edited
with many drawing applications, so they can be
3-D modeled to review form, fit, and function.
The chapter also describes how to create a custom
report that can be used for pick and place machines
during the assembly process.
