Designer's Den - Design Process

The PCB Design Process

Introduction and Table of Contents
This document gives some information about designing printed circuit boards. The procedures outlined here are for general use, double sided printed circuit boards that any board shop should be able to make. It is not intended to tell you anything about other kinds of board designs -- there are just too many different technologies out there to cover in one document. It also is not intended to cover "home-brew" manufacturing, since every setup is different and line widths and spacing are very dependent on the manufacturing process.
A PCB Designer is a person that enjoys puzzles, especially graphic puzzles such as mazes. You should work well with stress and time limitations, especially since the time allocated for the physical layout of a PCB is often eaten up by circuit design and parts selection. You have to be a person who can work well with people, since much of the success of a design can hinge on exchange of information between the PCB designer, the circuit designer, manufacturing technologists, and others. You have to be a self-starter, since you will often have to get information for yourself. You should know electronics, although many professional designers started as mechanical drafters. Above all, a PCB designer should be detail oriented, and must be able to think creatively, but in a logical fashion. PCB design is not only a techical skill, it is also an artistic one, where the ability to creatively solve problems is important.
I would strongly suggest purchasing a copy of the Design Standard for Rigid Printed Boards and Rigid Printed Board Assemblies, IPC-D-275, from the IPC if you are considering designing boards commercially. The standard contains much more information about board design than could be covered here. This information is necessary to do a good job with more complex PCB designs. The IPC also has many other standards for design, test, and manufacturing of PCBs and other packaging methods.
This document assumes an Electronic Computer-Aided Design (ECAD) program will be used to design the PCB. Using ECAD takes more time up front for setup and preparation than the old method of using colored tape and die-cut adhesive pads. ECAD offers many benefits to justify this extra time, such as accuracy, easier checking, more compact and error-free storage, and faster modification of existing designs. An ECAD program is  not the same as a general-purpose mechanical design program, although there are extensions to some mechanical CAD packages to allow them to be used for ECAD applications. It is beyond the scope of this document to help in the selection of a specific ECAD program, general procedures are explained that should be adaptable to any of them. The actual selection process is a matter of comparing the features of the programs and making a choice based on the features you find important. There are links to a number of ECAD vendors elsewhere in this site.

DISCLAIMER

I will accept no responsibility for errors or ommissions to this document, or any PCB or assembly created using this document as a guideline. It is impossible to cover every different technology or part or circuit that is placed on a circuit board -- I will not even try. It is up to the PCB designer to do as much as can be done to verify information used in a design, but it is the responsibility of the circuit designer to verify the design will work as intended.
PCB design is not a skill taught by most engineering schools, although some try a little harder than others. Although this document is intended to help you in the learning process, it is no substitute for experience. You learn by making mistakes, but those mistakes are not my fault.
Most of this following information is based on the ECAD package I am most familiar with (Cadence Allegro), you may find some differences in procedures with the ECAD program you are using. As always, you will have to RTFM to find the differences.

Contents

[*]Before the Design
[*]Preparing the Design
[*]Draw the Board
[*]Import the Net
[*]Place the Parts
[*]Route the Traces
[*]The Finishing Touches
[*]Getting it all Together
[*]Return to the Den

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