Apr 8, 2022|General
From the PCB’s debut in the early 1900s to its modern-day development, a circuit board is relevant in virtually every life. From our phones to our tablets, it’s those tiny green boards that allow our electronics to function correctly. With the discipline’s evolution, high-speed PCB design is undoubtedly something someone in the field will encounter. So, it’s essential to understand common issues that occur, like impedance, matching, and spacing.
However, we’re going to talk about the basic PCB steps, so if you want to learn more about the differences, see here.
What is PCB Design?
Table of Contents
- 1 What is PCB Design?
- 2 Overview of PCB Design
- 3 What Are the Basic Steps of PCB Design?
- 3.1 Step 1: PCB Schematic Creation
- 3.2 Step 2: Pre-layout Stage
- 3.3 Step 3: PCB Layout Stage
- 3.4 Step 4: Generate the Production Files
- 3.5 Popular PCB Design Software
A Printed Circuit Board (PCB) design consists of a non-conductive board and wires, usually copper, to create an electronic circuit to perform a task. Usually, a PCB design is a small green board consisting of many components and complex layers inside most electronic devices.
Overview of PCB Design
Designing a PCB is the process of planning, building, and analyzing the performance of a board. The PCB design phase begins with a design specification, a layout of the proposed function of the PCB, and mapping out the circuit design.
Next is the design schematic stage, which consists of a test stimulus to see if a designer needs to modify or change their PCB design and verification that it meets the required specifications.
Once the design is ‘okayed,’ the designer creates the PCB layout that, once completed, requires verification to see if the PCB functions as intended. In this stage, the PCB undergoes restimulation to check for parasitic elements, components that are unwanted for its purpose, and signal integrity tools to confirm functionality.
If a layout fails to pass any analysis tests, the PCB designer must modify the board.
What Are the Basic Steps of PCB Design?
The four stages of how to design PCB are PCB schematics creation, pre-layout, layout, and generating the production files. While we briefly discussed these steps, further discussion is necessary to understand the many facets of designing a successful PCB for manufacturing.
So, what are the steps in PCB designing?
Step 1: PCB Schematic Creation
After conceptualization, the next step is schematic creation using PCB design tools such as computer-aided design (CAD) software.
CAD software is a way to create 3D models of a board to show a designer the components and connections. Designers use their preferred software to make a board outline, add parts, place wires, and route traces.
Schematic Symbol Generation
Schematic symbol generation entails designating a symbol to represent an electrical component in the schematic. These symbols take the form of common shapes like rectangles, triangles, circles, and squares.
Connecting the Symbols
A PCB designer will need to connect their schematic symbols to validate that every component connects. For example, when two wires intersect or join, there should be a dot at the juncture to represent that the two paths use the same electrical current.
If two paths intersect or cross, but aren’t supposed to be connected, then there isn’t a need to place an indicator at the juncture.
PCB designers can manually trace routes to connect the symbols, but most CAD software provides tools to auto-route the board.
Step 2: Pre-layout Stage
The pre-layout stage is the testing stage to verify that the parts of the board are within standard fabrication allowances (SFAs) and ensure the availability of the necessary materials for the PCB.
Bill of Materials (BOM) is a dossier of the components needed to fabricate a PCB. A designer can record and update their BOM in a program like Microsoft Excel. The BOM should contain a comprehensive list of:
- Reference code
- Part code
It’s a good idea to keep the BOM updated to ensure an accurate list and quick verification.
Design the Stack-up with the Help of Contract Manufacturer (CM)
The stack-up of a PCB is the thickness of the board from layering copper and insulation sheets. PCB designers are responsible for designing the stack-up, but it’s helpful to contact the contract manufacturer (CM) for suggestions.
Here is a checklist from the IPC to see if your PCB meets standards.
Step 3: PCB Layout Stage
The third step involves the PCB layout with electronic design automation (EDA) tools.
Setting Up the Stack-up
Designers can use software tools to set up the stack-up by first adding a stack to the default single layer stack-up, labeling it, and adding new properties. Then, add more depending on the intended board layers.
Set the PCB Design Rules
Many PCB design standards apply to nearly every design, while others are situation-specific. Design rules are in place to guide engineers to reduce radiated emissions and interference to and from other electronics.
They also help designers ensure functionality, stability, and intended performance of the PCB creation.
Draw the PCB Outline
The outline is the shape of the PCB.
When outlining, designers should think about what they intend the size and shape of the board to be.
The component placement consists of grouping areas based on functionality, and careful placement is necessary for the PCB to reach optimal electrical performance. Some tips when placing components are:
- Separate analog and digital circuits
- Consider symmetry
- Try to line up components. For example, have corresponding pieces face the same direction.
Route the Board Nets
Routing or “tracking” the board nets means connecting components on the PCB. Most CAD software provides tools to route the board nets easily, but some basic tracking rules are no right-angle tracking and keeping the routes short to avoid resistance and inductance.
Perform a Design Rule Check (DRC)
A design rule check (DRC) is a way for designers to automatically check their PCB design’s circuit connectivity, electrical clearance, and manufacturing ability.
Most perform the test after the build, but some software can perform DRC throughout development.
Complete PCB Fab/Assembly Notes
Fabrication notes are documentation of the PCB, so the supplier has enough information to manufacture the boards to the designer’s desire.
For rigid (IPC-6012D) and flexible (IPC-6013D) printed boards, the IPC outlines what assembly notes should consist of:
- Outline of board
- Visual documents
- Performance classification and PCB type
- Material requirements specified by IPC
- Space performance classification
- PCB type
- Other specifics like solder masks, exposed surface features, trace wire, etc.
Step 4: Generate the Production Files
The last step is to generate the production files.
Generate Gerbers and Other Production Files:
A Gerber file compiles each PCB layer for manufacturers to fabricate the board. One Gerber file is one layer of the board, so, for example, a four-layered board will need four individual files. Some of the necessary information is:
- Profile – the overall space or area of the PCB
- Drill files – inner diameter and drill span
- Backdrilling – modifications needed for design integrity
- Drawings – drill map or assembly drawing
- Digital data – copper, solder mask, legend, etc.
- CAD Netlist – specifies function and layout of the board
Perform a DFM check
Design for Manufacturability (DFM) is a way to check the board design before the manufacturing stage to lessen the chance of expensive production costs. When performing a DFM check, issues to look out for include failed functionality, unintended functions, and unplanned failures.
Popular PCB Design Software
With the numerous stages involved in designing a PCB, it’s worthwhile for designers to research the best software to help them complete some of the tedious steps with ease.
Software with ready-to-use components will reduce time spent generating schematic symbols and footprints for a hobbyist. And, for professionals, advanced software like Cadence or Altium is best, especially for those in the profession.
Learn more here about popular PCB design software to help you choose the best one for you.
After covering the basic steps of PCB design, whether you’re a hobbyist or beginner, you’re hopefully on your way to a better understanding of the discipline with this basic run-down.