Introduction to PCB Design and EDA Software

Printed Circuit Board (PCB) design is the process of creating the physical layout and circuit connections for electronic devices. Modern PCB design relies heavily on specialized Electronic Design Automation (EDA) software to efficiently create precise board layouts, schematics, and manufacturing files.

Two popular EDA tools for PCB design are Express PCB and Express SCH from Express PCB. These affordable, Windows-based applications provide an integrated environment for schematic capture and PCB layout aimed at students, hobbyists, and professional engineers working on simpler 2-4 layer PCB designs.

In this article, we’ll take an in-depth look at the features and capabilities of Express PCB and Express SCH for the PCB design process. We’ll cover:

• The Express PCB design flow
• Schematic capture with Express SCH
• PCB layout with Express PCB
• Manufacturing outputs
• Pricing and availability
• Frequently asked questions

Whether you’re new to PCB design or an experienced engineer evaluating EDA tools, read on to learn how Express PCB and SCH can streamline your circuit board development.

The Express PCB Design Flow

Overview

Most PCB design projects follow a similar high-level flow:

1. Schematic capture – creating the logical circuit diagram
2. PCB layout – arranging components and routing traces
3. Manufacturing outputs – generating the files needed for PCB fabrication

Express PCB integrates tools for all three of these steps into a cohesive, easy-to-use interface. The two main applications are:

• Express SCH – for schematic capture
• Express PCB – for PCB layout

These tools are designed to work together seamlessly. You capture the circuit in Express SCH, then push a button to transfer the design into Express PCB for layout.

Design Flow Comparison

Here’s how the Express PCB flow compares to other EDA tool flows:

Design Step	Express PCB	KiCad	Eagle
Schematic capture	Express SCH	Eeschema	Eagle Schematic Editor
PCB layout	Express PCB	Pcbnew	Eagle PCB Designer
Manufacturing outputs	Express PCB	Pcbnew	Eagle CAM Processor

As you can see, Express PCB consolidates the flow into just two main applications, while other tools like KiCad and Eagle have separate sub-tools for each function. This integration makes the Express PCB flow very streamlined.

Now let’s look at each step in more detail, starting with schematic capture.

Schematic Capture With Express SCH

Creating a New Schematic

Express SCH makes it easy to start a new schematic:

1. Launch Express SCH
2. Click File > New Schematic
3. Set the sheet size and orientation
4. Click OK to open a blank schematic sheet

The sheet border and title block are automatically created based on the page size settings. You can customize these in the Sheet Properties dialog.

Adding Components

Express SCH includes a large library of built-in schematic symbols. To add a component:

1. Click the Toolbox > Component button
2. Browse or search for the desired component
3. Click to place the component on the sheet
4. Repeat for additional components

You can also create custom components by combining basic shapes and pins. This is useful for components not found in the built-in library.

Wiring and Buses

To make connections between component pins:

1. Click the Toolbox > Wire button
2. Click on the first pin
3. Click on the second pin
4. Repeat to connect additional pins

For connections between multiple components, you can use named nets instead of manually wiring each pin:

1. Click the Toolbox > Net Name button
2. Click near the desired pins
3. Type the net name
4. Click OK

Named nets are automatically connected, even if not visually wired together. This helps keep schematics clean and readable.

Buses can be used to consolidate multiple related nets, like address and data lines:

1. Click the Toolbox > Bus button
2. Draw the main bus line
3. Click the Toolbox > Bus Entry button
4. Draw bus entry lines from component pins to the main bus
5. Label bus entries with the net name, like ADDR0, ADDR1, etc.

Hierarchical Design

For more complex designs, Express SCH supports hierarchical schematics:

1. Create the top-level schematic
2. Create subsheets for functional blocks
3. Add sheet symbols to the top level, corresponding to each subsheet
4. Use net ports to pass signals between levels of hierarchy

Hierarchy helps divide large designs into manageable pieces and facilitates design reuse.

Electrical Rule Checks

Before transitioning to PCB layout, it’s important to validate the schematic:

1. Click Tools > Electrical Rule Check
2. Select the desired checks
3. Click Run Check
4. Fix any errors and rerun checks until the schematic is error-free

Common checks include unconnected pins, missing power pins, and illegal net names.

Transitioning to Layout

Once the schematic is complete, you’re ready to transition to PCB layout in Express PCB:

1. Click File > Save to save the schematic
2. Click Tools > Convert to PCB
3. Select the PCB template to use
4. Click OK to open the design in Express PCB

The component footprints and netlist will be automatically loaded, ready for board layout.

PCB Layout With Express PCB

Setting Up the Board

With the converted schematic open in Express PCB, you’re ready to define the basic board:

1. Click File > Board Properties
2. Set the board size, layer stackup, and design rules
3. Click OK

The blank board workspace is now set up per your specifications. Be sure to choose appropriate design rules for your PCB manufacturer’s capabilities.

Component Placement

Express PCB imports components onto the board based on their locations in the schematic. To place components:

1. Click and drag each component to the desired location
2. Pay attention to placement guidelines:
3. Group related components together
4. Decoupling capacitors close to ICs
5. Connectors near board edges
6. Avoid placement under large components like heatsinks
7. Use the alignment tools to line up components neatly

The Ratsnest view shows airwires between pins to help visualize connectivity. Placing connected components closer together will simplify routing.

Routing Traces

With components placed, you can start routing traces:

1. Click the Toolbox > Trace button
2. Select the desired trace width
3. Click to start the trace on a component pin
4. Click to add vertices and change direction
5. Click on the ending pin or double-click to finish the trace
6. Repeat for all connections

Express PCB supports both manual and autorouting. For autorouting:

1. Click the Autoroute button
2. Set the autorouting parameters
3. Click OK to route the entire board

Autorouting can save time, but often requires manual cleanup for optimal results. Use manual routing for critical nets like high-speed signals and power.

Placing Vias

To route traces on multiple layers, you’ll need to place vias:

1. Click the Toolbox > Via button
2. Select the desired via size
3. Click to place vias and switch layers while routing

Be sure to use an appropriate via size and drill diameter for your manufacturer. Vias can also be placed manually before routing.

Copper Pours and Planes

Copper pours are useful for creating ground and power planes, as well as providing shielding:

1. Click the Toolbox > Copper Pour button
2. Select the desired layer and pour properties
3. Click to define the pour outline
4. Double-click to complete the pour

Express PCB will automatically calculate the copper pour clearances and connections based on the design rules.

Design Rule Checking

Similar to the schematic ERC, Express PCB includes powerful design rule checks for the board layout:

1. Click Tools > Design Rule Check
2. Select the desired checks
3. Click Run Check
4. Fix any errors and rerun checks until the board is error-free

Common PCB DRC checks include clearance, trace width, via size, and unrouted nets. Carefully review the results before manufacturing.

Manufacturing Outputs

After the board is fully laid out and error-free, you’ll need to generate manufacturing files:

1. Click File > Manufacturing Outputs
2. Select the desired output files:
3. Gerber (RS-274X)
4. NC drill
5. Bill of Materials (BOM)
6. Pick and place
7. 3D view
8. Click OK to generate the files

These files are used by the PCB manufacturer to fabricate and assemble your board. Be sure to carefully review the generated files before submitting for production.

Express PCB includes a 3D view to help visualize the final assembled board. Use this to check component clearances and overall fit.

Pricing and Availability

Express PCB Pricing

Express PCB is available in three editions:

Edition	Price	Features
Free	$0	Schematic capture, PCB layout, 2 layer boards, 50 component limit
Standard	$149	4 layers, unlimited components, autorouter, 3D view
Pro	$349	6 layers, advanced rules, simulation, high-speed tools

The free edition is a great way to get started with Express PCB before upgrading for more advanced features.

Express SCH Pricing

Express SCH is included free with all editions of Express PCB. It can also be used standalone for schematic capture only.

Availability

Express PCB products are available directly from the Express PCB website:

• Express PCB Free Edition
• Express PCB Standard Edition
• Express PCB Pro Edition

Free trials of the Standard and Pro editions are also available, allowing you to evaluate the full capabilities before purchasing.

Frequently Asked Questions

What is the maximum board size in Express PCB?

Express PCB supports board sizes up to 32″ x 32″ (812mm x 812mm). This is sufficient for most common PCB designs.

How many layers does Express PCB support?

The free edition of Express PCB supports 2 layer designs (top and bottom). The Standard edition adds support for 4 layers, and the Pro edition supports up to 6 layers.

Can I create custom footprints in Express PCB?

Yes, Express PCB includes a footprint editor for creating custom component footprints. You can define pads, silkscreen, and 3D models for components not found in the built-in libraries.

Does Express PCB support high-speed design?

The Pro edition of Express PCB includes high-speed design features like length matching, differential pairs, and controlled impedance routing. These tools are commonly used for designing high-speed interfaces like DDR and PCIe.

Can I import designs from other EDA tools into Express PCB?

Express PCB can import schematic and PCB files from other tools in various formats:

• Schematics: EDIF, SDT Supermax, Protel ASCII
• PCBs: ODB++, IDF, PADS ASCII, DXF

Use these import options to migrate existing designs or collaborate with teams using other EDA software.

Conclusion

Express PCB and Express SCH offer a powerful yet easy to use solution for PCB design. With schematic capture, board layout, and manufacturing outputs integrated into a streamlined interface, the Express PCB suite is an excellent choice for electronics engineers of all skill levels.

The free edition is perfect for getting started, while the Standard and Pro editions add advanced capabilities for more complex projects. Whether you’re designing simple Arduino shields or high-speed digital boards, Express PCB has the tools you need for success.

To get started with Express PCB, download the free edition from the Express PCB website. You’ll be designing your own custom circuit boards in no time!