Know Circuit Board Design Basics & 4 Most Useful Design Practices Quickly

What is CAD?

When it comes to circuit board design, one has to mention CAD program and design, which is the process of drawing, designing, and developing a product or concept using computer software. CAD programs allow us to visualize design concepts and are useful not only for Circuit board design but for many other industries.

PCB Design & CAD

There are many different types of CAD software to choose from, including AD, PADS, etc. Although they do the same thing, each CAD program works slightly differently, so designers will choose the one that suits them best.

Schematic Design

The circuit board design process begins when a technician draws the component positioning and electrical connections on the board, which is a schematic design. Schematic It determines the components in the PCB and how they are connected, and designers can use existing schematic designs or create their own. Designers will run simulations to test the operation of the schematic as an actual circuit. This is also one of the main advantages of CAD design; when starting a Circuit board design by hand, there may be problems that go unnoticed until the circuit is fabricated.

Convert schematic to circuit layout

After the schematic has been tested and approved, the design must be converted into an actual CAD drawing of the board. Reflect the size of the PCB board, the placement of components, and the connection of electrical networks. Typically, there is a "Switch to Layout " (or similar) command on the CAD program, and the designer can then place components and label them with their names and values. Grids are not important when designing schematics, but become critical when editing actual boards. Select the Move tool to move parts (the action names vary in different CAD programs ), rotating them to fit your board. Designers avoid overcrowded component placements or crossed traces, which can short circuits.

Circuit board design becomes more complex when you add multiple board layers. Designers typically route one layer horizontally and the next layer vertically, taking into account the physical characteristics of the components, the taller ones must be placed in certain areas, depending on the end use of the board. Members must have complete information required to become part of the board, this includes drilling information, pad size, etc.

This is the stage where the designer routes the connections between components. The CAD software will route the connections based on the information captured by the schematic. Typically, the CAD software will have a " Route " tool to assist with manual routing. However, some programs have auto-routing capabilities. As mentioned earlier, it is necessary to avoid the intersection of traces when routing. If crossing traces are required, the designer will make them cross on opposite sides of the board. Vias can be used to transfer traces from one side of the board to the other, these are drilled holes where copper is poured over the actual circuit. Once all routing is complete, the CAD program usually provides an option to check for errors in the Circuit board design, and once all errors have been corrected, the circuit board design is complete, and can then generate Gerber file for production.

The 4 circuit board design best practices

#1 Determine your circuit board design rules before designing routing

When starting a new printed circuit board design, it is sometimes easy to forget the important design rules that govern your project. There are some simple clearances that, if identified early in the design, will avoid the need for extensive component shifting and rerouting later on.

To verify your design, you can contact your PCB manufacturer. A good manufacturer will usually post their process capability online, or you can please email them and ask about their process. It's a good idea to confirm this before you start laying out components.

Once the manufacturer's capabilities are determined, you should choose the more conservative design layouts needed to ensure manufacturability and reliability, and you can code these into your board design rules.

During your layout process, effective Circuit board design rules will help you eliminate most design errors that cause manufacturing and assembly problems. Once the design rules are set, you can start laying out components.

component placement stage of the PCB layout design process is both an art and a science. The goal of component placement is to create a board that is easy to route, ideally with as few layer transitions as possible. Additionally, the design must conform to the design rules and meet the requisite component layout. These points can be difficult to balance, but a simple process can help board designers place components that meet these requirements:

1. Place the prerequisites first. Sometimes components must be placed in specific locations due to mechanical enclosure limitations or due to their size. It's best to place these components and lock their positions before doing the rest of the layout.

2. Place large processors and ICs. Components such as high pin count ICs or processors often require connections to multiple components in the design. Centrally locating these components makes routing easier in the PCB layout.

3. Try to avoid crossing. Unrouted nets are usually visible when components are placed in the PCB layout. It is best to minimize the number of crossovers. Each intersection requires layer transitions through vias, and implementing optimal routing for your PCB design will be easier if you can eliminate routing intersections through creative component placement.

4. SMD circuit board design rules. It is recommended that all surface mount device (SMD) components be placed on the same side of the board. The main reason for this is that during assembly, each side of the board needs to self-go through the SMT solder wires, so having all the SMDs on one side will help you avoid some extra assembly costs. 

5. Component orientation settings. Components can be rotated to try to eliminate crossovers and later EMI interference, try to orient the connected pads so they face each other, as this helps simplify routing.

#2 Place Power, Ground, and Signal Wires

After the components are placed, it is time to route the power, ground, and signal traces to ensure that the signals have a clean and trouble-free path. Here are some guidelines to keep in mind at this stage of the layout process:

Placement of power and ground planes

Typically, power and ground are placed on two internal layers. For a double-sided board, this might not be so easy, so you might want to put a large ground plane on one layer, and route the signal and power traces on the other. For 4 -layer boards and higher, you should use a ground plane instead of trying to route ground traces. For components that require a direct power connection, if no power planes are used, it is recommended to use a common rail for each power supply; make sure you have sufficiently wide traces (100 mils for 5 A - 10A) and do not connect the power cord from one part to another.

Some suggestions state that layer placement must be symmetrical, but this is not a strict requirement for manufacturing. In large boards, this may be necessary to reduce the chance of warpage, but in smaller boards, this is not a problem. Focus on power and ground access, and first, make sure all traces have strong return path coupling to the nearest ground plane before worrying about the PCB Symmetry in the stack.

Routing recommendations

Next, connect your signal wires to match the nets in the schematic. Circuit board design layout best practices recommend that you place short, direct traces between components whenever possible, although this may not always be feasible on larger boards. If your component placement forces horizontal trace routing on one side of the board, always route vertically on the other side. This is one of many important double-layer Circuit board design rules.

As the number of stacked layers increases, PCB design rules and layouts become more complex. Your routing strategy will require alternating horizontal and vertical traces in alternating layers unless you separate each signal layer from a reference plane. In very complex boards for professional applications, many of the commonly touted routing recommendations no longer apply, and you need to follow the design guidelines for your application's specific PCB board.

Define the trace width

How wide should the traces on the PCB be? The trace width required for different nets depends on three possible factors:

DFM manufacturability. The traces cannot be too thin or they cannot be manufactured reliably. In most cases, you will use a trace width larger than the manufacturer's process minimum.

Current. The current carried in the trace will determine the minimum width required to prevent the trace from overheating. When the current is higher, the traces need to be wider.

Impedance. High-speed digital or RF signals require specific trace widths to achieve the desired impedance value. This doesn't apply to all signals or nets, so you don't need to enforce impedance control for each net in your board design rules.

For traces that do not require specific impedances or high currents, a 10 mil trace width is suitable for most low-current analog and digital signals. PCB traces carrying more than 0.3 A may need to be wider.

The through-hole component thermal dissipation

The ground plane can act as a large heat sink and then distribute the heat evenly across the board. Therefore, if a particular via is connected to a ground plane, omitting the thermal pad on that via will allow heat to conduct to the ground plane. This is preferable to keeping the heat close to the surface. However, this can be problematic if wave soldering is used to assemble through-hole components on a circuit board because you need to keep the heat close to the surface.

In PCB layout design, designers may need to ensure that the board can be fabricated in a wave soldering process, or other words, with through-hole components that connect directly to the plane. Because maintaining the process temperature can be difficult when the vias are solder joints that connect directly to the plane, it is recommended to use a heat sink to ensure that the solder temperature can be maintained. The idea behind heat dissipation is simple: it slows down the rate at which heat is dissipated to the plane during soldering, which will help prevent cold solder joints.

#3 Component grouping layout

practice how to group and separate components and traces to ensure that you can route easily while preventing electrical interference. These grouping guidelines also help with thermal management, as you may need to separate high-power components.

Combination components

In PCB layout design, some components are best grouped in one area for placement. The reason is that they may be part of a circuit and they may only be connected, so there is no need to place components on different sides or areas of the board.

In many layouts, there are some analog components and some digital components, and you should prevent the digital components from interfering with the analog components. It was practiced decades ago to separate the ground and power planes into distinct areas, but this is not a valid design choice in modern board design. Unfortunately, this still manifests itself in many board layout line choices and causes many to generate EMI problems.

Instead, use a full ground plane beneath the component, and don't physically divide the ground plane into sections. Keep the analog components working at the same frequency as other analog components. Also, place digital components with other digital components. You can think of it as a PCB layout design where each type of component occupies a different area above the ground plane, but the ground plane should be consistent across most board designs.

Separate high-power components

Components that dissipate a lot of heat from the board to different areas are also suitable. The idea behind separating these high-power components is to balance the temperature of the PCB, rather than creating large hot spots in the layout where high-temperature components are grouped. The temperature rise can be calculated based on the estimated heat dissipation by first referring to the thermal rating in your component datasheet. Heat sinks and cooling fans can be added to reduce component temperatures, and when designing a routing strategy, you may have to carefully balance the placement and connection of these components, which can be challenging.

#4 Check circuit board design and layout

It's easy to get overwhelmed at the end of a design project as you scramble to stack the remaining pieces together. It is a safer practice to have multiple inspections of your work at this stage.

It is always recommended that you use the Electrical Rules Check (ERC) and Design Rule Checking (DRC) to verify that you have satisfied all established constraints. Using these two systems, you can easily define gap widths, trace widths, common manufacturing requirements, high-speed electrical requirements, and other physical requirements for specific applications, which automates a PCB layout review to validate your layout.

The above list of suggestions, although not long and relatively basic, will help you design a functional, manufacturable PCB board in no time. If you want to design a more complex instance without spending too much time, you can contact PCBANow to perform an efficient and manufacturable PCB design for you.

Get Circuit Board Design Quote