PCB Layout-6 Important Things to Consider When Designing Your PCB
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Did you know that almost every electronic circuit includes a PCB Layout? Designing a PCB can be intimidating, especially since it involves placing several electronic components and optimal routing within a tightly constrained space. In this era of the Internet of Things, the demand and complexity of PCBs keep growing every day. Knowing your way around a PCB layout is crucial to getting it right the first time.
This article discusses the six essential things to consider when designing your PCB which will include a choice of material and components, component placement, PCB stack-up, PCB via types, power, and thermal issues, and board constraints.
Table of Contents
Did you know that almost every electronic circuit includes a PCB Layout? In this era of the Internet of Things, the demand and complexity of PCBs keep growing every day. Designing a PCB can be intimidating, especially since placing several electronic components and optimal routing within a tightly constrained space. Knowing your way around a PCB layout is crucial to getting it right the first time.
This article discusses the six essential things to consider when designing your PCB, including a choice of material and components, component placement, PCB stack-up, PCB via types, power, thermal issues, and board constraints.
1. Material and Components
You must consider the material and components you plan to use for your print on the pertinent details; you must first define the functions the PCB will have to perform, the approximate size of the final product, the PCB&#;s interconnection with other circuits, and of course, its placement in the product.
Some materials can operate in extreme temperatures; others may fail and result in short-circuiting. For this reason, keep in mind the working temperature of the final product concerning the material and components you choose for your printed circuit board.
Finally, consider the cost and availability of the materials. If you settle for hard-to-find material, they may be expensive and time-consuming to locate, which will eventually delay assembling your PCB. Consider choosing a PCB supplier that can maintain a steady supply of the necessary components for your PCB. Other areas to consider include spare parts, repairs, and replacements.
2. PCB Layout Component Placement
Laying out components on the board requires a lot of problem-solving skills and creativity. Because everyone has a unique design perspective, your component placement will be unique from someone else&#;s idea.
Consider the manufacturing of the PCB because that is the end goal. For instance, like-minded components such as transistors should face the same direction when you place them for easier installation and inspection by the manufacturer.
Keep in mind the size and height of an individual component. Some components will be larger than others and may result in uneven bumps on the circuit board when placed next to each other. Some taller details may block shorter elements, and when the board is passed through the soldering oven to engrave the parts onto the board, it may return with poorly connected solder joints. Always consider the height and width of components on the board &#; details of similar dimensions can be placed towards one side of the board, ensuring the soldering wave reaches the smaller parts without being blocked.
Allow space for routing. If you place components too close together, you will run out of reach when you start routing. Integrated circuits, for example, have lots of pins to be connected around the board. To prevent running out of space and jumping over your design layout again, give enough room for components that require lots of pins to be connected to make the process easy.
3. PCB Layout Stack Up
PCB stack-up forms the foundation of the entire PCB. It involves the placement of insulating layers and copper layers. The stack comprises the various layers within the PCB and allows you to establish the characteristic impedances at each layer. The more layers the PCB has, the costlier it becomes.
Printed Circuit Boards have layers of different materials which are laminated together with an adhesive. The top layer is the silkscreen that adds other indicators such as letters and symbols to the board. The bottom layer is the FR4, and it gives the board its rigidity and thickness. The next one is the copper layer, followed by the solder mask that provides the PCB with its distinctive green color. Optimal multilayer stack up minimizes radiation and external noise. It also allows for enhanced electromagnetic compatibility of your design, keeps the cost within budget, and ensures efficiency in the manufacturing technique.
4. PCB layout Via Types
A PCB Via allows interconnections between different layers of the board. Vias may join traces, pads, and other conductive elements and provide the path for electrical and thermal energy moving from one layer to another. Since we drill holes through the board to create the vias, you must consider each hole&#;s placement and size concerning the other PCB components. For efficiency in the manufacturing process, it&#;s good to ensure all the vias on the board are of the same size.
5. Power And Thermal Issues
While getting component placement is crucial to the design, getting those components to work, you also need to consider power routing. Power and ground planes should be internal within your board and centered and symmetrical to prevent board twisting or bowing cases.
Thermal issues affect larger circuit boards with higher density and excessive processing speeds. To avoid such problems, your PCB must allow heat to dissipate. During the material selection, identify components generating a lot of heat and find ways of diverting heat from them. Surface space around parts that quickly become hot is a crucial layout design consideration because they&#;ll need space to cool off. You may consider including heat sinks, cooling fans, and thermal reliefs. Some places to add thermal reserves include through-hole vias to slow down the rate of heat sinking through the PCB layers.
It affects signal integrity. You should expect electrical problems such as electromagnetic interference in electronic devices. To ensure your PCB doesn&#;t cause such issues, avoid laying tracks parallel to each other. For records that must crossover each other, ensure they are at right angles to minimize capacitance and mutual inductance.
6. Board Constraints
First, depending on the purpose of the PCB you are designing, you must consider the size and shape of the board. The board is a primary component of the PCB because it holds all the other parts. Factors determining the size and shape of the PCB include the functionality and size of the destination product. For example, wearable products such as activity trackers require way smaller PCBs as compared to televisions.
Some products require PCBs with more circuits than the board can hold. In such situations, you may need to use multi-layer high density interconnect PCBs(HDI PCBs) that allow packing more functionality into a smaller area. High density interconnects increased levels of reliability because they have robust interconnection of stacked vias. Another advantage of HDI PCBs is ensuring electrical signals take less time to travel because of the components&#; proximity.
PCB layout Issues
PCB assembly stage. A well-designed board helps avoid running into PCB layout issues such as starved thermals, insufficient annular rings, missing solder masks, acid traps, etc. Starved thermals occur when thermal relief traces and associated copper planes are improperly connected. Missing solder masks are likely to occur in tightly spaced boards during the Bill Of Materials (BOM) of a PCB get fitted onto aboard. Acid traps can cause open circuits on a PCB board because of disconnection traces from their assigned nets. Missed drill hits cause Annular rings. It&#;s crucial to consider the in manufacturing PCBs; there are high chances of layout failures, which can go a long way into negatively affecting the final product&#;s functionality. There are several PCB layout rules to avoid such problems resulting in losses, bad prototypes, and time wastage.
Conclusion
This article discussed the various issues to consider when designing a printed circuit board and some problems a poorly designed PCB may cause. Some topics discussed include component placement, board constraints, PCB stack-up, material and components, power and thermal effects, and PCB via types.
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To connect the various components of the PCB, we print conductive pathways on the board. Since the connections are internal, the complexity of the overall design is reduced tremendously. Elements such as integrated circuits, transistors, and resistors mount into the board through soldering.
PCBs are crucial to the functioning of IoT devices and graphics cards, motherboards, network interface cards, TVs, cellphones, tablets, and more. As technology continues to advance, so does the complexity of a PCB layout. With that said, getting the design right for production will pay off with a high-quality printed circuit board. Your end product should not only reliably work as expected but also stay within the budget. We hope this article guides you in reaching a good PCB layout.
As the applications for electronic circuit boards continue to expand, the demand for greater functionality in smaller products continues to increase. Evolutions in component manufacturing techniques and the range of materials used are the most significant advancements that enable these goals to be largely met. However, using these technological advancements requires improving how boards are designed and built. One of the important of these improvements is the implementation of multilayer PCB design guidelines.
PCBs can be classified in many ways. For example, high-speed and power group boards according to usage or application. The most common categorization is based on the PCB stackup, as listed below.
Types of Circuit Board Stackups
Single-sided PCB
Single-sided PCBs have parts on one side. This surface is the only signal layer in the stackup.
Double-sided PCB
Double-sided PCBs have two signal layers, which contain components: the top and bottom surfaces.
Multilayer PCB
Multilayer PCBs may be single-sided or double-sided. However, these boards typically have internal signal layers as well.
Although the manufacturing process is similar for all board types listed above, there are additional steps for multilayer PCBs. The inclusion of internal layers requires designers to make decisions and specify board parameters, if and where to use via-in-pads, that are otherwise not necessary.
It may not be intuitive; however, using multiple layers in your stackup affects virtually all aspects of the PCB design process. For example, spacing and clearance routing must now consider the angle of signal traces on adjacent (internal) layers. The most important multilayer PCB design guidelines to implement are described below.
Important Multilayer PCB Design Guidelines
PCB Design Guideline
Description
Choose board dimensions based on external and internal routing requirements
Board size must be selected to meet spacing and clearance standard requirements for component placement and trace routing. This includes ensuring adequate spacing for internal signal layer routing and ground planes.
Choose the number of layers based on pin count, density, and board size
Pins include discrete parts and ICs. To estimate pin density, the following equation can be used:
Pin density = Area/(pin number/14)
Do not place high-speed signal layers adjacent to each other
Having signal layers next to each other in the stackup will magnify EMI problems and degrade the quality of signal propagation through your circuit(s).
Route signals on adjacent layers perpendicular to each other
This orthogonality helps with signal integrity by reducing crosstalk between layers.
Utilize multiple ground planes to improve signal integrity
Avoid split ground planes and use vias for connecting between grounds.
Connect traces to a ground plane at a single point
Multiple ground connections can result in variable ground potentials or ground loops.
Ensure the stackup is symmetric
The best PCB stackup design is a symmetric architecture with an even number of signal layers. This helps ensure the board will maintain its structural integrity through the manufacturing process.
Choose vias in coordination with your CM&#;s DFM rules and guidelines
Aspect ratios, drill type, annular ring size, and other DFMA considerations are important manufacturing concerns and should influence whether you choose a micro, blind, buried, or another type of via.
The above list is not exhaustive. For example, it does not include impedance control which is a greater challenge for multilayer boards than for other designs. Yet, it does include important multilayer PCB design guidelines that should be followed to facilitate the optimal development of standard rigid circuit boards. For flex PCBs, there are additional issues to consider.
The increased use of full and rigid-flex circuit boards is one of the major trends in the electronic products industry. This is due to mounting and installation flexibility, ability to withstand vibration, and increased thermal resistance. These are common in harsh environments like space, factories, and automotive systems. To realize these advantages requires consideration of the following:
The multilayer PCB design guidelines above should be incorporated when designing rigid and flex boards. For most EDA programs, it will be necessary to edit or create constraints to ensure your DRC alerts you when there are errors. The best option may be to partner with an industry expert that can provide you with software tools and solutions that integrate with design software to help facilitate the most efficient development of your new product.
EMA Design Automation is a leading provider of the resources that engineers rely on to accelerate innovation. We provide solutions that include PCB design and analysis packages, custom integration software, and engineering expertise, which enable you to create more efficiently. For more information on important multilayer PCB design guidelines and how we can help you or your team innovate faster, contact us.
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