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.
1. Material and Components
You must consider the material and components you plan to use for your printed on the appropriate components, 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 them, 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 way of 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 when placed next to each other, may result in uneven bumps on the circuit board. Some taller components may block shorter components; 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 – parts of similar dimensions can be placed towards one side of the board; this will ensure the soldering wave reaches the smaller components without being blocked.
Allow space for routing. If you place components too close together, you will run out of space when you start routing. Integrated circuits, for example, have lots of pins to be connected around the board. To prevent running out space and having to start over your design layout again, give enough space 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 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. The top layer is the silkscreen that adds the different indicators such as the letters and symbols to the board. 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, other conductive elements, and provide the path for the movement of electrical and thermal energy from one layer to another. Since we drill holes through the board to create the vias, you must consider the placement and the size of each hole concerning the other PCB components. For efficiency in the manufacturing process, it’s good to ensure all the vias in the board are of the same size.
There are three basic types of vias: Through vias, blind vias, and buried vias. A through via connects two visible exterior layers. Blind vias connect a visible exterior layer with an invisible interior layer. Buried vias connect two invisible interior layers. Other types of vias include thermal vias for transferring heat from the top layer to the bottom or internal layers and tented vias that are enclosed with solder mask to prevent leakage of electrical and thermal components. Be sure to discuss with your PCB supplier about the capabilities of the via types you intend to use because different vias have different current carrying capacity.
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 cases of the board twisting or bowing.
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 components 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 reliefs include through-hole vias to slow down the rate of heat sinking through the PCB layers.
You should expect electrical problems such as electromagnetic interference in electronic devices. It affects signal integrity. 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
The board is a primary component of the PCB because it holds all the other parts. First, depending on the purpose of the PCB you are designing, you must consider the size and shape of the board. 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
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 a board. PCB assembly stage. 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 manufacturing of 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.
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.
To connect the various components of the PCB, wne 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.