When designing a PCB, many engineers tend to pay most of their attention to circuitry a critical part of electronics, the PCB layout, has been neglected. A poor circuit board layout can cause function and reliability issues. This article contains practical PCB layout tips that can help you keep your PCB projects running correctly and reliably, while contributing to efficient production.
At the designing a PCB there's a lot to see! It is possible that the focus is not always sufficiently placed on some aspects of the design. This while, for example, a Problematic PCB design can result in high costs. Avoid these mistakes and get started with the following 4 tips!
1. When designing a PCB, pay attention to the size of traces
Real copper traces have resistance. This means that a trace has a voltage drop, power dissipation and a temperature rise when current flows through it.
PCB designers typically use length, thickness and width to control the resistance of a PCB trace. Resistance is a physical property of the metal used to make the track. PCB designers can't really change the physical properties of copper, so focus on the trace size, which you can control. You measure the thickness of the PCB track in grams of copper. An ounce of copper is the thickness we would measure if we were to distribute 1 oz of copper evenly over an area of 1 square foot. This thickness is 1.4 thousandths of an inch. Many PCB designers use 1 oz or 2 oz copper, but many PCB manufacturers can supply 6 oz thickness. Note that fine features such as pins being close together are difficult to make in thick copper. Consult your PCB manufacturer about their capabilities. Use a PCB trace width calculator to determine how thick and wide your traces should be for your application. Aim for a temperature increase of 5°C. If you have extra space on the board, use larger tracks as they cost nothing.
When creating a multilayer board, remember that traces on external layers have better cooling than traces on internal layers because heat from the inner layers must travel through layers of copper and PCB material before being conducted, radiated, or bonded.
2. When designing a PCB, make loops small
Loops, especially high-frequency loops, are made as small as possible. Small loops have lower inductance and resistance. By placing loops over a ground plane you can further reduce the inductance. Having small loops reduces high frequency voltage spikes.
Small loops also help reduce the amount of signals that are inductively coupled into the node from external sources, or broadcast from the node. This is what you want unless you are designing an antenna. Also keep loops small for op-amp circuits. This prevents noise coupling in the circuit.
3. Note the decoupling capacitor placement
Place decoupling capacitors as close as possible to the power and ground pins of integrated circuits to maximize decoupling efficiency. Placing capacitors further away introduces stray inductance. Multiple vias from the capacitor's pin to a ground plane reduce induction.
4. A point of attention: the Kelvin connections
Kelvin connections are useful for measurements. Kelvin connections are made at the exact points to reduce stray resistance and induction. For example, Kelvin terminals for a current sense resistor are placed right on the resistor pads, not anywhere on the traces. Although on the schematic, placing the terminals on the resistance pads or at any point may look the same, real traces have inductance and resistance that can throw off your measurements if you don't use Kelvin terminals.
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