Guide

Top 10 PCB Board Layout Rules You Need to Know

PCB Layout

Nowadays, PCBs are becoming an essential part of almost every electronic device. For reliable electronic devices, it is important to have a fine PCB layout design. Following certain PCB board layout design rules helps to improve PCB reliability, manufacturability, and durability. An efficient PCB design minimises TAT (Turn Around Time) and lowers project costs in the long run. As this guide progresses, it covers the top 10 PCB board layout rules and recommendations every PCB layout designer must know to become efficient and successful, which allows PCB layout designers to minimise common errors in PCB layout manufacturing.

Top 10 PCB Board Layout Rules Explication

Rule 1: Define Design Rules before PCB Layout

Define Design Rules before the PCB Layout

It is good practice to define important design rules before starting the PCB layout, this allows PCB designers to design a PCB once and for all, in one go, and avoid the hassle of shifting components and re-routing, once the whole PCB layout is finalised. PCB design rules usually depend on two factors, the first one is PCB fabricator capabilities, and the second one is PCB design and application requirements. For example, in RF PCBs there is a possibility of crosstalk between tracks if placed closer than the certain threshold distance, if the designer defines a rule and sets a minimum threshold between track-to-track clearance then this crosstalk will never happen as the DRC check will show error if one or many tracks have lesser clearance. Similarly, rules must be defined for every important constraint before designing a PCB layout.

Rule 2: Optimized Components Placement

Optimised Components Placement

To have a successful PCB layout, efficient component placement in PCB board layout is considered important. The main goal of optimised component placement is to achieve PCB layout with easy routing, efficient utilisation of available space, heat management, and avoidance of crosstalk while keeping the PCB board layout design rules intact. Some points should be considered to have efficient component placement, as below.

  • Some components require specified placement, like connectors to the edge of the PCB, or other must-have components should be placed on priority.
  • Microcontrollers and other high pin-count ICs must be placed in the centre of the PCB layout, as such components are meant to be connected to several other components.
  • Heat-generating components must be placed away from heat-sensitive components, as placing them nearer can cause the malfunctioning of the PCB.
  • To have optimised routing and placement, there is an option for the PCB layout designer to rotate the component, and it’s ok to do so.

Rule 3: Thermal Management

Heat dissipation is important to have a reliable and efficient PCB, especially a PCB with high power rating components. PCB layout designers employed various techniques to cater to heat generation and its proper dissipation like placing heat-generation components at wider distances and on the edge of the PCB for proper airflow, thermal vias, and heat sinks. These thermal management techniques in PCB layout help to maintain optimal operational temperature, which eventually leads to more reliability and also extends the operating lifespan of electronic devices in which such PCBs are integrated.

Rule 4: Routing for Power and Ground Nets

Routing for Power and Ground Nets

After placing components, here comes the routing part. It is good practice to keep ground and power traces wider to ensure the signal that goes through them must have easy passage without any hindrance. Trace width consideration is generally for two-layer PCBs, for multi-layer PCBs full-length ground plane and power plane are used as inner layers. Efficient power distribution is crucial for reliable operational PCB while proper grounding helps to minimise noise and signal distortion and provides a reference voltage level for circuit operations.

Rule 5: Keep Things Separate

“Keep things separate” means analog and digital grounds must kept separate from each other to reduce noise. As these two, analog and digital, signals are of different kinds, combining ground for both can cause noise in many cases. Analog components must be grounded with analog ground trace or plane and the digital ground is used for digital components, this practice helps to reduce interference and avoids the propagation of noise within the PCB.

Rule 6: Good Bending Angle for Routing Traces

Good Bending Angle for Routing Traces

This consideration may not attract PCB layout designers’ attention, but it can lead to serious consequences. Bending the trace to 90 degrees makes the trace narrower which causes an increase in resistance and leads to trapping the heat at the bend, potentially causing severe thermal-related reliability problems. It is good practice to route the traces at a 45-degree or 135-degree angle, which caters to this heat-trapping issue in the trace.

Rule 7: Effective Usage of Silkscreen

PCB layout designers use silkscreen to print useful information on PCB. Useful information includes component designators, component rating, the orientation of components like polar capacitors and diodes, company logos, and informatics. PCB stuffing technicians seek help to place the right component at right in the right orientation without silkscreen PCB stuffing becomes the hardest to impossible task to do.

Rule 8: Placing Test Points

Testing is important for prototype validation and also for testing later on during production. Testing without test points becomes a hectic, lengthy, and risky task for example DMM probe can cause short circuits while testing, on greater pin-count IC. It is important to mark the net for test points on the schematic, place an extra header, make the PCB area intentionally empty for DMM or oscilloscope connection, and for automated testing place bed-of-nails points.

Rule 9: PCB Package Selection

PCB Package Selection

PCB layout designer must consult the datasheet of the electronic component and then according to the dimension given in the datasheet, the PCB layout designer must design the corresponding package for the component, and also it is the responsibility of the PCB layout designer to select that component which is readily available in the market so that after PCB fabrication, procurement will not be difficult otherwise it becomes hectic job to change the component package once the PCB is fabricated, by doing this, money and time both can be saved.

Rule 10: Communicate with PCB Fabricator

It is good practice to get in touch with the fabricator time after time, to know up to what extent chosen fabricators are capable of fabricating the desired PCB for example if the PCB layout designer designs the PCB of more than four layers with hidden vias and the chosen fabricator are not capable of designing more than 4 layer PCB with hidden vias technology then it’ll become difficult to re-route the whole PCB again.

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