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12 Useful PCB Design Rules and Tips to Follow - 2020 Newest Guide

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Fri, Sept 11, 2020

For every electronic engineer, learning how to design a PCB layout is a must, yet it may be difficult, especially when the PCB has to be in small size and the component density has to be high. That is why I write this post to help simplify your work.

In this post, you will learn 12 most basic but working PCB design rules and tips to make the PCB layout easier. The basic PCB layout rules will help a beginner avoid potential mistakes. And for an advanced-level engineer, tips in this post will also be beneficial to improve your PCB layout skill.

pcb design

Ready? Get start now!

1. Place the most important parts first

What are the most important parts?

Every part of a circuit board is important.

But those matters to the circuit configuration are the most important, and you can call them “core parts”. They include connectors, switches, power sockets, etc.

In your PCB layout, place these most components first.

2. Make core/large component(s) the center(s) of PCB layout

Core components are the parts that achieve vital functions of the circuit design.

Make it or them the center(s) of your PCB layout.

If a part is large in size, make it a center in the layout as well.

Then place other electrical components surrounding the core/large component(s).

3. Two short and four separate

Your PCB layout should meet the following six requirements as much as possible.

The total wiring should be short. The key signal should be short.

High voltage and high current signals are completely separated from the low voltage and low current signals.

The analog signals and digital signals are separated in the circuit design.

High-frequency signals and low-frequency signals are separated.

High-frequency components should be separated and the distance between them should be as far as possible.

4. Layout standard - uniform, balanced, and aesthetic

A standard circuit board is even, balanced in gravity, and aesthetic.

When you optimize your PCB layout, remember this standard.

Being uniform means the distribution of components and wiring is uniform in the PCB layout.

If the layout is uniform, it should also be balanced in gravity. This is important because a balanced PCB leads to a stable electronic product.

5. Signal protection first, wave filtering next

A PCB transmits various signals, and different parts of it transmit its own signals. So you should protect the signal of each part and prevent signal interference first, and then consider filtering undesired waves for the electronic part.

Always remember this rule.

Then what to do based on this rule?

My suggestion is to place the filtering, protection, and isolation conditions of the interface signal close to the interface connector. Signal protection first, waves filtering next.

6. Decide the size and layer number of the PCB at an early stage

Determine the size of the circuit board and the number of wiring layers at the early stage of the PCB layout.

This is necessary.

Below is the reason.

The layers and stack-up directly affect the wiring and impedance of printed-circuit lines. And if you decide the board size, you determine the stack-up and width of the printed-circuit lines to achieve the expected PCB design effect.

It is best to apply as many as possible circuit layers and make the copper evenly distributed.

7. Determine PCB design rules and constraints

For successful routing, you need to carefully consider design requirements and have the routing tool work under correct rules and constraints, which affect the performance of the routing tool greatly.

So what to do?

Classify all signal lines that have special requirements in the order of priority.

The higher the priority is, set up stricter rules to the signal line.

The rules involve the width of the printed-circuit lines, the maximum number of vias, parallelism, the mutual influence between signal lines, and layer restrictions.

8. Determine DFM rules for the layout of components

DFM is the short form of "design for manufacturability" and “design for manufacturing”. The DFM rules have a huge impact on the component layout, especially the optimization of the automobile assembly process. If the assembly department or PCB assembly company allows moving components, the circuit can be optimized to make automatic routing easier. If you are not sure about the DFM rules, you can get free DFM service from PCBONLINE . The rules include these:

  • In the PCB layout, the power supply decoupling circuit should be placed near relevant circuits rather than in the power supply part. Otherwise, it affects the bypass effect, and leads to the pulsating current flow on the power line and ground line, causing interference.
  • For the power supply direction inside the circuit, the power supply should go from the final to the prior stage, and the power supply filter capacitor should be placed near the final stage;
  • For some main current wiring, if you want to disconnect or measure current during debugging and testing, you should set up current gaps on the printed-circuit lines during PCB layout.
  • In addition, if possible, the stabilized power supply should be placed on a separate printed board. If the power supply and the circuit are on a printed board, you should separate the power supply and circuit components, and avoid using a common ground wire for them.
  • Why?

    Because we don’t want to cause interference. In addition, in this way, the load can be disconnected during maintenance so that we do not have to cut part of the printed-circuit lines and damage the printed circuit board.

    9. At least one via for each surface mount equivalent

    During the fan-out design, there should be at least one via for each surface mount equivalent of the component. In this way, when you want more connections, you can deal with internal connections, on-line testing, and circuit reprocessing on the circuit board.

    10. Manually route before automatic routing

    Manual routing was, is, and always will be a necessary process of printed circuit board design.

    Why?

    Without manual wiring, the automatic wiring tool won’t be able to complete the wiring successfully. Through manual wiring, you create a path that is the basis for automatic wiring.

    Then how to route manually?

    You may need to pick out and fix some important nets in the layout. First, route the key signals manually or with help of the automatic routing tool. Some electrical parameters like distributed inductance need to be set up as small as possible. Next, check your wiring for the key signals, or ask other experienced engineers or PCBONLINE to help check it. Then, if the wiring is okay, fix the wires on the PCB and start the automatic routing of other signals.

    Note
    Due to the impedance of the ground wire, there will be common impedance interference of the circuit.

    11. Set up constraints and rules for automatic routing

    Nowadays the automatic routing tools are very powerful and, if you set up constraints and rules appropriately, they can complete almost 100% of the routing.

    You will have to understand the input parameters of the automatic routing tool and their effects first, definitely.

    To route the signal wires, you should adopt the general rule, namely, deciding the layers and via the number that the signal pass by setting up constraints and not allowed routing areas. Following this rule, the automatic routing tool can work as you wish.

    When you complete part of the PCB design project, fix it on the circuit board in case it is affected by the routing of the next parts. And how many times the routing depends on the complexity of your circuit and its general rules.

    Note:

    If the automatic routing tool doesn’t complete the signal routing, you should continue its work to manually route the rest signals.

    12. Optimize routing

    If the wires for signals with few constraints are very long, find out which are reasonable and which are not, and shorten the wiring as much as possible and reduce the via quantity.

    Looking for a PCB service? Choose PCBONLINE

    If you are daunted by a tough PCB design project and are in want of some reliable PCB layout service, or you want someone to check your design for free, go to PCBONLINE. The reasons why you choose us are as below.

  • We have hundreds of professional engineers with 10+ years of R&D experience. We are experienced in microcontroller development, digital and analog circuit design, electronic product development, human-machine interface, system analysis, and optimization, etc.
  • Besides, we provide free DFM (design for manufacturing), DFT (design for test), and DFX (design for excellence).
  • We will make the PCB design successful at once and deliver the wonderful PCB layout to you in a quick manner.
  • If you have any concerns about PCB layout, or want to learn more PCB design tips, you are welcome to chat online with us or send an email to us at info@pcbonline.com.

    pcb layout

    Conclusion

    As electronic products are getting more and more advanced, electrical and electronic engineers have to master more PCB design skills. Learn the above 12 PCB design rules and tips and follow them as much as possible, and you will find the PCB layout not difficult anymore. If you still have concerns about the PCB design rules and tips or are looking for PCB layout service, get help online easily from PCBONLINE and you can get satisfying results.