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Design Rules

The Key PCB Design Rules You Have to Know

PCB (Printed Circuit Board) is not just a physical platform for design but also the most flexible part for electronic system design of prototyping. Put another way, even the most ordinary PCB plays a significant role in a project. This article will introduce the key PCB design rules summarized through decades that are widely suitable for all kinds of PCB design projects. These rules are greatly instructive for both novice PCB designers and experienced circuit board manufacturers.

The PCB design rules introduced in this article are the most effective rules engineers should remember and conform to. The rules are not arranged based on the degree of significance of each rule and greater optimizations will take place to PCB design as long as engineers follow the rules as many as possible.

Rule 1: PCB panelization is implemented by replicating the required circuit board on a board with much larger size for lots of times.

Selection of the size compatible with manufacturer's equipment is beneficial to the cost shrinking in terms of prototyping design and manufacturing. First, layout is carried out on the board and the primary specs of each board are acquired by the contact with PCB manufacturers. Then your design specs are modified and repeat your designs within the size of these boards.

Rule 2: Keep trace as short and direct as possible.

This rule sounds quite natural. However, it should be applied in each stage of design, including the circumstance in which PCB layout should be modified in order to optimize the trace length. Furthermore, this rule is especially applicable to analog and high-speed digital circuits whose system performance is always partially limited by impedance and parasitic effect.

Rule 3: Select the correct grid.

Grid spacing is set and always applied to match the most components. In spite of the obvious effect of multi-grid, if engineers are able to think more at the primary period of PCB layout design, they will avoid some problems in the process of spacing settings and apply circuit boards as much as possible. Since many components have packages with different sizes, engineers should make the best of self-designed products. Moreover, polygon is extremely important for copper coating of PCBs. In the process of polygon copper coating on multi-grid circuit boards, polygon filling deviation will be generated. Although it is far from the standard based on single grid, it will increase the life span of required circuit boards.

Rule 4: DRC (Design Rule Checking) should be implemented as much as possible.

Although it takes only a little time to implement the functionality of DRC on PCB software, in the more complicated design environment, as long as DRC circulates through the whole design process, much time will be saved, which is a good habit to maintain. Each routing decision is quite essential and each implementation of DRC will remind you of the most important routing.

Rule 5: Distribution of power lines and ground lines should be governed by power plane as much as possible.

Copper coating on power plane is relatively fast and simple selection for most PCB design software. Through the connection between numerous leads, the current can be ensured with the highest efficiency and the smallest impedance or pressure drop and sufficient ground loop paths can be provided. If possible, multiple power circuits can be set within the same area on the PCB in order to verify whether ground layer covers most of some layer of PCB, which is beneficial to the interaction between operation lines on adjacent layers.

Rule 6: Components are integrated.

As a designer, you could pick up some discrete components with high or low component value and equivalent effect. The integration within a relatively small standard value category is capable of simplifying bill of materials and decreasing the cost. If you have a series of PCB products based on primary component value, it will help you to formulate correct inventory management decisions as well.

Rule 7: Concerning components and required test points should be divided into groups together.

For example, discrete components required by OpAmp amplifier are placed adjacent to components so that bypass capacitor and resistor are allowed to cooperate with components at the same ground. As a result, trace length can be optimized and test and fault detection will become more convenient.

Rule 8: PCB manufacturing parameters are generated and verified before submitting the production.

Although most circuit board manufacturers are willing to directly download and verify your PCB design files, it's a good idea to output your Gerber file first and check it based on what you expected to avoid some misunderstandings. Self-verification will also make you find some careless mistakes so that you can avoid the loss caused by the manufacturing resulting from wrong parameters.

Rule 9: Silkscreen printing is flexibly applied.

Silkscreen printing can be applied to mark all kinds of useful information so that PCB manufacturers, service or test engineers, assemblers or device schedulers will make use of it in the future. Clear functionalities and test marks are not only marked but also the direction of components and connectors are marked even if the comments are marked under the components on the PCB. The application of silkscreen printing technology at the top and bottom surface of PCB is capable of decreasing duplicate work and simplifying production procedure.

Rule 10: Decoupling capacitor must be applied.

Never expect to optimize your design through avoiding decoupling power lines and the limited values in the component data sheet. Capacitors feature advantages including low price, solidity and durability. You can spend more time assembling capacitors and conforming to Rule#6 to maintain the orderliness of inventory within the category of standard values.

The rules introduced above are essentially important to PCB design. With these basic design rules, developers are capable of improving the value of products and obtaining the maximum benefit from the manufactured circuit boards. Even a PCB design novice is able to learn a lot from these rules and gain much confidence.