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Designing a PCB: Common Mistakes and Prevention Measures

PCBs are typically developed after the whole circuit design has been tested and finalized. When the PCB design is complete, the design file is delivered to the PCB manufacturer for manufacturing. On average, these boards will be made in huge quantities, and if any errors occur during fabrication, it will be a nightmare for the PCB Design engineer, since all fabricated boards must be discarded. This is why a PCB Design Engineer must ensure that his design is error-free before sending it out for manufacturing. Errors can occur at any point in the design process, from selecting the design tool through preparing the final Gerber file for fabrication.
In this post, we will review the most frequent mistakes made during PCB design so that we may be on the lookout for them and avoid making them in our own designs. So, let us get started....

 

Wrong choice of PCB Design Software

 
The choosing of design software is the first step in the design process. There are several PCB design tools available, some of which may be inefficient. Inefficient design tools cause difficulties such as delayed design time and increased production costs.

Before choosing on a certain design tool, you should perform a comprehensive study of the design tools to ensure that you choose the one that best meets the needs of your PCB. Ease of use should also be addressed when selecting a design tool to ensure that time spent learning how to use the tool does not divert from the design process. If you are unsure about which design software to use, you may read our post on how to choose the best PCB design software to help you decide.


Improper placement of Decoupling Capacitors

The use of decoupling capacitors ensures that the product has a steady power supply. These capacitors are connected to the power supply rail. The decoupling capacitors will not work properly if the PCB designer sets them improperly and too far away from the power supply pin.
 


To prevent making this error, make sure they are close to the pin that they are powering so that they work properly. Placing the capacitors correctly and at the appropriate spacing improves transient responsiveness.
 

Footprint / Landing Pattern Errors

 
All PCB design tools include libraries of electric components for the designer to use. The schematic symbol and landing patterns for the components are stored in the libraries. When a designer keeps to the components supported by the libraries, no errors arise.



However, when components change and shrink in size, the libraries of PCB design tools become more restricted. When the existing libraries are insufficient, the designer is forced to build his or her own footprints/landing patterns for the PCB. This design method necessitates great accuracy, which increases the likelihood of mistakes happening. For example, a fraction of a millimeter mistake in pad-to-pad spacing implies that the pins will not line properly, making soldering difficult, if not impossible. These errors are prevented by ensuring that all measurements are correct.
 

Not sticking to the Via rules

 
Vias link the board's several layers. A through through links all of the board's layers (L1, L2, L3, and L4, as indicated in the picture below). A blind through links an external layer to the board's internal layer. A buried passage links two interior layers.



The usage of vias should be monitored to ensure that they do not increase the size of the board by reducing the routing space on the layers. Layers that do not use vias are likewise impacted. Designers frequently make the error of creating buried or blind vias that are extremely difficult to produce or cannot be made at all. Fabricating using buried via or blind vias is a more costly process as compared to a standard through vias, which raises the total cost of the PCB. Additionally, the designer should take into mind the limits on which layers the different types of vias may or cannot be utilized to link.A buried via (3), for example, cannot be utilized to connect layer 1 (L1) to layer 3(L3).

 

Inefficient Wireless Antenna Layout

 
When building a PCB with wireless capabilities, the designer is frequently required to create an antenna on the PCB board. This is a sensitive procedure, and mistakes occur frequently when the impedance between the transceiver and the antenna is not matched. When this occurs, there is no maximum power transmission between the two, and your antenna simply does not operate.



A good microstrip simplifies the creation of a transmission line on the PCB; nevertheless, it must be utilized to match the impedance between the antenna and the transceiver. To create a microstrip transmission line that suits his or her demands, the designer must first thoroughly grasp it. In most situations, a microstrip with an impedance of 50 ohms offers maximum power transmission to the antenna and transceiver. To accomplish this impedance, the designer must determine the width of the microstrip based on the PCB's dielectric requirements. To obtain the right measurements, the designer might utilize online microstrip calculator tools, the majority of which are free.It is also critical to check with the fabricators to confirm that the transceiver and antenna are properly placed.

 

Insufficient width for Power Traces

Some designers, regardless of the amount of current going through a trace, utilize the minimal width allowed for a power trace. With example, for a 500mA current trace, the minimum permitted width would be inadequate.


  
The width of a trace is determined by its location on the external or internal layer, as well as its length. Traces on the external layers can carry more current than traces on the internal layers of the same thickness. This is due to the trace on the exterior layer's ability to readily disperse heat to the air. 

The breadth of the traces is determined by the thickness of the copper utilized in that layer. The copper thickness/weight permitted ranges from 0.5 to 2.5 oz/sq.ft. Designers may utilize online trace width calculators to ensure they select the correct copper thickness.
 
Conclusion
The design process of a PCB is plagued by the potential of errors due to the high accuracy involved with the process. However, these errors are preventable or may be rectified before the actual manufacture of the PCB. Using the proper design tools, adhering to the norms and limits of each component, and taking the proper measurements all aid in avoiding these errors.