6 Tips to Avoid Common Mistakes in PCB Design
Just like you and me, PCB designers can also make mistakes since they are also humans. Wooden (1999) once said, “If you are not making mistakes then you are not doing anything. I’m positive that a doer makes mistakes”. However, due to their experience in the PCB design field, PCB design engineers can avoid some of the most common mistakes that a newbie or a domestic PCB designer could make. The following 6 tips will help avoid PCB design mistakes
Be sure to include design reviews
The basic PCB design process commences with the discovery that a Printed Circuit Board is needed and proceeds to the final production stage. Despite the pressure that one is under to design a PCB, design review is a crucial element in the PCB design process. This includes taking into consideration factors like the interconnection of circuits, the approximate final dimensions, the functioning of the PCB, and the design features. It is critical to remember that theory is not reality but experienced PCB design engineers have a finely honed sense of where real-life implementation of theory begins to fall apart. The ideal PCB design process is shown in the figure below. This is crucial to help in preventing some of the most common PCB design mistakes.
The ideal PCB design flow begins when designers recognize a need that must be fulfilled, and it doesn’t end until testing verifies that the design can meet those needs (electronicdesign.com).
Excitingly, even after carrying out multiple PCB design reviews, errors will often slip into the designs although some of them can be solved earlier before the production process. However, if you are not much experienced in the PCB design field, there might be some simple errors that you can’t identify in the initial process so it is always good to bring in other sets of eyes!
Failing to back-up your work
During the PCB design process, software and a variety of data are used for perfect results. As an example, the EDA (Electronic Design Automation) software allows designers to create complex designs of their Printed Circuit Board. Due to the speed and high flexibility of PCB design software, the packages or data used can easily get lost even before saving them. It could be really sad to repeat a day’s or 2 of work after data vanishes and one has not saved it. Please ensure you save your packages regularly and create a variety of saving points so that if one storage point is corrupted the others are still okay. Moreover, as designs evolve, some previously saved work can have better versions thus it is better to rely on making many corrections to the existing document than to lose all the data and start working afresh.
Avoid having via-in-pads
A via-in-pad occurs when vias are put in component pads. This problem is very common in the production and prototyping of PCBs and it’s very hard to avoid it. By the same token, some components like QFN ICs and the BGAs require vias to be placed on pads but they should be avoided to the level best. Having vias in pads poses a problem to PCBs since they suck solder separating it from components placed on the other side of the PCB. Consequently, small components and parts that have no solder connection between them to the solder pads are formed. Moreover, poor mechanical connections especially on BGA balls and larger parts that get sucked off by BGA ICs result.
Design engineers always advise that if you must use vias in a pad, then they should be very small and covered with solder-mask if possible. Different from that, if the opposite side of a via is capped with solder masks, air can be trapped in the via it making it outgas during soldering resulting in poorly soldered components.
Many PCB design software have component footprint libraries. This saves one from a hard time creating their package, solder mask, PCB footprint, and silkscreen from scratch libraries which can sometimes have some errors in them. It’s always a good and professional practice to check that all footprints for every component and pinout are correct. This step is very crucial especially if you modify a footprint during defined your This mistake can be easily avoided by taking a few minutes to check whether every footprint is correct and the design is better than it was some hours ago. Hand soldering for tiny surface mount corrections on each board can also be carried out during this phase.
Keeping ICs floating on the solder
A very critical aspect of the footprint of a component is the solder mask. As already mentioned, when vias are used in a pad, a solder mask should be used to cover them to evade any component solderability issues. However, having too much solder on the pad is another solderability issue so the solder should be applied very carefully. When a solder paste or a stencil is used, a solder mask with openings that are large enough can allow excess solder to flow on the board. This is not a big problem for surface mount components although those with a large solder pad underneath which are normally used for heat sinking on higher power integrated circuits and QFN can be pushed up by the excess solder thus leaving the pins unconnected. To prevent this damage, a modified soldermask which has 50% coverage on the high power and QFN areas can be used.
Wrong parts substitution
Parts substitution is a paramount requirement in the design of any PCB or any other electronic component. This is because some parts have a higher tolerance of substations of their support components like inductors and resistors. Such parts are picky and they demand the use of components that match a specific range of values. The selection of components that are outside the acceptable range can cause the oscillation of components resulting in an error. The debugging of these errors can be the worst experience one can ever come across in the PCB design process. Moreover, replacing ICs can be a major problem, especially for drop-ins. replacements and pin for pin ICs. The components datasheet should be updated each time a new equipment is introduced or a replacement.