Any electrical circuit’s brain and heart are represented by the printed circuit board, or PCB. Being in charge of the electrical connections between the parts and the device’s interface with the outside world, it is obvious that even the tiniest design error can result in extra production delays or expenses, or even cause the circuit to malfunction or completely fail. PCB manufacturers can drastically lower production costs when compared to earlier times thanks to the most cutting-edge and creative design tools. However, on occasion, errors committed during the PCB design stage can result in higher production costs. The ten most frequent design faults, which we will now list, are avoidable by adhering to a few straightforward rules, yet even the most experienced PCB designers occasionally make mistakes.
Incorrect trace geometry
PCB traces are in charge of carrying electrical signals between the various circuit components while adhering to exact restrictions on the signal’s frequency, current strength, and speed. The geometry of each trace is crucial in this situation; in particular, the width and thickness of each trace must be sized correctly. When a trace’s current surpasses the indicative value of 0.5 A, it is considered to be a high current line or a power transmission line. The standard width used in low power circuits cannot be utilised in this situation; instead, it must be appropriately sized, maybe utilising calculators based on the IPC-2221 standard or later for internal (stripline) and external (microstrip) traces. It should be noted that the traces located on the PCB’s outer layers have the potential to benefit from greater airflow and heat dissipation, allowing them to carry a higher current at the same thickness. The amount of copper utilised for that layer determines the trace width. Each trace’s thickness must be the proper size in addition to its breadth. Most PCB manufacturers offer a range of copper thickness options, ranging from 0.5 oz/ft2 to 2.5 oz/ft2 and higher. The typical thickness value of one ounce of copper (1 oz, or 35 m), is a popular choice among designers. For high power tracks, where a thickness of 2 or 3 ounces is frequently utilised, this figure might not be adequate. Greater thickness has the benefit of presenting a reduced resistance to current flow, improving thermal dissipation in the process. The drawbacks stem from more weight and the requirement for better trace isolation.
Designers are compelled to use components with smaller footprints and close the spacing between components as the need for ever-smaller printed circuit boards grows. Connection or non-compliance problems could arise if an ineffective layout is chosen. When employing components with a smaller pitch and more pins, this is especially true. Selecting a layout method that is appropriate for the specific circuit is crucial to ensuring the intended functioning. Placing adequate room on the PCB for extra components (or replacements for the current ones) that may be required in the near future is a very helpful workaround. It is always possible to eliminate these extra components before manufacturing if they are not needed.
The decoupling capacitors are in the wrong place
On the PCB power supply lines, decoupling capacitors are necessary to ensure a reliable power supply free from transients or oscillations to all board components. These capacitors must always be located as close as feasible to the pins of the components that need power and connected in parallel with the power source. To reach the decoupling capacitor before reaching the pin that requires a stable voltage, the power line from the power source must be correctly routed on the PCB. Because all voltage regulators require a feedback circuit that can oscillate if improperly stabilised, it should be noted that the decoupling function cannot function effectively in the absence of this circuit.
Incorrect landing patterns
Despite the fact that the terms landing pattern and footprint are sometimes used interchangeably, they have a slight distinction. The landing patterns actually refer to the size of the pads, and each component’s pad area should always be a little bit bigger than its corresponding footprint. When soldering throughout the manufacturing process, even a half-millimeter measurement inaccuracy can be deadly and result in component and PCB misalignments. The most effective PCB CAD tools provide a sizable number of libraries that contain both the schematic symbol and the landing pattern for each component. It is important to manually enter the electrical symbol and the landing pattern for the PCB if a component not found in these libraries is utilised. Making mistakes at this stage is common; for instance, if there is less than one millimetre between two pads, the pins won’t line correctly, making soldering difficult. Directly taken from the datasheet, Figure 1 displays the landing pattern dimensions for a component with a PG-TQFP-64-19 package. The standards outlined in the IPC-7351B standard (“Generic Requirements for Surface Mount Design and Land Pattern Standards”) are typically followed by companies that produce electronic components.
Reliance on automatic routing excessively
Some designers frequently rely on the automatic routing feature now provided by the majority of PCB design tools for PCBs that are not overly complex. However, automatic routing frequently takes up more space on the PCB than is ideal and results in via holes that are larger than those produced by manual routing. It is a proven truth that the number of PCB tracks and through holes has a direct impact on the price of PCB manufacture.
Buried or invisible vias
Via holes are particularly practical since they make it possible to handle a variety of challenging routing issues and enhance PCB heat exchange, but they must be utilised with care and discretion. An exterior layer must be connected to an internal one using blind vias (type “1” in Figure 2), and two internal layers must be connected using buried vias (type “2” in Figure 2). The two external layers of the PCB and, perhaps, one or more internal layers must be connected solely through the through hole vias (type “3” in Figure 2), which are restricted to this usage. The overall size, hole size, tolerances, and other details must be specified in order to build a via hole. They can be defined instantly or constructed using templates. Additionally, it should be remembered that blind and buried vias have higher production costs, thus it is best to plan their use in advance to stay under the PCB budget.
An excessively long trace
High-speed signal traces should be as brief and straight as possible. In the event that the length is surpassed, there is a potential that major issues may arise, including signal reflection (which has an immediate impact on the signal’s integrity), increased sensitivity to electromagnetic interference (EMI), and, obviously, higher expenses. We can refer to a trace as a transmission line if its length is greater than a tenth of the wavelength of the signal it carries. In this situation, it becomes crucial to calculate the impedance in addition to the length (using one of the numerous specialised tools now available online) in order to establish impedance coupling and prevent signal power loss.
Electromagnetic interference (EMI)
A poor PCB design is frequently the cause of electromagnetic interference. It is advised to organise PCB components into functional groups, such as analogue and digital blocks, power sections, low-speed circuits, high-speed circuits, etc., in order to prevent electromagnetic interference (EMI). In order to reduce or even eliminate interference, it is also required to utilise insulated cables, metal containers, and fewer straight angles on the traces.
Inaccurate antenna layout
Designers must take great care to avoid layout errors if the PCB has antennas for wireless communication. The impedance between the transceiver and the antenna must first be adjusted in order to maximise power transfer. The transmission line that links the transceiver and antenna should typically have an impedance of 50. A Pi (LC) tuner filter or any other matching circuit should be installed between the antenna and the transceiver for precise impedance adjustment.
Insufficient project revision
Design review is actually one of the most crucial steps in the construction of a PCB, although being frequently overlooked. The project is periodically reviewed to ensure compliance with the high-level criteria, the PCB’s assigned functions, and the connections between the various circuits. This enables designers to prevent or identify common design faults in advance; peer reviews conducted by other members of the development team frequently enable designers to identify errors they had previously missed.
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Very nice article. PCB design is a tough task and, especially for novices, it’s not uncommon to make some mistake.
A good PCB design is the first step for a successful electronic circuit, so every step shall be performed with the proper knowledge and accuracy.