10 Common PCB Layout Mistakes and How to Avoid Them

Trying to design a Printed Circuit Board (PCB) is a balancing deception. It lies on the border of electrical engineering, mechanical constraints and manufacturing physics. At first sight, it appears to be a game of connecting dots but in the real sense, it is a puzzle that is difficult and requires each millimeter to count. One mistake during the pcb design and layout stage may result in signal integrity problems, a disastrous power event or a board that cannot be made at all.

Even engineers who have worked long enough can find themselves into traps when they have to meet deadlines. Whether prototyping a new IoT device or completing a complicated industrial controller, these traps are very important to avoid a working cost-efficient product. The ten pitfalls when designing PCB layouts and the professional tricks to prevent these pitfalls.

1. Poor Trace Widths of delivering power

The most common mistake is to consider all traces on an equal footing. Whereas sufficient thin traces can be used to transmit signals, the power lines that can conduct meaningful current must have considerable width. When the current carried is too large to fit in the trace, it will cause heating of the trace, which may lead to delamination of the board or the trace becoming a fuse and burning open.

How to prevent it: The width necessary should always be calculated in accordance to the weight it carries and the temperature it can safely raise. Adhere to IPC-2221 standards. In high-current designs, a polygon-poured design as opposed to the usual trace would be considered due to the load and help in heat removal.

2. Misplaced Capacitor of Decoupling

The decoupling capacitors are needed to filter noise and also to supply the ICs with a stable amount of voltage. One of the errors in design and layout of a PCB is to keep these capacitors overly distant to the power pins of the chip. The parasitic inductance of the trace between the capacitor and pin is parasitic and renders the capacitor useless as a noise filter in high frequency.

How to Prevent It: Decoupling capacitors should be as near to the power pin of the IC as they can be. Make sure that the trace is flowing out of the source of power, through the capacitor, and into the IC pin.

3. The construction of “Acid Traps” (Acute Angles)

In the case of traces forming acute angles (less than 90 degrees), they form sharp corner called an acid trap. The waste acid may be deposited in these corners during the PCB fabrication etching process. This trapped acid may over etch the trace with time resulting in open circuits or sporadic connections.

Prevention: 90 degree corners should be avoided; two 45 degree bends should be used to turn the direction. Make sure that the merging of traces should occur at angles more than 90 degrees to enhance easy flow of chemicals during the production process.

4. Overlooking Thermal Reliefs of Ground Plane

A direct connection of a component pin to a large copper plane (such as a ground plane) is excellent conductive to electricity, but horrible when it comes to soldering. The huge copper area is a huge sink of heat, and as such, heat is sucked out of the soldering iron so quickly that the solder does not flow accordingly, resulting in cold solder joints.

Prevention: Thermal relief pads. they are little spokes which join the pad to the plane and keep it electrically connected and limit the heat flow to the surrounding copper to allow easier soldering.

5. Poor Component Placement

Hurrying the component placement process is a cause of problems cascading. Having sensitive analog hardware nearby noisy digital circuits, or connectors on the other side of the board as compared to the drive circuitry it is handling causes excessive trace lengths and signal interference.

Ways to prevent It: Design treatment is 60% of the design. Keep the groupings of the schematic. Make signal paths as short as possible and direct and physically separate analog, digital and power.

6. Split Planes and Electromagnetic Interference (EMI)

High-speed signals have to have a continuous ground return, normally directly beneath the signal trace on the ground plane. One of the biggest errors is to pass a high-speed trace across a ground plane divide or a ground plane void. This compels the returning current to travel further around the split forming an antenna loop which radiates EMI and crosstalk.

How to Prevent it: Trace routing on the reference plane should never cross a gap. In case you need to pass through a split power plane, a stitching capacitor is used to bridge the gap to allow the return current to pass.

7. Blind and Buried Via Overuse

Blind vias (connecting an outer layer to an inner layer) and buried vias (connecting inner layers only) are all excellent when high density is needed, but are much more expensive and complex to manufacture. Inexperienced designers tend to apply them in an unwarranted manner.

How to Prevent It: Use through-hole vias as much as feasible. Blind/buried technology should only be considered when the board density cannot be true without it (e.g. in the HDI design). In case you do not know whether its budget can afford it, call a professional on the same immediately and talk about the cost considerations with a professional pcb design company.

8. Not to consider Tolerances in Manufacturing

It is dangerous to work out to the utmost capacity of your fabricator. Assuming that one manufacturer claims that their minimum trace spacing is 4 mil and you design the entire board with spacing of 4 mil, then any slight variance in the operation will create a fault.

Prevention Method: Design with a Safety Margin. Provided the space is available, set it to slightly larger than the minimums of the manufacturer in order to get higher yield and reliability.

9. Antenna Loops

In layout design, any conduit circuit becomes an antenna. Signal traces and their return paths may form large loops where noise in the environment may be picked up, or broadcast noise to other sections of the circuit.

How to prevent it: a minimum amount of loop areas is to ensure that signal traces and their ground return paths are as near as feasible to each other. This can best be solved by utilizing multilayer boards with special ground planes.

10. Failure to observe the Design Rule Check (DRC)

The Design Rule Check is your safety net in place. DRC errors should not be overlooked or the rules should not be set too loose so as to simply get the board done, and then a disaster is sure to follow. This may cause short circuits, violation of space and too close holes on the drill.

Avoiding It: Before routing, set the DRC options of your CAD software to suit the capabilities of your manufacturer. Test the check regularly during the design process, and not only in the end.

Conclusion

PCB design is a complex science that perceives patience and compliance to standards. Although the current CAD tools are effective, they are not able to substitute the engineering judgment needed to deal with heat, noise, and manufacturing limitation. These ten mistakes can be avoided, which will allow you to considerably decrease the revision of the board and offer a strong final product.

In the case of complicated projects where signal integrity and manufacturability are the major factors, there are at times instances when the best path is to reap the benefits of outside knowledge. Using professional PCB layout services like those of FanyPCB can help turn your design into a performing and production-friendly design even with the initial prototype.