Factors That Influence the Choice of Trace Width in PCB Design
Influence the Choice of Trace Width in PCB Design
When it comes to the metal connections fabricated into a printed circuit board called traces, width plays a key role in their performance. This is especially true for the current carrying capacity of these conductive paths that link components on different layers. Determining the proper trace width can be a tricky task because there are many factors to consider. These include signal integrity, manufacturability, and the current demands of the signals being transmitted.
The first and most obvious reason for using a wider trace is to increase its current carrying capability. The amount of current a conductor can carry is directly proportional to its cross-sectional area and the allowable temperature rise. If a signal is being transmitted at higher voltages, a larger trace is needed to accommodate the increased current and still maintain an acceptable temperature rise.
Another important factor to keep in mind is that every conductive material has resistance and as the distance of the conductor increases, so does its resistance. This can cause power loss which results in Joule heating that reduces the lifespan of a pcb. The lower the temperature rise, the less the energy is lost. Having wide traces can help reduce this type of power loss and extend the life of a circuit board.
Factors That Influence the Choice of Trace Width in PCB Design
A wider trace can also improve signal integrity by reducing the impedance of the path. This can be helpful when transmitting high frequency or fast signals that are prone to reflections and crosstalk. However, a trace that is too wide can suffer from other problems such as signal reflections and amplification which can lead to unwanted oscillations.
The thickness or weight of the copper on a layer is another factor to take into consideration when determining a trace width. Copper layers on a PCB come in a variety of thicknesses measured in ounces per square foot or mils. Thicker copper layers will require a greater trace width as they can accommodate more current than thinner ones.
Trace widths also depend on the layout and design of a circuit board. For example, a narrower trace may be used to route low level TTL (transistor-transistor logic) signals that don’t require any high current capabilities. These traces are typically found on the outer edges of a layer.
A wider trace is usually reserved for power rails and other high current signals that need to be transported throughout the board. Power traces that are buried in the center of the board need to be wider than their counterparts on the surface layer because they don’t have the benefit of being exposed to air for heat dissipation.
In general, the wider a trace is, the easier it will be to manufacture. This is because the fabrication etching process has a greater tolerance for wide traces than it does for narrow ones. However, there are some cases where a narrow trace must be used due to specific design requirements. This is common when working with Field Programmable Gate Array (FPGA) or processor chips that are in BGA or LGA packages and have high current requirements. In these cases, a designer should carefully weigh the design needs against manufacturing constraints and use a tool like a PCB trace width calculator to determine what current capacities can be safely supported.