Printed circuit boards consist of a complex network of conductive copper traces that carry electrical signals. The integrity of these traces is crucial for electronic devices to function properly, and failure can occur due to corrosion or external damage.
To maintain the functionality of PCBs, it is important to understand the microcalculations, formulas, and rules that govern their design. After the PCB laminate is coated with copper, the desired traces are protected with tin and the excess copper is removed through a process called etching. This leaves behind a precise network of copper traces that connect the various components.
Although the tracking network is thin, it must be able to withstand heat during the manufacturing process and remain reliable. Holes, pads, and vias are often overlooked but can significantly impact the path length of electrical signals and should be carefully considered in PCB design.
When designing a printed circuit board (PCB), it's important to consider the thickness of the traces. Inconsistent or insufficient trace thickness can result in problems such as power loss, voltage drop, and sparking.
The reason for this is that thin traces can't easily handle the electrical signal that controls the power and may cause slight temperature rises. Additionally, thin traces may not be able to effectively carry electrical signals.
PCB trace thickness is typically measured in terms of the volume of liquid copper applied to the board. The thickness can range from 0.3 mil to 7 mil, with standard values ranging from 0.25 oz to 5 oz.
During the design process, the volume of copper applied is selected based on the size of the board and the maximum current power. By considering trace thickness and other design factors, engineers can ensure that their PCBs perform reliably and efficiently.
PCB trace resistance - what it is and how to use it
Another interesting aspect is trace resistance. This parameter, together with the trace thickness, determines the potential for voltage drop and power loss in the trace.
Calculating PCB trace resistance should be as simple as the application of Ohm's law. Of course, given if the variable is known. Take a closer look at the formula in the image below.
The resistance of the final copper trace must be known to estimate the desired power signal and vice versa. Most likely, you don't have to calculate it yourself. Most programs for developing PCB designs can easily calculate trace resistance.
Let's start by defining the formula variables:
L, W, and T represent the physical area of the board, that is, height, width, and length.
R is the resistance, defined as P x area.
P is the resistivity of a given material (i.e. copper).
For example, given that copper heated to 25°C has a resistivity of 1724 (tables can be found online). This variable is multiplied by the area to get 6-10 ohms per square centimeter.
As mentioned, you don't have to apply the formula yourself. There are some software solutions that can do the job for you. However, there is another interesting thing to add.
There is a direct correlation between trace width and trace resistance. In other words, increasing the area of the copper traces leaves more room for experimenting with ohmic levels. Even without doing the calculations, you probably know that higher trace widths result in higher resistance.
Returning to the power loss experienced by many electrical components, this problem is exactly the case here. Depending on the type of traces used, small signal PCB have less impact on the trace resistance of the PCB. However, high power PCBs are more dependent on small changes in resistance.
This means uncompensated, unbalanced, inconsistent and varying trace widths and thicknesses can easily lead to blown traces in the event of a power surge. It leaves immediate and permanent damage.
A good way to deal with this problem is to adjust the design parameters. Increasing the trace area is the easiest way to increase the resistance of the outer and inner traces. That way, even unexpected power surges won't cause damage.
In addition, sensitive circuits of some electronic components have compensation branches. That's how the trace resistance of the PCB is eliminated. Also, you have good reason to use the trace width calculator.
There are several common issues that can arise when working with PCB traces. Here are some tips for addressing them:
Estimating PCB trace impedance To accurately calculate the trace impedance, you can use a Smith chart, run a computer simulation, or utilize an online calculator. The goal is to determine the reflection coefficient between the source impedance and the load impedance. Software add-ons can help determine controlled impedance or trace parameters if the impedance is already known.
Fixing PCB traces When you know the point of failure, the simplest solution is to reconnect the trace. To do this, scrape off the solder, remove the damaged portion of the trace, apply a drop of liquid copper, smooth it out to connect with the remaining trace, and then add some solder to join the two sections.
Soldering PCB traces If you need to repair a small section of a trace, scrape off a few millimeters, apply a small amount of photosensitive resin, and cure it with ultraviolet light. However, if you need to solder the entire trace network, make sure to prepare the surface and preheat it before applying the solder and curing it.