Selecting the correct trace width for the automotive electronics PCB is a complicated task. It is dependent on several factors. Standard trace width is mostly used while designing PCB. But it is modified according to the demand of the appliance for which it is manufactured.
A copper layer is spread over a non-conducting base of the PCB. This layer helps in the conductance of current and signals throughout the circuit. This layer has a specific length and width. The width of the copper trace is known as the trace width.
The trace width helps to ensure the PCB is providing the optimal function. It connects the electrical signal from one point to another.
Standard Trace Width:
The trace width is measured in mils (thousandth on an inch). The standard trace width is 6-12 mils, used for the transmission of ordinary signals. The higher minimum width is cheaper to manufacture as compared to the lower minimum lower width. It is recommended to avoid trace widths less than 6 mils unless it is necessary.
Picking the Right Trace Width:
It is crucial to pick the right trace width while routing the PCB. There are a few critical points to consider while choosing the trace width:
- Current carrying capacity
- Trace spacing
1. Current Carrying Capacity:
There is a maximum amount of current that a trace of PCB can carry. If the current exceeds the maximum capacity, the PCB is destroyed. There is excessive heat dissipation which leads to a change in the temperature of the board. It will eventually burn and break the board.
For high power signals and power traces, it is important to select trace width according to the amount of current that has to pass through it. Negligible current passes through low-power signals. So, the trace width does not depend on the current-carrying capacity for low-power signals.
2. Trace Spacing:
The cost of the PCB is directly proportional to its size. Therefore the HDI PCB manufacturing providers prefer to keep the size of the board small. The small-sized board makes trace routing difficult. Trace width and spacing should go hand in hand. If the spacing is too narrow, there is more chance of shorting. High-speed traces need large spacing to avoid signal transmission issues.
Wider spacing is required in power routing traces so that a higher amount of current can pass through it. Wider traces are easy to fabricate. In addition, the trace width is also dependent on the amount of copper used. More copper is required for higher current. Hence, it will not be possible to have thin trace width.
Specific impedance is required to minimize crosstalk. Along with current carrying capacity, copper also has some impedance. Hence impedance is also an important considering factor while determining the trace width. For lower frequencies, impedance does not have much value. With increasing frequencies, controlled impedance is taken into consideration. The controlled impedance includes trace width while designing PCBs.
Calculating Trace Width:
A trace width calculator is used to calculate the trace width. Certain design specifications are entered in the calculator. These specifications include; copper layer thickness, the trace length, estimated amount of current to be passed, and acceptable temperature changes according to the impedance. Calculated trace width is produced after entering these values.
Picking the right trace width for PCB design depends upon several factors. Temperature change is one crucial factor that is considered while selecting the trace width as it may lead to the destruction of the board with time. Sufficient spacing is also a key factor for power routing. Hence, the trace width should be such that it results in a cost-effective and functional PCB.