The first checklist we like to implement after receiving Gerber files is signal checks. This checklist holds key parameters that include conductor width, spacing requirements, and hole registration. We would like to shed some light on some of these DFM issues that often arise.
1. Conductor Width
Number one on our list of DFM issues is conductor width. Traces on circuit boards connect components to connectors. These traces can be identified as continuous paths of copper that exist on the surface of a PCB. The width of the conductor traces becomes crucial as it directly impacts the functionality of a board. And increasing the signal flow through traces leads to a fair amount of heat. Monitoring trace width also helps to minimize heat build-up that typically occurs on boards. The conductor width also determines the resistance of the traces that directly affect the transmission of a signal.
Many manufacturers opt for their default trace width value available, which may not be suitable for high-frequency applications. Moreover, depending on the application, the trace width is varied, thus affecting the current carrying capacity of the trace. The maximum current carrying capacity for 2 oz copper with temperature rise of 10°C is mentioned in this table.
Maximum Current Capacity (amps)
Trace Width (mil)
2
80
6
150
8
220
10
300
IPC-2221 gives the formula for calculating the trace width for allowable current:
Width[mils] = A[mils^2]/(Thickness[oz]*1.378[mils/oz])
As per IPC-2221, for internal layers k = 0.024 and for external layers, k = 0.048.
The cross-sectional area A is calculated by below formula:
A[mils^2] = (I[Amps]/(k*(ΔT[deg. C])^ 0.44))^(1/0.725)
Where I is the current, k is a constant, ΔT is temperature rise, and A is the cross-sectional area of the trace.
During the design phase, you should consider the trace width as one of the most important parameters. It is essential to decide the adequate trace width to ensure the performance of the circuit board. This also helps to ensure the safe transmission of current without overheating and damaging the board.
An Impedance and Trace Calculator to Avoid DFM Issues
We have developed the online Impedance Calculator tool for calculating the overall value of the minimum trace width. The minimum trace width is determined by the amount of required current and copper weight. We offer thicker conductor traces for higher current requirements. We also offer a thicker copper weight allows for thinner traces.
There are various factors that can affect the selection of the right trace width:
Thickness of the copper layer
Type of bottom or top layer
Length of the track
Dielectric height
Dielectric constant
Inductance and capacitance of the trace
