ANSI PCB Trace Width Calculator

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PCB Trace Width Calculator & PCB Trace Resistance Calculator per IPC-2152. Calculates the current a conductor needs to raise its temperature over ambient per IPC-2152. Now also calculates DC resistance with temperature compensation. Other conductor properties include: Conductor skin depth Conductor voltage drop Conductor DC resistance. The trace resistance of a microstrip is important in determining how much power it dissipates. By determining its trace resistance, the contribution of a microstrip to the overall circuit resistance can be evaluated. This tool is designed to calculate the resistance of a microstrip trace with a copper conductor.

New features in this version include:

• use of metric or imperial units for all major fields
• the ability to change units for any applicable field on the fly
• minor enhancements to some of the calculations - IPC-2221(A) changes the curve fit
• saving of all parameters in a cookie to keep your preferences between visits

Trace Width Calculator FAQs Q: Is there a limit to the amount of current this tool can calculate a width for? The IPC-2221 data from which these formulas are derived only covers up to 35 Amps, trace width up to 400 mils, allowable temperature rise from 10 to 100 degrees Celsius, and copper of 0.5 to 3 ounces per square foot. A 50 ohm trace (CPW, minimum clearance) is about 1mm wide, on 1.6mm board. Typical impedances are in the 100 ohm range (which, by the way, works very nicely with most CMOS logic; add a 47-100 ohm source termination resistor, and you're mostly good to go).

This page calculates approximations to the ANSI / IPC-2221/IPC-2221A design standards for PCB trace width - this is the replacement for IPC-D-275.

The approximations and rationale are described in Trace Currents and Temperatures Revisited by Douglas Brooks, UltraCAD Design, Inc.

The figures returned by this calculator are to be taken as a guide only. I will not be held responsible for any mishap or loss, either direct or consequential, that may occur as a result of relying on the figures herein.

The trace width formulas are:

50 Ohm Pcb Trace Width

Please note that IPC-2221(A) equations are subtly different from those in IPC-D-275 in that they are typically slightly more conservative and are impicitly derated to compensate for manufacturing effects, i.e. they should be more reliable in practice.

The values calculated here compare very closely with those derived by the UltraCAD PCBTEMP utility, and like the diagrams in the standards documents, are valid up to 35A for external traces and 17.5A for internal, 400mil widths and a maximum temperature rise of 100°C.

I've added a recommended track clearance value based on the UL rule:

The formulae as it stands is simplistic, but is reasonable for V > 50. Note that there are many international standard for this sort of thing, e.g. EN60065:1994, which for European mains of 230V, allows for about 120mil for Class I (protected by earthing) and 240mil for Class II (double isolated). Note that if there is no conformal coating and the environment is dirty/humid/condensing then all bets are off. Please read the standards documents yourself.
Ideally, keep 'hot' and 'cold' areas of your board well apart.

Change a value in an input field, then press TAB to move to the next field. The results tables will be updated automatically.

The old expression is, “give them an inch and they will take a mile.” I may not have completely understood that expression when I was younger, but it sure has come into focus now that my teenagers have started asking me for money. On the bright side, there is a lot more room in my wallet these days for things other than cash.

It is not unusual for people to always want more, especially when laying out a printed circuit board. We want more room for placing components, we want smaller traces to make our routing easier, and we want fewer design restrictions so we can easily hook up the connections. Going down this particular path of least resistance, however, usually results in some big problems with our PCB layout. There are reasons why these restrictions are in place, both from a board performance perspective as well as manufacturing. Let’s take a look at some of the common reasons behind PCB trace width and spacing restrictions, and how by working within these restrictions, you can design a better board.

Congested PCB Layout

Performance Considerations for PCB Trace Width and Spacing Restrictions

When trace routing is used to distribute power and ground throughout the components on your circuit board, the traces must be large enough for the current they are carrying. To do this, the trace can be wider, thicker, or both. Whereas trace width is determined by your CAD tool’s routing rules, the thickness of the trace is determined by the amount of copper weight that is used to build that layer of the circuit board. A half ounce of copper spread evenly over a square foot of circuit board will be 0.7 mils thick, one ounce will be 1.4 mils, and so on. To route the correct width trace for power traces then, you need to calculate the current along with the copper weight of the layer. Which layer of the board you are routing on is also important because external layers have better heat transfer than internal layers as the air dissipates the heat better than the internal dielectric layers.

There are also restrictions on traces used for high speed signals such as controlled impedance lines. Using an impedance calculator, you can enter the board width, type of materials, and layer stackup, in order to determine the trace width needed to hold a specific impedance value, such as a 50 ohm line. High speed design routing will also require certain spacing restrictions as well in order to control noise that could be picked up from adjacent lines that are too close. Serpentine routing patterns for traces that have to be tuned to precise lengths also require specific spacing, which is usually at a ratio of three times the trace width.

Trace Width and Spacing Rules for Manufacturing

So far, we have looked at how trace width and spacing restrictions affect the performance of the board electrically, but there are also manufacturing concerns as well. Traces that are too close to each other or to other metal features of the board could potentially develop shorts during fabrication. Each fabricator will have its own minimum trace width that they will build, but 3 mils is a common minimum spacing value. Copper weight also must be factored in here as well. The higher the weight, the larger the minimum spacing is needed by the fabricator to build the board. Although a higher copper weight is more desirable for routing that carries high levels of current, it can pose a problem for fabricating narrow signal trace widths. Another routing concern is acid traps, which can occur when trace angles are too sharp.

Here are some other manufacturing considerations for trace width and spacing restrictions:

• Traces running between the pads under small surface mount components may have the minimum trace to metal spacing, but can still cause manufacturing problems. The part may not sit squarely resulting in tombstoning, or form a solder bridge with a trace and cause damage if the part is lifted for re-work.
• Metal that is too close to the edge of the board could present depanelization problems. Additionally, exposed copper could come into contact with other conductive elements and cause a short on the board.
• Traces that are too wide on the surface mount pads could form solder bridges with adjacent pads or traces. These could cause excess current or shorts.
• It is also important that drill hole sizes match the traces to which they connect. Although vias run through the board they serve the same function as traces that run along the surface. In many cases, they are extensions of them.

Go to the Experts: Ask Your CM About Trace Width and Spacing Restrictions

Circuit Board Trace Width Calculator

The good news is that you have an excellent resource in your contract manufacturer to help you through these types of trace width and spacing restrictions. Your CM has many years of experience building boards of all kinds of different technologies, and they already have the answers you will need for your specific project. The best thing that you can do is to engage early on in your design with your CM to determine the proper trace widths and spacing that your PCB design will need.

At Tempo Automation, we are ready to work together with you from day 1 of the PCB manufacturing process. We have the experience and the resources that you need to answer your design specific questions in order to make sure that your design is manufactured to the highest levels of quality.

And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.

50 Ohm Pcb Trace Width Calculator Estimate

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on PCB trace width and spacing restrictions, contact us.