Monitoring Standard PCB Trace Thickness and Width in OrCAD X

Key Takeaways

• Copper thickness in PCBs is commonly measured in oz/ft², where 1 oz/ft² equals 35 µm or 1.38 mils, establishing a uniform thickness across boards.

•  The default trace thickness for most PCB designs is 1 oz/ft², but higher voltage or special requirements might necessitate thicker layers, with options ranging from 0.5 oz/ft² to 6 oz/ft².

• Designers can use standards like IPC-2221 and various software tools or online calculators to determine the optimal trace dimensions based on current capacity, signal integrity, and thermal management needs.

OrCAD X makes routing with specified trace thicknesses simple

In the PCB industry, copper thickness is typically measured in ounces. This might seem odd since ounces are a unit of weight, not thickness. However, when 1 ounce (28.35 grams) of copper is spread evenly over one square foot of surface area, it forms a layer 1.37 mils (0.0348 mm) thick. This standard measurement helps maintain consistency across different PCBs.

Most commonly, PCBs are produced with a copper thickness of 1 oz (or 1 oz/ft2). In other words, without specific instructions in the design files, manufacturers usually assume a standard PCB trace thickness of 1 ounce for all layers. A thicker copper layer may be required for designs that need to withstand higher voltages or have specific resistance or impedance requirements. Various online calculators are available to assist in determining the necessary thickness, width, or length of traces to meet design specifications.

Default PCB Trace Thickness of Common PCB Manufacturers

PCB trace width, thickness, and length illustrated.

Alt-text: PCB trace width, thickness, and length illustrated.

PCB Trace Width vs. Thickness

When referring to a copper PCB trace, there are three main dimensions: 

• Width
• Thickness
• Length

The designer determines the length as they route and subsequently determines things like impedance. You may see resources that refer to width and thickness interchangeably. In this article, the thickness specifically refers to the dimension perpendicular to the PCB plane. In other words, how far out of the board it measures. 

The standard PCB trace thicknesses available from most PCB manufacturers start at 0.5 oz/ft² (approximately 17.5 µm) and typically go up to 2, with some options up to 6 oz/ft² (approximately 210 µm, although quite uncommon) or more for high current applications. 

Calculating Trace Thickness

The IPC-2221 standard provides a comprehensive methodology to calculate the appropriate trace thickness. It considers the maximum current carrying capacity, allowable temperature rise, and ambient operating conditions. Software tools such as OrCAD X (discussed below) and online calculators are available to assist designers in applying these standards.

Factors Determining Trace Widths and Thickness

Designers can choose any size for traces, provided they meet the minimum size and spacing requirements that the PCB manufacturer stipulates for a chosen price level. For multilayer PCBs, particularly those with more than two layers, it's important to use thicker traces on the inner layers. This is because heat disperses less efficiently from the inner layers compared to the outer layers. The choice of inner layer copper foil can vary among 0.5 ounces, 1 ounce, or 2 ounces.

How OrCAD X Helps With Standard PCB Trace Thickness Monitoring

When working with a standard PCB trace thickness, ensure your designs meet industry standards without compromising efficiency with OrCAD X. OrCAD X streamlines your design process, from calculating trace dimensions to ensuring you meet industry standards. Discover OrCAD X now!