You want to put how much current through your PCB?
For years engineers used the data presented in IPC-2221 and were happy with the results because they were using so much copper, nothing ever overheated, so no one ever questioned the results. Many online calculators still use the equations in IPC-2221. As the saying goes: “Anyone can design a bridge that stands. It takes an engineer to design a bridge that barely stands.” The problem is that IPC-2221 is entirely too conservative and is based on incomplete research from six or seven decades ago
when PCBs were only one or two layers and made on materials such as phenolic resin. Fortunately Mike Jouppi and the team responsible for the IPC-2152 standard discovered the faulted origins of the data, threw it out, and conducted fresh research using modern materials. To be clear, you should not use IPC- 2221 trace width and thickness calculators in high current designs or your PCBs will be the size of pizza boxes.
Sierra Circuits has an excellent online calculator based on IPC-2152 at https://www. protoexpress.com/tools/trace- width-and-current-capacity- calculator/, but even IPC-2152 is based on a limited dataset and is more conservative than necessary. [Callout: The equations in IPC-2152 tell engineers to use more copper than they actually need. The equations in IPC-2221 tell engineers to use far more copper than they actually need.]
This graph shows the minimum trace width required to maintain a temperature rise of no greater than 20° C at a given current in a variety of copper weights. To use this graph, assume your components can handle a 20° C rise, and on the horizontal axis find the current through your trace, then move vertically to find an acceptable copper weight and thickness. The graph uses equations derived from IPC-2152 data from the graphs by Douglas Brooks. It uses logarithmic axes and reimagined horizontal and vertical variable choices to produce graphs that look decidedly different from the graphs the IPC-2152 team created. You can download a complete assortment of these graphs in grams, ounces, mics, mils at https://aapcb.com/ wp-content/uploads/2020/03/ HeavyCopperGraphics.zip According to IPC-2152, if you want the temperature of your board to rise no more than 20° C above ambient temperature, the minimum copper weight and trace width needed to conduct 5 amps of current in 4 [oz][ft] -2 is approximately 50 mils. The minimum width of 2 [oz][ft] -2 copper is ~100 mils. If you don’t have 100 mils you can neck the trace down and hope for the best, or consider running the current over multiple layers of your
[oz][ft] -2 copper, the minimum advertised trace width is usually 3 mils and for 4 [oz][ft] -2 copper, the minimum copper width is approximately 7 mils -- in both cases, the fabricators can produce thinner traces if asked, but we’ll work with advertised minimums for now. Trace and space minimums impact the size of components you can place on your board. Dies shrink every year, and when they do, package sizes often shrink with them. It doesn’t take long for engineers to find themselves with parts that no longer fit on their old land-patterns.
A quick interpretation of IPC-2152 The inner and outer layers of a PCB are made with different processes. In one single lamination stackup, the inner layers are etched into the board, then the outer layers are electroplated, and then copper is etched away from the entire board, leaving only the desired copper traces and land patterns behind. To ensure there is enough room for acid etching, there are minimum trace widths and air-space ( trace and space ) based on copper weight. For example, if you’re using 0.5
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