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Calculating trace current .

Lennie

Hi,

I previously used and IPC 2221 calculator for calculating trace widths for internal and external layers. I then started using Saturn PCB Toolkit since it used IPC-2152 to calculate the trace widths.

recently I did a board where the customer used the IPC-2221 to provide values for trace widths and I used the Saturn Toolkit. The inner layer widths came out so much smaller that I started to question the calculator.

I then read a number of articles and it looks like the IPC 2221 is very old and the inner layer calculations were just a guess at double the values. The IPC-2152 actually did testing on generating there charts and also

came up with the plane layers help in reducing the current. So perhaps the inner layers can handle more current ?

In doing more reading and looking at the manuals it looks like the Saturn calculator can produce IPC-2221 values. IPC 2152 without modifiers, with modifiers and with modifiers with planes.

Also I bought Ultra-cads calculator just to check the Saturns result.

So I have a IPC-2221 calculator , two IPC 2152 calculators , a number of IPC-2152 charts and  a spreadsheet with various results from all the calculators.

I do not believe the Saturn calculators values for IPC-2152 are accurate as they are different than the IPC 2152 charts. Need to do more comparisons on the ultracad calculator to see how close they are to the charts.

Just curious of what others use and of they have any experience with the IPC 2152 Calculator ?

 

  • Current carrying capability really depends on the PCB design (layout,stackup). So the 2221 and 2152 can give a rough estimation of the required track width, but to know for sure you would need to do an IR loss simulation. 

    The key factor is the heat build up in the track. Basically you can put a lot of current through a track, but at some point it will vapourize :) 

    For different reasons you would like to keep the delta-T low, around 10-20K. The surrounding tracks and planes act like a heatsink, or worse, creating a hotspot when other current carrying tracks are routed close to each other. 

    So from my own experience the only way to be (more) sure is to do such thermal IR simulation. There is specific simulation software for this (Sigrity), but comes with a large pricetag...

  • Saturn PCB has a great free Toolkit.  It  is based on the IPC-2152 standard.  This is a get starting point, but simulation is recommendated if there are concerns.

  • in reply to Wild

    I had been using the Saturn calculator previously but question the results as they do not seem correct or come close some of the IPC-2152 tables. It looks like the best option is IPC-2152 without modifier for the Saturn program. Unfortunately the results seem to match the IPC-2221 inner layer values for both internal or external layers.

    For most of us Simulation in not an option.

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