Track width calculation

[SARAVANAN R]

I have a Class 3 design, Where 40 Amp, will be drawn in PCB Tracks for 1 Sec duration(Max).

I don't have the space for the thickness as per IPC Calculation. What is the track width required

It is 2 oz , 10 Layer PCB.

 

[barry]

What?
1) You already know the REQUIRED trace width.
2) You say you don‘t have space for the REQUIRED trace width.
3) Then you ask for the REQUIRED trace width.
4) See #1.

you can use thinner traces if you can tolerate higher temperature rise. Other than that, your question makes no sense.

 

[SARAVANAN R]

you can use thinner traces if you can tolerate higher temperature rise. Other than that, your question makes no sense.

Thank you for replying. For the continuous current of 40 Ampere, the required track width is known to me.
My design is 40 A, 1 Second duration is the requirement.

 

[c_mitra]

I have a Class 3 design, Where 40 Amp, will be drawn in PCB Tracks for 1 Sec duration(Max).

You calculate the RMS value of the current; if the current is on for 1s and off for 2s, the RMS current will be
sqrt((40*40*1+0*0*2)/3)=23A. Use this value for the calculation for trace width. Such calculators are available on the internet.

But you cannot use the RMS value if the on times are too long; I guess 1s should be the cut off.

 

[SARAVANAN R]

Thank you for the reply, My current requirements are not repetitive. It is one 40 Amp, 1 Second duration. Never repeats again.

 

[barry]

Thank you for the reply, My current requirements are not repetitive. It is one 40 Amp, 1 Second duration. Never repeats again.

Well, if it “never repeats again”, then I guess it won’t matter if the trace burns up. And one second sounds like an ENORMOUS amount of time to me. Your trace is basically a fuse. How fast do you think it will take for a 10 mil trace to melt with 40 Amps? How about a 100 mil trace? You haven’t said how wide a trace you CAN fit.

 

[SARAVANAN R]

Well, if it “never repeats again”, then I guess it won’t matter if the trace burns up. And one second sounds like an ENORMOUS amount of time to me. Your trace is basically a fuse. How fast do you think it will take for a 10 mil trace to melt with 40 Amps? How about a 100 mil trace? You haven’t said how wide a trace you CAN fit.

Thank you for the reply. The 40A, 1 second duration is command given to Pyro devices. During testing & integration , The system need to be tested for n number of times by applying 40A , 1 second duration. The testing does not happen continuously. Enough time is available to cool the board to room temperature . I can provide up to 2.5mm, 2 oz track width , Maximum track length is 255mm, Board Material is FR4 ISOLA HR370. I think now it is clear.






Ith

 

[FvM]

I think the requirement is pretty clear, it's similar to the "single pulse" case in transistor SOA curves, however I'm not aware of tables with dynamic thermal PCB data. If I had to solve the problem, I'd perform a simulation with a FEM tool, e.g. free FEMM. You mentioned 10 layer 2 oz stackup but didn't tell about the actual geometry, one or multiple paralleled layers, plane assignment etc.

 

[barry]

The question is not whether there is enough time to cool the board, the question is whether the trace will melt or delaminate from one pulse. my GUESS is it will probably be ok as long as your ambient isn’t too high.