Formula for current carrying capacity of a trace in PCB

[SughiRam P.]

Hai,

I have used calculators for maximum current carrying capacity of a trace. The formula they used is I= K*(T^0.44)*(A^0.725). Here, K-Derating constant, T-Max temperature rise above ambient, A- Cross sectional Area (Copper thickness * Trace width).

My Doubt is, The Notation "T" is denoted as Max temperature rise above ambient. Whether it means maximum possible temperature the board will work? Is ambient temperature means Room Temperature?
Why we are using this derating constant?

My assumption is, T denotes the possible rise in Temperature around the Trace or board and Derating constant relates to plating. Can anyone Help me on this?

 

[kj.singh]

Yes, "T" refers to the max. temperature rise the board will work at and the track is subject to accomodate the drop due to the operational rise in temp. The ambient temp. is assumed to be 25degC here.
Derating constant is not related to plating constant since it changes for outer and inner layers.

 

[SughiRam P.]

Thank u. De-rating constant given in the formula is 0.024 for Inner and 0.048 for Outer. So, i thought it may be related to plating.

 

[SughiRam P.]

Can anyone explain why we are using De-rating constant in above formula?

 

[mishrashashi]

Derating of current/voltage depends on ambient temperature and pcb material. for further information please refer following link
**broken link removed**

hope this is helpful.

 

[D.A.(Tony)Stewart]

fiberglass/epoxy boards with the Fire Retardant rating level4 (FR4) are considered insulators so we choose a conservative temperature rise to compute the copper size.

https://circuitcalculator.com/wordpress/2006/01/24/trace-resistance-calculator/