[pcbforum] Coppersize&weight
- From: "vishwanath HS" <vishwa@xxxxxxxxxxxx>
- To: pcbforum@xxxxxxxxxxxxx
- Date: Thu, 29 May 2003 09:11:51 +0530 (IST)
Copper weight and size of copper required for a PCB to withstand a surge
current of 10KA, 20KA or 30KA for PCB board design? :
The number of variables for calculating what current a track can withstand
depends on a huge amount for variables. If you are not using high
frequenciesat high currents, then the greatest factor limiting the track
thickness is „Ohmic Heat . In essence the heating of the track against
the ability of the track to cool itself. It follows that the outer tracks
will cool at a faster rate than the inner layer tracks, should the PCB be a
Multi layer. One Should also remember that a continous current will be more
beneficial to a tracks lifetime, than when the current through the track
oscillates causing repeated expansion and contraction. Assume the following:
The copper thickness on the PCB is 35�m, the rise in temerature is
approximately 10�C, and the tracks are alone, i.e, not near a heat sink. It
foll ows: Track width: Current capacity: 0.25mm 0.8 Amps 0.5mm 1.5 Amps
1.27mm 3.2 Amps 2.5mm 6.0 Amps Some rules of thumb: To increase the capacity
of current in the track by a factor of the square root of 2 ( ca 1.4) you
should double the track thickness. You can use the power rule I� = W/R. To
increase the capacity of current in the track by a factor of approximately
1.65 you should double the track width. For saftey reasons one should always
derate the practical values compared to the theoretical values. There is
another formula that maybe used for more prescise calculations 0.44 0.725 I
=0.048 T A Where I = Current in Amps / T = temperature rise in �C / A =
Crosssection area in mils� Please see the link below to find the Current
Capacity Calculation formula of Beta LAYOUT GmbH
http://www.pcb-faq.de/download/Email_Strombelastbarkeit.doc
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