The driving issue, if I understand your question, would be the current
carrying capacity of the trace structures. 'Cross sectional area' is more
important when higher current is involved. Also, if you have any control
circuits with fine lines, you may want to steer away from very thick copper
and go with wider traces for the high current lines. Very thick copper will
limit the smallest trace you can make. 4 amp traces are not uncommon. 
The real target for your design depends a lot on what you are trying to
accomplish, and for how long and for what cost... 

The duty cycle of the 15 amp current... if it's very short, may allow you to
use smaller traces. The relatively high voltage of 90 volts will most likely
be unaffected by low resistance values in thinner traces... But if the duty
cycle is significant you may need to increase the copper on the board. 

Remember as you thicken the copper you also increase the thermal conduction
of the traces, and anything you wish to solder to the copper will need a
bigger heat source to get the land area hot enough to solder to. Also if it
gets too hot for too long you will damage the fiberglass epoxy laminate.

 What you mean by 'mounted rails' is somewhat unclear to me. Are you getting
copper bar stock and machining it to mount it on the board? Are you
referring to 'Bus Bars' that solder into the card? Please explain.. 

Bill Brooks, CID

-----Original Message-----
From: Brian Guralnick [mailto:[EMAIL PROTECTED] 
Sent: Monday, August 04, 2003 11:42 AM
To: Protel EDA Forum
Subject: [PEDA] PCB Copper thickness VS mounted rails.

I'm designing a power supply with will have a large ripple current.  This
power supply will be on it's own PCB and it's 1 layer.  Am I better off
mounting high current rails, or, increasing the PCB copper thickness from
1oz to something like 4-6oz?

The power supply will be 90 vdc, continuous dc current of 4 amps, with
current surges & ripple current above 15 amps.

Brian Guralnick

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