Gerry,
     
     We have used the graphs and current carrying information in Harper's 
     "Handbook of Wiring, Cabling, and Interconnecting for Electronics", 
     Chapter 8, "Rigid Printed Wiring and Connector Systems", published by 
     McGraw-Hill, as a basis for our design rules in this respect.
     
     A point to watch if you are in a high current rating situation is to 
     ensure that your VIAS are appropriately rated, and have not only 
     enough copper in the hole (circumference/plating thickness), but also 
     have sufficient copper VIA CONTACT cross-sectional area around the via 
     circumference, within the plane/tracking. You may need to use multiple 
     vias to achieve this.
     
     Also, if your current rating is not continuous, you may be able to 
     down-rate. Within the plane areas, it will be the current carrying 
     paths that really matter - between obstacles, unconnected vias etc.
     
     I always start with 1oz Cu and only go to 2oz if there is a (for 
     instance, current carrying) need. We have only used 4oz Cu for thermal 
     planes/thermal conductivity purposes, within a high cold wall 
     temperature environment (80degC), which from what you have implied, 
     may be similar to yours.
     
     Hope this helps,
     
     Clive ffitch
     MBUK

______________________________ Reply Separator _________________________________
Subject: DES: Current carrying capacity of innerlayer planes
Author:  [log in to unmask] at INTERNET
Date:    17-05-97 7:49


     
Hi All
     
I'm looking for a methodology for determining the current carrying 
capacity of an innerlayer power plane as a function of copper weight. 
Let's assume the max op temp of the laminate is 105C which allows a 30 
degrees temp rise above ambient(?)
     
It's the old "one ounce copper versus two, three, or four ounce 
copper" plane design question again ...... Data, viewpoints, and 
experiences would be welcome as well. I do know that for high speed 
situations, IR drop is the limiting factor. In this case, it's current 
carrying capability.
     
Thanks in advance
     
Gerry
     
     
     
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