On 9 Jul 96 at 16:25, Jack Olson <[log in to unmask]> wrote: >As I was browsing through some previous discussions, I came across >the following question (yeah, I'm quoting myself). It was regarding >the use of Figure 3-4 in IPC-D-275 to determine an appropriate trace >width based on current. > >> As an example, say I need 5amps and 20 degrees over ambient is a >> safe assumption. The chart gives ABOUT 100 square mils, which >> corresponds to ABOUT a 75mil trace width on the 1oz copper curve. >> OK, how many of you use 75mils? How safe is this number? > >Many of you responded (THANK YOU) but one issue was never brought up >and I am still curious about it. > >According to IPC-RB-275 Table 7, a conductor width can be reduced >20% by a nick or scratch for a length of 0.5 inches and still be >acceptable, plating thickness can vary (as well as the 1oz copper >stock), traces can be over-etched, etc. > >So does the chart indicate that I should use 75mil aperture in my >CAD system, or is my goal to take all factors into account and try >to ensure the END RESULT is 75 mils minimum? > >Am I splitting hairs? Jack > Yes. If you're still concerned, use the line on the chart for a 10 degree rise. I've never been burned doing that. OK, bad pun, sorry. --- Ross LaGue < [log in to unmask] > Dayton, Ohio The mail list is provided by IPC using SmartList v3.05 To unsubscribe from this list at any time, send a message to: [log in to unmask] with <subject: unsubscribe> and no text.