wow, I just realized that ipc.org doesn't work, you have to use www.ipc.org (someone should fix that) onward thru the fog, Jack . On Fri, Feb 13, 2009 at 8:55 AM, Jack Olson <[log in to unmask]> wrote: > There is no such thing as "permissible current and voltage" > in circuit board design, (except by safety regulations, and > those requirements differ). > > There is a relationship between current, trace size and temperature > (which is described by the curves in IPC-2221 Figure 6-4) > so by increasing the current or decreasing the trace cross section, > you increase the temperature. > > The curves will show the "temperature rise" above ambient for > any given trace size and current. The key is in knowing what your > "ambient temperature" is. > ...and that's why we designers make the big bucks (just kidding!) > > The caution is that you don't want the temperature to affect > the integrity of the board material, so for example if the Tg of > a particular material is 170 degrees C, we may limit the maximum > operating temperature to something like 135 degrees C > (by adjusting the trace width or copper thickness, or by moving > the trace from an internal to an external layer, or by pouring copper > planes near it to dissipate the heat, etc.) > > also, clearances define maximum voltage, not trace size. > > You can get a better description of these concepts by downloading > a draft of the new IPC-2152 (Current Carrying Capacity) at ipc.org > under "Status of Standardization" in the Knowledge menu. > > hope that helps, > Jack > > --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------