By coincidence, someone asked me a similar question just a couple of days ago. I copy below my reply with his original e-mail below it: Subject: Re: Can u please help me? Date: Mon, 23 Apr 2001 18:51:53 +0300 From: Brian Ellis <[log in to unmask]> To: <snipped> References: 1 <snip> Unless I'm mistaken with my mental arithmetic, your mean current will be about 60 mA. In view of the high thermal mass of the substrate, equilibrium would be reached as if this were DC, in terms of the thermal effect. It would therefore be theoretically OK to go down to a track width of about 20 um for a temperature rise of c. 50°C (if you could find someone to make it!!!). This leaves four other factors: the dynamic IR drop. You would need to make sure that you did not lose too many volts for your app, if the conductors are long. It may help you to design your PCBs with the Vutrax CAD system ( http://www.vutrax.co.uk ) which has a facility for calculating the resistance of any net or track. The next one is the L/C effect. If your pulses have a very sharp leading and/or trailing edge, the L and C of the track may resonate, giving a ringing effect (undamped high-pass filter effect), or it may cause the pulse edges to be rounded off (damped low-pass filter effect. This will depend on many parameters. The next problem may be cross-talk. With an obviously high dI/dt, there may be considerable crosstalk to neighbouring tracks which may cause undesirable effects. Lastly, there is EMC. If your tracks radiate, you may need to take special measures to reduce the susceptibility (Vutrax will also give an indication of sensitive EM radiation tracks, without actually giving figures.). You may wish to consider tracks with a fixed characteristic impedance to avoid these effects, if it is possible. Brian <snip> wrote: > > Dear Sir/Madame, > I was wondering if you would be kind enough to give me a rough idea of > what the track width should be for the following specs: > 100 microsecond pulses that are pulsed at 200Hz at 3Amps!!! > > THe mean current is obviously very low but I was a bit concerned about the > "high" current. Would a 10 thou track width be sufficient? > > I need to pack as many tracks as possible in a confined area and thus need > to find the minimum track width possible. Thanking you !! I hope this helps Brian > "May William D (Dean) CNIN" wrote: > > IPC-D-275 has information giving temperature rise of conductors, external > and internal, for different constant current values. Is there any > information that exists for determining the same information for pulsed > currents? I would surmise that the conductor widths and weights would > decrease from the DC values for the same temperature rises? > > Wm. Dean May > NSWC Crane > Bldg. 38, Code 8086 > 300 Highway 361 > Crane, IN 47522 > 812-854-3073 > > --------------------------------------------------------------------------------- > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d > 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 delivery of Technet send the following message: SET Technet NOMAIL > Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 > --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------