Why go through all this bother? This is a back of the envelope calculation. There is a few microwatts of dissipation in this system, 3V * 30 uA = 90 uWatts. The duty cycle of the transmitter, assuming 1%, will contribute will add a couple of more uWatts. If you assume 100 degrees C per watt thermal resistance from the board to the outside world, the temperature rise will be 92uWatts *100C/watt yields 0.0092C. Plug in whatever thermal resistance you have and you have the answer. To use a simulator you are going to have to give it the thermal resistance anyway. Tom Dagostino Teraspeed Labs 9999 SW Wilshire St. Suite 102 Portland, OR 97225 USA 971-279-5325 Office 971-279-5326 FAX 503-430-1065 Cell tom@xxxxxxxxxxxxx www.teraspeed.com Teraspeed Consulting Group LLC 16 Stormy Brook Road Falmouth, ME 04105 401-284-1827 -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Ihsan Erdin Sent: Friday, November 30, 2012 5:00 PM To: sunil_bharadwaz@xxxxxxxxx Cc: SI LIST Subject: [SI-LIST] Re: PCB in plastic enclosure Sunil, With a 10cm2 plane and 75uA current, I wouldn't even bother about the thermal issues on that card. But if you want precision you should characterize the dc current on the card first. Sigrity and SIwave are the two tools that can do that. There are probably others, too, but those two are the ones familiar to me. Once you get the current distribution and power density on the metal structure you can derive the thermal profile of the card with simple circuit equations after mapping thermal parameters to equivalent circuit parameters. For the overall system evaluation, you can feed the power density data to a dedicated thermal simulator (flotherm, icepack, etc.) and get the results. Regards Ihsan On Fri, Nov 30, 2012 at 10:06 AM, sunil bharadwaz <sunil_bharadwaz@xxxxxxxxx > wrote: > Hi All , > We have designed a battery operated wireless system placed in a > plastic casing. > The PCB has a battery & other electronic components . It continuously > draws about > 30 uA ( sleep current ) .The Tx gets switched ON at a relatively low > duty cycle , where in the total average current becomes about 75 > uA.The PCb has a ground > plane of 10 sq cms.Battery is at 3.0 V. > > > The board is enclosed in a plastic casing , which is thermally insulated . > > Considering that the battery would last for say an year or two - does the > temperature of the PCB , increase continuously ?How do we ensure > > that the temp stays with in limits . > > > What tools are required for such an analysis . Pls point me to any > relevant > links .I did try to do some homework - but not much luck so far. > > Any info in this regards would be highly appreciated .Thanks to you > all in advance . > > Best Regards > Sunil.Bh > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > -- Ihsan Erdin ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu