Mostly the thermal mass of a board is not calculated - it's judged on a relative basis against what you already know for boards done in the past. If you judge a number of different assemblies as being similar to each other in terms of board material, size, thickness, copper content, size, weight, density and distribution of components, then you can judge that one thermal profile will suffice for them all. If, however, you find you have some boards with a few light-weight components, you will probably need a profile that's different from one that has a lot of large, heavy components. You would be seriously wasting your time to minutely calculate and work out a profile for evey board, as the profiles you get would be so similar to one another as to not have been worth the effort. If you've never profiles any boards in the past, you may want to profile si ilar boards individually just to prove to yourself that the resultant profiles are very similar, and that minor differences have no detectable effect. Have fun. Peter Yannick Brisson <[log in to unmask]> 16/01/2003 01:09 AM Sent by: TechNet <[log in to unmask]> Please respond to "TechNet E-Mail Forum."; Please respond to Yannick Brisson To: [log in to unmask] cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Subject: [TN] Thermal Mass Hi, For quiet long I've heard people said that the reflow profile must be change for each board depending of the thermal mass of the board. My question is how do you calculate this Thermal mass? Or to have a good profile do you take all the datasheet of the component on the board and take an average of that? Hope you can help me with this issue. Thanks You Yannick Brisson ============================ Technicien SMT Technician SMT M2S Électronique 2855, Rue de Celles Québec, Québec G2C 1K7 Téléphone: (418) 842-1312 Ext: 264 Télécopie: (418) 842-0123 [log in to unmask] ============================ --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- [This e-mail is confidential and may also be privileged. If you are not the intended recipient, please delete it and notify us immediately; you should not copy or use it for any purpose, nor disclose its contents to any other person. Thank you.] --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------