Novice question . . . I was told that the heating imbalance "goes away" in the IR reflow process, since "the whole thing" has been brought up to temperature at "the same time". Question: can we "mostly ignore" potential thermal imbalances caused by asymmetrical traces shape/width for IR reflow process boards? (or have I been lied to, again . . .) Thanks, Carl -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg Sent: Wednesday, January 12, 2011 6:46 AM To: [log in to unmask] Subject: Re: [TN] Trace Widths Entering SMT Also, if there is a large trace going to one side of a 2 terminal device, and a small trace from the other side, it can cause a heating imbalance, one side will reflow before the other (the side with the smaller trace), and sruface tension could pull the part toward that pad and possibly cause a tombstone. Blair On Tue, 11 Jan 2011 14:27:02 -0800, Phil Bavaro <Phillip.Bavaro@L- 3COM.COM> wrote: >I will hazard the guess or give at least one rational why they are >asking for this, as I have asked for similar rules in the past. > >When you have a pad that is edge defined and not soldermask defined, >having a 50 mil trace come in on one side will create a bigger pad in >effect. This will affect the skew that occurs when the part floats on >the molten paste during reflow. We ask for the smaller "spokes" so >that the swimming effect is minimized and the part stays put in the >center of the pad. > >The smaller the component and pad, the more that this affects the >alignment of the component. > >Think of it as a parking lot and your Manufacturing Engineer is trying >to keep all the cars parked parallel. > >Hope this helps.... > >Phil > >-----Original Message----- >From: TechNet [mailto:[log in to unmask]] On Behalf Of Cote, Clint (GE >Intelligent Platforms, US) >Sent: Tuesday, January 11, 2011 9:58 AM >To: [log in to unmask] >Subject: [TN] Trace Widths Entering SMT > >Our Manufacturing Engineer requires us to have a maximum 0.020" trace >entering an SMT pad. This is regardless of the size of the pad. He >will allow multiple 0.020" traces to the same pad. For instance he will >allow >3 0.020" traces into a pad but reject one 0.050" trace. Does this make >any sense? > >Thanks, >Clint Cote > --------------------------------------------------- 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.aspx?Pageid=E-mail-Forums for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- 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.aspx?Pageid=E-mail-Forums for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------