I use vias, too. The vias should be as small as possible. I use solder paste dots between the via holes so that the solder is not sucked down the holes in reflow. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Frank Kimmey Sent: Thursday, April 05, 2007 10:51 AM To: [log in to unmask] Subject: Re: [TN] Thermal via's on D2PAK Kenny, There are lots of issues to deal with when placing vias under any soldered component. We almost always use thermal vias under hot parts to help. You will need to calculate a few items prior to completing layout. 1. PCB thickness (higher aspect ratio helps reduce bleed through) 2. Via diameter (larger vias allow more solder to flow through the PCB) 3. Solder availability (solder starvation beneath the part can be an issue) 4. Final finish and solder process (again, how much solder will go down the holes) 5. How to keep the backside from being a mess Call me if you want to discuss in further detail. Hope it helps, FNK Frank N Kimmey CID+ Principal PCB Designer PCB Programs Powerwave Technologies Inc Office 916-941-3159 Fax 916-941-3195 Mobile 916-670-0645 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Bloomquist, Ken Sent: Thursday, April 05, 2007 8:43 AM To: [log in to unmask] Subject: [TN] Thermal via's on D2PAK Do any of you see an issue with putting thermal via's under the bodies of a D2PAK? Do you have any recommendations for the number or size or the via's to help transfer heat to the other side of the board? Thanks, KennyB --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------