Hi Mark - if you leave the thermal vias open then the solder will thieve down them leaving the center pad "solder starved". I recommend you use some fabrication format which permits the vias not allowing solder to thieve - aka either capping them or filling them. The IPC-7093 standard on Bottom Termination Components also may have some helpful information. Dave Hillman Rockwell Collins [log in to unmask] Mark Larson <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 08/31/2011 02:52 PM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Mark Larson <[log in to unmask]> To <[log in to unmask]> cc Subject [TN] QFN with solder slug I am curious how others are handling these parts for soldering. Do you leave the thermal vias in the slug covered or uncovered with solder mask? Do you fill with anything? What size hole on a 62 mil board? Tie to all GND planes or just the back side? Thermal relief the via or bury it in the plane? --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 16.0 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 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 16.0 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 For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------