Hi John! Of course, this problem depends on a lot of stuff. Where is the sink you are looking to dump the heat into? Sometimes the ground planes of the board the device is attached to is the best place. It may be advantageous to run a thermal model to determine an optimal strategy. In almost every case, you will probably want to use a good underfill product--either it will assist by transferring a bunch more heat into the substrate than just the balls would allow or it will assist with supporting the mass of a heat sink attached to the top of the device. The "best" way to attach those is dependent on the expected thermal cycling profile, operating life, sizes involved, etc. It may be that an adhesive could do the job. For tough environments and massive heat sinks, then you will need to use some kind of spring mechanism to hold the heat sink against the device. I think I've seen a heat sink attached with an adhesive some time in the past, but I sure don't recall where (of course, a ground plane actually can be considered a heat sink attached with an adhesive, so I don't think anyone could rationally make a categorical denial that this can be done reliably). Good Luck, Wayne Thayer >>> [log in to unmask] 5/21/2007 5:42:14 pm >>> We are using some BGA's that are going to run very hot. What is the best way to attach heatsinks to these devices? Any help will be appreciated Thanks John Foster --------------------------------------------------- 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 -----------------------------------------------------