HI, Joyce, Can't think of another answer to the one you've come up with yourself. Sounds very like you have some very high internal stresses in the heatsink that have been relieved at soldering temperature. Clamping the heatsink and annealing it after its manufacture should be enough to keep it flat - just make sure it cools slowly or you'll still trap stresses. For those heatsinks already chipped, heating them up, clamping them and continuing to anneal them might get them back into shape, but the tolerences may be a bit out afterwards unless you have a very good clamp/jig and a good annealing process. What happened to the board the heatsink was presumably mounted to for reflow? Has it potato chipped as well? Peter joyce <[log in to unmask]> 11/07/2002 08:16 PM Sent by: TechNet <[log in to unmask]> Please respond to joyce.koo To: [log in to unmask] cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Subject: [TN] warpage heat sink Guys, I got a heat sink look like potato chips after reflow using conduction hot plate (230-240 C). The heat sink is 1 cm thick Cu with few position screw holes on 2 sides. The size is 13.0x10.0x1.0 cm with 0.45 mm diagonal height variation at the moment (one corner point to the sky and one down to the earth). Any remedy for the "cure"at this stage? ? (it is Au/Ni plated). Anything I can do to prevent from happening besides specify the annealed Cu must be used? (can't reflow on the other side, it has to bond to fan by thermal compound). Never see anything like that. The internal residual stress must be extremely high! Thanks in advance for all your help...;-( jk --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 ---------------------------------------------------------------------------------