Genny First off, as an assembler I'd worry about exactly what you conclude - will the pad make soldering a problem? I'd worry about coplanarity, among other things. If this were my problem to worry about I'd look at it this way: 1) is it really a problem? The designer (you?) should know the power use of the chip, as well as the expected operating environment. Is it going to run hot? 2) if it is a problem, can some sort of underfill be used? I'm not in favor of messing with an unsoldered part... good luck! regards Graham Collins Process Engineer, Litton Systems Canada, Atlantic Facility (902) 873-2000 ext 6215 >>> [log in to unmask] 08/21/01 02:54PM >>> We use an IC that sits min 0.25mm, max 0.5mm off the PCB according to the datasheet. There is a heat slug embedded in the bottom. Fine pitch 120 pin, PQFP The data sheet says nothing about requirements for heat sinking, but when there's a slug you kind of feel you should help it out, right? For reliability, MTBF,... Due to the fine pitch, placement is critical. We are looking for a thermal pad of some sort to place under the device, as that thick a layer of heatsink compound under it is probably not a good idea, causing more problems than it solves. Possible running of the compound, contamination of the lands, causing the part to move while in the oven... We get the boards reflowed out of house. The co. we use suggested a sil pad, and said they could possibly pick and place the pad. My questions: How thick a pad should we look for, 0.25mm or thicker? What if the gap is the max for some IC's - will the pad be of any use when not making contact? If we spec thicker, will the pad keep pins from soldering when the IC high centers on the pad? Anyone have other ideas? Genny Gibbard (mailto:[log in to unmask]) Product Transition and Support Wavecom Electronics Inc. --------------------------------------------------------------------------------- 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------------