what is thermal shock requirement of the system? over what temp range? if it is medical room temp equipment with proper cooling, no problem for 1ppm (room temp with equipment temp rise of 5-10 C max). if it is -65 to 150 C thermal shock.. you might want to consider that 1 ppm...especially MCM, it is normally larger than the standard devices (corner to corner)... jk (my 2 cents) -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Valerie St.Cyr Sent: Thursday, March 10, 2005 11:12 AM To: [log in to unmask] Subject: [TN] CTE matching I have a question for the forum: We have an engineer who will be using an MCM on his PCB, and he has said that the CTE is 11-12 ppm/C (I have no other information as yet on this MCM). He believes that because of this he needs to use a material with a closer x,y CTE. There is a material where the specs give the x,y CTE as up to 14, which is the material we would typically use; and there is an alternate material where the specs say the max CTE is 13. Of course the alternate material costs more. First, is there any practical information on matching MCM CTE? Would a 1 ppm per deg C make a difference? Second, I was under the impression that to match CTE we would only have to change the top layer, where the joint between the device and the board is formed. He believes that we would need to change all the cores and prepregs in the stackup. This will be somewhere over 24 layers (26, 28 , 30?? don't know just yet) so the cost delta for the material will be magnified if the entire stackup is converted. The alternative material which is proposed is not Thermount; but I did go out to Dupont's web pages and read all their papers on CTE matching. I sent those to the Engineer but it wasn't enough to convince him. Does someone have any alternative links to papers detailing real life projects for CTE matching and what they did and what was achieved, and so forth? Is there a board fabber on distribution with a lot of background/customer demand for this who would care to comment on my two questions? Thank you all, Valerie --------------------------------------------------- Technet Mail List provided as a 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/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 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------