To paraphrase Paul Reid's comment: given you have a well filled through via The stacked structure that you describe is very common, but perhaps less so in North America. For example, Intel has been sourcing their Pentium CPU substrates (using similar stacked structures) from Japan for more than a decade. Regarding reliability, there are numerous factors that come into play. The obvious ones are the Tg and z-axis CTE of the fill material. In addition, one must also consider the adhesion of the fill material to the barrel wall, dimensional stress induced during planarization, method of surface prep cleaning used prior to Cu cap plating, adhesion between fill material and Cu cap, etc. Regarding the level of competency among fabricators that do via fill processing, I have found those in North America to be primarily cost-driven, whereas the technology leaders in Japan and Taiwan are performance-driven. The point I am trying to make here is that the reliability of a via fill material in your application should not be judged exclusively by what a fabricator, particularly in North America, can deliver to you. There are via fill materials readily available that meet your Tg and CTE targets; however, this is just one piece of the puzzle. Stephen Pierce SGP Ventures, Inc. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Mark F. Focht Sent: Wednesday, December 12, 2007 4:37 AM To: [log in to unmask] Subject: [TN] Stacked Via Help I have a design that,due to space constraints, requires stacking microvias (L1- L2) directly on top of (in line with) drilled buried vias (L2-L7, L2-L11). I am receiving conflicting information about this strategy being reliable (storage temp. range -50C to 110C, operating temp. range -40C to 85C) because of the different CTE's of the via fill material used in the L2-L7/L2-L11 vias and the board material (FR406, 170Tg). While the board shops that will fab this admit they prefer the vias be staggered (not very pratical in this design), they claim they have produced boards of this type without negative feedback or issues. The CM that will be assembling this is extremely hesitant about using this via strategy. Does anyone have experience using a stack-up similar to this? Would this be reliable? Is there a plugging paste material that very closely matches the CTE of FR406, 170Tg? Any and all comments are welcome. Thanks, Mark Focht C.I.D.+ Pole/Zero Corporation 5530 Union Centre Dr. West Chester, Oh 45069-4821 Voice: 513.870.9060 X173 FAX: 513.870.9064 Email: [log in to unmask] --------------------------------------------------- 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 -----------------------------------------------------