Hi, Marie, You have a bit of a "mule" here. I can comment with some confidence about the via holes and conductive epoxy filling, and my general experience is that holes 10 mils (0.25mm) are just OK to fill as long as the aspect ratio (hole diameter : hole depth) is not more than 1:6. Many fab shops, though, do not like aspect ratios greater than 4:1. With a 2.3mm (92 mils) thick board, via hole diameter at 1:4 would have to be 23 mils (0.575mm). At 1:6, the diameter would have to be 15.3 mils (0.383mm). Adding the usual preferred "pad diameter over finished hole diameter" size of 22 mils, you end up with pad diameters of 45 mils (1.125mm) and 37.3mils (0.9325mm). I have 1.27 mm pitch BGA's with pad diameter only 0.5 mm, so I think that the design idea of via-in-pad is a non-starter. With 1.27mm pitch BGA's, there is enough room to design in offset vias that don't therefore need to be epoxy filled, except perhaps for test points. I would also worry - a lot - about the copper thickness, especially at that thickness of PCB. What is the working environment of this board to be? Peter ME Magnin <[log in to unmask]> 14/03/2003 03:45 PM Sent by: TechNet <[log in to unmask]> Please respond to me.magnin To: [log in to unmask] cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Subject: [TN] 2.3mm thick PCB and BGA Technetters, I have received a query from a customer : he is designing a PCB for a BGA , as described below : 35 mm ´ 35 mm, cavity up, 352-pin plastic ball grid array (PBGA) package. Package Outline 35 mm ´ 35 mm Interconnects 352 Pitch 1.27mm Solder Balls 62Sn/36Pb/2Ag Solder Ball Diameter 0.75 mm Maximum Module Height 1.65 mm Co-Planarity Specification 0.15 mm Maximum Force 6.0 lbs. total, uniformly distributed over package (8 grams/ball) He needs a 2.3mm thick PCB, 10 layers, 4 or 6 of them with 70um copper. He wants 0.25 mm via holes underneath the BGA, which must be also used as test pads. For this reason, he wants these holes filled with conductive material to increase the contact surface. He has contacted his usual PCB manufacturers who are not really confident with such a design. Who has any experience abour this topic ? Which solution would you propose ? Waitnig for your answer, Kind regards Marie Magnin FIRSTEC SA Rue du Grand Pré 70 CH 1211 Genève 2 Tél. : +41(0)22 918 36 85 Fax : +41(0)22 918 36 93 mailto:[log in to unmask] http://www.firstec.ch --------------------------------------------------- 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 ----------------------------------------------------- [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 -----------------------------------------------------