Janine, The first and probably most important question is whether the controlled impedance is for high speed logic or is it actually an RF design. Then the next question is whether or not you have 50 ohm traces on both sides of the board. Are any if your 50 ohm lines going to be stripline (internal, between planes), or are they all microstrip (external, above a plane). Once you know those, and can estimate the remainig needs in terms of layers, you can probably look at what your controlled impedance stackup is going to have to be (trace width, dialectric constant, height above ground plane / distance between internal planes, etc.). Somewhere in the middle of all that, you have to address the issue of termination. What kind of termination is required and where are you going to put it. There is much much more to it, but this can be a starting point. All this in a 71 mil board ... have fun. JaMi Smith * * * -----Original Message----- From: Janine Badcock [mailto:[log in to unmask]] Sent: Tuesday, April 02, 2002 4:28 AM To: [log in to unmask] Subject: [TN] BGA/Highspeed Design Technologies We are just about to embark on our first BGA/highspeed design. Board specification : - Double Side Surface Mount Board. With 225 pin 1mm pitch BGA's on each side Datalines @100Mhz and impedance matched to 50 ohms. Powerplanes 3V3 and DGND (digital ground) Military specific applications Maximum Board Thickness 1.8mm Could anyone with any experience of the above please comment on the following : - 1. Layer stack (blind & buried vias?) 2. Technology (microvias?) 3. Via size 4. Track size 5. Materials We have been advised that for high speed digital designs that we should limit the number of vias through ground and powerplanes. If you have any additional information/comments about the design you feel would be useful for us, we will be grateful. In anticipation Many Thanks ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** ------------------------------------------------------------------------ --------- 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 e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest 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 e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest 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 ---------------------------------------------------------------------------------