Hello Darcy, I'll see if I can be of some help to you. I've done a number of BGA designs using via-in-pad, but only down to 0.8mm pitch using 0.4mm pads with 0.25mm vias. The vias were through hole drilled, filled with non-conductive epoxy, planerised and overplated to provide via-in-pad. I used 4/4 technology. (1.6mm thick finished board) Vias-in-pad can be blind laser drilled microvias, or drilled, filled and overplated regular vias as I have used. Laser drilled microvias are limited by their aspect ratio - usually 0.75:1 or 1:1. So, as a blind via, you can only go from the outside layer to the next internal layer. You will need to work closely with whoever is manufacturing your boards as to their capabilities and cost comparisons. (If a manufacturer is set up for laser drilling, I've heard that the cost should not be prohibitive) Is the inner row all power / ground? If so, you could use drilled vias to connect the inner row and break out the outer 2 rows as you have suggested using 3/3 technology. Of course you need enough space around the device to break out, but this removes the need for laser drilled microvias. There is some good information on merix.com that may be of some help (they made the boards I've described above, and I've had no problems with them)
regards, Phil. Phil Dutton C.I.D.+ Senior CAD Technician IPC Certified Interconnect Designer Tenix Defence Pty Ltd Electronic Systems Division ================================ Internet Page http//www.tenix.com ================================ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Darcy Davis Sent: Friday, 20 October 2006 8:42 AM To: PEDA ([email protected]) Subject: [PEDA] Suggestions on BGA layout Hey folks, We're about to delve into our first design with a real BGA. I've certainly been able to find a few helpful documents online, but I thought I'd run a couple questions past this knowledge base. The part is an 84 pin VFBGA with a ball dia. of 0.3mm (nominal) and a pitch of 0.5mm (~20mil). The array is 10x10 with a 4x4 area in the center with no balls (this leaves three "rows" of pads around the outside of the component). We're trying to balance the cost of new PCB technologies with the risk of poor solder joints, so I'm looking for some recommendations. Just so you know where we're coming from, we're currently doing 2-4layer boards with 10/26mil vias and 4/4mil trace/space. We do most designs with 0.062" FR4, but have done 20, 30 and 40mil thicknesses as well. No laser drilled or blind/buried vias. 1) The manufacturer recommends a 260u pad (~10mil), leaving a gap of 240u (~9mil) between pads. For fanout, we're considering doing 3 mil traces with a 3 mil spacing. Is this reasonable? Will this technology likely be less expensive then microvias or other fanout alternatives? 2) Does "via-in-pad" refer to a microvia within a pad? or does it specifically refer to a via that has been plugged to prevent solder wicking? I assume they can plug using a conductive material as opposed to epoxy? Is it reasonable to assume that this isn't applicable to our part since microvias don't need plugging and conventionally drilled vias would be too big? 3) Could we put a microvia all the way through a 2-layer 40mil PCB? 60 mil? or is their a limit to the thickness one can laser drill? (Therefore limiting its use to 4-layer boards only). 4) The mfgr recomends "via-in-pad" as a preference to routing out on the top layer. What size of annular ring is necessary on the inner layer for a microvia? If the inner layer pad has to be 10 mil, we're still limited to 3/3mil trace/space to get the middle row of signals out. Sounds like an expensive endeavor when you account for microvias and 3/3mil traces. Hmm. That should at least get me going. Has anybody got a fanout of a similar BGA that they would be willing to share? I'm just really shakey on the "right" way to fanout a BGA using micro/blind/buried vias. Thanks in advance. Darcy Davis Mechanical Team Leader DYNASTREAM INNOVATIONS INC. 228 River Ave. Cochrane, AB Canada T4C 2C1 T 403-932-9292 ext. 132 F 403-932-6521 E [EMAIL PROTECTED] W www.dynastream.com www.thisisant.com ____________________________________________________________ You are subscribed to the PEDA discussion forum To Post messages: mailto:[email protected] Unsubscribe and Other Options: http://techservinc.com/mailman/listinfo/peda_techservinc.com Browse or Search Old Archives (2001-2004): http://www.mail-archive.com/[email protected] Browse or Search Current Archives (2004-Current): http://www.mail-archive.com/[email protected] Disclaimer : The contents of this e-mail including any attachments are intended only for the person or entity to which this e-mail is addressed. If you are not, or believe you may not be, the intended recipient, please advise the sender immediately by return e-mail, delete this e-mail and destroy any copies. Tenix does not warrant nor guarantee that this email communication is free from errors, virus, interception or interference. ____________________________________________________________ You are subscribed to the PEDA discussion forum To Post messages: mailto:[email protected] Unsubscribe and Other Options: http://techservinc.com/mailman/listinfo/peda_techservinc.com Browse or Search Old Archives (2001-2004): http://www.mail-archive.com/[email protected] Browse or Search Current Archives (2004-Current): http://www.mail-archive.com/[email protected]
