Coincidently, the board house rep was in town today with a new DFM manual. We've been doing the 0.15mm drill on 0.5mm pitch BGA's, via-in-pad, filled and plated flat&flush both sides on 40 mil thick boards. We require flat&flush on both sides because we do automated micro-probing on the side opposite the mounted BGA. I was surprised that their manual says those drills can go to 150 mil thick, an aspect of 25:1. I have no idea how they get those things plated. The rep claims those are reliable for production boards. We've had good luck with them on our test fixture boards, but have only done them at the 40 mil thickness on a few hundred total quantity boards What's more, they've just got new drilling machines that can now do, as part of their standard rules, 0.10mm mechanical drills on 0.4mm pitch BGA pads on boards up to 62 mils thick. I'm sure I'll have some .4 pitch parts in the next few months, and will be eager to give that a try. They claim to be more economical than laser vias. The advantage for our application is that I can go all the way through the board in a single via without having to stairstep or stack micro vias. Their 'immerging technology' is the same drills on 72mil and 200mil boards, respectively. 34:1 AR. Obviously to do this they have improved positional accuracy - I've never seen a breakout on a pad. I wouldn't doubt that they are beyond IPC standards - doesn't matter for our test fixture boards. Wouldn't be the first time that IPC needed to catch up though. The board house we're working with is Gorilla Circuits in San Jose, but I doubt that they're unique. Gary > -----Original Message----- > From: piclist-bounces@mit.edu > [mailto:piclist-bounces@mit.edu] On Behalf Of Vasile Surducan > Sent: Monday, September 29, 2008 12:18 PM > To: Microcontroller discussion list - Public. > Subject: Re: [EE] BGA board processes > > Who is manufacturing for you 0.15mm drill (I gues you're talking about > mechanical drill not laser drilled nor microvias) with 0.35mm outer > ring on 40mil thick board ? > Looks to me is not an IPC standard. > thx, > Vasile > > On 9/25/08, gacrowell@micron.com wrote: > > FWIW I've been using 0.2mm (8mil) drilled vias all the time > on 0.8 pitch > > BGA's - dogbone from the pads to the offset encroached-mask > vias. On > > 0.5 pitch I have used a filled 0.35mm pad via-in-pad, 0.15mm drill, > > plated flat & flush. Needs .05mm traces to get out. But > those are on > > 40mil thick boards. 6mil drills might be a problem on > thicker. And, I > > don't know the cost trade-off between microvias and filled > vias. Also, > > I am not using either of these methods on > production-quantity boards. > > But I can get them fabbed that way, routinely, no problem. > It's worth > > discussing with your fabricator/assembler as an alternative to > > microvias. > > > > Gary Crowell, CID+ > > Micron Technology -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist