This is a good compromise that doesn't have reliability risks. > [Original Message] > From: Robert Szumowicz <robert.szumowicz@xxxxxxxxxx> > To: <si-list@xxxxxxxxxxxxx> > Date: 1/21/2010 1:30:56 AM > Subject: [SI-LIST] Re: BGA Breakout. > > I have designed boards where 2 traces are routed between 1mm BGA vias > without going for very thin traces/clearances or small drills (for me it > meant 0.125mm trace/clearance and 0.25mm/0.5mm vias). I used a trick > with a non regular via pattern what allowed routing two traces between > every second routing channel (not two traces in-between all vias). As a > result ~30% more traces can escape a BGA per an internal signal layer. > > Non regular via patter which I invented meant that vias were not centred > between four BGA pads but rather placed with an varying offset to build > an extra horizontal and vertical routing channels. > > Robert > > > Lee Ritchey wrote: > > Sol, > > I have attached an analysis I did of clearances, tolerances and reliability > > requirements when routing PCBs. Hope this makes it clear what the risks > > are when routing 2 between on 1 mm pitch BGAs. > > > > Lee > > > > > > > >> [Original Message] > >> From: Sol Tatlow <Sol.Tatlow@xxxxxxxxxxxxxxxxxxxx> > >> To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx> > >> Cc: Surita Chandani <surita.chandani@xxxxxxxxx>; <si-list@xxxxxxxxxxxxx> > >> Date: 1/18/2010 1:39:42 PM > >> Subject: [SI-LIST] Re: BGA Breakout. > >> > >> With all respect, Lee, I beg to differ (at least a little bit ;)!): I > >> personally have routed many boards with 1mm BGAs of over 1700 balls > >> (with 1200+ signals, ALL 1700+ balls connected), and, depending upon how > >> these signals are to be routed (which is, admittedly, a fairly big > >> 'depending'), 18 layers can be (and usually is) enough already. > >> Since roughly 2001/2002, I have had such BGAs on boards where I > >> generally have around 18-20 layers in <2,0mm (78 mil) together with > >> 0,5mm (20mil) via pads (the drill doesn't really interest me, in > >> general, just the reliability of the results!) - this leaves 0,1mm (4 > >> mil) track and gap (roughly speaking) for 2 tracks between vias... and > >> the '2 traces between the vias' is the key to holding down board > >> thickness and layer count. This has worked for me even up to 26 layers > >> and ~2,5mm board thickness. > >> > >> With (in the meantime) 30,000-60,000 component pins/balls per board, and > >> a resulting via count of only somewhat less than the pin count, it is > >> still possible to have these boards manufactured in series quantities at > >> affordable prices from a comfortable number of manufacturers around the > >> world; the results, in some cases, have been in operation since 2002 and > >> we have very good reliability results across the board (I sweated back > >> then a little, but in the meantime, it's 100% normal... I sleep easily > >> at night now :D!!). > >> > >> One typical problem occurs, of course, in the planning phase: if you > >> assume too many power/gnd _pairs_ (as opposed to _individual_ gnd or pwr > >> layers), you are automatically forced to have a thicker board, where it > >> may no longer be possible to have small enough vias to route 2 tracks > >> between the vias; this is a downward spiral, of course, forcing the > >> number of signal layers up, and then again, the pwr/gnd count. > >> > >> I have, up until now, avoided having exclusively pwr/gnd power > >> sandwiches (however nice an idea these are) for exactly this reason; > >> instead, alternating (in general) GND-SIG-SIG-PWR-SIG-SIG- etc. coupled > >> with good routing strategies has given me very good results - there are > >> many proponents for always using pwr/gnd 'sandwich' pairs, but this is, > >> quite simply, not always necessary). > >> > >> Not that I want to start a fight, Lee, just wanted to voice my > >> experience/opinion :D!! > >> > >> Regards, > >> Sol > >> > >> P.S. What 'affordable' means, depends, of course, on the end product ;), > >> but usually, the 0,1mm track and gap means reduced costs in comparison > >> to thicker boards with more coarse structures and higher layer count... > >> in some cases, you might even go to slightly bigger via pads and LESS > >> than 0,1mm track and gap, to reduce costs... this depends upon the > >> manufacturer, thickness of the board, availability of specific > >> materials, etc. > >> > >> Lee Ritchey schrieb: > >> > >>> Surita, > >>> > >>> I believe this kind of routing is possible with very thin PCBs with very > >>> small holes such as in laptop motherboards. However, with very large > >>> > > BGAs > > > >>> such as yours, it is unlikely that it w ill route on a thin PCB. My > >>> experience with BGAs of your size is that a 22-26 layer PCB will be > >>> > > needed > > > >>> and that will likely be 100+ mils thick resulting in the need for 12 mil > >>> drills. > >>> > >>> Lee > >>> > >>> > >>> > >>> > >>>> [Original Message] > >>>> From: Surita Chandani <surita.chandani@xxxxxxxxx> > >>>> To: <si-list@xxxxxxxxxxxxx> > >>>> Date: 1/15/2010 11:43:41 AM > >>>> Subject: [SI-LIST] Re: BGA Breakout. > >>>> > >>>> Thanks Lee for your comments. > >>>> The suggestions for two traces between Vias comes directly from Intel > >>>> > >>>> > >>> document, also this document is from 2002. Their pitch is 1.067 mm. The > >>> document itself is available at: > >>> > >>> > >>>> http://download.intel.com/support/processors/xeon/sb/25039702.pdf > >>>> ; Page 43. > >>>> > >>>> > >>>> > >>>> --- On Fri, 1/15/10, Lee Ritchey <leeritchey@xxxxxxxxxxxxx> wrote: > >>>> Surita, > >>>> > >>>> You are right, you cannot successfully route two traces between pins > >>>> > > on a > > > >>>> > >>>> > >>> 1 > >>> > >>> > >>>> mm pitch BGA without significant risk of shorts. > >>>> > >>>> If you drill a 12 mil hole, your antipad does not have to be larger > >>>> > > than > > > >>>> > >>>> > >>> 32 > >>> > >>> > >>>> mils. This leaves you with a 7.37 mil web, which works nicely for a > >>>> > >>>> > >>> single > >>> > >>> > >>>> trace, but not two traces.. Your surface or signal layer pads can be > >>>> > > 24 > > > >>>> mils for 1 mil annular ring and 26 mils for 2 mil annular ring. > >>>> > >>>> There will only be pads on inner layers where traces connect. > >>>> > >>>> By the way, what vendor told you to route 2 traces between pins? > >>>> > >>>> Lee Ritchey > >>>> > >>>> > >>>> > >>>> > >>>> > >>>>> [Original Message] > >>>>> From: Surita Chandani <surita.chandani@xxxxxxxxx> > >>>>> To: <si-list@xxxxxxxxxxxxx> > >>>>> Date: 1/14/2010 9:19:08 AM > >>>>> Subject: [SI-LIST] BGA Breakout. > >>>>> > >>>>> > >>>>> > >>>>> > >>>>> Hello Gurus; > >>>>> > >>>>> > >>>>> > >>>>> I am doing some preliminary calculations on the breakout of > >>>>> a 1,400+ Ball , BGA. Roughly one half of them are signal > >>>>> connections which would need traces running up to them. The vendor > >>>>> > >>>>> > >>> claims > >>> > >>> > >>>> you > >>>> > >>>> > >>>>> can run two traces between Vias, my calculations are not adding up, I > >>>>> > >>>>> > >>>> have a > >>>> > >>>> > >>>>> few questions. > >>>>> > >>>>> > >>>>> > >>>>> 1. Generally, do the Vias have a pad even on the signal > >>>>> layer it is not connecting to?. > >>>>> > >>>>> > >>>>> > >>>>> 2. Do the Vias have a larger pad on the inner layers? > >>>>> > >>>>> > >>>>> > >>>>> 3. With a Ball pitch > >>>>> of 1 mm (39 mils.) and an Antipad of 35 mils, there is hardly any room > >>>>> > >>>>> > >>>> for one > >>>> > >>>> > >>>>> trace between Vias, what am I doing wrong? > >>>>> > >>>>> > >>>>> > >>>>> Thanks, > >>>>> > >>>>> > >>>>> > >>>>> Surita Chandani > >>>>> > >>>>> > >>>>> > >>>>> > >>>>> > >>>>> ------------------------------------------------------------------ > >>>>> To unsubscribe from si-list: > >>>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >>>>> > >>>>> or to administer your membership from a web page, go to: > >>>>> //www.freelists.org/webpage/si-list > >>>>> > >>>>> For help: > >>>>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >>>>> > >>>>> > >>>>> List technical documents are available at: > >>>>> http://www.si-list.net > >>>>> > >>>>> List archives are viewable at: > >>>>> //www.freelists.org/archives/si-list > >>>>> > >>>>> Old (prior to June 6, 2001) list archives are viewable at: > >>>>> http://www.qsl.net/wb6tpu > >>>>> > >>>>> > >>>>> > >>>> > >>>> ------------------------------------------------------------------ > >>>> To unsubscribe from si-list: > >>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >>>> > >>>> or to administer your membership from a web page, go to: > >>>> //www.freelists.org/webpage/si-list > >>>> > >>>> For help: > >>>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >>>> > >>>> > >>>> List technical documents are available at: > >>>> http://www.si-list.net > >>>> > >>>> List archives are viewable at: > >>>> //www.freelists.org/archives/si-list > >>>> > >>>> Old (prior to June 6, 2001) list archives are viewable at: > >>>> http://www.qsl.net/wb6tpu > >>>> > >>>> > >>>> > >>> ------------------------------------------------------------------ > >>> To unsubscribe from si-list: > >>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >>> > >>> or to administer your membership from a web page, go to: > >>> //www.freelists.org/webpage/si-list > >>> > >>> For help: > >>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >>> > >>> > >>> List technical documents are available at: > >>> http://www.si-list.net > >>> > >>> List archives are viewable at: > >>> //www.freelists.org/archives/si-list > >>> > >>> Old (prior to June 6, 2001) list archives are viewable at: > >>> http://www.qsl.net/wb6tpu > >>> > >>> > >>> > >>> > >> -- > >> ________________________________________ > >> > >> Sol Tatlow, M. Eng. (Oxon) > >> Product Developer > >> > >> Pro Design Electronic GmbH > >> Albert-Mayer-Str. 16 > >> D-83052 Bruckmuehl > >> Phone: +49 (0) 8062/808-302 > >> PCFax: +49 (0) 8062/808-2302 > >> sol.tatlow@xxxxxxxxxxxxxxxxxxxx > >> www.prodesign-europe.com > >> ________________________________________ > >> > >> Vertretungsberechtigte Geschaeftsfuehrer: > >> Helmut Mahr, Ulrike Angersbach, Stephan Roeslmair, Dieter Lessenich > >> > >> Registergericht: Amtsgericht Traunstein Registernummer: HRB 13 002 > >> > >> > >> > >> ------------------------------------------------------------------ > >> To unsubscribe from si-list: > >> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >> > >> or to administer your membership from a web page, go to: > >> //www.freelists.org/webpage/si-list > >> > >> For help: > >> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >> > >> > >> List technical documents are available at: > >> http://www.si-list.net > >> > >> List archives are viewable at: > >> //www.freelists.org/archives/si-list > >> > >> Old (prior to June 6, 2001) list archives are viewable at: > >> http://www.qsl.net/wb6tpu > >> > >> > > > > > > > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > > or to administer your membership from a web page, go to: > > //www.freelists.org/webpage/si-list > > > > For help: > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > > > > List technical documents are available at: > > http://www.si-list.net > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > > > > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List technical documents are available at: > http://www.si-list.net > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu