[SI-LIST] Re: BGA Breakout.
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
- Date: Wed, 20 Jan 2010 13:35:04 -0800
Scott,
On the other side of the equation, I could say a similar thing about your
knowledge of very high speed signaling. Same with testing. I tend to keep
your papers as good references and use some of them in classes.
Keep up the good work.
See you at DesignCon.
Lee
----- Original Message -----
From: Scott McMorrow
To: leeritchey@xxxxxxxxxxxxx
Cc: Sol Tatlow; Surita Chandani; si-list@xxxxxxxxxxxxx
Sent: 1/20/2010 1:14:12 PM
Subject: Re: [SI-LIST] Re: BGA Breakout.
Lee
As you know, we don't always agree. But when it comes to PCB manufacturing
process and reliability, I'm sure you've forgotten more than I'll ever know.
best regards,
Scott
Lee Ritchey wrote:
Gosh! Scott, what a nice thing to say! Some claim I started making PCBs out of
stone!
Lee
----- Original Message -----
From: Scott McMorrow
To: Lee Ritchey
Cc: Sol Tatlow; Surita Chandani; si-list@xxxxxxxxxxxxx
Sent: 1/20/2010 10:53:36 AM
Subject: Re: [SI-LIST] Re: BGA Breakout.
In my opinion, this is one area where everyone should listen to Lee. He's been
creating successful, highly manufacturable designs for at least a few years.
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
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Scott McMorrow
Teraspeed Consulting Group LLC
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(401) 284-1827 Business
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--
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
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