[PCB_FORUM] Re: BGA Fanout / Filled vias
- From: <george.h.patrick@xxxxxxxxxxxxxx>
- To: <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Thu, 16 Feb 2006 08:42:18 -0800
Mark:
We typically do a secondary soldermask "via cap" on fine pitch BGA vias
so there is NO copper showing on the via. The secondary soldermasking
operation typically will not have as much "slump" and does not run as
far into the via holes as a single soldermask that is tenting the vias.
Your mileage may vary, as others have said check with your board fab and
assembler to verify what they really want.
--
George Patrick
Tektronix, Inc.
Central Engineering, Engineering Design Services
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
* 503-627-5272 (voice) * 503-627-5587 (fax)
<http://www.tektronix.com/>
http://www.tektronix.com <http://www.pcb-designer.com/>
http://www.pcb-designer.com
"Off-Grid and Proud of it!"
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Meier
Sent: Thursday, February 16, 2006 07:15
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: BGA Fanout / Filled vias
Mark,
I would definitely ask my CM. If he says yes then I would do a via plug
and the entire via would be covered with mask. I don't know how much
soldermask dam you have if it's at least 5 mils you may be OK. Be sure
to specify your via encroahment and or plugging etc in your pcb notes or
requirement doc to your fabricator.
One other thing if your pad is 18 mil dia and your soldermask opening is
14 mil dia you only have a 2 mil encroachment. The requirement I have is
for a min of 3 mil encroachment. In my scenario a min soldermask opening
diameter would be 12 mil dia. So also check if the 2 mil is OK
regards,
Gerry
Gerry Meier
Sr. PCB Designer
Freedom CAD Services, Inc.
Voice: (603) 864-1300 x1350
AL Voice: (256) 417-6944
Email: gerry.meier@xxxxxxxxxxxxxx
Visit us at www.freedomcad.com <http://www.freedomcad.com/>
_____
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Mark Salberg
Sent: Thursday, February 16, 2006 8:53 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: BGA Fanout / Filled vias
Yes Gerry,
That is what I consider "copper to copper".
On my 1mm BGA, I have 11.8mil. (18mil BGA pad, 18mil via encroached to
14mil)
Now, on my .75mm BGA using the same via: 6.5mil ball pad to encroached
via
Should this drive me to filling or tenting the vias?
Thanks for all the great responses!
Mark
Gerry Meier wrote:
Mark,
I am not sure what you are asking "is this atrue statement' ?
If the soldermask is encroached on the via the copper to copper is the
bga pad to the encroachment area.
There should also be a min 5 mil soldermask dam.
Gerry Meier
Sr. PCB Designer
Freedom CAD Services, Inc.
Voice: (603) 864-1300 x1350
AL Voice: (256) 417-6944
Email: gerry.meier@xxxxxxxxxxxxxx
Visit us at www.freedomcad.com <http://www.freedomcad.com/>
_____
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Mark Salberg
Sent: Thursday, February 16, 2006 8:03 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: BGA Fanout / Filled vias
On my 1mm BGA, I have an 18mil BGA pad and (18mil via pad, encroached to
14mil with a 8mil hole).
BGA pad (not mask) to via encroachment = 11.8mil.
However, the assembler specified "copper to copper" which would be
"airgap" pad to via measurement.
Copper to copper / airgap = 9.8mil.
The via encroachment to ball copper pad (not larger mask) sounds like
what they should spec.
Is this a correct statement?
Looks like he may be in the "Ball-park" with the filled vias for .8mm
and below pitch BGA's.
On my .75mm BGA I have: 6.5mil ball pad to encroached via.
airgap = 4.5mil. (same for mask to encroached mask on via) = 4.5mil.
Our thought was that if there is a soldermask dam, then there should be
no paste wicking in the via.
But with 10mil min airgap, they must be filled and possibly tented.
When you epoxy fill the vias, do you also tent the vias with mask?
Gerry Meier wrote:
Mark,
If you encroach your vias you would measure from pin to encroachment
area. This should give you enough Pin to Via/Encroachment (copper to
copper) clearance for your Assembler. The formula I have used is for a
min 3 mil encroachment is Formula: Pad size diameter - Soldermask
opening diameter > or = to 6 mils. But Soldermask opening diameter is
not < the drill size (nominal hole size + 3 mils). Sample: 18 mil pad -
11 mil soldermask opening = 7 mil + 9.8 = 16.8 pad to via/encroachment
(copper to copper).
This may also work for the .75mm BGA however some Assembler's or CM's
require BGA's with an .8mm pitch or smaller have their vies plugged
under the BGA's.
Hope this helps,
Gerry
Gerry Meier
Sr. PCB Designer
Freedom CAD Services, Inc.
Voice: (603) 864-1300 x1350
AL Voice: (256) 417-6944
Email: gerry.meier@xxxxxxxxxxxxxx
Visit us at www.freedomcad.com
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Mark Salberg
Sent: Thursday, February 16, 2006 3:25 AM
To: Cadence User Group
Subject: [PCB_FORUM] BGA Fanout / Filled vias
Hello all,
What BGA Ball pad to via clearance is needed for BGA fanout?
Our Assembly house is telling us that we need 10 mil copper to copper
(15mil preferred).
On 1mm BGA's using an 18mil via with 8mil drill gets us 9.8mil via to
pad.
On our .75mm BGA this via gets us 4mil via to pad. Which also breaks the
soldermask dam.
Is epoxy filled and tented vias our best or only option at this point?
Thanks for any input.
Mark
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