[PCB_FORUM] Re: BGA Fanout / Filled vias

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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