[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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