[PCB_FORUM] Re: BGA Fanout / Filled vias

 

-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx 
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of Mark Salberg
Sent: Thursday, February 16, 2006 7:33 PM
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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