Hi David

The first question is:  Is the BGA package a CBGA with high melting solder
balls.  If yes I can offer a stencil solution.  You can do a step up stencil
to print higher solder paste height in the region of the CBGA.  A typical
CBGA step up stencil will have a 5 mils thick for the normal SMD's  and 8
mil thick for the CBGA region.

Regards,


William E. Coleman
Vice President - Technology
Photo Stencil An ISO 9001 Registered Company
4725 Centennial Blvd.
Colorado Springs, CO 80919
Phone # 719-535-8528
Fax #      719-599-4334
Cell #      719-331-2433
email:      [log in to unmask] <mailto:[log in to unmask]>

        ----------
        From:  David Harman [SMTP:[log in to unmask]]
        Sent:  Monday, August 25, 2003 3:05 PM
        To:  [log in to unmask]
        Subject:  [TN] FW: BGA question




        Hello,

        I have seen an increase in problems with electrical testing and it
has been traced to BGAs.
        I have a few questions regarding BGA and processes.  I am trying to
understand if the problem is process related (SMT) or do I have a vendor
issue with BGA.

1.      Open contact between the ball and the package.  This is verified by
pressing onto the package while testing.  Pressing the package down causes
the board to pass.
2.      Visual inspection reveals the ball not touching the PCBA. (You may
have a ball in  the middle not touching and the balls on each side are)
a.      Question:  With on ball in the middle not touching and the balls
next to it are, is this indicative to SMT process issues or BGA package
issues?
b.      Question:  What type of inspection can be performed on BGAs prior to
SMT to capture Bad BGA?
                                                                       i.
Is the industry standard 100% or Sample inspection for out going quality
inspection?
c.      Question: Is it easy to identify a BGA that has been re-balled and
if so how?
d.      Is it customary for distributors to re-ball BGA
e.      What other test or inspections can be performed to capture BGA with
open contacts?
f.      As indicated above, pressing down the package causes the board to
pass, how do I detect micro cracking of the solder joint? And what would
cause micro cracking?

        I am lost at this point and am looking for additional suggestions
and assistance in educating me on BGA.

        David Harman

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