Peter,

Voiding is worse with a poorly formed or damaged via/micro-via. I have seen
some crushed vias where the side wall buckle produce some stupendous
voiding. Voiding happens worse with vias that are narrower at the top
surface of the board because solder has a more difficlt time filling the
hole at solder printing. Remember most no-clean solder is 50% flux by volume
and the volatiles need to do their thing and leave. Some think that trapped
volatiles and flux when they cannot leave become viscous clumps in the via
hole and then when the eutechtic BGA ball collapses the clump moves up into
the ball. This gets worse with a site that goes through a double reflow
process. One suggestion is to fill and plate over these vias so this cannot
happen. Another suggestion is to offset the via from the center to about 2
mils from the pad edge so the clumping happens outside the component ball.

Regards,

Dorothy Lush

-----Original Message-----
From: Peter Lee [mailto:[log in to unmask]]
Sent: Tuesday, December 18, 2001 11:20 PM
To: [log in to unmask]
Subject: [TN] Voiding on BGA with uVias


Hello,

We have encountered major BGA voiding issue. The void is sometimes up to
70% of the joint. Under X-ray inspection we found a blind 0.006" uVia,
0.01" deep under each void. Other BGA solder joint on board w/o uVias do
not have any void problems. Board is gold over Nickel finish and 2mm
thick.

Things we tried:
Reflow profile - WS/ no-clean paste, longer soak
Washing/ baking the bare PCB
Reworked by cleaning the uVias/pads and filled with solder but still
seeing void

Has anyone seen this before? Micro-sectioning clearly showed the void
originated from the uVia. We are trying to convince the board house that
it's not our process.


Rgds,
Peter



_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com

----------------------------------------------------------------------------
-----
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
----------------------------------------------------------------------------
-----