I agree that sealing up, at least between reflow and cleaning, is the proper approach. Some might argue that if left in DI water long enough and enough circulation is available, that it will be cleaned acceptably. But it is usually better to not get the contaminants in there than try to clean them out.
Try kapton tape with silicone based adhesive and/or a liquid flexible peelable mask.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards
Sent: Thursday, June 17, 2010 4:11 PM
To: [log in to unmask]
Subject: Re: [TN] BGA AFTER 2 YEARS IN FIELD FAILED - Found word(s) list error in the Text body
To add to John's comment...
While working with chip manufacturers, we have found that sometimes the C4ed chip under the lid has decoupling caps that are soldered to the IC substrate with no-clean flux (as is the IC)...Additionally the metal lidded BGAs typically have a heat sink compound attaching the back of the die to the metal lid. Ideally you need to clean the area under the lid and seal not only to holes but the periphery of the lid...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roberts, Jon (SA-1)
Sent: Thursday, June 17, 2010 7:31 AM
To: [log in to unmask]
Subject: Re: [TN] BGA AFTER 2 YEARS IN FIELD FAILED - Found word(s) list error in the Text body
Thanks to all of you who responded to my question and I forward some of
those to our reliability engineer and hardware QA investigation the
field failure. They found your responses "very informative". Currently
we do not cover the holes with anything because the manufacture of the
BGA recommend we do not. Should we have? Thanks again, Jon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Wednesday, June 16, 2010 5:14 PM
To: [log in to unmask]
Subject: Re: [TN] BGA AFTER 2 YEARS IN FIELD FAILED
Those lids are made with holes in them, this is to stop the lid being
forced
off during a reflow cycle by the air under the lid expanding and
breaking
the bond line.
The corrosion you are seeing is likely to be due to ingress of water
during
a water wash after reflow. The boards should be allowed to fully cool to
room temp before entering the wash as if they are at a temperature above
the
wash water the cooling effect of the wash water will cool down the bga
and
the air under the BGA lid and could lead to water ingress as a result.
Best regards,
John Burke
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roberts, Jon (SA-1)
Sent: Wednesday, June 16, 2010 12:26 PM
To: [log in to unmask]
Subject: [TN] BGA AFTER 2 YEARS IN FIELD FAILED
Has anyone experience a BGA failure after about 2 years, where under the
heat sink of the actual part (metal lid) corrosion has occurred. The
lid does pop off, if you applied some pressure to examine, and what we
found was corrosion. There appears to be two weep holes on the inside
of the part. Unless you have seen it you are probably going to ask me
for some more information. I will try and obtain any pictures as long
it as it does not show the manufacture. Thanks, Jon
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