Hi All,
I would agree with Chris.
Clearly, the largest stresses occur on cooling. While it is possible with severe T-shock to cause significant BGA warpage, I would think to observe pad cratering at a later stage simply means that there already was an unobserved 'pad cratering' present.
Werner
-----Original Message-----
From: Chris Mahanna <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, 12 Jun 2009 1:25 pm
Subject: Re: [TN] Corner ball pad cratering
Genny and Bev,
Out of curiosity- are you sure that the cratering was not: induced thermally
(during reflow cool down), but did not manifest itself as a problem until other
mechanics came into play?
It just seems like that would be more common.
Chris
Chris Mahanna
Robisan Laboratory
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Friday, June 12, 2009 12:12 PM
To: [log in to unmask]
Subject: Re: [TN] Corner ball pad cratering
As always, Steve, you are a wealth of information. That article is perfect,
thank you. This seems to mirror what Amol said about doing a
1/4 of the length. This article said to do an L shaped bead 2-6 balls along
each corner side.
Here are some photos to post. Would you oblige?
BGA is 40mm per side. PCB is ~1 ft sq. A little bigger than what is found in
the typical blackberry, I think... Ball pitch is 1.27mm.
We believe the cause is mechanical, not thermal.
Thanks everyone.
Genny
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: June 12, 2009 6:35 AM
To: TechNet E-Mail Forum; Genny Gibbard
Subject: RE: [TN] Corner ball pad cratering
Morning Genny,
Since you said you were going to look at corner bonding, here is a really good
article (if you haven't seen it already) that Michael Kochanowski from Intel and
Brian Toleno from Henkel did about it:
http://www.trafalgar2.com/documents/Technical_Articles/6.09-kochanowski.
pdf
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Thursday, June 11, 2009 3:10 PM
To: [log in to unmask]
Subject: [TN] Corner ball pad cratering
Hello all,
If you have identified a BGA with corner ball pad cratering, what would be your
suggestions to correct this condition?
Our thoughts:
1. We plan to evaluate our handling processes to reduce/remove excessive
flex/strain occurring around this part 2. We plan to evaluate corner bonding or
underfilling for the BGA.
Which do you feel would be the best direction to go? Do you have other
suggestions?
Thanks in advance for all your help
Genny
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