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----- Original Message -----
From: Morse, Carrie
To: [log in to unmask]
Sent: Tuesday, August 26, 2003 5:29 AM
Subject: Re: [TN] FW: BGA question

Dave,
Here are some quick answers to your questions based on some of the things we have seen:
a. This problem may be package and may be SMT process. It's possible that the component is warping or, has delaminated due to moisture cause this effect. The component may come in this way, or, the problem may be induced prior to SMT (moisture), or, due to excessive heat/improper profile. Also, it may be due to improper screening (too much/not enough/inconsistent paste deposition). May also be due to inconsistent BGA spheres from supplier.
b. Inspection prior to SMT may include a simple visual or, may be as in depth as using an automated optical inspection machine (i.e.: RVSI) to inspect sphere size and coplanarity. We do not do any visual inspection prior to placement.
c. I do not know if you can tell if a BGA has been re-balled. There are so many means of doing so. Some entail reballing with actual balls. Others entail reballing by screening paste. Depending on the method, my best guess is that the spheres would be shinier if done with just paste. But, I'm not sure.
d. I do not know if it is customary for distributors to reball. It is probably more likely for assembly houses to reball. But, there are some really good reballing capabilities out there, so, reballing may not be the root cause.
e. Don't know.
f. Black pad may be the root cause of poor contact. You may want to remove the BGA and take a look. Another root cause may be insufficient profile. Another root cause may be insufficient cleaning after reflow if using an OA paste.

When you X-ray, do some of the spheres look oblong? Do some look much larger than others? If so, what is the pattern of those that look larger?

-Carrie
-----Original Message-----
From: David Harman [mailto:[log in to unmask]]
Sent: Monday, August 25, 2003 5:05 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)
1.. 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?
2.. 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?

3.. Question: Is it easy to identify a BGA that has been re-balled and if so how?
4.. Is it customary for distributors to re-ball BGA
5.. What other test or inspections can be performed to capture BGA with open contacts?
6.. 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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Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
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