Hi Richard,
We've been using BGAs for nearly 5 years now in similar applications
(Commercial Off-The-Shelf defense and high-end commercial) with success. We
use a variety of PBGA, CBGA, and TBGA devices.
We don't do any ICT on our boards....yet. We've been using functional
tests and boundary scans. From what I've heard, ICT is feasible, but the
fixturing has to be designed properly to avoid placing a large concentrated
force directly beneath the device. I've heard stories of people breaking
solder joints with improper designs.
We really don't inspect our BGA solder joints, other than a periodic scan
of the outer row. If your assembly process is truly controlled and you
start out with good quality PWBs, you really shouldn't need any additional
visual inspection. X-ray is nice for process development and to check out
questionable connections, but in my opinion it shouldn't be implemented
as an in-line process.
Repairs are done fairly easily, but it does take some process development
time and a decent quality repair station. Proper design improves rework
success rates. Items such as device placement, rework clearance, board
stackup, dielectric material composition, and via size are some of the
factors that can influence your success.
Good luck!
Greg Bartlett
Mercury Computer Systems, Inc
Chelmsford, MA
[log in to unmask]
-----
Blanchet,Richard wrote:
>Hello,
>
>As we hear more and more about BGAs, my perception is that there's some
>issues to be improved. From a military/high-end commercial application
stand
>point, I have the following questions:
>
>1- Do people put a lot of vias under BGAs to perform ICT or do they just
>perform functional tests ?
>
>2- How do you guys inspect your BGA solder joints once on the card ?
Are
>X-ray practical and reliable in a production mode ? What about Scanning
>Acoustic Microscopy (like a system from Sonoscan) ?
>
>3- And what about repairs ? Are they easily done with a high success
rate ?
>
>I'm trying to learn anything I can about BGAs, so any info is welcome,
even
>the most basic ones.
>
>You can reach me off-line at [log in to unmask]
>
>Thank you.
>
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