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Subject:	Re: double sided BGAs
From:	Jason Gregory <[log in to unmask]>
Reply To:	TechNet E-Mail Forum.
Date:	Wed, 17 Oct 2001 12:04:21 -0500
Content-Type:	text/plain
Parts/Attachments:	text/plain (55 lines)

Larry,
X-ray will, indeed, be a problem if the bottom BGA's are directly underneath the top BGA's. You will have heavy shading and opens could be virtually undetectable. I program an Agilent 5DX here and even with the superior 3D operation of the machine, opens are very difficult to detect, even on BGA's with nothing underneath. Shorts and misalignment issues should pose no inspection problem, though. Hope this helps.

Jason Gregory
Software Specialist - NPI Group
SCI Systems/Plant 2
13000 S. Memorial Pkwy.
Huntsville, AL. 35803
(256) 882-4107 x3728
[log in to unmask]

>>> [log in to unmask] 10/17/01 11:32AM >>>
Dear TechNet,
My company has been asked to bid on assembling a board that would have
two BGAs on the topside and two more BGAs mirrored on the bottomside.
That is, they will be directly across from each other on both sides. I
never done them on both sides. So far, everything that I have done has
been on one side only. Has anyone done them on both sides before?
I am figuring xray will be a problem as after the second side is
placed, because the pads/balls will mirror each other on both sides.
Would I be able to tell the difference between the two BGA connections?
Suggestions?
Will I need to epoxy the first side BGAs so they would not drop off
during my second reflow? Wouldn't I need to epoxy them after first
reflow so that the balls could collapse?
Thanks,
Larry Koens
SMT Manufacturing Engineer
E.I. Microcircuits
Mankato, MN

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