Hi Larry,

I just got through x-ray inspecting some test boards where the FBGA's where
specifically mirrored for solder joint studies.  Inspection was not a
problem both because of parallax and the slight misalignment of the source
from being perfectly perpendicular to the board.  This all means that if I
try really hard, the planets come into perfect alignment, and I shake the
chicken feet over the x-ray, I can get one joint (and only one joint) to be
perfectly lined up over the other.  All other joints are naturally offset
from each other.

The joints will be overlap slightly, and will require some sleuthing to
determine which side a defect belongs to.  Further, the overlap of the
joints might cause problems for automated x-ray inspection.

Kind Regards

Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]


> -----Original Message-----
> From: Larry Koens [SMTP:[log in to unmask]]
> Sent: Wednesday, October 17, 2001 10:33 AM
> To:   [log in to unmask]
> Subject:      [TN] double sided BGAs
>
> 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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