Subject: Re: [TN] BGA bridging...
> Steve - This may be a long shot, but you may also have a slight warping
> problem where the BGA is located. The slight bending might flatten the BGA
> spheres at the corners with the added weight of the heat sink. What may
make
> it more difficult to spot id that the warping may only occur at reflow
> temperatures, and then may flatten out when the board cools possibly due
to
> large power and/or ground plane areas. - Just a thought. Ed/
>
> Ed Valentine
> Electronics Manufacturing Solutions
> 8612 Mourning Dove Road, Raleigh, NC 27615
> Phone: (919) 270-5145, Fax: (919) 847-9971
> Email: [log in to unmask]
> Website: http://www.ems-consulting.com
>
> ----- Original Message -----
> From: d. terstegge <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Monday, July 24, 2000 3:58 AM
> Subject: Re: [TN] BGA bridging...
>
>
> Hi Steve,
>
> I can't explain why your bridges are all in the corners, but I do have an
> idea why some folks are more succesfull than others: are the pads
soldermask
> defined or not ? With soldemask defined pads you'll get a larger stand-off
> height but less "squishing" then with non soldermask defined pads (see
> Motorola's application note AN1231). Or maybe these boards have some kind
of
> undefined mixture of SMD and NSMD? Other factors of influence are size of
> the pads and the soldermask quality (how good does it prevent solder from
> flowing over the edge of the pad). With an unlucky combination of these
and
> your metal-plate BGA you have the ingredients for misery.
>
> Kind regards,
>
> Daan Terstegge
> Unclassified mail
> Personal Website: http://surf.to/smtinfo
>
> >>> "Stephen R. Gregory" <[log in to unmask]> 07/22 2:42 am >>>
> This is a subject that has come up before...it has to do with the TI BGA's
> with the metal heat sink incorporated into the top of the device. I have
> x-ray but it doesn't have enough power to penetrate the heatsink. We've
> recently aquired a Ersascope, I've been using that to inspect first
article
> placement to make sure that we're getting it on the pads...it's been fine.
> But we still have had a problem with bridging.
>
> Out of 50 or so boards, there's been maybe 5-6 boards that have bridged.
The
> bridges have all been in the corners. The balls all seem "squished"
because
> of the weight of the heatsink. I've been looking closely at everything,
> making sure the print is good, placement is accurate, and that my reflow
> profile is good too, but I still am seeing this bridging problem...
>
> The last time I brought this subject up, I did get conflicting
perspectives
> on this problem with the T.I. parts with the heatsinks in them. One
> experience shared was that they were having problems processing this part
> without bridging, and another perspective was from someone that said they
> built many, many boards with this part and didn't have a problem at all...
>
> I'm really trying hard to make sure that everything is as it's supposed to
> be, print definition and registration, placement accuracy, and reflow
> profile, but I'm still experiencing this bridging problem, 5 or 6 boards
out
> of 50 isn't good at all...now that I have a Ersascope (because I can't
> x-ray)
> it's painfully easy to see the bridges...and like I said, they're mostly
on
> the corners..
>
> Any ideas?
>
> -Steve Gregory-
>
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