Hi jeremy,
I believe that Motorola used your suggested approach about 3 years ago on their
Bravo pagers.... it had a 256 I/O BGA device in it where they implemented
through holes as the pads for thier BGA device... however, pagers use very thin
boards and I believe that theri motivation was for inspection rather than
rework....
Marcelo
-----Original Message-----
From: Jeremy POLLARD [SMTP:[log in to unmask]]
Sent: Saturday, May 30, 1998 11:15 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Footprint
Many thanks for your reply, perhaps some futher information would be
helpfull.
Rework on this board is difficult due to the density, There are over
1600 (Total) components over both sides of a PCB measuring 220mm x 235mm. To
rework a single BGA ie remove and replace, we need to remove several other
devices and R,s and C,s to get rework equipment, masks etc into the area. Our
initial Prototype run was x-rayed to verify the solder joints but costs are
prohibitive to do this on a production basis
in Australia. As a result we need a better method of reworking failed
ball joints during
production.( or at least have a method that will work should it be
needed).
The key to the suggested method is to allow sufficient volume of solder
paste
that allows for the volume required by the hole in the land. During
reflow, surface tension 'should' impose a self limiting factor on the flow of
solder away from the ball joint into the hole.
Iam attempting to see if this has been tried by anyone else, if not we
may just be the first.
Regards
Jeremy Pollard
Production Engineer
Quiktrak Technologies Pty Ltd
[log in to unmask]
>>> Bev Christian <[log in to unmask]> 29/05/98 21:34:26 >>>
Jeremy,
My guess is you will still get some solder wicking down the hole.
Anyone
else try this yet? But I don't understand why you can't rework your
BGAs,
not that you should have to rework many anyway. AirVac, SRT,
Conceptronics
and others make very nice equipment for BGA rework.
regards,
Bev Christian
> ----------
> From: Jeremy POLLARD[SMTP:[log in to unmask]]
> Sent: Friday, May 29, 1998 1:00 AM
> To: [log in to unmask]
> Subject: [TN] BGA Footprint
>
> Hello,
> am hoping that someone out there has experience with BGA footprints.
>
> We have completed Rev 1 of a double Eurocard PCB, 10 Layers with 7 x
356
> pin BGA devices on board. While everything went well with this run and
we
> had no problems with ball connections, it is impossible to perform any
> rework or modifications if required.
> The footprint was the recommended pad with track out to a via or "
Dog
> bone". On the next revision we would like to do the following,
Elimnate
> the "dogbone", place a through hole in the actual pad for the ball and
> adjust the solder paste stencil so that the volume of paste deposited
> allows for the hole through the board.
> I would use a hole size of 0.3mm (12mil) to 0.4mm(16mil) certainly no
> larger.
> This approach should enable us to rework dodgy joints from the solder
side
> of the PCB
> It will also allow us access possibly to test the pins from the BGA.
>
> Has anyone done this ?
> Was it succesfull in a production environment ?
>
> Many thanks foryour help.
>
> regards
>
> jeremy
>
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