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May 1998

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Subject:
From:
Brad Kendall <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 29 May 1998 13:10:21 -0400
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text/plain (116 lines)
As far as getting the initial solder joint to work using this pad you may
be successful.  You are obviously aware that you will get solder wicking
into the via and possibly starving your solder joint, but with a PBGA with
eutectic balls you should be fine.  However, to rework the joint through a
12-16 mil via?  If you apply heat to the via it will pull the solder away
from the part because solder flows toward the heat source.  If you did
force enough solder through the via to heap up and touch the BGA, you have
not heated the BGA pad and thus you will not get a good solder joint to the
BGA.

I guess it is worth a try.  But the rework part is questionable.

Brad Kendall
Hella Electronics Corp.






[log in to unmask] on 05/29/98 08:04:26 AM

Please respond to [log in to unmask]; Please respond to
      [log in to unmask]

To:   [log in to unmask]
cc:    (bcc: Brad Kendall/Hella North America Inc.)
Subject:  Re: [TN] BGA Footprint




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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