Jorge,

first of all, are you placing the BGAs on printed pads, that is on paste? If
so, in case the vias are very close to the pads, you may end up with shorts
between pads and vias. You could try to place the 324 pins BGA on flux only,
preferably on a rework machine. You also may want to check the IPC
specifications concerning the distance between via and pads.

Second, running the BGA on a steel plate could change the thermal profile in
the joint area so things may happen in a different manner with the real PCB,
so the experiment may not be relevant.

Then, if humidity would be present in the BGA, before the splashing you
would have a delamination of the component.

What I would suggest as a solution for the solder through via problem is
rather having the vias covered by solder mask than covering with tape. If
you have the PCBs manufactured this way and the vias are covered from the
component side, you would also be sure there are no shorts between vias and
the balls of the BGA.

Good luck,       Ioan
> -----Original Message-----
> From: Jorge Engenharia [SMTP:[log in to unmask]]
> Sent: Tuesday, March 23, 1999 8:31 AM
> To:   [log in to unmask]
> Subject:      [TN] Bga solder ball failure.
>
>  Hi technos,
>
>    We run PC boards with chipset INTEL 82371EB 324 pins and 82443BX 492
> pins both BGA package.
>    First we had bad performance due solder that comes under BGA through
> the via holes located under the component during solder wave process. We
> fixed that using adesive tape to cover the via holes during solder wave.
>    After using the tape we still had solder short only at the small BGA
> ( 324 pins ). We bake some boards and components to verify if humidity
> were causing some solder balls to splash away due high vapor formation
> during reflow, but the problem still happened.
>    We run some BGA parts ( 324 pins ) above one stainless steel plate
> inside the oven and could observe that some balls drop off from the
> package and splash under the component.
>    The 492 pins BGA came from KOREA and the 324 pins BGA came from
> PHILIPINES.
>
>    My question:
>    Why I had problem only at 324 pin BGA if both BGA are subject at the
> same process enviroment ?
>    Anybody had already problem with this BGA from PHILIPINES ?
>    There is one way to avoid this problem ?
>
>    Any help will be very apreciated.
>
> Thanks
>
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