Jim,

We do just the opposite of what Steve G. has described.  We tent the
primary side of our
boards to try and keep "stuff" from getting trapped under BGAs.  I'm not
sure if either
method is better then the other, but from my perspective, having tenting on
the secondary
side presented more of a risk then the primary side as far as providing a
place for getting
"stuff" trapped  under the BGA was concerned.
I suspect Steve has his perspective as well, and I have no data to say one way
or the other, but we tent the primary side, to give you another datapoint.

Regards......DT




At 06:28 PM 3/23/99 EST, you wrote:
>In a message dated 3/23/99 2:52:22 PM Pacific Standard Time,
>[log in to unmask] writes:
>
>> Are you guys building cards with partially closed VIA's?  What about
>>  >contamination getting trapped in the VIA?  Is this a valid concern?
>>  >
>>  >Appreciate any comments.
>>  >
>>  >Jim Kittel
>
>Hi Jim,
>
>    If your board is going to be waved and the vias are open on the side
>exposed to the wave, then you do have some concern. Flux could get trapped
>inside the vias by solder should there be surface area enough for the solder
>to wet to.
>
>    You may also see little solder bubbles from where the solder has tried to
>close the via, but then the flux volatiles outgassed as the solder was going
>solid forming these little bubbles that are attached to the via...they'll
look
>almost like a bunch of solderballs. If one side is going to have the vias
>open, it should be the side away from the wave.
>
>-Steve Gregory-
>
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