RE: BGA Assembly

["John Haddy" <john.haddy@radiata.com>]

The holes in pads are fine if you're using solder paste attachment.
In prototype boards, however, it is often the case that the only
solder used is that already contained within the solder ball. This
latter situation is where you run into problems with holes in pads.

Cheers,

John Haddy
Radiata Communications
Sydney Australia

> -----Original Message-----
> From: Tom Stamp [mailto:toms@optiscan.com]
> Sent: Monday, 27 November 2000 9:38 AM
> To: pci-sig@znyx.com
> Subject: RE: BGA Assembly
>
>
> Holes in BGA pads are ok IF they are small enough - we have three 256 ball
> BGA packages mounted on one of our boards. Each BGA pad that
> requires a via
> has a 10 thou (thousandth of an inch) via in the middle of the
> pad. There is
> a very small degree of wicking that occurs, but the paste that is
> placed on
> the pads more than compensates for this. So far we have a 100%
> hit rate with
> this technique.
>
> I am not sure how big the via hole has to be before the wicking away of
> solder becomes significant.
>
> Our  BGA's are just placed onto the paste which holds them in place before
> they go to the reflow oven.
>
> Hope this is useful.
>
> regards,
>
> Tom Stamp
> Optiscan Imaging
> Melbourne Australia
>
...