Ernst,
In a previous employ, I used land and mask sizes as you mention, but
suggest allowing the vias size to be selected by the substrate vendor.  We
used a .0145 inch drill on many of these types.  The edge of the drilled
hole should not be closer to the part edge than .025 inch.
Alex

----------
> From: Wallisch, Ernst <[log in to unmask]>
> To: [log in to unmask]
> Subject: [TN] BGA land patterns
> Date: Monday, June 15, 1998 1:15 PM
>
> Fellow Technetters:
>
>         Could anyone recommend land pattern size, via size /
configuration,
> and mask size / configuration for a 357 full matrix 1.27 mm pitch PBGA?
>
>         I am thinking of using a "dog-bone" pad/via configuration with
> 0.025" pad diameter and 0.030" mask opening. Pad to via distance of
0.035"
> (centres).  Via pad diameter of 0.024" and 0.017" mask opening.
>
>         Is this reasonable?  Any recommendations?
>
> Thanks,
>
> Ernst Wallisch
> Manufacturing Engineering
> Computing Devices Canada
> [log in to unmask]
>
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