Richard and all,
I'm sorry to hear that they have placed a minimum tolerance on the
pitch. The appropriate methodology would have been a radius or diameter
of true position for the ball location. A minimum tolerance leaves the
door open for an unlimited maximum dimension, as was stated by another
post. Years ago, the IPC land pattern committee saw the component
industry go rampant with their smt dimensioning practice, to the extent
that we could not recommend a suitable land pattern, without tailoring
the component dimensions to suit our needs. We were able to influence
them to correct the dimensions, for a period of time, but I notice that
they have gone rampant once again.
Oh well, some days peanuts and some days shells.
Gary
Stadem, Richard D. wrote:
> While doing the laser ball attachment on other BGAs, the company that did it noted that there was up to a +- 3 mil deviation in the pitch in earlier revisions of various BGA substrate drawings, so we asked for a tighter spec for the center-to-center distance from the BGA substrate fabricators because the laser is very precise and it is faster when the machine does not have to autocorrect frequently. So instead of a standard 1mm [.040"] with no tolerance (as an example), it became 1mm [.040"] minimum to ensure no two pads were less than that from each other, center-to-center. It should not affect your stencil file, in fact it should help ensure your stencil artwork will be properly aligned by ensuring less of a stackup variation in the artwork, the pad locations on the BGA substrate, and the pad locations on the PWB substrate. This was carried over to other BGA fabricators as well. If you check other BGA drawings you will note the same wording. This is then flowed down to t
he PWB design requirements, provided the CID diligently notes the artwork requirements when specifying the BGA artwork on his/her PWB.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of bob wettermann
> Sent: Tuesday, May 19, 2009 7:44 AM
> To: [log in to unmask]
> Subject: [TN] Strange Tolerances on BGA Pitch-How to Accomodate the Stencil File?
>
> In working with some newer Intel BGA datasheets we
> Dear Technetters:
>
> In working with some newer Intel BGA datasheets we are noting tht the pitch is indicated as a minimum dimension. For instance on a current job the spec indicates "Min 1mm". Has anyone else seen this trend? Explanations?
>
> How are you acoomodating your stencil files?
>
> Regards
> Bob Wettermann
> PH 847-767-5745
>
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