Richard,
The interposer on the chip side is basically a PWB boards, small but
still boards. Many are manufactured out of BT epoxy, flex, etc. Be that
as it may, a standard dimensioning system still apples. Geometric
dimensioning, Y14.5, has been around for longer than I can remember, and
the concepts are solid. Mismatching dimensioning systems builds
tolerances, instead of reducing tolerances. I still remain disappointed.
I guess today must be the shell day :-)
Gary
Stadem, Richard D. wrote:
> We were talking about the pad dimensioning on the BGA substrate, prior
> to ball attachment.
>
> -----Original Message-----
> From: Gary Ferrari [mailto:[log in to unmask]]
> Sent: Wednesday, May 20, 2009 4:49 PM
> To: TechNet E-Mail Forum; Stadem, Richard D.
> Subject: Re: [TN] Strange Tolerances on BGA Pitch-How to Accomodate the
> Stencil File?
>
> 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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