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 >> >> --------------------------------------------------- >> Technet Mail List provided as a service by IPC using LISTSERV 15.0 >> To unsubscribe, send a message to [log in to unmask] with following text > in >> the BODY (NOT the subject field): SIGNOFF Technet >> To temporarily halt or (re-start) delivery of Technet send e-mail to > [log in to unmask]: SET Technet NOMAIL or (MAIL) >> To receive ONE mailing per day of all the posts: send e-mail to > [log in to unmask]: SET Technet Digest >> Search the archives of previous posts at: > http://listserv.ipc.org/archives >> Please visit IPC web site > http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional > information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 > ext.2815 >> ----------------------------------------------------- >> >> --------------------------------------------------- >> Technet Mail List provided as a service by IPC using LISTSERV 15.0 >> To unsubscribe, send a message to [log in to unmask] with following text > in >> the BODY (NOT the subject field): SIGNOFF Technet >> To temporarily halt or (re-start) delivery of Technet send e-mail to > [log in to unmask]: SET Technet NOMAIL or (MAIL) >> To receive ONE mailing per day of all the posts: send e-mail to > [log in to unmask]: SET Technet Digest >> Search the archives of previous posts at: > http://listserv.ipc.org/archives >> Please visit IPC web site > http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional > information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 > ext.2815 >> ----------------------------------------------------- >> > > --------------------------------------------------- > Technet Mail List provided as a service by IPC using LISTSERV 15.0 > To unsubscribe, send a message to [log in to unmask] with following text in > the BODY (NOT the subject field): SIGNOFF Technet > To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) > To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest > Search the archives of previous posts at: http://listserv.ipc.org/archives > Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 > ----------------------------------------------------- > --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------