> Date:          Wed, 20 Sep 2000 16:36:44 -0500
> Reply-to:      Combined Forum of D-33a and 7-31a Subcommittees
>                <[log in to unmask]>,
>                John Perry <[log in to unmask]>
> From:          John Perry <[log in to unmask]>
> Subject:       [IPC-600-6012] End Product Requirements for Board Thickness
>                Tolerances
> To:            [log in to unmask]

> Hello Everyone,
>
> IPCWorks 2000 has come and gone.  Ready for Expo in Anaheim?  Sheez, are you kidding?
>
> As participants in the IPC-6012 and IPC-A-600 groups, many of you have also been involved with the IPC-2220 design series, and many of you may recall the ancient IPC-D-300G Printed Board Dimensions a>
> One, however, hasn't been transferred to the appropriate requirements documents, and I wanted to make sure that it was an intentional exclusion.  IPC-D-300G used to provide tolerances for board thick>
> Best Regards,
>
>
>
> John Perry
> Technical Project Manager
> IPC
> 2215 Sanders Road
> Northbrook, Il 60062
> 1-847-790-5318 (P)
> 1-847-509-9798 (F)
> [log in to unmask]
>

John,
There was discussion of board thickness and tolerances amongst the
committee members involved in IPC-2221, IPC-2223, IPC-6012, IPC-6013
specifications.  There were some questions of which spec. to put the
criteria in---higher level documents, design docoments, or
performance documents, etc???  My best recollection of the agreed
upon criteria for thickness tolerance is:

1)  One mil (.001") tolerance per layer count or 10% of thickness
whichever was greater.  As an example a 12 layer with 1oz copper
planes could be fabricated at a thickness of .065" which would have a
tolerance of ±.007" normally, but based on layer count the tolerance
would be ±.012"
2)  Thickness should be specified over the base dielectric whenever
possible, to meet the thickness tolerances.  Thickness over the
conductors would be .008-.010" greater than the base thickness,
especially when reflowed solder is the final conductor finish
3) Tolerances tighter than these may be as agreed upon between user
and manufacturer.

My verbage may not be exactly how we put this into whatever spec.,
but it would be very close to conceptual agreements we discussed.

Regards,
Dennis J Cantwell
Dir-QA Eng
Printed Circuits Inc.
612-888-7900