One problem is you _can't_ just add the tolerances of the raw materials to
get the finished board thickness. Fabrication process variations
(particularly in lamination and electroplating) aren't taken into account by
that method.

Another issue I see is putting the default tolerance into the design
standard, and then designers thinking of that as a manufacturing standard,
and not putting the tolerance on their drawings, but expecting it just the
same.

Timothy Reeves
QA Manager/Process Engineer
ECD Circuit Board Division


|-----Original Message-----
|From: Barnett, Richard [mailto:[log in to unmask]]
|Sent: Friday, September 22, 2000 11:44 AM
|To: [log in to unmask]
|Subject: Re: [IPC-600-6012] End Product Requirements for Board
|Thickness
|T olerances
|
|
|Folks,
|I can't see the applicability of this requirement, when overall board
|thickness is a variable based on system level design and
|integration. If we
|are seeking default tolerances, then these should be applied
|to the "raw"
|materials (glass, weave, cores, copper...etc). The board
|thickness will be a
|function of all these combined, but the applicability of a
|default tolerance
|for overall thickness on end-product just doesn't seem to fit.
|
|Rich Barnett
|Corporate Component Procurement,
|PCA Technology Engineering
|Compaq Computer Corporation
|
|-----Original Message-----
|From: Rene Martinez [mailto:[log in to unmask]]
|Sent: Friday, September 22, 2000 9:12 AM
|To: [log in to unmask]
|Subject: Re: [IPC-600-6012] End Product Requirements for Board
|Thickness
|Tolerances
|
|
|I also think a default is in order.  Especially because the
|designers need
|to know the limitations of how tight of a tolerance can be
|called out when
|you add inherent tolerances of copper,laminate, plating, etc.
|
|-----Original Message-----
|From: Jih Yuan [mailto:[log in to unmask]]
|Sent: Friday, September 22, 2000 5:47 AM
|To: [log in to unmask]
|Subject: Re: [IPC-600-6012] End Product Requirements for Board
|Thickness
|Tolerances
|
|
|John, From an OEM perspective, I think it's always good to
|have a default
|value. That's what the industry standard is about.  Jih
|
|-----Original Message-----
|From: IPC-600-6012 Mail Forum [mailto:[log in to unmask]]On Behalf Of
|John Perry
|Sent: Wednesday, September 20, 2000 5:37 PM
|To: [log in to unmask]
|Subject: [IPC-600-6012] End Product Requirements for Board Thickness
|Tolerances
|
|
|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 and Tolerances
|document.
|This old dinosaur was recently replaced by the IPC-2615,
|thankfully without
|the outdated end-product requirements such as bow and twist and annular
|ring, all of which have been updated through the years where
|they belong -
|in the design and performance specs.
|
|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 thicknesses.
|We don't have
|any applicable tolerances for this in any of the other spec.
|Sure, IPC-4101
|does provide tolerances for laminate materials (Table 7) , and
|IPC-6012 and
|IPC-A-600 provide thicknesses for foil plus plating (under
|review now as we
|speak!), but did we intentional avoid the transfer of nominal thickness
|tolerances for finished rigid boards to the design and
|performance series of
|documents that we currently use for boards?  Should we point
|people to the
|use of IPC-4101 in conjunction with the IPC-6012?  As always,
|your input is
|much appreciated.
|
|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]
|