Mike
You make a good point. There is not a suitable test method in 650.
Performing this measurement in a repeatable fashion will be difficult. The
procedure may actually be to measure the relative heights of the SMT lands
and then place a spec on the maximum variation within a pattern. Even this
will be difficult and require some specialized equipment.
Best regards
Lee
J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389
----- Original Message -----
From: "Mike Hill" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, May 11, 2006 8:27 AM
Subject: Re: [IPC-600-6012] IPC-6012B Bow and Twist Requirements
> Do we have an IPC test method to cover the measurement of localized
> flatness? If not, do we need one?
>
> Mike Hill
>
> -----Original Message-----
> From: IPC-600-6012 [mailto:[log in to unmask]]On Behalf Of Montgomery,
> Scott D
> Sent: Wednesday, May 10, 2006 6:02 PM
> To: [log in to unmask]
> Subject: Re: [IPC-600-6012] IPC-6012B Bow and Twist Requirements
>
>
> I also concur that not all designs need to be tighten.
>
> If there is a concern for bow and twist for a specific family of
> components, we will define a localized flatness for those component
> areas on the fab drawing. This has worked very well. My recollection is
> that less than 5% of our boards were scraped by the fabricator due to
> out-of-spec flatness.
>
>
> Thanks
> Scott
>
>
> -----Original Message-----
> From: Mark Harvey [mailto:[log in to unmask]]
> Sent: Wednesday, May 10, 2006 2:43 PM
> To: [log in to unmask]
> Subject: Re: [IPC-600-6012] IPC-6012B Bow and Twist Requirements
>
> Concur.
>
> If a design requires a tighter tolerance than they should identify that
> on the print or by spec.
>
> Forcing all product to that will drive up cost for all.
>
> True story some designs do need a tighter tolerance.
> -----Original Message-----
> From: Franklin D Asbell [mailto:[log in to unmask]]
> Sent: Wednesday, May 10, 2006 1:15 PM
> To: [log in to unmask]
> Subject: Re: [IPC-600-6012] IPC-6012B Bow and Twist Requirements
>
> I don't believe tightening these requirements would benefit all
> companies as a whole. The problems I've seen experienced are isolated to
> specific designs, on specific equipment.
>
> I would propose something more clarified in respect to customers (i.e.
> assemblers) and suppliers reviewing designs more closely together.
> Customer A may have equipment to handle a certain amount of warp (as
> noted below) while Customer B may not, Customer B could then tighten
> this specific tolerance to a certain supplier who might make adjustments
> for a certain amount of additional processing or even yields.
>
> A general tightening of bow/twist may cause acceptable product to be
> scrapped that might otherwise be used if pre-fabrication including
> fabrication requirements discussions were performed.
>
> Franklin D Asbell
>
> -----Original Message-----
> From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of John Perry
> Sent: Wednesday, May 10, 2006 2:49 PM
> To: [log in to unmask]
> Subject: [IPC-600-6012] IPC-6012B Bow and Twist Requirements
>
> Colleagues,
>
> IPC continues to receive queries from industry as to whether or not
> there will be a tightening of the bow and twist requirements for printed
> boards that are given in both IPC-2221A and IPC-6012B.
>
> I would like the members of this forum to provide their feedback on
> these requests.
>
> There are currently two arenas where we are getting requests for
> alteration to the requirements: BGA devices and screen printing
> technology.
>
> Regarding BGA technology, Don Dupriest of Lockheed Martin Missiles and
> Fire Control provided a .ppt file at the IPCWorks 2005 meeting for these
> groups where the recommendation for bow and twist acceptance for
> isolated BGA areas is 0.50%.
>
> This presentation file is available at
> http://www.ipc.org/committeedetail.asp?Committee=D-33A
>
> Within "Drafts", under the titled "PCB Bow and Twist - BGA Devices"
>
> Regarding screen printing technology, we recently received the following
> request:
>
> We had a board that was slightly warped, make contact with and damage
> the camera in one of our screen printers. Of course, when I measured the
> bow and twist, it was well within acceptable limits for bow and twist.
>
> My question is this: Are the bow and twist specifications tight enough?
> For over 15 years, I have been "jumped on" by the line operators and
> maintenance guys to fixed warped boards only to find that the boards are
> usually not any where near the limits. Since I have worked for multiple
> companies, I see that this is an industry wide dilemma. Board
> manufacturers typically can hold bow and twist requirements, but
> different SMA machines (especially screen printers) aren't able to run a
> board that has bow or twist near but within the specification limits.
> Should I be asking why machines built for the surface mount industry
> can't run boards that meet industry specifications, or if the
> specifications that once fit, are in need of revision?
>
> Larry D. Roberts
> Quality Engineer
> Andrew Corporation
>
> Thanks for taking the time to review and respond to these industry
> requests.
>
> Regards,
>
> John Perry
> Technical Project Manager
> IPC
> 3000 Lakeside Drive # 309S
> Bannockburn, IL 60015
> [log in to unmask]
> 1-847-597-2818 (P)
> 1-847-615-7105 (F)
> 1-847-615-7100 (Main)
>
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