Gary,
Information on breakaways in the current standards are there for
reference of the important criteria for breakaway design. The actual
configuration is, of course, design specific and needs to be shown on
the master drawing. You should consult with your board suppliers for
recommendations based on the type of material used and thickness. They
have seen many configurations and usually can recommend something that
will meet your requirements. Also remember, you are the one that knows
what components need close-by support for a tab. You are the one that
also knows the stresses that are placed on the board during component
mounting. The board fabricator only sees the bare board. Lastly, I am
looking to expand this area in IPC-2221 at the next revision.
Summary recommendation, show the exact configuration you desire on the
master drawing.
Regards,
Gary Ferrari
FTG Circuits
Director, Technical Support
860-350-9300
John Parsons wrote:
> Gary,
>
> I don't have a copy of the current standard IPC-7351 which supersedes SM-782
> so I don't know how tabs are detailed in there. My copy of SM-782 is pretty
> old but it does show some examples of breakaway tab details. As you
> suggest, I think that most shops have developed their own "standard" tab
> designs which they use unless otherwise specified by the fabrication
> documents. We certainly do. If you are determined to use the suggested
> design you have found in the IPC doc's I would think there is nothing wrong
> with that but would suggest that you go to the trouble of duplicating the
> detail on your fab drawing rather than specifying the IPC document alone.
> First off, the document you have referenced below (IPC-SM-782A) is obsolete,
> having been superseded in 2005 by IPC-7351 and second, many fab shops may
> not have a copy of that document so referencing it without providing the
> detail on the fab drawing will only draw out the quote/fab process
> unnecessarily.
>
> John Parsons
>
> -----Original Message-----
> From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Gary M.
> Koven
> Sent: Wednesday, August 23, 2006 8:22 AM
> To: [log in to unmask]
> Subject: [DC] Breakaway tab specification
>
> Gentlemen,
>
> I'm looking for confirmation and/or correction on breakaway tab
> specification.
>
> On my drill drawings, this is my first note for a blanket default:
>
> "FABRICATE PER IPC-6012 CLASS 2 UNLESS OTHERWISE SPECIFIED"
>
> However, 6012 is uselessly vague about breakaway tabs...referring the user
> to the acceptability requirements of the assembly.
>
> In the Depanelization/Singulation section, I don't call out a specific IPC
> standard for breakaway tab acceptability. The only statement I make is:
>
> "BREAKAWAY TABS MUST SHEAR BELOW EDGE OF BOARD OUTLINE"
>
> In the past, that has always been adequate.
>
> However, I now have a board for which I've been tasked to pre-determine a
> certain number of how many up.
>
> On page 35 of IPC-SM-782A, Figure 3-31 "Breakaway (routed pattern)" shows
> some better detail on their so-called Low-Stress (Mouse Bite) Breakaway.
> The figure shows approximate center to center spacing of 75mm (3.0in)
> between tabs and maximum indent of 0.4mm (0.016in).
>
> Is it kosher to call out something like this:
>
> "BREAKAWAY TABS TO BE LOW-STRESS MOUSE BITE PATTERN PER IPC-SM-782"
>
> Or, is it not kosher because there exists a different standard in the
> Acceptability series (like IPC-A-600, which I don't have here) which might
> supersede a Design-series standard such as 782?
>
> I've always in the past left arcana such as this to the assembly shop who
> typically work with their chosen fabricator to pick a panel size, how many
> up, tooling hole location, yada yada. Now that I must own this step on this
> one board, I will have to issue some sort of panelization drawing, and I
> want to be careful not to put too much information on drawing which might
> add to the cost of the boards.
>
> TIA and Best Regards,
>
> ===========================
> Gary M. Koven, C.I.D.
> Dynazign, Inc.
> Charlotte, NC, USA
> Veteran of the Marsh School
>
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