Hey Gary,
I agree with Ray. By now you should have realized that if you want something "planned well," you might as well plan it yourself. I suggest you educate yourself on the subject as much as possible, decide on the hole sizes and locations that meet your needs, and create a mechanical symbol for the break-tab in your CAD tool. You can then place them anywhere you desire. You can create several different versions to meet different needs and requirements. I would also suggest a detail on the fab drawing and a panel outline drawing. The benefits and cost prevention associated to this approach far outweigh the very small cost that may or may not be charged for setup by the fab shop. Afterall, the idea is to design a specific panel for a specific purpose right? Why leave anything to chance? A picture is worth a thousand words.
The symbols can include the padstacks / drill hits, SM clearance, and panel drawing lines. They can even contain comp/CU keepouts to aid in the design phase. What if the fabricator forgets to back off the planes around the holes they add? Scary... but it happens.
The benefits to using this approach are as follows:
1) Guess work and spec interpretation is eliminated by the fabricator
2) The break-tab drill hits are included in the drill data (You control their locations)
3) Assembly / Quality / and Test issues can be avoided such as vias, TP's, lands, other features being too close to the break tab holes. Solder joints and via barrels can be damaged during depanelization if they are too close.
4) Hardware and artwork becomes more predictable between vendors and for future revisions.
5) Language barriers are dissolved (useful for overseas mfg.)
I hope these ideas can help you make the right decision.
Regards
Patrick Courtade, CID
CAD Manager - Dallas
7Core Inc
214-347-4274
www.7core.biz
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Ray Johnston
Sent: Wednesday, August 23, 2006 11:09 AM
To: [log in to unmask]
Subject: Re: [DC] Breakaway tab specification
Gary,
IPC-7351 - 3.4.8 Panelization - gives a general idea, but also states that
it really depends on the board handling and fixture equipment. Under panel
construction (3.4.8.1) it states, "the panel must be planned well".
I would say that more than just specifying IPC-7351 Figure 3-21 is needed
on a multi-board panel.
We have small details that we add to our drill files that show what we want
between board to board and one like figure 3.21 board to panel edge.
Ray Johnston
Lead CAD Designer
Rane Corporation
425-355-6000
rayj@rane,com
----- Original Message -----
From: "Gary M. Koven" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, August 23, 2006 8:35 AM
Subject: Re: [DC] Breakaway tab specification
> OK, I'll correct my own error first.
>
> I used the obsolete spec IPC-SM-782A Figure 3-31. I should have used
> IPC-7351 Figure 3-21.
>
> Regardless, is 7351 kosher for this? Or do I need a different reference?
>
> Thanks,
> Gary
>
> -----Original Message-----
> From: Gary M. Koven [mailto:[log in to unmask]]
> Sent: Wednesday, August 23, 2006 11:22 AM
> To: IPC Designers Council ([log in to unmask])
> Subject: 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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