Patrick,
I ended up creating a separate panel layout drawing whereby I dimensioned
the overall panel, vertical distance between boards, horizontal distance to
inside rail, and maximum incursion into the board outline from the drilled
low stress mousebite breakaway tab hole pattern. I located and dimensioned
the tabs. Then I went back to the design and double checked to make sure
the tab locations would not impinge upon any circuit pattern features.
I put a note that panel tooling holes were to be located and sized at shop
option. One shop might use 3 0.140 holes 0.200 in from each edge and one
corner with no tooling hole, another shop might use 4 0.156 holes 0.250 in
from each edge on every corner, etc.
Thanks for the input!
Gary
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Patrick
Courtade
Sent: Wednesday, August 23, 2006 1:08 PM
To: [log in to unmask]
Subject: Re: [DC] Breakaway tab specification
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
>
>
----------------------------------------------------------------------------
-----
> DesignerCouncil Mail List provided as a free service by IPC using LISTSERV
> 1.8d
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
> To temporarily stop/(restart) delivery of DesignerCouncil send: SET
> DesignerCouncil NOMAIL/(MAIL)
> Search previous postings at: www.ipc.org > On-Line Resources & Databases >
> E-mail Archives
> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
> for additional information, or contact Keach Sasamori at [log in to unmask] or
> 847-615-7100 ext.2815
>
----------------------------------------------------------------------------
-----
----------------------------------------------------------------------------
-----
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV
1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET
DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
----------------------------------------------------------------------------
-----
--
No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.1.405 / Virus Database: 268.11.5/425 - Release Date: 8/22/2006
--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.405 / Virus Database: 268.11.5/425 - Release Date: 8/22/2006
----------------------------------------------------------------------------
-----
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV
1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET
DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
----------------------------------------------------------------------------
-----
---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
---------------------------------------------------------------------------------
|
