Jack,
Center is Geometric, which in 98% of the time is also the Center of Gravity.
Respecting the "Note" on the Fab Drawing, all joking aside, I would say yes by all
means, and I would additionally put an "arrow" which defines "zero rotation" in any
case that deviated from the normal right reading orientation of the PCB as shown on
the Fab Dwg.
JaMi
----- Original Message -----
From: "Jack C. Olson" <[log in to unmask]>
To: "(Designers Council Forum)" <[log in to unmask]>; "JaMi Smith"
<[log in to unmask]>
Cc: <[log in to unmask]>
Sent: Tuesday, October 26, 2004 2:53 PM
Subject: Re: [DC] Pin Numbering Question
>
>
>
>
>
> I don't have a copy of the new standard.
>
> Just out of curiousity, do they define the
> center of a component as the center of
> gravity, or the geometric center?
>
> I still don't understand your prediction
> that people will be upset by the move
> towards a consistent standard. I applaud
> it wholeheartedly. My prediction is that
> some companies simply won't change.
> (speaking from experience)
> The problem in my mind is that a vendor
> won't know which customers follow the
> IPC and which don't. Should we start
> adding a fab dwg note that says
> "component rotations conform to IPC-7351"?
>
> HA! (just joking)
>
> Jack
>
> (p.s. you put 112 quotation marks in one post,
> that's gotta be a record!)
>
>
>
>
>
>
> JaMi Smith
> <jamismith@SBCGLO
> BAL.NET>
> Sent by: To
> DesignerCouncil To
> <DesignerCouncil@ [log in to unmask]
> ipc.org> cc
>
>
> 10/26/2004 03:39
> PM
>
> Subject
> Please respond to Re: [DC] Pin Numbering Question
> "(Designers
> Council Forum)"
> <DesignerCouncil@
> IPC.ORG>; Please
> respond to
> JaMi Smith
> <jamismith@SBCGLO
> BAL.NET>
>
>
>
>
>
> Caterpillar: Confidential Green Retain Until: 11/25/2004
> Retention Category: G90 -
> General
> Matters/Administration
>
>
> The "orientation" of components when packaged in "Tape and Reel" is defined
> by
> ANSI/EIA-481-C (specifically see Figure 1), and is fairly well followed by
> a
> majority of manufacturers when packaging a majority, although not all, of
> their
> components in "Tape and Reel".
>
> The problem here is that there is no specific "standard" on how to "orient"
> or
> "mount" a "Reel" into a "Pick and Place" machine, and there are in fact
> many
> different machines that "orient" or "mount" the "Reels" in many different
> ways such
> that they may "feed" the components in any of the four basic directions.
>
> The problem of "Tape and Reel" mounting or loading orientation in any given
> location
> in any given "Pick and Place" machine is a matter which has to be
> individually
> resolved by each individual Manufacturing Engineer, for his individual
> "Pick and
> Place" machine, which usually taken care of in the programming of that
> machine.
>
> Additionally, components also come in "Tubes", "Coin Stacks", "Magazines",
> or
> "Trays", (much of which is defined by JEDIC JEP95), which packaging
> presents similar
> problems to the Manufacturing Engineer, respecting their orientation in his
> particular individual "Pick and Place Machine".
>
> IPC-7351 is not intended to specify either how components are mounted in
> "Tape and
> Reel" or "Trays" or any other type of "packaging", or how such "packaging"
> is to be
> "mounted" or "loaded" into any given automated assembly equipment. This is,
> and
> always has been, and always will be, the individual responsibility of the
> Manufacturing Engineer and or the operator of such equipment.
>
> IPC-7351 is however specifically intended to be a standard for Library
> Components
> and the orientation of those Library Components, as used in the "design" of
> a
> Printed Circuit Board, such that respecting "component orientation", all
> components
> in any given "design" will have a common standard "zero degrees of
> rotation" ("zero
> rotation"), with respect to the "zero rotation" of the PCB, which is
> defined by the
> Gerber File and Fabrication Drawing (which should correspond to each other
> unless
> specifically noted on the Fab Dwg).
>
> IPC-7351 can not dictate how manufacturers package their components, nor
> can it
> dictate how those packaged components are mounted or loaded into automated
> assembly
> equipment.
>
> IPC-7351 does dictate that when individual components within "Component
> Libraries"
> that are defined in accordance with IPC-7351 are utilized, that those
> components
> will have a "standard orientation", and that any "rotation" of any
> individual
> component will be based upon a standardized "zero rotation", with respect
> to the
> "normal" orientation of the PCB itself, such that any Manufacturing
> Engineer will
> have a "standard component orientation" to rely upon with respect to each
> component
> on that PCB, such that the Manufacturing Engineer can make such
> "compensations" or
> "adjustments" as may be necessary with regards to the "mounting" or
> "loading" of any
> components into any automated manufacturing equipment, and the
> "programming" of such
> equipment, irrespective of how each component is packaged or oriented
> within that
> packaging.
>
> The bottom line is this. IPC-7351 defines how components are to be made in
> a
> "Standard Library", which will among other things insure that all of the
> components
> within that "Standard Library" follow a standardized orientation based upon
> a
> standard "zero rotation", which in turn will mean that your data in your
> "Pick and
> Place File" will be correct and can be relied upon by the Manufacturing
> Engineer to
> make your PCB quicker and without any errors, and cheaper without any
> additional
> setup and NRE charges.
>
> IPC-7351 resolves many of the problems that now exist with respect to
> component
> "land patterns" and "component orientation", such that it will allow the
> utilization
> of the automation that is already built into most of today's EDA / PCB
> Design
> Software, as well as most of today's automated manufacturing equipment such
> as "Pick
> and Place" machines.
>
> While IPC-7351 may not satisfy everyone in every situation, it certainly is
> a
> monumental step forward in standardizing the "Design" of PCB's such that
> the current
> avenues of automation can be fully utilized, and new avenues of automation
> can be
> developed, such as for example, the future standardization of "Pick and
> Place" file
> "data" and "format".
>
> While on the topic of IPC-7351, I should probably also mention that the
> "center" of
> a component is chosen as the standard for locating all components, as
> opposed to Pin
> 1 or any other feature, such that the component can be "rotated about its
> center".
> This will undoubtedly make some people happy, while upsetting others.
>
> JaMi Smith
>
>
>
>
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