Jack,
Not only have the IPC added too many terms, their explanation of allowable protrusions is virtually nil except for the section in IPC-A-600 on nicks and burrs, which still doesn't really address it well.
IPC-7351A had the best Figure on low-stress mousebite design, but manufacturing shops don't usually have design standards on hand. This belongs in either IPC-A-600 or 610, I would think.
Hopefully the Committees will clean up the terminology in IPC-T-50 and then extend the cleaned-up consistent terms and definitions in the next rev of specs.
As usual you hit the nail on the head, though!
Gary
>________________________________
> From: Jack Olson <[log in to unmask]>
>To: [log in to unmask]
>Sent: Wednesday, February 13, 2013 9:50 AM
>Subject: Re: [DC] Board panelization techniques
>
>I think there needs to be some distinction made between two separate things:
>1) arranging individual boards on a fabrication panel to get the best yield
>2) designing an array for assembly, which may require v-scores or breakaway
>tabs
>
>The IPC was trying to use consistent terminology to avoid confusion by
>calling the bare board fabrication material a "panel", and calling an
>assembly array a "pallet". Unfortunately, they added another term called
>"Delivered Panel" to mean the same thing, which just adds to the confusion
>in my opinion (also, some of the other definitions in IPC-T-50 aren't
>consistent, like the one for "breakaway" or "multiple printed board". I
>never noticed that until just now!)
>
>Anyway, I think the "panel drawing" that Greg is warning against is the
>result of a board designer trying to optimize the yield of the fabrication
>panel. I agree with him, you shouldn't waste your time (and probably waste
>money in the long run) trying to do that.
>
>However, if you need assembly pallets to add rails to a board or to create
>an array of boards that will require operations after the assembly to
>separate, you should document that. Do not leave that up to the bare board
>fabricator.
>
>onward thru the fog,
>Jack
>
>
>On Tue, Feb 12, 2013 at 5:10 PM, Greg Smith <[log in to unmask]> wrote:
>
>> Hello
>>
>> I'm going to have to respectfully disagree with the need for a panel
>> drawing.
>>
>> It depends...
>>
>> I have worked for companies that bought their bare boards from outside fab
>> shops and did the PCB assembly in house.
>> We always did a panel drawing as we knew exactly what our tooling,
>> equipment, and design needs were.
>>
>> I have worked on designs where the PCBA was an assembled panel that did
>> not get broken up until final assembly in the end product. That required a
>> panel drawing.
>>
>> Other times the company worked with a specific fab house and a separate
>> specific assembly house. We did not supply a panel drawing but asked the
>> fab shop to supply a Gerber or pdf of their proposed panel for our approval
>> and, more importantly, the assembly shops approval. This allowed both shops
>> to negotiate the design that best met their capabilities.
>>
>> I have also worked on designs where I would not even know what continent
>> the fab and assembly shops were located in. The contracted manufacturers
>> had locations world wide and would use the appropriate facilities that had
>> time available to meet the order. This means the panel size could be
>> different for every order placed as the location could change. That means
>> the panel could, for instance, be prototyped in a shop using inch
>> dimensions, and mass produced in a shop using metric dimensions. A panel
>> drawing would then tie the shops to a possibly wasteful or inefficient
>> design.
>>
>> However, if there are specific design needs that require that break-away
>> tabs or scoring areas not be located in certain places, then this needs to
>> be on the fab drawing. You just don't need a panel drawing to do this.
>>
>> Greg Smith
>>
>>
>>
>>
>> On 2/12/2013 1:21 PM, Pete wrote:
>>
>>> If you don't wish to make panelization drawings as a time savings, you'll
>>> spend more time fixing issues. Always make a panel drawing, the fab house
>>> doesn't know the board assembly, the CM doesn't know the end product. You
>>> know what you need, put it on a drawing so there's no doubt.
>>>
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