One more consideration: Any copper exposed on the edge of a PCB will not
have any plating, mask, or other protection to prevent corrosion. If the
board will be used in an environment where it will be exposed to any
sort of corrosive material (even atmospheric moisture) the copper will
corrode. Corrosion on an inner layer could creep inward to affect other
traces etc. This is usually a slow process but it has to be considered
with the desire service life of the board & its end-use environment.
When I was first starting out in PCB design (a while ago) this was the
primary reason given for not running copper to the edge of a board.
Greg Smith
On 6/5/2013 9:50 AM, Brooks, William wrote:
> Board houses tend to not like having to deburr the edges after routing... when you have copper to the edge this becomes an manual labor/inspection issue. That being said, nothing says you can't do what you need to do... There are always trade-offs. What you get for your pads may be useful when first designing, but do you want to pay to have them replicated on every part that goes thru production for hundreds or thousands of boards? You pay for that step, every time they print another board of the same construction, same artwork, etc...
>
> Alternately, you could make a view window that had registration features that don't go to the edge in it that could be inspected.... But typically, the board house does this sort of checking when they make the boards anyway outside the board area in the manufacturing panels. They x-ray the boards to check registration and layer order to prevent making bad boards on every board.
> Once the recipe is known, they repeat it over and over and monitor the processes to keep things in line...
>
> Only you can decide what is an important feature or not... you can also control costs and reduce labor and mistakes by the decisions you make in the design.
>
>
> William Brooks, CID+
> Senior MTS (Contract)
> 2747 Loker Ave West
> Carlsbad, CA 92010-6603
> 760-930-7212
> Fax: 760.918.8332
> Mobile: 760.216.0170
> E-mail: [log in to unmask]
>
>
>
>
> -----Original Message-----
> From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Gary Crowell
> Sent: Wednesday, June 05, 2013 8:36 AM
> To: [log in to unmask]
> Subject: Re: [DC] Exposed edge copper - internal planes
>
> I have done that in the past on boards where I was concerned with the stackup. Always worked out very well but it required a fab note to prevent the board house from removing the pads.
>
> Gary
>
> On Wed, Jun 5, 2013 at 4:53 AM, Matthias Mansfeld < [log in to unmask]> wrote:
>
>> Hello all,
>>
>> Just a question: If there is exposed edge copper, which is NOT
>> electrical stuff, would it be allowed or tolerable? I used to put
>> different non-electrical, sufficiently isolated dummy pads on inner
>> layers directly on the board edge, staggered like a stair, which get
>> milled apart later and thus allow to check the correct layer order and
>> stackup with a simple magnifying glass, but learned that the board
>> manufacturers don't like any kind of exposed copper and would remove
>> this anyway.
>>
>> Regards
>> Matthias
>>
>> On 3 Jun 2013 at 12:06, James Jackson wrote:
>>
>>> Is there an IPC callout for exposed edge copper?
>>>
>>> I seem to remember it not being allowed, but cannot locate an actual
>>> statement in any of the IPC documentation.
>>>
>>> What I am referring to is when you have a negative copper plane (or
>>> copper pour) on an internal layer that extends to the edge of the PCB.
>>> When it gets fabricated, there would be a small line of internal
>>> copper for each of the planes that extend to the edge of the PCB -
>>> which could be shorted together, if a metal object were brought into
>>> contact with the exposed copper.
>>>
>>> Any thoughts?
>>>
>>> Regards,
>>>
>>> James Jackson
>>> Oztronics
>> --
>> Matthias Mansfeld Elektronik
>> * Printed Circuit Board Design and Assembly Neithardtstr. 3, D-85540
>> Haar, GERMANY
>> Phone: +49-89-4620 0937, Fax: +49-89-4620 0938
>> E-Mail: [log in to unmask]
>> Internet: http://www.mansfeld-elektronik.de
>>
>>
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>
> --
> ----------------------------------------------
> Gary A. Crowell Sr., P.E., CID+
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