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April 2017

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Subject:
From:
Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 26 Apr 2017 10:48:23 -0400
Content-Type:
text/plain
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text/plain (86 lines)
what is the copper thickness?
> I have to wonder why the plane was pulled back.  Looks like a DB9, so I'm
> thinking, low speed signals, possible RS232.  But it could be some high
> impedance circuit where capacitive loading is a big problem.  Perhaps not.
>  Perhaps the pullback was done not to limit capacitive effects on the
> traces on that DB9, just a pullback to prevent coupling, as a plane wasn't
> required.  Just guessing, so as to not impact circuit performance.
>
> If low capacitance is required, it might be a bit more work than just
> adding a split plane or thieving, as it couldn't be added under the
> traces--but it could be brought "near" for the desired effect.  But if it
> was just a "we don't need a plane here, just remove it" then a split plane
> should be easy enough to use, with a full or crosshatched pour.
>
> Shawn Upton
> Section Head, Test Engineering
> Sensors Business Unit
> Allegro MicroSystems, LLC
> [log in to unmask]
> 603.626.2429/fax: 603.641.5336
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl Van Wormer
> Sent: Wednesday, April 26, 2017 9:51 AM
> To: [log in to unmask]
> Subject: [TN] PCB delamination at area with ground-plane cutout
>
> We received pictures from our contract manufacturer, marked to show
> delamination occurring in 2 areas on our 6-layer boards.  The delamination
> areas were at the electrically isolated communication interfaces that were
> made with no copper on the power and ground planes to reduce capacitive
> coupling.  The response from the PCB manufacturer is:
>
> ​​​​​1)defect reason: we used our stock boards to run the
> thermal shock test, we see the de-lam is only taking place in the two
> areas without copper (pic 1.jpg),
>     There is insufficient glue in this area that happened during
> lamination and that is why the de-lam is happening when the customer
> is assembling under the high temp, 2)correction action:  if the
> customer needs us to remake, we suggest to modify the design a little,
> pls see pic 2.jpg, we will fill the marked area with solid copper .
> Please confirm if a remake is needed, we will arrange right away.
>
> Steve Gregory has posted the pictures at:
> http://stevezeva.homestead.com/Carl1.jpg (board cut open for evaluation at
> board house)
>
> http://stevezeva.homestead.com/Carl2.jpg (picture showing where they want
> to add copper)
>
> (and 2 pictures of the delaminated areas)
> http://stevezeva.homestead.com/Delamination_-_is_it_caused_by_missing_ground_plane__1_.jpg
> http://stevezeva.homestead.com/Delamination_-_is_it_caused_by_missing_ground_plane__2_.jpg
>
>
> Question to the group:  Will adding copper on the electrically isolated
> open areas eliminate this type of delamination?  We could add the copper,
> but not connect it to the system ground.
>
> Thanks,
> Carl
>
>
>
>
>
>
> Carl B. Van Wormer, P.E., AE7GD
> Senior Hardware Engineer
> Cipher Engineering LLC
>     21195 NW Evergreen Pkwy Ste 209
>     Hillsboro, OR  97124-7167
>     503-617-7447x303
>     [log in to unmask]<mailto:[log in to unmask]>
> http://cipherengineering.com<http://cipherengineering.com/>
>
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