[SI-LIST] Re: PCB STACKUP
- From: Jeff Seeger <jseeger@xxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 23 Jan 2004 16:43:00 -0500
Perry Qu wrote:
>
> snip <
> Also, what is causing warpage other than copper unbalance in an
> assymetrical stackup ? From our experience, copper balance is an issue on
> its own especially when dealing with large boards.
Also consider laminate imbalance. Each sheet type (between
layers may include multiple sheets) will have a different
behavior. This can be seen if one looks into the efforts
a vendor does in precompensating the images used before a
board is laminated.
I have seen asymmetric stackups get adjusted by changing
the construction between layers to become symmetrical. In
other words the complement that lacks a copper layer gets a
surface where that copper layer would have been.
Addition and removal of non-functional copper is only one
part of the bow & twist scene. I would guess that Mr Sef-
ton's fortunate result may have had some behind the scenes
machinations as above in addition to the weight changes.
This sort of situation depends a great deal on the fabri-
cator's engineering expertise and will likely increase the
base materials cost at least to a small extent.
Best regards,
--
Jeff Seeger Applied CAD Knowledge Inc
Chief Technical Officer Tyngsboro, MA 01879
jseeger "at" appliedcad "dot" com 978 649 9800
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