[SI-LIST] Re: Impact on Copper Thieving on 10G Routing

  • From: "Lee " <leeritchey@xxxxxxxxxxxxx>
  • To: <sij99@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 7 Mar 2014 09:22:10 -0800

Seems like there is a lot of confusion as to what thieving is.  So, here is 
what it is.

Thieving is copper added to outer layers of a PCB to create a uniform 
distribution of copper across the surface.  The reason this is done is to 
make sure the copper plating in the holes is uniform.  If the copper 
distribution in the artwork is not uniform, areas with little exposed copper 
will plate very heavy while areas with large amounts of copper, such as BGAs 
or connector pin fields will not plate properly.  So, "thieving" steals some 
of the plating current that would otherwise concentrate on features that are 
sparse and be spread thin in areas with areas that are dense with features.

Again, thieving is an outer layer only process.  All of the discussions that 
mention doing things to inner layers are not thieving.  They are signal 
layer fills to even out the resin flow from the prepreg.  I have designed 
thousands of complex PCBs with many signal layers in each one and have never 
encountered a stackup that required inner layer signal layer fill to achieve 
a usable, flat PCB.

Long ago, before call plates were inserted between PCBs in a laminator 
opening, it was possible to have PCBs with low spots where there was little 
copper on inner signal layers.  That problem has pretty much gone away, so 
it is not necessary to do inner layer fills.

When a fabricator is allowed to add thieving to outer layers, one only need 
to keep it away from other features on that layer to comply with typical 
spacing standards and away from traces enough that it does not adversely 
affect impedance.  If the next layer down is a plane layer, that is all that 
is needed.  If the next layer down is a signal layer (buried microstrip) 
thieving should not be placed over traces in the buried layer.

I hope this helps clear up this issue.

Lee Ritchey

-----Original Message----- 
From: Jack Si
Sent: Thursday, March 06, 2014 11:53 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Impact on Copper Thieving on 10G Routing

Hi Experts,
What are the major impact created by Copper Thieving in the 10G signals and 
the precautions to avoid it.


Thanks and Regards,
Jack


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