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[SI-LIST] Re: Surface roughness of PCB tracks at track/substrate interface ?

From: "Zabinski, Patrick J." <zabinski.patrick@xxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Date: Mon, 11 Jun 2001 06:15:33 -0500

Steve,

When speaking to PCB vendors, they typically refer to
surface roughness as "toothing profile", and most PCB 
manufacturers are able to select a particular toothing 
profile from their material vendor(s).

From cross sections of actual boards, peak-to-peak surface
roughness is in the range of 7 to 18 microns for common
PCBs.

If you're interested in reading bit more on surface roughness,
I suggest obtaining/reading a copy of:

   TITLE   Effect of Surface Roughness on Eddy Current Losses 
           at Microwave Frequencies
   AUTHOR  Samuel P. Morgan, Jr.
   SOURCE  Journal of Applied Physics
   VOLUME  20
   DATE    April, 1949
   PAGES   352-362

The paper takes an analytical approach to determining the
loss in a conductor due to surface roughness with different
profiles (e.g., sawtooth, square, etc.) and shows that
surface roughness can sometimes double the loss when compared
to a smooth conductor.

Pat


> Hello all,
> 
> I am trying to find out value for the roughness of PCB traces on the
> substrate side of the track.
> As I understand it, a level of roughness is essential in 
> order that the
> metal bonds mechanically with the substrate material. However 
> I do wonder
> how much this rougness effects the Resistance of the trace at high
> frequencies. Some recent experiments I have carried out 
> suggest that it may
> be quite significant. The skin depth is half the solution (I 
> think), but I
> need some idea of how 'rough' typical surfaces are in order 
> to get some idea
> of losses?
> 
> All suggestions on this one are welcome
> 
> Many thanks in advance
> 
> Steve Rogers
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