Francis,
99% of the EM wave travels thur what is three times the clasical skin depth
thickness which for copper at 10 MHz is 0.8 mils. The classical skin depth
thickness is proportional to 1/sq rt of conductivity x frequency. For
simiplicy assume no waveguide effect in the PTH and one can see why the min.
thicknesses are stated as they are. Reduced conductivity and porous Cu in
the direction of EM propagation are explained by appplication of aperture
theory.  I will give a course again at the Electroplating and Surface
Finishing Society National Convention in June99. If you need more please
advise.
Richard Haynes
609-497-4584

-----Original Message-----
From: Francis Lai <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Saturday, October 31, 1998 10:31 AM
Subject: [TN] Copper plating & Copper thickness


>Dear Sir :
>
>I work inn a high frequency PCB manufacturing company and I have the
>
>following questionns :
>
>1/ Why is it for copper plating (acid copper plating) the lower the
>   current, the more the throwing power ? If I start to plate copper
>   on the PTH walls with high current density after PTH, what will
>   happen ?
>
>2/ Our customer always specify to have a certainn thickness innside the
>   PTH walls for copper. Why is that so for high frequency PCB ?
>   What happen if copper thickness is thinner than the specified
>   thickness at high frequencies ?
>
>Thanks for your help !!!!!!!
>
>my e-mail : [log in to unmask](this is only text base, pls do not
send
>                                      graphics)
>
>Thamks again!!!!!!!
>
>Francis
>
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