Hello to all,

based on > 10 year of experience with microwave circuits up to 20 GHz I
wonder what people are discussing on the influence of lead or no lead within
solder.

First of all: due to skin effect the current is present near the surface of
the conductive line with roughly 7 µm at 1 GHz where 99.9 % of all current
is present. This value is proportinal to 1 / sqrt(f), e.g. the values are 70
µm at 10 Mhz resp. 0.7 µm at 100 Ghz.

Second: due to proximity effect the current on a microstrip is mainly on the
lower side (near the ground plane). So only at solder joints the current has
to pass the solder.

My experience with FR4 boards is that the attenuation at > 1 GHz will far
away from neglectable values (using SnPb-solder) and at power amps even at
lower frequencies - all due to the resins influence. So I wonder how you
will detect the difference between 63%SN+37%Pb and 96%Sn+... regarding the
small dimensions of a solder joint compared to line lengths.

Normal FR4 material is a mixture of glass with an epsilon of about 6
meanwhile resin is at about 3.5 (data from ISOLA) - but who knows what
percentage of glass and resin is present in your board ? The effective
epsilon influences the characteristic impedance of a line.

And the last tip: if anyone will discuss on digital circuts and
characteristic impedances: please visit the Texas Instruments sites and look
for two interesting articles:
- K. Fleder: "The Bergeron Method: A Grafic Method for Determining Line
Refelctions in Transient Phenomena", SDYA014
- "Input and Output Characteristics of Digital Integrated Circuits", SDYA010
Maybe you'll change yourr thinking on that item.

best regards
Wolf-Dieter Schmidt
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THALES Defence Deutschland GmbH
Industrial Engineering
Land & Joint Systems
Ostendstrasse 3
D-75175 Pforzheim - Germany
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Telefon: +49 7231 15 3386
Telefax: +49 7231 15 3390
mailto: [log in to unmask]
http://www.thalesgroup.com




-----Original Message-----
From: to Paul Taylor [mailto:[log in to unmask]] 
Sent: Tuesday, April 13, 2004 9:44 AM
To: [log in to unmask]
Subject: [LF] Effects of WEEE and RoHS on EMI, etc


I agree with Brian in principle, however I have seen no data on any 'GHZ'
related issues with lead free soldering, and would agree that the metallic
make up of the joint would resonate at different frequencies.  In this
case, some EMI checks should be done, at least early on in lead free
manufacture until we have enough data to say where the retest should be
done or not.  This also applies mainly to product in the high GHz/microwave
sphere where layout, manufacture and even pcb manufacture are critical.  I
would be really interested to see a comparison between two exactly the same
boards built with tin-lead and lead free.  Does Nokia (as a world leader in
mobile comms) have any views or data on this that they could share with the
group?

By 2006 all product will be lead free, so manufacturers embarking on new
product would have completed EMC testing on their new product by then.

I think for those of us in the Mhz range (domestic equipment etc), I very
much doubt that our EMC will be affected by small GHz resonancies, we are
much more worried about motor noise for example at the low end!!!!

regards
Paul

Paul R Taylor
Senior Engineer, Product Supply Group
Pitney Bowes Ltd
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