Inge,

OK, I'll ask the question: is this report available somewhere? Would you...

Thanks,

Ioan

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Hernefjord Ingemar
Sent: Thursday, June 14, 2007 4:19 AM
To: [log in to unmask]
Subject: Re: [TN] Nickel barrier and RF applications


Now, Paymon's case was not a RF unit, but sort of a magnetic one, but as
many are interested in microwave issues I noted some matters years ago,
one connected to flux, the other to barrier layers. Sandia Labs had
something called 'Low Residue Soldering Task Force'. Dr Laura Turbini
and her group found a clear connection between the solder residues and
increased RF loss. 

From her report: 'It has been shown that polyglycols and hydrobromic
acid (constituents in some fluxes)diffuses into epoxy during the HASL
process. Under the humid conditions of this test, these processing
chemicals may change the dielectric properties of the test board, which
affect the RF signal integrity.' 451

After that report and some others, we are more motivated to keep
critical RF boards as clean as possible. Normally, flux residues are not
an issue, but some regions of a circuit can be very sensitive to losses.

The other object is rare. I'll send two pictures to Steve's Wax Cabinet.
These show how NiCr leaked out from the edges of the hot RF line and
deposited on the substrate. Caused severe changes in the circuit's RF
properties. We have seen it just a couple of times. No explanation found
how this works. Mystery among many other RF mysteries. The only thing we
could verify was that the 'bleeding' NiCr coincided with the electrical
field. 

Inge
 

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