The problem with tin and lead is that it is so 'flat' , seen from a 
nano-level. Conductive silver (or other metal) filled adhesives do not stick 
to the metal part chemically, at least not on a essential basis, but rather 
on a mechanical one. There are more binding mechanisms, but let's discuss 
the one that is most important for succeeding for glueing to a solder. A 
solder is amazingly smooth and dense, still seen microscopically, depending 
on the way it solidifies. One could see that indirectly by putting a drop of 
water on the solder: it forms a sphere instead of wetting and spreading. 
High surface tension, with other words. The solder could not break the 
droplet's surface tension. Adhesives have a liquidous part, which is 
necessary for being dispensable. That ingredient is not very wetting by 
nature either, and furthermore, the whole paste has a very high viscosity. 
Now, we want a surface that is like a burdock, or how can I describe it, a 
surface with billions of microscopic superficial voids and cavities. If the 
wet phase of the glue has matching surface tension, and a low viscosity, and 
you give it time, it will creep into all the microscratches and after curing 
creating millions of micro'hooks'. How do we obtain such a condition with 
solder then? You need both remove the always present oxide and also create 
the rough surface.  We found that a slight etching  could do the job. We 
were in a situation when we just had to fix it. Did not like it, but got a 
acceptable result. I don't recommend the method, too many traps to fall 
into, but thought it might be of interest to someone, who could perhaps 
develop the idea on a more adequate way,  the inventor of 1LMI, for 
instance. Let's see if he takes the bate.

What adhesive? Don't remember exactly, think it was a 1,000 mPas light 
curing epoxy, probably from Epotek, as it was named at that time. The 
bonding had no requirements on being very strong, and was not either. Just 
had to keep a grounded copper foil. Soldering was forbidden of a special 
reason.

Inge

----- Original Message ----- 
From: "Douglas O. Pauls" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, October 01, 2008 12:06 PM
Subject: Re: [TN] "Conductive" Bonding Material


> Thermally conductive or electrically conductive?
>
> Doug Pauls
> Rockwell Collins
>
>
>
> "Joe Lara (Select Circuits)" <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 10/01/2008 01:03 PM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> "Joe Lara (Select Circuits)" <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> [TN] "Conductive" Bonding Material
>
>
>
>
>
>
> Good Morning / Afternoon Tech Net Guru's,
>
> Has anyone used a "Conductive" bonding material on a ceramic circuit
> board?
> If so what material was used and what was the quality of the result.
>
>
>
> Thanks in advance!
>
> Joe
>
>
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