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April 2009

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TechNet E-Mail Forum <[log in to unmask]>, Inge <[log in to unmask]>
Date:
Fri, 10 Apr 2009 22:19:13 +0200
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It's an interesting question. You need know what 'adhesion' means in a
deeper meaning. Ask an adhesive specialist and he will give you a whole
bunch of explanations, like chemical bonds, atomic bonds, van de Vaals
bindings (not sure I spell it correctly), electrostatic bindings, mechanical
bindings etc. The little I've understood gives, that an essential part of
bindings in fact are mechanical. Depending on the viscosity of the epoxy and
its wetting characteristics, the micro roughness is important. Hence, the 
tin process
(and the copper etching) ought to be such that you get as much porosity as 
possible.
It reminds of thickfilm technology in a way. Here, mechanical binding are a 
big percentage
of the binding, besides the oxide binding. One way to 'roughen' the tin 
could be a second or
 two etching. I've studied the result in a SEM. The difference between the 
etched and non etched
tin is obvious. I realize that performing such a treatment on a one micron 
tin layer is not to
be done by others than experts. Will be interesting to see what Rudy Sedlak 
and like will
add as professionals.  And finally I wonder how the epoxy process will be 
done without
voids and gas bubbles. Vacuum oven?

Here is a good paper that explains in detail.

http://www.sjsu.edu/faculty/selvaduray/page/papers/mate210/interfacial.pdf

Inge


----- Original Message ----- 
From: "bob wettermann" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, April 10, 2009 5:16 PM
Subject: Re: [TN] Friday Theorizing


> Thanks all to have responded.
>
> More options came up yesterday in speaking with other suppliers of the 1oz
> base copper material. There are versions which have :
>
> 1. 8-10 microns roughness on one side (this will be electroplated with
> 1-1.4 microns of tin)
>
> 2. 0.3-0.4 microns roughness on the other side (this too will be
> electroplated with 1-1.4 microns of tin)
>
> So now my question for you metalurgists out there is the same .....if I
> bond at room temp for room temp use using a 2-part epoxy SIDE 1 described
> above to the FR4 should I expect adequate adhesive strength (compared to a
> 1oz copper trace/pad run through an initial mfg process)?
>
> Happy Easter
>
> Bob Wettermann
> PH 847-767-5745
>
>
>
>
> ________________________________
> From: Richard Stadem <[log in to unmask]>
> To: [log in to unmask]
> Sent: Friday, April 10, 2009 8:58:26 AM
> Subject: Re: [TN] Friday Theorizing
>
> As I stated in my earlier posting, there are certain epoxies that bond
> well to
> tin-plated copper. One that I described was pull-tested to 18 lbs before
> it
> pulled the foil away from the PWB. On the side where the same epoxy was
> used to bond the plated foil to the PWB, parts of the FR-4 substrate came
> up
> with it.
> Of course, this has to be done after reflow.
>
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