Hakan
What you wish to do is ***very*** difficult. My guess is that the
preforms are oxidised and argon plasma would not remove the oxide film:
you need a reducing plasma to give a significant effect, but the
preforms would re-oxidise within the first seconds of contacting air. To
do fluxless soldering, everything MUST be oxide-free and
contamination-free if you wish to stand half-a-chance. At the very
least, you need a reducing atmosphere (not an inert one) in the oven, as
well. 5% hydrogen 95% nitrogen may do the trick provided that the
preforms are freshly deoxidised (chemically may be easier than plasma)
and that all components are not contaminated in any way. A minute amount
of flux would help, as well. Also, please remember that the metals,
however noble, in the fired paste, are held in a glass matrix, however
thin, and that glass is not the easiest material to tin, short of using
indium, of course.
FWIW
Brian
Håkan Törnqvist (EMW) wrote:
>
> Hi,
>
> Does anyone have experience from flux free soldering of Sn60/Pb40 on thickfilm. I have tried, but I just can't get the solder to adhere (it peels right off when I'm using a scalpel). I'm using solder preforms and Du Pont's thickfilm paste 4596 (Pt/Pd/Au) in a convection oven with nitrogen atmosphere. I have burnished the thickfilm with an eraser and tried to plasma etch the preforms in argon.
>
> What am I doing wrong? My guess is that there is a thin oxide layer on the preform. Should I use any other method of removing it or should I plasma etch more (I used Ar, 80mTorr, 500W, 13.56 MHz for 5, 10 and 20min).
>
> I'd be very grateful for any tips!
>
> Hakan Tornqvist
> Ericsson Microwave Systems
>
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