Hakan
I have done solder spreading experiments Sn/Pb on Au with a gaseous mixture of formic acid and nitrogen.
It was based on some work done at Sandia National Labs:
D.R. Frear et al, Fluxless soldering for Microelectronic Applications in Materials for electronics packaging edited by D.D.L Chung Butterworth Heinmann, Boston 1995.
All plumbing needs to be glass or Teflon and the formic acid needs to be dehydrated. I bubbled N2 through liquid formic acid that contained boric anhydride to keep H2O to a minimum. We can discuss further if you choose to do this.
Also some other work was done by IBM using CF4, CF2Cls and SF6 where CF4 worked the best since did not leave behind corrosive byproducts. The IBM process may be patented.
P.A. Moskowitz, H.L.Yeh and S.K. Ray, Thermal dry process soldering, J. Vac. Sci. Technol. A 4 (3) May/June 1986 pp. 838 - 840
If you sputter etch the preforms and follow that with an Au deposition without opening the chamber that might work for you.
There is also the option of removing the oxide on the preform using the ROSA process developed by Morgan Tench and Dave Hillman at Rockwell Collins. The ROSA baths can be purchased from Rockwell. Here are some references:
D.M.Tench et al, A new reduced-oxide soldering activation method, JOM June 1995 pp. 36-41.
D.M.Tench et al, Reduction of metallic surface oxides via an electrochemically-generated redox species, J. of Applied Electrochemistry 25 (1995) pp. 947-952.
Good luck.
Steph
Stephan Meschter [log in to unmask]
BAE Systems Controls Phone:(607)770-2332
600 Main Street, MD R52F FAX :(607)770-2056
Johnson City, NY 13790-1888
> ----------
> From: Brian Ellis[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Brian Ellis
> Sent: Friday, October 27, 2000 5:31 AM
> To: [log in to unmask]
> Subject: Re: [TN] Flux free soldering of Sn/Pb
>
> 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
>
> H> åkan 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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