Hi Technet! Sorry Peter but I respectfully disagree with  your ".... is not
compatible with leadfree solder." statement. I have very successfully
soldered components with PdAg and PtAg terminations with SAC305 solder for
an Class 3 IPC application (yes, I did complete long term reliability
testing). The soldering operation required a bit more reflow oven profiling
and process attention but if was not impossible.  Perhaps a better
characterization would be that soldering Pd/Ag or Pt/Ag terminations with
Pbfree solder is more problematic (as you detailed in your email) and that
alternative terminations would be preferable.

Dave Hillman
Rockwell Collins
[log in to unmask]



                                                                           
             "P. Langeveld"                                                
             <p.langeveld@GMAI                                             
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                                                                   Subject 
             01/31/2007 11:01          Re: [TN] Soldering to Pt/Ag         
             AM                        conponent terminations.             
                                                                           
                                                                           
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              "P. Langeveld"                                               
             <p.langeveld@GMAI                                             
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Hello Peter,
 Soldering PdAg or PtAg metallisations is not compatible with leadfree
solder. The silver from the metallisation leaches out from the
metallisation structure during the soldering operation and forms
little holes (voids) at the interface. The remaining intermetallic
structure is solid and brittle at the interface solder/Pd. In time the
phenomenon increases by solid state diffusion of the silver from the
metallisation into the bulk of solder and forms Kirkendahl voids, see
picture 446.
But the solution is there: Also capacitors with NiSn metallisation is
available, see picture 457.

Peer Langeveld
Consultant Soft Soldering Processes
The Netherlands



2007/1/31, Peter Barton <[log in to unmask]>:
> We are seeing unusual soldered joints when soldering to components with
> Platinum/Silver metallised terminations. At the margin between the bottom
of
> the component termination and the PCB surface there are a number of
> blowholes in the bulk solder. There also appears to be poor wetting to
the
> vertical end of the termination itself. All other solder joints on the
> assembly in question are good, well wetted and on a number of other
plating
> finishes.
>
> The solder paste is SAC305 and the PCB finish is ENIG. Reflow is carried
out
> in a vapour phase process with a maximum assembly temperature of 235 deg.
C.
> Time above liquidus (217 Deg C.) is around 50 seconds.
>
> I have requested feedback from the component manufacturer but it's like
> pulling teeth so in the meantime I an seeking your considered opinions.
>
> Many thanks
>
> Peter Barton
> Senior Process Engineer
> ACW Technology Ltd
> Dinas Isaf West
> Tonypandy
> Mid Glamorgan. CF40 1XX  Wales
>
> Tel: 01443 425275 (direct)
> Fax:  023 8048 4882
> International Tel : +44 1443 425200
> International Fax : +44 23 8048 4882
> Website/URL:  www.acw.co.uk

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