Ditto here. But if you CAN'T get alternatives, you CAN make reliable
joints to these devices, but the profile is very tough to optimize. I
haven't tried Pb-free with this metallization yet, so I don't know how
big the profile "window" is. The main problem is that with too much
time above liquidus, the Pt/Ag will go into the solder mix. Don't try
to get a wetting angle significantly better than the minimum acceptable.
When the termination starts to dissolve into the solder mix, first the
wetting angle will degrade, then tiny "raspberries" will form on the
fillet, with the wetting angle getting even worse, and then the
termination will "de-wet".
I suspect that the blowholes are due to the crevices and porosity of
this finish--the flux gets into those areas and won't come out (until it
explodes!). These same features make them the ONLY parts where I have
had reliable successes with conductive epoxy attach on FR-4 boards. So
I actually sometimes seek this finish out.
I don't know if you've tried SSD (Solid Solder Deposition) for this
app, but it would certainly help. The one I use is called SIPAD. Such
processes dramatically increase the solder profile "window" and reduce
the required amount of flux.
Wayne Thayer
>>> [log in to unmask] 1/31/2007 6:02:46 am >>>
We always have problems (both at assembly and more import
Peter,
We always have problems (both at assembly and more importantly with
reliability) when we use PtAg or PdPtAg terminated components. If you
can find another component that isn't terminated with one of these
noble
metal terminations use the alternative.
Regards,
George
George M. Wenger
Andrew Corporation Wireless Network Solutions
Senior Principal FMA / Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 [Office] (732) 309-8964 [Cell]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Peter Barton
Sent: Wednesday, January 31, 2007 5:18 AM
To: [log in to unmask]
Subject: [TN] Soldering to Pt/Ag conponent terminations.
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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