Hakan,
Its been a while since I did any gas soldering, but I have never
heard of inert gas soldering before, especially without a flux of some type.
In the past I have managed to get active gas soldering to work, with a mix
of Hydrogen in Nitrogen (2-4%H2, although have done it in 100% H2!) but
again never on thick film, the substrate - thick film bond relies on oxide
bonding of the glass fritt, (or it did in my time, probably got some funky
combined bond chemistry now) and the introduction of an active gas broke
that bond, and I found it just lifts the whole thick film off the alumina or
AlN, which is not good! possible a good rework method for substrates though?
I do remember a while ago that somebody asked something similar to
this before in TN, take a look through the archives for I think it was
fluxless soldering, there were some responses and I think there was even a
real fluxless system discussed.
I dont know if a longer plasma etch would solve the problem, as I
guess the surface would just oxidise before it gets into the reflow oven.
One question though, does the solder wet if a flux is used, could be
the thick film has been over fired and there is a thick glass layer on the
top of the solder pads.
Good luck
Roger
Via Systems
UK
-----Original Message-----
From: Håkan Törnqvist (EMW) [mailto:[log in to unmask]]
Sent: Thursday, October 26, 2000 4:50 PM
To: [log in to unmask]
Subject: [TN] Flux free soldering of Sn/Pb
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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