Summary for vacuum soldering lead free alloy Discussion
Vacuum soldering of lead free alloy is discussed in the context of using a Sn/Cu/Ag preform in a flux-free, low-pressure process on clean gold surfaces. Adrian Kendall asked what etch or etch sequence could remove oxides from the solder preform to improve wetting and reduce voiding. Mike Fenner replied that using formic acid in preform soldering is a normal approach when post-solder cleaning is important: it cleans surfaces and then breaks down during soldering into H2O and CO2 with no residue. He cautioned, however, that it only works where it physically contacts the surfaces and can be aggressive on equipment. He also noted that fluxes avoid some of these issues but may need removal afterward. Finally, he warned that SAC solder on gold can be problematic depending on the gold thickness.
Q. Not being a chemist maybe someone can suggest a procedure…
Intending to use a Sn/Cu/Ag alloy in an flux free low pressure soldering process. Surface to solder are gold and clean. To ensure good wetting and low voiding I believe I will pre clean and etch the solder (preform) to remove oxides.
Can some one suggest a suitable etch or sequence of etches to achieve this.
Thanks
Adrian Kendall
laser diodes – Glasgow, Lanarkshire, UK
2004
A. The best way to treat the surface and to keep the substrate clean from any flux, will be to use a vacuum soldering furnace which will support a cleaning step with formic acid.
On a pressure of about 10 E-1 mbar and a substrate temperature below the liquidus of the solder, formic acid will be feed into the vacuum chamber from a bubbler using nitrogen as a tracer gas. The formic acid will react with the substrate surface and removing all oxides.
Even if you would not use any soldering past, but preforms without flux, you will get a perfect wetting of the surfaces and a voidless connection.
If there is any specific question, please let me know.
Best regards
Volker Kinzig
– Gelnhausen, Germany
2004
Q. How to reduce solder splatter, solder balling?
Jeff Gilbert
– Malvern, Pennsylvania
February 18, 2010
A. Hi, Jeff. Hopefully someone experienced in this will try to help, but your question sounds rather vague to me :-)
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
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February 18, 2010
A. Use of formic in the way described is a normal procedure in preform soldering where post solder cleaning is an issue. The acid will clean surfaces, but is totally dissipated on soldering and broken down to H20 CO2 leaving no residues. Spatter of solder is not therefore an issue. So that’s handy.
Disadvantages are that it only works where it touches (i.e. possibly not on touching surfaces), and can be pretty fierce on equipment. Fluxes do not have these problems, but may need to be removed, depending on flux application
Use of SAC on gold surfaces may be a problem depending on the gold thickness.
Hope this helps.
Mike
Mike Fenner
– Milton Keynes, Bucks, United Kingdom
February 23, 2011