Ultrasonic soldering has been used without flux for many years, this certainly works with Die attach how ever not sure how useful it would be on standard PCB design (localised damage to other components). You can get Nitrogen re-work pens these should work on PWBs where solder still remains on pads and if there is a good finish on the components. How ever as there would be substantially less solder than would be normal and as the intermetalic would not be guaranteed then it would be difficult to confirm a good joint. To have any form of reliability it would be better to use a flux in conjunction with the solder.
Richard Boyle
Global Product Champion, Henkel Electronics
Richard Boyle is a Global Product Champion at Henkel Electronics. He has over 25 years experience in the electronics assembly industry and is responsible for the global technical service of all of Henkel's solder materials.
I do not know of such a thing and there are a number of potential problems the main ones are how to prevent the Nitrogen form leaking out an depleting the oxygen and causing asfixiation of the operators. Second is how do you ensure that you have oxide free, contaminant free surfaces going into the soldering process.
Neil Poole
Senior Applications Chemist, Henkel Electronics
Dr. Poole is a Senior Applications Chemist in Henkel Technologies, electronics assembly materials application engineering group. He is responsible for all of Henkel's assembly products including soldering products, underfills, PCB protection materials, and thermally conductive adhesives.
The purpose of a flux is to reduce oxide and fluxless soldering could involve (a) ultrasonic soldering to scrub the oxide away; (b) forming gas / formic acid to reduce oxide. Ultrasonic hand soldering may be possible without a flux, but will need new equipment and training To a use a flux and eliminate cleaning for hand-soldering:- A no-clean flux can be used. If there are concerns that the no-clean flux is not completely activated, there are no-clean rework fluxes that pass SIR unactivated. This means that even if the flux saw no heat, there would be no reliability issue.
Karthik Vijay
Technical Manager - Europe, Indium Corp.
Currently with Indium Corporation and responsible for technology programs and technical support for customers in Europe. Over 15 yrs experience in SMT, Power, Thermal & Semiconductor Applications. Masters Degree in Industrial Engg, State University of New York-Binghamton.
I am not aware of "fluxless" soldering using metallic solder (not conductive adhesives).
One should consider the other residues potentially on an assembly besides flux residues.
In addition to the elimination of post-reflow residue related product failures, the cleaning of electronic assemblies, while intended for the removal of flux residues, actually provides for the removal of other contamination species. While the emphasis of a cleaning program is flux removal it is important to consider the many other sources of potential contamination.
BOARD FABRICATION
| COMPONENT FABRICATION
| ASSEMBLY PROCESS
| Etch residues
| Plating bath residues
| Solder paste
| Developer chemicals
| Water quality rinses
| Flux - wave / core
| Water quality rinses for inner layers
| Deflashing chemicals
| Reworked/Repaired
Fluxes
| Water quality rinses for outer layers
| Mold release agents
| Cleaning chemicals
| HASL Fluids (HO) and
final rinses
| Preplating oxide cleaning
| Water rinse Quality
| Alkaline cleaners
| Pretinning flux residues
| Rework Cleaner
|
Mike Konrad
President, Aqueous Technologies
Mr. Konrad has been in the electronic assembly equipment industry since 1985. He is founder and CEO of Aqueous Technologies Corporation, a manufacturer of automatic de-fluxing equipment, chemicals, and cleanliness testing systems.
|
