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May 28, 2012

Flux Aging Study

What parameters would you look at when doing a study on aging of liquid flux?

J.H.

Experts Comments

For most cases, the most measurable difference over time is acid number. This is particularly relevant for low-solids, no-clean fluxes. Most fluxes have a shelf life of 1 to 3 years, and the main driver of the shelf life measurement is the fact that the acid number of the flux declines over time. That decline in acid number can result in poorer soldering performance during wave soldering.  

As long as the container is sealed, specific gravity should stay fairly constant over time.

Some fluxes can also demonstrate a change in color over time; these changes are generally not impactful to performance, so the user should not be alarmed by this if it occurs. Acid number is really the best measurement to measure the consistency of the flux over time.
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Brian Smith
General Manager - Electronic Assembly Americas
DEK International
Mr. Smith has been supporting customers in the electronics assembly industry since 1994. His expertise is focused on solder paste printing and reducing soldering defects. He holds a BS in Chemical Engineering and an MBA in Marketing. He has authored several papers in trade magazines and at industry conferences. He is an SMTA Certified Process Engineer.
The typical parameters are acid number, density, solids percent and solderability testing using a wetting balance to determine the Force versus Time curve in original and aged flux. These are normally done to determine shelf life of fluxes at the manufacturing level.

Other tests are color change and turbidity, these may be impacted by age and exposure to light.
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Peter Biocca
Senior Market Development Engineer
Kester
Mr. Biocca was a chemist with many years experience in soldering technologies. He presented around the world in matters relating to process optimization and assembly. He was the author of many technical papers delivered globally. Mr. Biocca was a respected mentor in the electronics industry. He passed away in November, 2014.
Refer to J-STD-004. This is the industry standard for requirements for soldering fluxes, and has a lot of information on certification, shelf life info, and re-certification methods for fluxes. The standard also lists all of the appropriate test methods within IPC-TM-650, which is a free download from the IPC's web site at http://ipc.org/ContentPage.aspx?pageid=Test-Methods.
Richard D. Stadem
Advanced Engineer/Scientist
General Dynamics
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.
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