Ask the Experts
May 28, 2012 - Updated
May 22, 2012 - Originally Posted

Flux Aging Study

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


Expert Panel Responses

For most cases, themost measurable difference over time is acid number. This is particularlyrelevant for low-solids, no-clean fluxes. Most fluxes have a shelf lifeof 1 to 3 years, and the main driver of the shelf life measurement is the factthat the acid number of the flux declines over time. That decline in acidnumber can result in poorer soldering performance during wave soldering. As long as thecontainer is sealed, specific gravity should stay fairly constant over time. Some fluxes can alsodemonstrate a change in color over time; these changes are generally notimpactful 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 ofthe flux over time.

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 percentand solderability testing using a wetting balance to determine the Force versus Time curvein original and aged flux. These are normally done to determine shelf life of fluxes at themanufacturing level. Other tests are colorchange and turbidity, these may be impacted by age and exposure to light.

Peter Biocca
Senior Market Development Engineer
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 industrystandard for requirements for soldering fluxes, and has a lot of information oncertification, shelf life info, and re-certification methods for fluxes. Thestandard also lists all of the appropriate test methods within IPC-TM-650,which is a free download from the IPC's web site at

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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