We have very good results using the Nordson RMA Paste Flux P/N 7019057. This is a no clean flux, not aqueous clean.
Andy Price
Sales Engineer, Circuit Technology Center
Mr. Price has been a key member of the team at Circuit Technology Center since 1985. He has vast expertise, experience and understanding of complex circuit board rework, repair and modification operations. He is one of the most knowledgeable experts in this area across the globe.
Never use liquid flux for BGA rework, it will not stick around long enough, as you have discovered. As the experts here have stated, use a GOOD tacky flux formulated just for BGA rework. The type of flux (water soluble, RMA, or No-clean) should be the same as the type of flux in your solder paste, so the appropriate cleaning process is used and there are no potential reaction issues.
Attempting to use an RMA flux when you only have water-soluble cleaning processes will lead to horrible results. I actually have several processes where I call out the tacky flux instead of the typical liquid benchtop flux because I know they are superior, proven (qualified)to be easier to clean, and less likely to seep under pads and other areas and cause damage during soldering and/or rework.
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.
It is best to use proper Rosin based rework flux gel as this will aid with the heat transfer to the balls much more efficiently and last the soldering process so you only have to do the job once.
Greg York
Technical Sales Manager, BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.
BGA rework should be done with rework flux paste, which is designed to stay active and will remain in place through the full range of reflow processes experienced during rework operations. In addition, rework flux paste is tacky and will hold components in position the same way as solder paste.
John Vivari
Application Engineering Supervisor, Nordson EFD
Mr. Vivari has more than 15 years of electronic engineering design and assembly experience. His expertise in fluid dispensing and solder paste technology assists others in identifying the most cost effective method for assembling products.
All the major brands have a BGA Rework specific tacky flux formulation. I would start with the vendor you currently purchase your flux and solder paste from. This will ensure that your tacky flux is compatable with what you are currently using.
Edward Zamborsky
Regional Sales Manager, OK International Inc.
Ed Zamborsky is a Regional Sales & Technical Support Manager for Thermaltronics, located in New York. His position requires frequent customer visits throughout North America and the Caribbean and his position encompasses not only sales but the role of trainer and master applications engineer for all of Thermaltronics products. His expertise includes such specialties as hand soldering, convection and conduction reflow techniques, array rework, fluid dispensing equipment, and fume extraction. Ed has authored many articles and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead-Free Hand Soldering, High Thermal Demand Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
A flux with a good oxidation barrier (that protects molten solder from oxidizing for as long as possible) will do the job - typically no-clean rosin-based fluxes have a better oxidation barrier than water-wash fluxes. The oxidation barrier in the flux is crucial towards eliminating head-in-pillow as well.
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.
The key phrase in the question is "under prolonged heating". In principle, the same flux or flux type as was used for reflow should be fine for rework. However, care must be taken to ensure that the flux is not overheated.The rework thermal cycle should be as close as possible to the one that was used in the reflow ovenincluding ramp, preheat, peak temperature, time above liquidus and cool down. Following this simple rule should resolve the problem.
Harold Hyman
Consultant, VJ Electronix
Harold Hyman has been involved in metallurgical aspects of the electronics industry since the 1950's, and in semiconductor development and engineering for STL, Ediswan & RCA. He later joined HTC, a pioneer of vapor phase soldering and continued industry experience Dynapert, GenRad, Teradyne, SRT and VJ Electronics.
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