|Ask the Experts|
June 7, 2018
BGA Rework Flux Recommendation
Is there a specific flux, or flux type, we should evaluate when we replace BGA components? We currently use a standard flux and it seems to have problems maintaining its activity under prolonged heating during BGA rework.
|Expert Panel Responses|
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.
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.
Technical Manager - Europe
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.
Regional Sales Manager
OK International Inc.
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.
Application Engineering Supervisor
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.
Technical Sales Manager
BLT Circuit Services Ltd
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.
I would recommend a no clean tacky flux for cleaning pads and replacing BGA components.Ray Clark, TT Electronics
We have very good results using the Nordson RMA Paste Flux P/N 7019057. This is a no clean flux, not aqueous clean.
Circuit Technology Center
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