|Ask the Experts|
December 24, 2020
Dendritic Growth and Contamination at BGA Sites
We are now experiencing latent failures due to dendritic growth. (see photo) Is there any way to recover these boards?
|Expert Panel Responses|
Obviously this was an error as all active flux residues must be cleaned.
The question is, what type of active flux exactly, OA, RMA, RA? You may be able to salvage the boards by using a cleaning agent with a low surface tension (either vapor defluxing or a specialty hydrocarbon, such as one of the d-limonene based products). Most solvent manufacturers have a lab where they can run aboard or two for you at now charge to verify the process.
Contact me directly if you'd like more info. Good luck!
It might be possible. Foresite in Kokomo Indiana is an IPC member and has had success with many cleaning failure challenges. I don't know if they have tackled the BGA problem that you are seeing but I think it is worth a call to Terry Munson.
VP International Relations
If these boards are not considered to be "beyond repair" then yes they can be recovered. It would be of great importance to confirm whether the dendrites have consumed enough of the metals to cause concern for reliable operations after the cleaning process.
We have been using a combination of saponified in-line wash and steam energy from a handheld type system for close to a decade now to recover assemblies in this exact condition. The important thing to remember is using the proper type of steamer with experienced operators that will not increase the potential for other component damage.
In an effort to remain non-commercial in this forum I would encourage you to contact me offline for further information.
My suggestion is to remove BGA's and clean the boards in a water wash or solvent cleaner after removing the BGA component and also brush them with a brush in alcohol to insure complete removal of the ionic contamination and the physical dendrite itself.
It is not unusual for ionics to be imbedded in the dendrite itself thus the need to wash and brush the board clean. I would then replace the BGA back onto the board with correct flux system and then clean again.
VP Engineering Services
STI Electronics Inc.
Electrolytic corrosion resulting in dendritic growth results in metal crystals across the isolation zones and, although difficult to clean thoroughly, can be removed if it is a freely accessible area with a mixture of solvent and mechanical brushing. Underneath a BGA it would be virtually impossible without removing the BGA first.
Perhaps, you could remove the BGA, then clean up the area and replace the BGA again. This would be the only possibility in my opinion and even then the clean up would have to be very thorough.
Principal Engineer - CMA Lab
The fact that dendrite has grown indicated the unit has been powered and it is not clear any failures namely shorting was reported. Usually dendrite will grow not only below BGA also under other components if ionic contamination and moisture is present.KN Murli, Astra Microwave Products, Hyderabad, AP India
If there repeated shorting and opening of the dendrite takes place, carbonization on the track can form which could be difficult to clean. This face also be considered while salvaging the card.
An unfortunate situation where process control was lacking but I believe that it is certainly possible to successfully recover the boards.David Bonito, Technical Manufacturing Corporation
In my opinion, I would not think that simply trying to clean them after the fact would suffice as just removing flux residue from underneath BGA components is generally very difficult to do even with automated cleaning systems, never mind doing it to remove dentritic growth and expecting to have any confidence level. From a very general standpoint without knowing any specifics and assuming that scrap is not an option, I would rework by replacing each site with a new device using no-clean flux after first cleaning and validating the site area. I would also ensure that the correct BGA rework equipment is used in order to prevent further damage to the assembly.
I might also recommend that you require approval of any rework process with your supplier going forward in order to mitigate risk like this. Rework also opens the door to additional damage so you might also need approval from the end user as well to rework the assemblies depending on the end use or application especially if you don't have MRB authority.
I agree that the original flux chemistry must be identified and thoroughly cleaned. Removal of the BGAs would be required to do a thorough cleaning, and the dendritic growths should be removed with mechanical brushing during this cleaning step. This is a manual process done with an ESD-safe, organic bristle brush. Even if the boards (now without the BGAs) are to be cleaned in a high pressure wash system with lots of nozzle force, manual brushing still will be required to remove the dendrites. So, the most economical method is to clean the sites manually with brushing and a compatible solvent. When the BGAs are replaced, a cleanable flux and a compatible solvent for cleaning should be chosen.Russell Claybrook, MicroCare LLC
This is very important and apparently was skipped in the initial process. There are a lot of solder pastes and fluxes from which to choose. If you choose one that requires cleaning, be advised to clean right after the BGA has been soldered for best results. Solvent should be applied underneath the BGA to dissolve any remaining flux and to flush it away to a dam on the opposite side of the BGA. The dam is made of a lint-free cloth that wicks up fluid.
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