Ask the Experts
September 14, 2018
Dendritic Growth and Contamination at BGA Sites
We have 180 assemblies where our subcontractor replaced five BGA memory devices. Unfortunately they utilized active flux and then did not perform an automated cleaning, instead they hand washed. 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 erroras all active flux residues must be cleaned. The question is, whattype of active flux exactly, OA, RMA, RA? You may be able tosalvage the boards by using a cleaning agent with a low surface tension (eithervapor defluxing or a specialty hydrocarbon, such as one of the d-limonene basedproducts). Most solvent manufacturers have a lab where they can run aboard or two for you at now charge to verify the process. Contactme directly if you'd like more info. Good luck!
Rick Perkins is a chemical engineer with more than 33 years of Materials & Processes experience. He has worked with Honeywell Aerospace in high-reliability manufacturing, as well as with several oil-field manufacturing companies. He also has a good understanding of environmental, health, and safety regulations.
It might be possible. Foresite in Kokomo Indiana is an IPC member and has had success with manycleaning failure challenges. I don't know if they have tackled the BGAproblem that you are seeing but I think it is worth a call to Terry Munson.
VP International Relations
David W. Bergman is Vice President of International Relations for IPC. He has worked at IPC for more than 30 years responsible for IPC standardization efforts, education and certification programs. Currently, David is responsible for globalization activities, including IPC's China and India offices and reps in Europe and Russia.
If these boards are not considered to be "beyond repair"then yes they can be recovered. It would be of great importance to confirmwhether the dendrites have consumed enough of the metals to cause concern forreliable operations after the cleaning process.
We have been using a combination of saponified in-linewash and steam energy from a handheld type system for close to a decade now torecover assemblies in this exact condition. The important thing toremember is using the proper type of steamer with experienced operators thatwill not increase the potential for other component damage.
In an effort toremain non-commercial in this forum I would encourage you to contact me offlinefor further information.
Eric has been in the electronics industry for over 14 years and manages the C3 technical user group, Failure Analysis project management, Rescue Cleaning Division and is one of three Lead Investigators at Foresite.
Mysuggestion is to remove BGA's and clean the boards in a water wash or solventcleaner after removing the BGA component and also brush them with a brush inalcohol to insure complete removal of the ionic contamination and the physicaldendrite itself. It is not unusual for ionics to be imbedded in thedendrite itself thus the need to wash and brush the board clean. I would thenreplace the BGA back onto the board with correct flux system and then cleanagain.
VP Engineering Services
STI Electronics Inc.
Mark T. McMeen is STI Electronics Inc.ʼs Vice President of Engineering Services. He oversees the daily operations of the Engineering Services division of STI. He has over 18 years experience in the manufacturing and engineering of PCBs.
Electrolytic corrosionresulting in dendritic growth results in metal crystals across the isolationzones and, although difficult to clean thoroughly, can be removed if it isa freely accessible area with a mixture of solvent and mechanical brushing.Underneath a BGA it would be virtually impossible without removing the BGAfirst. Perhaps, you could remove the BGA, then clean up the area and replacethe BGA again. This would be the only possibility in my opinion and even thenthe clean up would have to be very thorough.
Principal Engineer - CMA Lab
Bryan Kerr has 35 years experience in providing technical support to PEC assembly manufacturing. His experience ranges from analysis of materials and components to troubleshooting and optimizing, selecting reflow, cleaning, coating and other associated processes.
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. 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.
KN Murli, Astra Microwave Products, Hyderabad, AP India