BGA Parameter Damming

During temperature cycling we have determined that the conformal coating wicking underneath our BGAs has caused fractures in our solder balls. One proposed solution is to run an RTV dam around the parameter of the BGA to prevent the CC from wicking underneath. Does anyone have any experience with this technique? After researching the use of underfills, I believe they might cause more harm than good with our temperature ranges. Any help would be greatly appreciated.

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