BGA shear force

I am tyring to find out shear force requirement for BGA attached on board .I measured two group for shear force to check underfill process effectiveness on BGA .Two group showed siginificant force diferrence .I am very sure underfill process is effective to increase shear force of BGA on board .What is normal requirement ?The size of BGA is 9.0mm*9.0mm. I need someon's comments

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