Scatter circles on surface with maximum distance between borders

Hello everyone. I am trying to scatter a set of circles of two types of diameter on a surface. I want to scatter them randomly but in a way that tey are never more than 7 meters in distance between eachother (counting from the borders). Does anyone know how I could do that?? If that is not possible, at least to do the same thing but counting their maximum distance from their respective centers. Thanks a lot in advance.

Tomás