update panel - how to prevent parent panel from updating

I have a parent UpdatePanel (panelParent) and within it, I have another UpdatePanel (panelChild).

I have parentChild set to:
 - ChildrenAsTriggers = false
 - UpdateMode = conditional

When I click on my linkbuttons within the panelChild panel, the entire panelParent refreshes.

How can I prevent the parent control from updating?

Thanks,
John