An electrical structure and method of forming. The electrical structure includes a first substrate, first dielectric layer, an underfill layer, and a second substrate. The first dielectric layer is formed over a top surface of the first substrate. The first dielectric layer includes a first opening extending through a top surface and a bottom surface of said first dielectric layer. The underfill layer is formed over the top surface of the first dielectric layer and within the first opening. The second substrate is formed over and in contact with the underfill layer.