Anchor-containing underfill structures for a chip package and methods of forming the same

A bonded assembly comprising a fan-out package, the fan-out package comprising:

• an interposer comprising first interconnects embedded in first dielectric layers which have a first horizontal surface located within a first horizontal plane and further comprising on-interposer bump structures overlying the first horizontal plane, and having sidewalls of which bottom peripheries are located within the first horizontal plane, wherein the interposer comprises recesses located in corner regions of the interposer and vertically extending from the first horizontal plane toward a backside horizontal surface of the interposer such that recessed surfaces of the first dielectric layers are located within a second horizontal plane that is located at a depth which is in a range from 5% to 99.9% of a thickness of the interposer such that the recessed surfaces are located below a horizontal plane containing bottommost surfaces of the on-interposer bump structures and is more proximal to the backside horizontal surface than the first horizontal plane is to the backside horizontal surface;
• at least one semiconductor die attached to the interposer through a respective array of solder material portions that are bonded a respective one of the first bump structures, wherein the bottom peripheries of the sidewalls of the on-interposer bump structures are more distal from the at least one semiconductor die than top peripheries of the sidewalls of the on-interposer bump structures are from the at least one semiconductor die;
• an underfill material portion located between the interposer and the at least one semiconductor die and comprising downward-protruding anchor portions that fill the recesses in the interposer;
• and
• a molding compound die frame laterally surrounding the at least one semiconductor die, wherein bottommost surfaces of the downward-protruding anchor portions are in direct contact with the recessed surfaces of the first dielectric layers within the second horizontal plane and are vertically spaced from the bottom peripheries of the sidewalls of the on-interposer bump structures which are located within the first horizontal plane, wherein:
• the first surfaces of the first dielectric layers comprise concave surface segments having a concave vertical cross-sectional profile;
• the downward-protruding anchor portions comprise convex surface segments in direct contact with the concave surface segments;
• the recesses and the downward-protruding anchor portions received therein constitute a mechanical interlock structure having a non-planar interface between the first interconnect-containing structure and the underfill material portion, reducing a stress on the underfill material portion at corner segments of the underfill material portion, and reducing delamination or cracking of the underfill material portion;
• and
• the recesses comprise additional sidewalls connecting bottom peripheries of the concave surface segments and peripheries of the second surfaces and having cylindrical configurations.

A bonded assembly comprising:

• a first interconnect-containing structure including first interconnects formed within first dielectric layers which have a first horizontal surface located within a first horizontal plane, wherein the first-interconnect structure comprises recesses located in corner regions and having sidewalls containing first surfaces of the first dielectric layers and having recessed surfaces containing second surfaces of the first dielectric layers located within a second horizontal plane that is vertically spaced from, and recessed relative to, the first horizontal plane;
• first bump structures located directly on a subset of the first interconnects, wherein bottom peripheries of the first bump structures are located within the first horizontal plane, wherein the recessed surfaces are located at a depth which is in a range from 5% to 99.9% of a thickness of the first interconnect-containing structure such that the recessed surfaces are located below a horizontal plane containing bottommost surfaces of the first bump structures;
• at least one second interconnect-containing structure including second interconnects and attached to the first interconnect-containing structure through a respective array of solder material portions that are bonded a respective one of the first bump structures, wherein the bottom peripheries of the first bump structures are more distal from the at least one second interconnect-containing structure than top peripheries of the first bump structures are from the at least one second interconnect-containing structure;
• and
• an underfill material portion laterally surrounding each of the solder material portions and comprising downward-protruding anchor portions that protrude downward from a horizontally-extending portion of the underfill material portion such that bottommost surfaces of the downward-protruding anchor portions are in direct contact with the recessed surfaces of the first dielectric layers within the second horizontal plane and are vertically spaced from the bottom peripheries of sidewalls of the first bump structures which are located within the first horizontal plane, wherein:
• the first surfaces of the first dielectric layers comprise concave surface segments having a concave vertical cross-sectional profile;
• the downward-protruding anchor portions comprise convex surface segments in direct contact with the concave surface segments;
• the recesses and the downward-protruding anchor portions received therein constitute a mechanical interlock structure having a non-planar interface between the first interconnect-containing structure and the underfill material portion, reducing a stress on the underfill material portion at corner segments of the underfill material portion, and reducing delamination or cracking of the underfill material portion;
• and
• the recesses comprise additional sidewalls connecting bottom peripheries of the concave surface segments and peripheries of the second surfaces and having cylindrical configurations.