Abstract: In some embodiments, an interconnection structure can electrically and physically couple a first semiconductor die and a second semiconductor die. The interconnection structure can include a first portion at the first semiconductor die and a second portion at the second semiconductor die. The first portion can include a first conductive pillar with a concave bonding surface, a first annular barrier layer, and a first annular solder layer. The first annular barrier layer can surround a sidewall of the first conductive pillar, and the first annular solder layer can surround the first barrier layer. The second portion can include a second conductive pillar having a convex bonding surface, the convex bonding surface coupled to the concave bonding surface. The second interconnection structure can further include a second annular solder layer surrounding a second annular barrier layer surrounding the second conductive pillar.