A semiconductor package, comprising: a lower package to which elements are mounted; a metal post connected to the lower package and including at least one metal material portion (510; 520); and an upper package to which elements are mounted, and which is connected to the metal post via a solder ball; wherein the metal post is configured such that a width of one end of the metal post connected to the solder ball is smaller than that of another end, the width of the metal post reducing gradually from the other end to the one end; wherein the lower package includes: a substrate; and a first seed pattern portion formed on the substrate, wherein the metal post is formed on the first seed pattern portion, a solder resist pattern formed on the substrate so that a part of an upper surface of the first seed pattern portion can be exposed, a second seed pattern portion formed at the side surfaces of the solder resist pattern, connected to the first seed pattern portion and partially on the upper surface of the solder resist pattern, wherein the one end of the metal post connected to the solder ball is entered into the solder ball, and in that the metal post includes a solder portion formed of Sn disposed on the first seed pattern portion formed of Sn and a metal material portion formed of Cu on the solder portion, wherein a width of an upper surface of the solder portion is same as a lower surface of the metal material portion, wherein the second seed pattern portion is in direct physical contact with the surface of the solder portion on the portions between said solder resist pattern and said solder portion, and wherein the first seed pattern portion is in direct physical contact with a lower surface of the solder portion. a lower package to which elements are mounted; a metal post connected to the lower package and including at least one metal material portion (510; 520); and an upper package to which elements are mounted, and which is connected to the metal post via a solder ball; wherein the metal post is configured such that a width of one end of the metal post connected to the solder ball is smaller than that of another end, the width of the metal post reducing gradually from the other end to the one end; wherein the lower package includes: a substrate; and a first seed pattern portion formed on the substrate, wherein the metal post is formed on the first seed pattern portion, a solder resist pattern formed on the substrate so that a part of an upper surface of the first seed pattern portion can be exposed, a second seed pattern portion formed at the side surfaces of the solder resist pattern, connected to the first seed pattern portion and partially on the upper surface of the solder resist pattern, wherein the one end of the metal post connected to the solder ball is entered into the solder ball, and in that the metal post includes a solder portion formed of Sn disposed on the first seed pattern portion formed of Sn and a metal material portion formed of Cu on the solder portion, wherein a width of an upper surface of the solder portion is same as a lower surface of the metal material portion, wherein the second seed pattern portion is in direct physical contact with the surface of the solder portion on the portions between said solder resist pattern and said solder portion, and wherein the first seed pattern portion is in direct physical contact with a lower surface of the solder portion. a substrate; and a first seed pattern portion formed on the substrate, wherein the metal post is formed on the first seed pattern portion, a solder resist pattern formed on the substrate so that a part of an upper surface of the first seed pattern portion can be exposed, a second seed pattern portion formed at the side surfaces of the solder resist pattern, connected to the first seed pattern portion and partially on the upper surface of the solder resist pattern, wherein the one end of the metal post connected to the solder ball is entered into the solder ball, and in that the metal post includes a solder portion formed of Sn disposed on the first seed pattern portion formed of Sn and a metal material portion formed of Cu on the solder portion, wherein a width of an upper surface of the solder portion is same as a lower surface of the metal material portion, wherein the second seed pattern portion is in direct physical contact with the surface of the solder portion on the portions between said solder resist pattern and said solder portion, and wherein the first seed pattern portion is in direct physical contact with a lower surface of the solder portion.