Fabrication method of packaging substrate, and fabrication method of semiconductor package

A fabrication method of a packaging substrate, comprising the steps of:

• providing a metal board having a first surface and a second surface opposite to the first surface and forming a plurality of first openings in the first surface of the metal board so as to define a first core circuit layer between the first openings, wherein each of the first openings has a wide outer portion and a narrow inner portion;
• forming a first encapsulant on the first surface and in the first openings and forming a plurality of openings in the first encapsulant for exposing the first core circuit layer;
• forming a surface circuit layer on the first encapsulant and in the openings of the first encapsulant such that the surface circuit layer electrically connects the first core circuit layer;
• forming a plurality of second openings in the second surface of the metal board so as to define a second core circuit layer between the second openings, wherein each of the second openings has a wide outer portion and a narrow inner portion, and the inner portion of each of the second openings is in communication with the inner portion of a corresponding one of the first openings;
• and
• forming a second encapsulant in the second openings.