A method of manufacturing a ball grid array substrate includes: forming a first circuit pattern and a second circuit pattern on a first metal carrier and a second metal carrier, respectively; stacking a first insulating layer and a second insulating layer with a separable material interposed therebetween, wherein each of the first and second insulating layers has first and second surfaces opposing each other, and the first surface contacts the separable material; burying the first and second circuit patterns in the second surfaces of the first and second insulating layers, respectively; removing the first and second metal carriers; removing the separable material to separate the first and second insulating layers from each other; and forming an opening in each of the first and second insulating layers to connect the first and second surfaces with each other. The method may also be part of a process for manufacturing a semiconductor package.