In this chapter, two problems of flip chip on glass-core package substrate will be investigated. The first problem deals with the flip chip on glass-core package substrate with microbumps and the other deals with the flip chip on glass-core package substrate with Cu-Cu hybrid bonding. Emphasis is placed on the solder joint reliability due to the glass-core substrate. Some recommendations will be provided. The advantages and disadvantages, glass-core substrate vs. glass-core interposer, through-glass via (TGV), and redistribution-layers (RDLs) will be briefly mentioned first.