Electrical connectors 124, which are formed of a non-solder metallic material(s), are formed at the bottom surface of bottom package 100. In accordance with some embodiments of the present disclosure, electrical connectors 124 are metal pads. In alternative embodiments, electrical connectors 124 include metal pillars such as copper pillars. Throughout the description, electrical connectors 124 are referred to as metal pads 124, although they may have forms other than metal pads. Metal pads 124 may comprise copper, aluminum, nickel, palladium, gold, or multi-layers thereof. Solder regions 126 are attached to the bottom surfaces of metal pads 124 and bond bottom package 100 to package component 300. In some exemplary embodiments, Under Bump Metallurgies (UBMs) 127 are formed at the bottom surface of package component 100, with solder regions 126 attached on. In alternative embodiments, no UBM is formed, and solder regions 126 are in contact with metal pads 124. Package component 300 may include a Printed Circuit Board (PCB), a package, or another type of package component.